2,5-Bis(3,2':6',3”-Terpyridin-4'-Yl)Benzene Ligands with Cobalt(II) Thiocyanate

crystals

Article Trinodal Self-Penetrating Nets from Reactions of 1,4-Bis(alkoxy)-2,5-bis(3,2’:6’,3”-terpyridin-4’-yl)benzene Ligands with Cobalt(II) Thiocyanate

Giacomo Manfroni 1, Alessandro Prescimone 1 , Stuart R. Batten 2, Y. Maximilian Klein 3 , Dariusz J. Gawryluk 3 , Edwin C. Constable 1 and Catherine E. Housecroft 1,*

1 Department of Chemistry, University of Basel, BPR 1096, Mattenstrasse 24a, CH-4058 Basel, Switzerland; [email protected] (G.M.); [email protected] (A.P.); [email protected] (E.C.C.) 2 School of Chemistry, Monash University, Victoria 3800, Australia; [email protected] 3 Laboratory for Multiscale Materials Experiments, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland; [email protected] (Y.M.K.); [email protected] (D.J.G.) * Correspondence: [email protected]; Tel.: +41-61-207-1008

Received: 27 September 2019; Accepted: 10 October 2019; Published: 15 October 2019

Abstract: The tetratopic ligands 1,4-bis(2-ethylbutoxy)-2,5-bis(3,2’:6’,3”-terpyridin-4’-yl)benzene (1) and 1,4-bis(3-methylbutoxy)-2,5-bis(3,2’:6’,3”-terpyridin-4’-yl)benzene (2) have been prepared and characterized by 1H and 13C{1H} NMR, IR, and absorption spectroscopies and mass spectrometry. Reactions of 1 and 2 with cobalt(II) thiocyanate under conditions of crystal growth at room temperature result in the formation of [{Co(1)(NCS) } MeOH 3CHCl ]n and [{Co(2)(NCS) } 0.8MeOH 1.8CHCl ]n. 2 · · 3 2 · · 3 Single-crystal X-ray diﬀraction reveals that each crystal lattice consists of a trinodal self-penetrating 2 4 4 2 5 (6 .8 )(6 .8 )(6 .8)2 net. The nodes are deﬁned by two independent cobalt centres and the centroids of two crystallographically independent ligands which are topologically equivalent.

Keywords: three-dimensional network; self-penetration; 3,2’:6’,3”-terpyridine; tetratopic ligand; cobalt(II) thiocyanate

1. Introduction The coordination chemistry of 2,2’:6’,2”-terpyridine (2,2’:6’,2”-tpy, preferred IUPAC name 12,22:26,32-terpyridine) is well established and is dominated by chelation to a single metal centre [1,2], with mono or bidentate modes being less common [3]. As Scheme1 shows, tridentate bonding by 2,2’:6’,2”-tpy is synonymous with binding one metal ion and the ligand is classed as monotopic (having a single metal-binding domain) [4]. The incorporation of two or more 2,2’:6’,2”-tpy units into a single organic molecule leads to a multitopic ligand [2,5–7] and is a design strategy that has been used to access high nuclearity coordination assemblies [8–10]. An alternative approach is to use isomers of terpyridine, such as 3,2’:6’,3”-tpy (PIN 13,22:26,33-terpyridine) and 4,2’:6’,4”-tpy (PIN 14,22:26,34-terpyridine), in which chelation is not possible (Scheme1). Both 3,2’:6’,3”-tpy and 4,2’:6’,4”-tpy coordinate to metal ions through only the outer nitrogen atoms and are therefore ditopic ligands [4] with two discrete pyridine metal-binding domains. Connection of two 3,2’:6’,3”-tpy or 4,2’:6’,4”-tpy domains through a spacer leads to tetratopic ligands with four discrete pyridine metal-binding domains (Scheme2), which are suitable as building blocks for 2D- and 3D-coordination networks [4,11–18].

Crystals 2019, 9, 529; doi:10.3390/cryst9100529 www.mdpi.com/journal/crystals Crystals 2019, 9, x FOR PEER REVIEW 2 of 14 Crystals 2019, 9, x FOR PEER REVIEW 2 of 14 Crystals 2019, 9, 529 2 of 13 Crystals 2019, 9, x FOR PEER REVIEW 2 of 14

Scheme 1. Conformational change for monotopic 2,2’:6’,2’’-tpy as it binds a metal ion, and the Scheme 1. Conformational change for monotopic 2,2’:6’,2’’-tpy as it binds a metal ion, and the structuresScheme 1. ofConformational 3,2’:6’,3’’-tpy and change 4,2’:6’,4’’-tpy. for monotopic 2,2’:6’,2”-tpy as it binds a metal ion, and the structures structuresScheme 1. of Conformational 3,2’:6’,3’’-tpy and change 4,2’:6’,4’’-tpy. for monotopic 2,2’:6’,2’’-tpy as it binds a metal ion, and the of 3,2’:6’,3”-tpy and 4,2’:6’,4”-tpy. structures of 3,2’:6’,3’’-tpy and 4,2’:6’,4’’-tpy.

Scheme 2. Connection of two 3,2’:6’,3’’-tpy or 4,2’:6’,4’’-tpy domains through a spacer gives SchemetetratopicScheme 2. Connection 2. ligands. Connection of two of 3,2’:6’,3”-tpy two 3,2’:6’,3’’-tpy or 4,2’:6’,4”-tpy or 4,2’:6 domains’,4’’-tpy through domains a spacerthrough gives a tetratopicspacer gives ligands. tetratopicScheme 2.ligands. Connection of two 3,2’:6’,3’’-tpy or 4,2’:6’,4’’-tpy domains through a spacer gives Despitetetratopic ligands.the fact that Cave and Raston reported the synthesis of bis(4,2’:6’,4’’-terpyridin-4’-yl)benzenebis(4,2’:6’,4”-terpyridin-4’-yl)benzeneDespite the fact that inCave in 2001 2001 [19], [and19], the Rastoncoordination reported chemistry the of bis(4,2’:6’,4’’-tpy) bis(4,2’:6’,4”-tpy)synthesis of Despite the fact that Cave and Raston reported the synthesis of ligandsbis(4,2’:6’,4’’-terpyridin-4’-yl)benzene has only developed significantly significantly in 2001in the [19], last the few coordination years.years. With phenylenechemistry of spacers, bis(4,2’:6’,4’’-tpy) the ligands bis(4,2’:6’,4’’-terpyridin-4’-yl)benzene in 2001 [19], the coordination chemistry of bis(4,2’:6’,4’’-tpy) areligands only has poorly only solubledeveloped [[16,20],16, 20significantly], but the introductionintroductiin the laston few of years. solubilizingsolubilizing With phenylene alkoxy substituents spacers, the increases ligands solubilityareligands only has poorly in only CHCl soluble developed3 and [16,20], allows significantly but the the development introductiin the laston few ofof years. asolubilizing versatile With phenylene toolboxalkoxy substituents of spacers, functionalities the increases ligands for solubility in CHCl3 and allows the development of a versatile toolbox of functionalities for tuning are only poorly soluble [16,20], but the introduction of solubilizing alkoxy substituents increases theirtuningsolubility electronic their in CHCl electronic and3 and steric and allows stericproperties. the properties. development We have We of have recentlya versatile recently reviewed toolbox reviewed ofour functionalities our own own progress progress for tuningin in the solubility in CHCl3 and allows the development of a versatile toolbox of functionalities for tuning coordinationtheir electronic chemistrychemistry and steric of of ditopic ditopic properties. and and tetratopic tetratopic We have ligands ligands recently with with 4,2’:6’,4”-tpy reviewed 4,2’:6’,4’’- tpyour metal-binding metal-bindingown progress domains domains in [21the]. their electronic and steric properties. We have recently reviewed our own progress in the The[21].coordination coordinationThe coordination chemistry behavior behavior of ditopic of bis(3,2’:6’,3”-tpy) of and bis(3,2’:6’,3’’-tp tetratopic remainsligandsy) remains littlewith little explored4,2’:6’,4’’- exploredtpy [13, 22 metal-binding[13,22].]. Rotation Rotation about domains about the coordination chemistry of ditopic and tetratopic ligands with 4,2’:6’,4’’-tpy metal-binding domains theinter-ring[21]. inter-ring The coordination C–C C–C bonds bonds in behavior 3,2’:6’,3”-tpy in 3,2’:6’,3’’-tpy of bis(3,2’:6’,3’’-tp (shown (shown in redy) in inremains Schemered in littleScheme3) results explored 3) in results conformational [13,22]. in conformationalRotation changes about [21]. The coordination behavior of bis(3,2’:6’,3’’-tpy) remains little explored [13,22]. Rotation about changesthat,the inter-ring in turn, that, define C–Cin turn, thebonds vectorial define in 3,2’:6’,3’’-tpy arrangementthe vectorial (shown of thearrangement nitrogenin red in lone Schemeof pairsthe innitrogen3) theresults metal-binding lonein conformational pairs domains in the the inter-ring C–C bonds in 3,2’:6’,3’’-tpy (shown in red in Scheme 3) results in conformational (Schememetal-bindingchanges 3).that, This domainsin resultsturn, (Scheme indefine bis(3,2’:6’,3”-tpy) 3).the This vectorial results ligands inar rangementbis(3,2’:6’,3’’-tpy) being especially of the ligands nitrogen flexible being buildinglone especially pairs blocks flexiblein forthe changes that, in turn, define the vectorial arrangement of the nitrogen lone pairs in the buildingthemetal-binding assembly blocks ofdomains 2D-for andthe (Scheme assembly 3D-networks. 3). ofThis 2D- Here,results and we in3D bis(3,2’:6’,3’’-tpy) report-networks. the synthesis Here, ligands we and report being characterization the especially synthesis flexible of twoand metal-binding domains (Scheme 3). This results in bis(3,2’:6’,3’’-tpy) ligands being especially flexible characterizationbis(3,2’:6’,3”-tpy)building blocks of ligandsfor twothe 1bis(3,2’:6’,3’’-tpy)assemblyand 2 (Scheme of 2D-4) andligandsand their 3D -networks.1 reactions and 2 (Scheme with Here, cobalt(II) we 4) reportand thiocyanate their the reactionssynthesis to assemble withand building blocks for the assembly of 2D- and 3D-networks. Here, we report the synthesis and cobalt(II)self-penetratingcharacterization thiocyanate 3D-frameworks.of two to assemblebis(3,2’:6’,3’’-tpy) self-penetrating ligands 3D-frameworks. 1 and 2 (Scheme 4) and their reactions with cobalt(II)characterization thiocyanate of two to assemble bis(3,2’:6’,3’’-tpy) self-penetrating ligands 3D-frameworks. 1 and 2 (Scheme 4) and their reactions with cobalt(II) thiocyanate to assemble self-penetrating 3D-frameworks.

Scheme 3.3. SomeSome of of the the possible possible conformations conformations that that a 3,2’:6’,3”-tpy a 3,2’:6’,3’’-tpy unit can unit adopt can byadopt virtue by of virtue rotations of rotationsaboutScheme the 3.about transannular Some the of transannular the C–C possible bonds C–C conformations (shown bonds in (shown red). that 3,2’:6’,3”-tpy in ared). 3,2’:6’,3’’-tpy 3,2’:6’,3’’-tpy coordinates unit coordinates can only adopt through onlyby thevirtue through outer of Scheme 3. Some of the possible conformations that a 3,2’:6’,3’’-tpy unit can adopt by virtue of (red)therotations outer N atoms. (red)about N the atoms. transannular C–C bonds (shown in red). 3,2’:6’,3’’-tpy coordinates only through therotations outer (red)about N the atoms. transannular C–C bonds (shown in red). 3,2’:6’,3’’-tpy coordinates only through the outer (red) N atoms.

Crystals 2019, 9, 529 3 of 13 Crystals 2019, 9, x FOR PEER REVIEW 3 of 14

Scheme 4. Structures of ligands 1 and 2 with atom labels used for NMR spectroscopic assignments. Scheme 4. Structures of ligands 1 and 2 with atom labels used for NMR spectroscopic assignments. 2. Materials and Methods 2. Materials and Methods 2.1. General 2.1. General 1H and 13C{1H} NMR spectra were recorded on a Bruker Avance III-500 spectrometer (Bruker BioSpin1H and AG, 13 Fällanden,C{1H} NMR Switzerland) spectra were at 298recorded K. The on1H a andBruk13erC NMRAvance chemical III-500 shiftsspectrometer were referenced (Bruker BioSpinwith respect AG, Fällanden, to residual Switzerland) solvent peaks at 298 (δ TMSK. The= 10).H and Matrix-assisted 13C NMR chemical laser shifts desorption were referenced ionization withtime-of-ﬂight respect to (MALDI-TOF) residual solvent mass peaks spectra (δ wereTMS recorded= 0). Matrix-assisted on a Shimadzu laser MALDI desorption 8020 (Shimadzuionization time-of-flightSchweiz GmbH, (MALDI-TOF) 4153 Reinach, mass Switzerland) spectra were using recordedα-cyano-4-hydroxycinnamic on a Shimadzu MALDI acid 8020 as (Shimadzu the matrix. SchweizElectrospray GmbH, ionization 4153 Reinach, (ESI) mass Switzerland) spectra were using recorded α-cyano-4-hydroxycinnamic using a Shimadzu LCMS-2020 acid as the instrument matrix. Electrospray(Shimadzu Schweiz ionization GmbH, (ESI) Reinach, mass spectra Switzerland). were recorded Samples using were a introduced Shimadzu asLCMS-2020 200–800 µ Minstrument solutions (Shimadzuin MeOH, in Schweiz some cases GmbH, with NaClReinach, added. Switzerland). High resolution Samples electrospray were introduced (HR-ESI) mass as 200–800 spectra wereμM solutionsmeasured in on MeOH, a Bruker in some maXis cases 4G QTOF with NaCl instrument added. (Bruker High resolution BioSpin AG, electrospray Fällanden, (HR-ESI) Switzerland). mass spectraPerkinElmer were UATRmeasured Two on (Perkin a Bruker Elmer, maXis 8603 4G Schwerzenbach, QTOF instrument Switzerland) (Bruker BioSpin and Cary-5000 AG, Fällanden, (Agilent Switzerland).Technologies Inc.,PerkinElmer Santa Clara, UATR CA, US)Two instruments (Perkin Elmer, were used8603 to Schwerzenbach, record FT-infrared Switzerland) (IR) and UV-VIS and Cary-5000absorption (Agilent spectra, respectively.Technologies Inc., Santa Clara, CA, US) instruments were used to record FT-infraredCommercial (IR) and chemicals UV-VIS absorption were 3-acetylpyridine spectra, respectively. from Acros Organics (Chemie Brunschwig AG,Commercial 4052 Basel, Switzerland),chemicals were 2,5-dibromohydroquinone 3-acetylpyridine from Acros from Organics Tokyo Chemical(Chemie Brunschwig Industry (4-10-2 AG, 4052Nihonbashi-honcho, Basel, Switzerland), Chuo-ku, 2,5-dibromohydroqu Tokyo 103-0023, Japan),inone andfrom Co(NCS) Tokyo 2 Chemicalfrom Sigma Industry Aldrich (Sigma(4-10-2 Nihonbashi-honcho,Aldrich Chemie GmbH, Chuo-ku, 89555 Steinheim,Tokyo 103-0023, Germany). Japan), These and chemicals Co(NCS) were2 from used Sigma as received. Aldrich (Sigma Aldrich Chemie GmbH, 89555 Steinheim, Germany). These chemicals were used as received. 2.2. 1,4-Dibromo-2,5-bis(2-ethylbutoxy)benzene 2.2. 1,4-Dibromo-2,5-bis(2-ethylbutoxy)benzene Dry DMF (30 mL) was added to a mixture of anhydrous K2CO3 (2.19 g, 15.8 mmol), 2,5-dibromohydroquinoneDry DMF (30 mL) was (1.50 added g, 5.6 to mmol) a mixture and 1-bromo-2-ethylbutaneof anhydrous K2CO3 (2.19 (2.31 g, g, 15.8 14.0 mmol), mmol). 2,5-dibromohydroquinoneThe solution was heated (with(1.50 g, stirring) 5.6 mmol) to 100 and◦ C1-bromo-2-ethylbutane under N2 for 18 h. The(2.31 mixture g, 14.0 mmol). was cooled The solutionto room temperature,was heated (with poured stirring) onto ice to/water 100 °C (100 under mL), andN2 for stirred 18 h. for The 20 min.mixture The was resulting cooled suspension to room temperature,was extracted poured with CH ontoCl ice/water(3 75 mL) (100 and mL), then and the stirred volume for was 20 reducedmin. The and resulting dried insuspension vacuo for was 15 h 2 2 × extractedat 45 ◦C to with yield CH 1,4-dibromo-2,5-bis(2-ethylbutoxy)benzene2Cl2 (3 × 75 mL) and then the volume was reduced as a dark and brown dried oil in (2.33 vacuo g, 5.34for 15 mmol, h at 1 3 a 4595.4%). °C to Hyield NMR 1,4-dibromo-2,5-bis(2-ethylbutoxy)benzene (500 MHz, CDCl3) δ/ppm 7.08 (s, 2H, H ), as 3.84 a dark (d, J =brown5.6 Hz, oil 4H, (2.33 H ),g, 1.77–1.63 5.34 mmol, (m, b c d 13 1 95.4%).2H, H ),1H 1.58–1.43 NMR (500 (m, MHz, 8H, H CDCl), 0.943) δ (t,/ppmJ = 7.5 7.08 Hz, (s, 12H, 2H, H 3),). 3.84C{ (d,H} J NMR= 5.6 Hz, (126 4H, MHz, Ha), CDCl 1.77–1.633) δ/ppm (m, 2 3 1 a b c d 2H,150.3 H (Cb), 1.58–1.43), 118.4 (C (m,), 111.2 8H, H (Cc),), 0.94 72.3 (t, (C J =), 7.5 41.1 Hz, (C 12H,), 23.5 H (Cd). ),13C{ 11.31H} (C NMR). MALDI-TOF-MS (126 MHz, CDClm3/)z δ436.04/ppm 150.3[M+H] (C+2),(calc. 118.4 436.04). (C3), 111.2 (C1), 72.3 (Ca), 41.1 (Cb), 23.5 (Cc), 11.3 (Cd). MALDI-TOF-MS m/z 436.04 [M+H]+ (calc. 436.04). 2.3. 2,5-Bis(2-ethylbutoxy)benzene-1,4-dicarbaldehyde 2.3. 2,5-Bis(2-ethylbutoxy)benzene-1,4-dicarbaldehyde 1,4-Dibromo-2,5-bis(2-ethylbutoxy)benzene (1.50 g, 3.4 mmol) was dissolved in dry Et2O (100 mL) and a1,4-Dibromo-2,5-bis(2-ethylbutoxy)benzene solution of n-BuLi in n-hexane (1.6 M, 6.5 (1.50 mL, g, 10.0 3.4 mmol) mmol) was was added dissolved slowly in dry at 0 Et◦C2O under (100 mL)an N and2 atmosphere a solution over of n a-BuLi period in ofn-hexane 15 min. (1.6 After M, 2 h,6.5 dry mL, DMF 10.0(0.80 mmol) mL, was 10.0 added mmol) slowly was added at 0 °C to under an N2 atmosphere over a period of 15 min. After 2 h, dry DMF (0.80 mL, 10.0 mmol) was added to the white suspension. The mixture was stirred for one day under N2 while warming from

Crystals 2019, 9, 529 4 of 13

the white suspension. The mixture was stirred for one day under N2 while warming from 0 ◦C to room temperature. The reaction mixture was neutralized with saturated aqueous NH4Cl solution and extracted with CH2Cl2 (150 mL). The organic layers were dried over MgSO4 and concentrated in vacuo. The product was obtained as a yellow oil (1.15 g, 3.40 mmol, 100%). 1H NMR (500 MHz, CHO 3 a b CDCl3) δ/ppm 10.52 (s, 2H, H ), 7.44 (s, 2H, H ), 3.99 (d, J = 5.6 Hz, 4H, H ), 1.77–1.68 (m, 2H, H ), c d 13 1 1.54–1.45 (m, 8H, H ), 0.94 (t, J = 7.5 Hz, 12H, H ). C{ H} NMR (126 MHz, CDCl3) δ/ppm 189.5 (CCHO), 155.6 (C2), 129.5 (C1), 111.7 (C3), 71.3 (Ca), 41.1 (Cb), 23.6 (Cc), 11.30 (Cd). MALDI-TOF-MS m/z 336.17 [M+2H]+ (calc. 336.23); ESI-MS (MeOH, NaCl) 421.21 [M+2MeOH+Na]+ (calc. 421.26), 389.20 [M+MeOH+Na]+ (base peak, calc. 389.23).

2.4. 2,5-Bis(3-methylbutoxy)benzene-1,4-dicarbaldehyde 2,5-Bis(3-methylbutoxy)benzene-1,4-dicarbaldehyde has previously been reported [23,24]. It was prepared in the same manner as 2,5-bis(2-ethylbutoxy)benzene-1,4-dicarbaldehyde, and the 1H and 13C{1H) NMR data were in accord with published data [23,24].

2.5. Synthesis of 1,4-Bis(2-ethylbutoxy)-2,5-bis(3,2’:6’,3”-terpyridin-4’-yl)benzene (1) 2,5-Bis(2-ethylbutoxy)benzene-1,4-dicarbaldehyde (570 mg, 1.7 mmol) was dissolved in EtOH (50 mL). 3-Acetylpyridine (927 mg, 0.84 mL, 7.65 mmol) was added followed by crushed KOH (429 mg, 7.65 mmol) in one portion. Aqueous NH3 solution (30%, 14.3 mL) was slowly added and the reaction mixture was stirred at room temperature for three days. The solid that formed was collected by decantation, washed with water (3 10 mL) and ethanol (3 10 mL) and then dried in vacuo overnight. × × The product was isolated as a light-yellow powder (317 mg, 0.43 mmol, 25.2%). M.p. = 209–212 ◦C. 1 A2 H NMR (500 MHz, CDCl3) δ/ppm 9.39 (dd, J = 2.3, 0.9 Hz, 4H, H ), 8.72 (dd, J = 4.7, 1.7 Hz, 4H, HA6), 8.54 (m, 4H, HA4), 8.02 (s, 4H, HB3), 7.48 (m, 4H, HA5), 7.17 (s, 2H, HC3), 3.95 (d, J = 5.5 Hz, 4H, Ha), 1.65–1.58 (m, 2H, Hb), 1.42–1.32 (m, 8H, Hc), 0.82 (t, J = 7.5 Hz, 12H, Hd). 13C{1H} NMR B2 C2 A6 A2 C1 A3 (500 MHz, CDCl3) δ/ppm 154.8 (C ), 150.8 (C ), 150.4 (C ), 148.5 (C ), 148.2 (C ), 134.8 (C ), 134.6 (CA4), 129.5 (CB4), 123.8 (CA5), 120.4 (CB3), 115.2 (CC3), 71.7 (Ca), 41.3 (Cb), 23.6 (Cc), 11.3 (Cd). UV-VIS (CHCl , 1.2 10–5 mol dm–3) λ/nm 244 (ε/dm3 mol–1 cm–1 52,000) 278 sh (42,300), 318 (18,100), 3 × 354 (9,800). MALDI-TOF-MS m/z 741.34 [M+H]+ (calc. 741.39). Found C 77.25, H 6.56, N 11.03; required for C48H48N6O2 C 77.81, H 6.53, N 11.34. The FT-IR spectrum of 1 is shown in Figure S1 (see Supplementary material).

2.6. Synthesis of 1,4-Bis(3-methylbutoxy)-2,5-bis(3,2’:6’,3”-terpyridin-4’-yl)benzene (2) 2,5-Bis(3-methylbutoxy) benzene-1,4-dicarbaldehyde (510 mg, 1.66 mmol) was dissolved in 30 mL EtOH (30 mL) and then 3-acetylpyridine (905 mg, 0.82 mL, 7.47 mmol) was added. Crushed KOH (419 mg, 7.47 mmol) was then added in one portion. Aqueous NH3 solution (30%, 12.8 mL) was slowly added and the reaction mixture was stirred at room temperature for one day. The solid that formed was collected by ﬁltration, washed with water (3 10 mL) and ethanol (3 10 mL) and then dried in × × vacuo for three days. The product was isolated as a slightly yellowish powder (207 mg, 0.29 mmol, 1 A2 17.5%). M.p. = 220–221 ◦C. H NMR (500 MHz, CDCl3) δ/ppm 9.38 (dd, J = 2.3, 0.9 Hz, 4H, H ), 8.72 (dd, J = 4.7, 1.7 Hz, 4H, HA6), 8.53 (dt, J = 8.0, 2.0 Hz, 4H, HA4), 8.03 (s, 4H, HB3), 7.48 (ddd, J = 8.0, 4.8, 0.9 Hz, 4H, HA5), 7.17 (s, 2H, HC3), 4.09 (t, J = 6.4 Hz, 4H, Ha), 1.79–1.71 (m, 2H, Hc), b d 13 1 B2 1.66 (m, 4H, H ), 0.86 (d, J = 6.6 Hz, 12H, H ). C{ H} NMR (500 MHz, CDCl3) δ/ppm 154. (C ), 150.71 (CC2), 150.4 (CA6), 148.5 (CA2), 148.1 (CC1), 134.9 (CA3), 134.6 (CA4), 129.4 (CB4), 123.8 (CA5), 120.4 (CB3), 115.3 (CC3), 68.1 (Ca), 38.2 (Cb), 25.2 (Cc), 22.6 (Cd). UV-VIS (CHCl , 1.0 10–5 mol dm–3) 3 × λ/nm 244 (ε/dm3 mol–1 cm–1 44,600) 279 sh (36,200), 318 (16,500), 354 (9,800). MALDI-TOF-MS m/z 713.41 [M+H]+ (calc. 713.36). HR-MS m/z 713.3587 [M+H]+ (calc. 713.3599), 357.1836 [M+2H]2+ (calc. 357.1836). Satisfactory elemental analysis could not be obtained. The FT-IR spectrum of 2 is shown in Figure S2 (see Supplementary material). Crystals 2019, 9, 529 5 of 13

2.7. Synthesis of [{Co(1)(NCS) } MeOH 3CHCl ]n 2 · · 3 A MeOH (8 mL) solution of Co(NCS)2 (1.75 mg, 0.01 mmol) was layered over a CHCl3 (5 mL) solution of ligand 1 (7.41 mg; 0.01 mmol) in a crystallization tube (inner dimeter = 13.6 mm, volume = 24 mL). This was left to stand at room temperature. Orange block-like crystals visible to the eye were first obtained after 15 days, and a single crystal was selected for X-ray diffraction after another four days. A portion of the remaining crystals was mounted wet in a sample holder (to avoid loss of solvent from the crystals) and analyzed by powder X-ray diffraction (PXRD).

2.8. Synthesis of [{Co(2)(NCS) } 0.8MeOH 1.8CHCl ]n 2 · · 3 A MeOH (8 mL) solution of Co(NCS)2 (1.75 mg, 0.01 mmol) was layered over a CHCl3 (5 mL) solution of ligand 2 (6.33 mg, 0.01 mmol) in a crystallization tube (inner dimeter = 13.6 mm, volume = 24 mL) which was left to stand at room temperature. Orange block-like crystals visible to the eye were ﬁrst obtained after seven days, and an X-ray quality crystal was selected after two months. A portion of the remaining crystals was mounted wet in a sample holder (to avoid loss of solvent from the crystals) and analyzed by PXRD.

2.9. Crystallography Single crystal data were collected on a Bruker APEX-II diffractometer (CuKα radiation) with data reduction, solution and refinement using the programs APEX, ShelXT, Olex2 and ShelXL v. 2014/7, or using a STOE StadiVari diffractometer equipped with a Pilatus300K detector and with a Metaljet D2 source (GaKα radiation) [25–28]. The structure was solved using Superflip and Olex2 [27,29,30]. The model was refined with ShelXL v. 2014/7 [28]. Structure analysis used Mercury CSD v. 4.2.0 [31,32]. In [{Co(1)(NCS) } MeOH 3CHCl ]n, one CHCl molecule was located and refined, and the Olex2 2 · · 3 3 implementation of SQUEEZE [33] was used to treat the rest of the solvent region. A solvent mask was 3 calculated, and 1044.0 electrons were found in a volume of 3742.0 Å− in one void. This is consistent with the presence of 2CHCl3 and 1CH3OH per formula unit which account for 1072.0 electrons. The formulae and dependent numbers were adapted to account for this. Due to their thermal motion, the aliphatic chains had to be heavily restrained with SIMU, SADI, and DFIX restraints and were refined isotropically. H atoms were positioned geometrically, then allowed to ride on their parent atom. In [{Co(2)(NCS) } 0.8MeOH 1.8CHCl ]n, the aliphatic chains display orientational and vibrational 2 · · 3 disorder and were modelled with the use of SADI and DFIX restraints, one chain over two sites of partial occupancies 0.60/0.40 and the other chain with equal occupancy sites. Some atoms were refined isotropically. Disorder in one thiocyanate ligand was modelled with two sites for the S atom of partial occupancies 0.75/0.25. All the solvent molecules present in this structure were modelled with partial occupancies. H atoms were positioned geometrically, then allowed to ride on their parent atoms. Phase purity of bulk samples of the two compounds was confirmed at room temperature by PXRD in transmission mode using a Stoe Stadi P diffractometer equipped with a Cu Kα1 radiation (Ge(111) monochromator) and a DECTRIS MYTHEN 1K detector. The single crystal of [{Co(1)(NCS) } MeOH 3CHCl ]n is representative of the main phase of the bulk sample. Minor phases 2 · · 3 are also present in the bulk, which can be attributed to solvent loss during sample preparation and measurement. The bulk sample of [{Co(2)(NCS) } 0.8MeOH 1.8CHCl ]n corresponds to the material 2 · · 3 characterized in the single crystal structure. The reflections of the main phases were indexed with a monoclinic cell in the space group C2/c (No. 15). The whole-pattern decomposition (profile matching) analysis of the diffraction patterns was done by the package FULLPROF SUITE [34–37] (version July-2019) using a previously determined instrumental resolution function (based on the silicon NIST standard 640d). The crystal model for the two compounds was taken from the single crystal diffraction data. Refined parameters were zero shift, sample displacement, transparency, lattice parameters, and peaks shapes (Y) as a Thompson-Cox-Hastings pseudo-Voigt function. Crystals 2019, 9, 529 6 of 13

Crystals 2019, 9, x FOR PEER REVIEW. 6 of 14 2.10. [{Co(1)(NCS) } MeOH 3CHCl ]n 2 · 3 CC5454Cl9CoHCoH5454NN8O8O3S32S, 2M, Mr =r 1305.15,= 1305.15, orange orange block, block, monoclinic, monoclinic, space space group group C2/Cc,2 a/c =, a37.514(3),= 37.514(3), b = 3 –3 b17.4813(11),= 17.4813(11), c = 26.6265(17)c = 26.6265(17) Å, β Å,= 133.660(3)°,β = 133.660(3) V =◦ 12632.4(15), V = 12632.4(15) Å3, Dc Å= 1.373, Dc = g 1.373cm–3, gT cm= 130, K,T =Z 130= 8, K,Z’ –1 Z= =1, 8,μ(CuKZ’ = 1,α)µ =(CuK 6.630α )mm= 6.630–1. Total mm 69,524. Total reflections, 69,524 reflections, 9110 unique 9110 unique(Rint = 0.02879). (Rint = 0.02879). Refinement Refinement of 5412 ofreflections 5412 reflections (552 parameters) (552 parameters) with I with> 2σ(I)> converged2σ(I) converged at final at R final1 = 0.1118R1 = 0.1118(R1 all (dataR1 all = data0.1470),= 0.1470), wR2 = wR0.32362 = 0.3236(wR2 all (wR data2 all = data0.3606),= 0.3606), gof = 1.228, gof = max1.228, = 59.311°.max = CCDC59.311◦ 1954948.. CCDC 1954948.

2.11. [{Co(2)(NCS) }. 0.8MeOH. 1.8CHCl ]n 2.11. [{Co(2)(NCS)22}·0.8MeOH·1.8CHCl33]n

CC50.650.6HH4949ClCl5.45.4CoNCoN8O8O2.82.8S2,S M2, rM =r 1128.46,= 1128.46, orange orange plate, plate, monoclinic, monoclinic, space space group group C2/C2c/,c a, a= =37.7611(9),37.7611(9), b 3 –3 b= =17.3396(3),17.3396(3), c =c 27.5031(6)= 27.5031(6) Å, β Å, = β135.1980(10)= 135.1980(10)o, V =◦, 12689.5(5)V = 12689.5(5) Å3, Dc Å = 1.181, Dc = g1.181 cm–3, gT cm= 130, K,T = Z 130= 8, K,Z’ µ α –1 Z= =1, 8,μ(GaKZ’ = 1,α) =(GaK 3.447 )mm= 3.447–1. Total mm 91,813. Total reflections, 91,813 reflections, 12996 unique 12996 unique(Rint = 0.1323). (Rint = 0.1323).Refinement Refinement of 8243 ofreflections 8243 reflections (655 parameters) (655 parameters) with I with> 2σ(I)> converged2σ(I) converged at final at R final1 = 0.1424R1 = 0.1424(R1 all (dataR1 all = data0.1884),= 0.1884), wR2 = wR0.41802 = 0.4180(wR2 all (wR data2 all = data0.5084),= 0.5084), gof = 0.918, gof = max0.918, = 57.448max o=. CCDC57.448◦ 1954949.. CCDC 1954949.

3. Results and Discussion 3. Results and Discussion 3.1. Synthesis and Characterization of Ligands 1 and 2 3.1. Synthesis and Characterization of Ligands 1 and 2 The strategy for the preparation of compounds 1 and 2 was similar to that used to synthesize The strategy for the preparation of compounds 1 and 2 was similar to that used to synthesize related tetratopic ligands [11] and is adapted from a procedure reported in the literature [38]. The route related tetratopic ligands [11] and is adapted from a procedure reported in the literature [38]. The is summarized in Scheme5. MALDI-TOF mass spectra of 1 and 2 are shown in Figures S3 and S4 route is summarized in Scheme 5. MALDI-TOF mass spectra of 1 and 2 are shown in Figures S3 and (see Supplementary material). The base peak in both spectra arises from the [M+H]+ ion (m/z = 741.34 S4 (see Supplementary material). The base peak in both spectra arises from the [M+H]+ ion (m/z = for compound 1, and m/z = 713.41 for compound 2). 741.34 for compound 1, and m/z = 713.41 for compound 2).

Scheme 5. Synthetic route to 1 and 2. Conditions (see Materials and Methods for full details): (i) RBr, Scheme 5. Synthetic route to 1 and 2. Conditionsn (see Materials and Methods for full details): (i) RBr, anhydrous K2CO3, dry DMF, 100 ◦C, 18 h; (ii) BuLi, Et2O, 0 ◦C; dry DMF, warmed to room temperature, anhydrous K2CO3, dry DMF, 100 °C, 18 h; (ii) nBuLi, Et2O, 0 °C; dry DMF, warmed to room 17 h. (iii) 3-acetylpyridine, KOH, EtOH, aqueous NH3, room temperature, three days for 1 and one day temperature, 17 h. (iii) 3-acetylpyridine, KOH, EtOH, aqueous NH3, room temperature, three days for 2. for 1 and one day for 2. 1 31 1 The H and C{ H} NMR spectra of 1 and 2 were recorded in CDCl3 and signals were assigned 1 31 1 usingThe the COSY,H and NOESY,C{ H} NMR HMQC spectra and HMBC of 1 and spectra. 2 were The recorded spectroscopic in CDCl signatures3 and signals of the were tpy domainsassigned areusing not the aﬀected COSY, by NOESY, the change HMQC in the and alkoxy HMBC substituent, spectra. and The the spectroscopic aliphatic regions signatures of the spectraof the aretpy consistentdomains are with not the affected 2-ethylbutoxy by the and change 3-methylbutoxy in the alkoxy groups substituent, in 1 and 2and, respectively the aliphatic (Figure regions1). HMQC of the andspectra HMBC are spectraconsistent of thewith two the compounds 2-ethylbutoxy are shownand 3-methylbutoxy in Figures S5–S8 groups (see Supplementary in 1 and 2, respectively material). The(Figure solution 1). HMQC absorption and spectra HMBC of spectra compounds of the1 and two2 compoundsare displayed are in Figureshown2 andin Figures are similar S5–S8 to that(see observedSupplementary for 1,4-bis( material).n-octyloxy)-2,5-bis(3,2’:6’,3”-terpyridin-4’-yl)benzene The solution absorption spectra of compounds [13 ].1 and Absorptions 2 are displayed arise from in spin-allowedFigure π2* π andandπ* n transitions.are similar to that observed for 1,4-bis(n-octyloxy)-2,5-bis(3,2’:6’,3’’-terpyridin-4’-yl)benzene← ← [13]. Absorptions arise from spin-allowed π*←π and π*←n transitions.

CrystalsCrystals 20192019, ,99, ,x 529 FOR PEER REVIEW 77 of of 14 13 Crystals 2019, 9, x FOR PEER REVIEW 7 of 14

Figure 1. 1H NMR (500 MHz, CDCl3, 298 K) of (a) 1 and (b) 2. Chemical shifts in δ/ppm. * = CHCl3, ** 11 =Figure Figurewater. 1. 1. HH NMRNMR (500(500 MHz,MHz, CDCl3,, 298 298 K) K) of of ( (aa)) 11 and ( (bb)) 22.. Chemical Chemical shifts shifts in in δδ/ppm./ppm. * *== CHClCHCl3, 3**, **= =water.water.

Figure 2. Solution absorption spectra of 1 and 2 in CHCl (1.2 10–5 mol dm–3 for 1, 1.0 10–5 mol dm–3 for 2). Figure 2. Solution absorption spectra of 1 and 2 in CHCl3 3 (1.2× × 10–5 mol dm–3 for 1, 1.0× × 10–5 mol dm– –5 –3 –5 – 3 Figure 2. Solution absorption spectra of 1 and 2 in CHCl3 (1.2 × 10 mol dm for 1, 1.0 × 10 mol dm 3.2. Crystal for 2). Growth and Powder X-ray Diffraction 3 for 2). Single crystals of [{Co(1)(NCS)2} MeOH 3CHCl3]n and [{Co(2)(NCS)2} 0.8MeOH 1.8CHCl3]n were · · · · grown under ambient conditions by layering a methanol solution of Co(NCS)2 over a chloroform 3.2.solution Crystal of Growth ligand and1 orPowder2. After X-ay selectionDiffraction of crystals for single-crystal X-ray diffraction studies (see3.2. SectionCrystal Growth3.2), the and bulk Powder materials X-ay Diffraction were analyzed by powder X-ray diffraction (PXRD). Despite Single crystals of [{Co(1)(NCS)2}.MeOH.3CHCl3]n and [{Co(2)(NCS)2}.0.8MeOH.1.8CHCl3]n were carefulSingle handling crystals of theof [{Co( crystals,1)(NCS) loss2} of.MeOH solvent.3CHCl could3]n notand be [{Co( prevented2)(NCS) completely,2}.0.8MeOH.1.8CHCl and as a3] result,n were grown under ambient conditions by layering a methanol solution of Co(NCS)2 over a chloroform the PXRD spectra were of poor quality. Figure3 shows a refinement of the PXRD pattern for solutiongrown underof ligand ambient 1 or 2 conditions. After selection by laye ofring crystals a methanol for single-crystal solution of X-ray Co(NCS) diffraction2 over studiesa chloroform (see each bulk material compared with that determined from the single crystal structure of each of Sectionsolution 3.2), of theligand bulk 1 materialsor 2. After were selection analyzed of crystals by powder for single-crystal X-ray diffraction X-ray (PXRD). diffraction Despite studies careful (see [{Co(Section1)(NCS) 3.2), 2the} MeOH bulk materials3CHCl3] nwereand analyzed [{Co(2)(NCS) by powder2} 0.8MeOH X-ray1.8CHCl diffraction3]n .(PXRD). The profile Despite matching careful handling of the ·crystals,· loss of solvent could not be prevented· completely,· and as a result, the PXRD refinementhandling of confirmed the crystals, that loss the of single solvent crystal could structures not be prevented of [{Co( 2completely,)(NCS)2} 0.8MeOH and as a 1.8CHClresult, the3] nPXRDand spectra were of poor quality. Figure 3 shows a refinement of the PXRD pattern· for each· bulk material [{Co(spectra1)(NCS) were2 of} MeOH poor quality.3CHCl Figu3]n arere 3 representative shows a refinement of the of bulk the PXRD sample pattern and the for main each phasebulk material of the compared with· that· determined from the single crystal structure of each of bulkcompared sample, with respectively. that Minordetermined phases from observed the in thesingle PXRD crystal spectrum structure of thebulk of materialeach ofof [{Co(1)(NCS)2}.MeOH.3CHCl3]n and [{Co(2)(NCS)2}.0.8MeOH.1.8CHCl3]n. The profile matching [{Co(1)(NCS)2}.MeOH.3CHCl3]n and [{Co(2)(NCS)2}.0.8MeOH.1.8CHCl3]n. The profile matching refinement confirmed that the single crystal structures of [{Co(2)(NCS)2}.0.8MeOH.1.8CHCl3]n and refinement confirmed that the single crystal structures of [{Co(2)(NCS)2}.0.8MeOH.1.8CHCl3]n and [{Co(1)(NCS)2}.MeOH.3CHCl3]n are representative of the bulk sample and the main phase of the bulk [{Co(1)(NCS)2}.MeOH.3CHCl3]n are representative of the bulk sample and the main phase of the bulk

Crystals 2019, 9, x FOR PEER REVIEW 8 of 14 Crystals 2019, 9, 529 8 of 13 sample, respectively. Minor phases observed in the PXRD spectrum of the bulk material of [{Co(1)(NCS)2}.MeOH.3CHCl3]n could not be assigned and most likely appear as a consequence of [{Co(1)(NCS) } MeOH 3CHCl ]n could not be assigned and most likely appear as a consequence of solvent loss during2 · sample· preparation3 and measurement. solvent loss during sample preparation and measurement.

Figure 3. Laboratory X-ray diffraction (CuKα1 radiation) pattern (red crosses) of [{Co(Figure1)(NCS) 3. }LaboratoryMeOH 3CHCl X-ray]n (experiment diffraction I) and(CuK [{Co(α12 )(NCS)radiation)} 0.8MeOH pattern1.8CHCl (red] n (experimentcrosses) of 2 · · 3 2 · · 3 II)[{Co( (space1)(NCS) group2}.MeOHC2/c, .3CHClNo. 15)3]n at(experiment room temperature. I) and [{Co( The2)(NCS) black2}.0.8MeOH line corresponds.1.8CHCl to3]n the(experiment best fit fromII) (space the profile group matchingC2/c, No. 15) refinement. at room temperature. Lower vertical The marksblack line denote corresponds the Bragg to peakthe best positions fit from for the [{Co(profile1)(NCS) matching} MeOH refinement.3CHCl ]n andLower [{Co( vertical2)(NCS) marks} 0.8MeOH denote1.8CHCl the ]Braggn phases. peak The positions bottom grey for 2 · · 3 2 · · 3 line[{Co( represents1)(NCS)2} the.MeOH difference.3CHCl between3]n and experimental[{Co(2)(NCS)2 and}.0.8MeOH calculated.1.8CHCl points.3]n phases. The bottom grey line represents the difference between experimental and calculated points. 3.3. Single Crystal Structures 3.3. Single Crystal Structures Ligands 1 and 2 react with Co(NCS)2 to form structurally similar three-dimensional networks [{Co(1)(NCS) } MeOH 3CHCl ]n and [{Co(2)(NCS) } 0.8MeOH 1.8CHCl ]n. The change from the Ligands2 1· and 2 ·react with3 Co(NCS)2 to form 2structurally· · similar three-dimensional3 networks 2-ethylbutoxy[{Co(1)(NCS)2} to.MeOH 3-methylbutoxy.3CHCl3]n and substituents [{Co(2)(NCS) on the2}.0.8MeOH central phenylene.1.8CHCl3]n spacer. The inchange the ligand from hasthe little2-ethylbutoxy impact on to the 3-methylbutoxy structural assembly. substituents Both compoundson the central crystallize phenylen ine spacer the C2 in/c thespace ligand group has with little similarimpact cellon the dimensions structural (see assembly. Sections Both 2.10 compounds and 2.11). crystallize We therefore in the discuss C2/c space only group one structure with similar in detail. In [{Co(2)(NCS) } 0.8MeOH 1.8CHCl ]n, the 3-methylbutoxy chains are disordered and cell dimensions (see Sections2 · 2.10 and· 2.11). 3We therefore discuss only one structure in detail. In were[{Co( modelled2)(NCS)2}.0.8MeOH using restraints..1.8CHCl3] Then, the structure 3-methylbutoxy chosen chains for the are detailed disordered discussion and were is thereforemodelled [{Co(1)(NCS) } MeOH 3CHCl ]n. The asymmetric unit contains two independent cobalt atoms and using restraints.2 · The· structure3 chosen for the detailed discussion is therefore two[{Co( independent1)(NCS)2}.MeOH half-ligands.3CHCl3]n1. The(Figure asymmetric S9), and unit the secondcontains half two of independent each ligand cobalt is generated atoms and by inversion.two independent Atom Co1 half-ligands resides on 1 an (Figure inversion S9), centre and the (Wycko secondff notation half of neach), while ligand Co2 is lies generated on a 2-fold by axis.inversion. Figure Atom4 shows Co1 the resides repeat on unit an inversion of the coordination centre (Wyckoff network notation with symmetry-generated n), while Co2 lies on atoms,a 2-fold andaxis. bond Figure distances 4 shows for the the repeat coordination unit of the spheres coordination of Co1 network and Co2 with are givensymmetry-generated in Table1. All bondatoms, lengthsand bond are typical.distances Both for atomsthe coordination Co1 and Co2 spheres are octahedrally of Co1 and coordinated Co2 are given with intrans Table-arrangements 1. All bond oflengths thiocyanato are typical. ligands, Both and atoms N–Co–N Co1 and bond Co2 angles are octahedrally lie in the 87.0(2) coordinated◦ to 93.1(3) with◦ range.trans-arrangements Each metal atomof thiocyanato binds to one ligands, pyridine and donor N–Co–N atom bond of four angles different lie in ligands the 87.0(2)°1, thereby to 93.1(3)° acting asrange. a 4-connecting Each metal

Crystals 2019, 9, x FOR PEER REVIEW 9 of 14 atom binds to one pyridine donor atom of four different ligands 1, thereby acting as a 4-connecting node. For comparison, the asymmetric unit and repeat unit in [{Co(2)(NCS)2}.0.8MeOH.1.8CHCl3]n are depicted in Figures S10 and S11.

Table 1. Important bond lengths in [{Co(1)(NCS)2}.MeOH.3CHCl3]n and

[{Co(2)(NCS)2}.0.8MeOH.1.8CHCl3]n.

Corresponding Bond Lengths in [{Co(1)(NCS)2}.MeOH.3CHCl3]n Bond a [{Co(2)(NCS)2}.0.8MeOH.1.8CHCl3]n Bond Length/Å Bond Length/Å Co1–N1 2.171(6) 2.175(6) Co1–N6 ii 2.229(6) 2.244(6) Co1–N8 2.065(6) 2.091(5) Co2–N3 2.136(6) 2.138(6) Crystals 2019, 9, 529 9 of 13 Co2–N4 2.145(6) 2.134(6) Co2–N7 2.074(6) 2.107(7) a node.In [{Co( For1 comparison,)(NCS)2}.MeOH.3CHCl the asymmetric3]n, symmetry unit code and repeatii = 1 unit− x in, [{Co(−1 +2 )(NCS)y, ½ −} 0.8MeOHz (see Figure1.8CHCl 4). In]n 2 · · 3 [{Co(are depicted2)(NCS)2}.0.8MeOH in Figures.1.8CHCl S103] andn, symmetry S11. code ii = x, 1 − y, −1/2 + z (see Figure S11).

Figure 4. The repeat unit in the coordination network of [{Co(1)(NCS)2} MeOH 3CHCl3]n with · . ·. Figuresymmetry-generated 4. The repeat atoms.unit in For the clarity, coordination H atoms andnetwork solvent of molecules[{Co(1)(NCS) are2 omitted,} MeOH 3CHCl and only3]n thewith O symmetry-generated atoms. For clarity, H atoms and solvent molecules1 1 are omitted, and only the O atoms of the alkoxy groups are shown. Symmetry codes: i = /2 x, /2 y, z; ii = 1 x, 1 + y, atoms1 of the alkoxy1 groups3 are1 shown. Symmetry codes: i = 1/2 − x1, 1/−2 − y, 1−z; −ii = 1− − x, −1 + y−, 1/2 −− z; iii = /2 z; iii = /2 + x, /2 y, /2 + z; iv = 1 x, 1 y, 1 z; v = /2 + x, /2 + y, 1 + z; vi = 1 x, 2 y, −1/2 +− x, 3/2 − y−, −1/2 + z; iv =1 −1 − x−, 1 − y, 1 1− z; v = −11/2 + x,− 1/21 + y,− 1 + z; vi = 1 − x, 2 1− y, 1 − z; vii = 1 − x−, 1 + y,− 1/2 1 z; vii = 1 x, 1 + y, /2 z; viii = /2 x, /2 + y, /2 z; ix = 1 x, y, /2 z. For an ORTEP-style − 1 − 1 1 − −1 − − − −ﬁgure z; viiiof = the/2 − asymmetricx, /2 + y, /2 − unit, z; ix see= 1 Figure− x, y, S9/2 −in z. theFor Supplementaryan ORTEP-style material. figure of the asymmetric unit, see Figure S9 in the Supplementary material. Table 1. Important bond lengths in [{Co(1)(NCS) } MeOH 3CHCl ]n and [{Co(2)(NCS) } 0.8MeOH 1.8CHCl ]n. 2 · · 3 2 · · 3 The tpy unit of each independent ligand 1 is twisted to give a conformation close to . . Corresponding Bond Lengths in a [{Co(1)(NCS)2} MeOH 3CHCl3]n . . conformationBond III in Scheme 1. Coordination occurs only through[{Co(2)(NCS) the two2} outer0.8MeOH nitrogen1.8CHCl atoms3]n (see the discussion in the introduction). Angles between the least squares planes through pairs of Bond Length/Å Bond Length/Å pyridine rings containing N1/N2, N2/N3, N4/N5 and N5/N6 are 10.6(4), 18.6(4), 29.8(3) and 36.1(3)°, Co1–N1 2.171(6) 2.175(6) respectively. The phenylene ring is twisted 39.1(3)° with respect to the pyridine ring to which it is Co1–N6 ii 2.229(6) 2.244(6) Co1–N8 2.065(6) 2.091(5) Co2–N3 2.136(6) 2.138(6) Co2–N4 2.145(6) 2.134(6) Co2–N7 2.074(6) 2.107(7) a 1 In [{Co(1)(NCS)2} MeOH 3CHCl3]n, symmetry code ii = 1 x, 1 + y, 2 z (see Figure4). · · −1 − − In [{Co(2)(NCS) } 0.8MeOH 1.8CHCl ]n, symmetry code ii = x, 1 y, / + z (see Figure S11). 2 · · 3 − − 2

The tpy unit of each independent ligand 1 is twisted to give a conformation close to conformation III in Scheme1. Coordination occurs only through the two outer nitrogen atoms (see the discussion in the introduction). Angles between the least squares planes through pairs of pyridine rings containing N1/N2, N2/N3, N4/N5 and N5/N6 are 10.6(4), 18.6(4), 29.8(3) and 36.1(3)◦, respectively. The phenylene ring is twisted 39.1(3)◦ with respect to the pyridine ring to which it is bonded in one independent ligand 1 and 38.8(3)◦ in the other. These values are typical for bonded aromatic rings. Crystals 2019, 9, x FOR PEER REVIEW 10 of 14

o bondedCrystals 2019 in, 9one, 529 independent ligand 1 and 38.8(3) in the other. These values are typical for bonded10 of 13 aromatic rings. The structure propagates into a three-dimensional network which possesses four chemically distinctThe nodes, structure all of propagates which are 4-connecting. into a three-dimensional These nodes networkare defined which by atoms possesses Co1 and four Co2 chemically and the centroidsdistinct nodes, of the all oftwo which independent are 4-connecting. phenylene These rings. nodes The are deﬁnedtwo ligand by atoms nodes Co1 are and topologically Co2 and the equivalentcentroids of (this the twowas independentconfirmed using phenylene the program rings. The Systre two [39]) ligand and nodes thus arethe topologicallyunderlying topological equivalent (thisnet is was trinodal. conﬁrmed The full using vertex the program symbol is Systre (62.84 [)(639])4.8 and2)(65 thus.8)2, with the underlying the individual topological symbols net referring is trinodal. to 2 4 4 2 5 Co1,The fullCo2 vertex and the symbol ligands, is (6 respectively..8 )(6 .8 )(6 Figure.8)2, with 5 displays the individual part of symbolsthe net viewed referring down to Co1, the Co2a- and and c axes.the ligands, A view respectively. down the b-axis Figure is5 shown displays in partFigure of theS12. net In viewedthese representations, down the a- and Co1c axes. atoms A vieware shown down inthe blue,b-axis Co2 is shown in orange, in Figure and S12. the In ligand these representations,nodes in green. Co1 Combination atoms are shown of Co2 in blue,and Co2ligand in orange,nodes generatesand the ligand sheets nodes that inare green. coplanar Combination with the bc of-plane, Co2 and while ligand sheets nodes composed generates of sheets Co1 and that ligand are coplanar nodes withslice theobliquelybc-plane, through while sheetsthe unit composed cell. The ofnet Co1 is sel andf-penetrating, ligand nodes with slice the obliquely shortest through circuits the of unit the cell.net penetratedThe net is self-penetrating, by rods of the same with thenet shortest [40], and circuits is highly of the unusual, net penetrated with the by net rods not of appearing the same net on [40the], Reticularand is highly Chemistry unusual, Structure with the Resource net not (RCSR) appearing databa onse the of Reticular3D nets [41]. Chemistry The self-penetration Structure Resource can be (RCSR)appreciated database by inspection of 3D nets of [41 Figure]. The 6. self-penetration The catenated can shortest be appreciated circuits comprise by inspection four ofCo1 Figure atoms6. linkedThe catenated by ligand shortest nodes, circuits and three comprise such four circuits Co1 atomsare depicted linked byin ligandred and nodes, magenta and threein Figure such circuits6. This representationare depicted in redhighlights and magenta the ininterlocking Figure6. This of representationthe shortest highlightscircuits thewhich interlocking produces of thethe 2 4 4 2 5 self-penetratingshortest circuits which(62.84)(6 produces4.82)(65.8)2 the net. self-penetrating (6 .8 )(6 .8 )(6 .8)2 net.

Figure 5. PartPart of of the the 3D 3D net net in in [{Co( [{Co(11)(NCS))(NCS)2}2.MeOH} MeOH.3CHCl3CHCl3]n3 viewed]n viewed down down the thecrystallographic crystallographic (a) Crystals 2019, 9, x FOR PEER REVIEW · · 11 of 14 a(a-axis) a-axis and and (b) (cb-axis.) c-axis. Colour Colour code code for forthe thenodes: nodes: Co1 Co1 blue, blue, Co2 Co2 orange, orange, ligand ligand centroids centroids green. green.

FigureFigure 6. Part 6. Part of the of 3Dthe net3D net in [{Co(in [{Co(1)(NCS)1)(NCS)}2}MeOH.MeOH.3CHCl3]n] nhighlightinghighlighting the theinterlocking interlocking of the of the 2 · · 3 shortestshortest circuits circuits (shown (shown in red in andred magenta).and magenta). Colour Colour code code for for the the nodes: nodes: Co1 Co1 blue, blue, Co2 Co2 orange, orange, ligand centroidsligand green. centroids green.

The structural similarity between the nets in [{Co(1)(NCS)2}.MeOH.3CHCl3]n and [{Co(2)(NCS)2}.0.8MeOH.1.8CHCl3]n indicates that both the 2-ethylbutoxy and 3-methylbutoxy groups are accommodated within the cavities in the network and that there is little difference between the steric requirements of these substituents. Significantly, if the substituents are replaced by n-octyloxy chains in [{Co(3)(NCS)2}.4CHCl3]n where 3 is 1,4-bis(n-octyloxy)-2,5-bis(3,2’:6’,3’’-terpyridin-4’-yl)benzene, a switch in assembly is observed to an {42.84} lvt net [13]. In this structure, the long n-octyloxy chains are in non-extended conformations and each lies over a 3,2’:6’,3’’-tpy unit with close C–H...π contacts.

4. Conclusions We have described the synthesis and characterization of the tetratopic bis(3,2’:6’,3’’-tpy) ligands 1 and 2. Reactions of 1 and 2 with Co(NCS)2 under ambient conditions lead to the assembly of [{Co(1)(NCS)2}.MeOH.3CHCl3]n and [{Co(2)(NCS)2}.0.8MeOH.1.8CHCl3]n, the structures of which are similar. Each exhibits an unusual trinodal, self-penetrating (62.84)(64.82)(65.8)2 3D-net with the nodes defined by two independent cobalt centres, and the centroids of two crystallographically independent but topologically equivalent ligands. PXRD confirms that the single crystal structures are representative of the bulk material. The similar steric requirements of the 2-ethylbutoxy and 3-methylbutoxy substituents leads to a reproducible 3D-assembly, contrasting with the assembly of a 3D {42.84} net when n-octyloxy substituents replace the 2-ethylbutoxy and 3-methylbutoxy groups. We will now further explore how choice of substituents leads to a switch in network.

Supplementary Materials: The following are available online at www.mdpi.com/xxx/s1, Figures S1 and S2: FT-IR spectra of 1 and 2; Figures S3 and S4: mass spectra of 1 and 2; Figures S5–S8: NMR spectra of 1 and 2; Figure S9: Figures S9–S12: additional crystallographic diagrams

Author Contributions: Investigation and methodology, G.M.; crystallography, A.P.; powder diffraction, Y.M.K., D.J.G.; manuscript writing, C.E.H., G.M., Y.M.K., S.R.B.; manuscript editing, E.C.C.; S.R.B.; supervision, C.E.H.; E.C.C.; project administration, C.E.H.; E.C.C.; funding acquisition, C.E.H.

Funding: This research was funded by the Swiss National Science Foundation (grant number 200020_182559).

Acknowledgments: We acknowledge support from the University of Basel. We thank Fabian Baca for preliminary work preparing the aldehyde precursors.

Conflicts of Interest: The authors declare no conflict of interest.

Crystals 2019, 9, 529 11 of 13

The structural similarity between the nets in [{Co(1)(NCS) } MeOH 3CHCl ]n and 2 · · 3 [{Co(2)(NCS) } 0.8MeOH 1.8CHCl ]n indicates that both the 2-ethylbutoxy and 3-methylbutoxy groups 2 · · 3 are accommodated within the cavities in the network and that there is little diﬀerence between the steric requirements of these substituents. Signiﬁcantly, if the substituents are replaced by n-octyloxy chains in [{Co(3)(NCS) } 4CHCl ]n where 3 is 1,4-bis(n-octyloxy)-2,5-bis(3,2’:6’,3”-terpyridin-4’-yl)benzene, 2 · 3 a switch in assembly is observed to an {42.84} lvt net [13]. In this structure, the long n-octyloxy chains are in non-extended conformations and each lies over a 3,2’:6’,3”-tpy unit with close C–H...π contacts.

4. Conclusions We have described the synthesis and characterization of the tetratopic bis(3,2’:6’,3”-tpy) ligands 1 and 2. Reactions of 1 and 2 with Co(NCS)2 under ambient conditions lead to the assembly of [{Co(1)(NCS)2} MeOH 3CHCl3]n and [{Co(2)(NCS)2} 0.8MeOH 1.8CHCl3]n, the structures of which · · · · 2 4 4 2 5 are similar. Each exhibits an unusual trinodal, self-penetrating (6 .8 )(6 .8 )(6 .8)2 3D-net with the nodes deﬁned by two independent cobalt centres, and the centroids of two crystallographically independent but topologically equivalent ligands. PXRD conﬁrms that the single crystal structures are representative of the bulk material. The similar steric requirements of the 2-ethylbutoxy and 3-methylbutoxy substituents leads to a reproducible 3D-assembly, contrasting with the assembly of a 3D {42.84} net when n-octyloxy substituents replace the 2-ethylbutoxy and 3-methylbutoxy groups. We will now further explore how choice of substituents leads to a switch in network.

Supplementary Materials: The following are available online at http://www.mdpi.com/2073-4352/9/10/529/s1, Figures S1 and S2: FT-IR spectra of 1 and 2; Figures S3 and S4: mass spectra of 1 and 2; Figures S5–S8: NMR spectra of 1 and 2; Figure S9: Figures S9–S12: additional crystallographic diagrams Author Contributions: Investigation and methodology, G.M.; crystallography, A.P.; powder diffraction, Y.M.K., D.J.G.; manuscript writing, C.E.H., G.M., Y.M.K., S.R.B.; manuscript editing, E.C.C.; S.R.B.; supervision, C.E.H.; E.C.C.; project administration, C.E.H.; E.C.C.; funding acquisition, C.E.H. Funding: This research was funded by the Swiss National Science Foundation (grant number 200020_182559). Acknowledgments: We acknowledge support from the University of Basel. We thank Fabian Baca for preliminary work preparing the aldehyde precursors. Conflicts of Interest: The authors declare no conflict of interest.

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