And Silver(I) Coordination Polymers Based on 1,3-Bis(1,2,4-Triazol-1-Yl)Adamantane

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Article Synthesis, Crystal Structure, and Luminescence of Cadmium(II) and Silver(I) Coordination Polymers Based on 1,3-Bis(1,2,4-triazol-1-yl)adamantane

Roman D. Marchenko 1, Taisiya S. Sukhikh 2 , Alexey A. Ryadun 2 and Andrei S. Potapov 2,*

1 Kizhner Research Center, National Research Tomsk Polytechnic University, 30 Lenin Ave., 634050 Tomsk, Russia; [email protected] 2 Nikolaev Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences, 3 Lavrentiev Ave., 630090 Novosibirsk, Russia; [email protected] (T.S.S.); [email protected] (A.A.R.) * Correspondence: [email protected]; Tel.: +7-(383)-330-94-90

Abstract: Coordination polymers with a new rigid ligand 1,3-bis(1,2,4-triazol-1-yl)adamantane (L) were prepared by its reaction with cadmium(II) or silver(I) nitrates. Crystal structure of the coordination polymers was determined using single-crystal X-ray diffraction analysis. Silver formed

two-dimensional coordination polymer [Ag(L)NO3]n, in which metal ions are linked by 1,3-bis(1,2,4- triazol-1-yl)adamantane ligands, coordinated by nitrogen atoms at positions 2 and 4 of 1,2,4-triazole

rings. Layers of the coordination polymer consist of rare 18- and 30-membered {Ag2L2} and {Ag4L4} metallocycles. Cadmium(II) nitrate formed two kinds of one-dimensional coordination polymers depending on the metal-to-ligand ratio used in the synthesis. Coordination polymer [Cd(L)2(NO3)2]n Citation: Marchenko, R.D.; Sukhikh, was obtained in case of a 1:2 M:L ratio, while for M:L = 2:1 product {[Cd(L)(NO3)2(CH3OH)]·0.5CH3OH}n T.S.; Ryadun, A.A.; Potapov, A.S. was isolated. All coordination polymers demonstrated ligand-centered emission near 450 nm upon Synthesis, Crystal Structure, and excitation at 370 nm. Luminescence of Cadmium(II) and Silver(I) Coordination Polymers Keywords: adamantane; 1,2,4-triazole; silver; cadmium; coordination polymer; crystal structure; Based on 1,3-Bis(1,2,4-triazol-1-yl) luminescence; thermal analysis; 1,3-bis(1,2,4-triazol-1-yl)adamantane adamantane. Molecules 2021, 26, 5400. https://doi.org/10.3390/ molecules26175400

Academic Editor: Piersandro 1. Introduction Pallavicini Since its discovery adamantane has gained a wide spectrum of applications—from polymer design to biological activity. As a rigid building unit, mono-, di-, tri-, and tetra- Received: 24 August 2021 substituted adamantanes are used to construct covalent organic frameworks, hydrogen Accepted: 3 September 2021 bounded networks, and metal-organic frameworks [1,2]. Similar to aromatic ligands, Published: 5 September 2021 adamantane retains the rigidity, but it exhibits additional benefits: its tetrahedral structure offers access to unique node geometry, the non-polar backbone introduces hydrophobicity, Publisher’s Note: MDPI stays neutral and the conformational stability provides a pool of multiple ligand geometries in solu- with regard to jurisdictional claims in tion [1]. Adamantane derivatives are promising materials for porous recyclable catalytically published maps and institutional affil- active metal-containing polymers, in which they prevent metal leaching, polymer matrix iations. loss, intercalation, and porosity deterioration [2]. Natural and synthetic adamantanes possess a wide range of biological activity. Aman- tadine, memantine, rimantadine, tromantadine, vildagliptin, saxagliptin, and adapalen are used in worldwide clinical practice for treatment of viral infections, acne, neurodegen- Copyright: © 2021 by the authors. erative disorders, and type 2 diabetes [3–6]. Amantadine and memantine demonstrated Licensee MDPI, Basel, Switzerland. significant benefits in preventing and treating COVID-19 [7]. This article is an open access article 1,2,4-Triazole is a versatile nitrogen-donor ligand capable of forming strong coor- distributed under the terms and dination bonds with various metal ions [8,9]. Derivatives of 1,2,4-triazole are known conditions of the Creative Commons as anticancer, antiproliferative, anti-inflammatory, anticonvulsant, analgesic, antioxidant Attribution (CC BY) license (https:// agents, and possess activity against wide, but specific spectrum of living organisms [10]. creativecommons.org/licenses/by/ 1,2,4-Triazole cycles and rigid adamantane structures can be combined in bis(1,2,4-triazolyl) 4.0/).

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1,2,4-Triazole cycles and rigid adamantane structures can be combined in bis(1,2,4-triazolyl)adamantane ligands, which could be useful N,N’-linkers for constructing coordina- Molecules 2021, 26, 5400 2 of 10 tion polymers. Coordination polymers and metal-organic frameworks in particular are promising materials with a wide range of potential applications—gas storage and separation [11,12], enantioselective catalysis [13,14], supramolecular systems design [15], pollu- adamantane ligands,tant sensing which could[16,17] be, water useful purificationN,N’-linkers [18] for, fabrication constructing of coordinationelectrochemical poly- devices [19,20], mers. Coordinationand bio polymerslogical activity and metal-organic [21]. Coordination frameworks polymers in particular based on are1,3-bis promising(1,2,4-triazol-4-yl)ad- materials with aamantane wide range with of potential Mo(IV), applications—gas Cu(II), Zn(II), Cd(II), storage Ag(I)and separation, bimetallic [11 , Ag(I)/V(V),12], and enantioselectiveCu(II)/Mo(IV) catalysis [13 were,14], successfully supramolecular synthesized systems and design characterized [15], pollutant by Domasevitch sens- research ing [16,17], watergroup puriﬁcation [22–31], but [18], the fabrication coordination of electrochemical chemistry of its devices isomer, [1,319,-20bis],(1,2,4 and- bio-triazol-1-yl)ada- logical activity [mantane21]. Coordination remained polymersunexplored based. on 1,3-bis(1,2,4-triazol-4-yl)adamantane with Mo(IV), Cu(II),Following Zn(II), Cd(II), interest Ag(I), in the bimetallic coordination Ag(I)/V(V), chemistry and of Cu(II)/Mo(IV) heterocyclic adamantane were deriva- successfully synthesizedtives [32–34] and, we characterized have prepared by a Domasevitchnew ligand 1,3 research-bis(1,2,4- grouptriazol [-221-yl–31)adamantane], but (L) and the coordinationexplored chemistry its reactions of its isomer, with 1,3-bis(1,2,4-triazol-1-yl)adamantaneCd(II) and Ag(I) ions. As a result, three remained new Ag(I) and Cd(II) unexplored. coordination polymers were synthesized and characterized. Following interest in the coordination chemistry of heterocyclic adamantane derivatives [32–34], we2. haveResults prepared and Discussion a new ligand 1,3-bis(1,2,4-triazol-1-yl)adamantane (L) and explored its reactions2.1. Synthesis with Cd(II) of the Coordination and Ag(I) ions. Polymers As a result, three new Ag(I) and Cd(II) coordination polymers were synthesized and characterized. Silver coordination polymer [Ag(L)NO3]n (1) was synthesized from silver nitrate(I) and L in methanol at room temperature (Scheme 1). Molar ratio Ag:L = 1:1 was used, but 2. Results and Discussion the same product formed with Ag:L = 1:2 or 2:1. 2.1. Synthesis of the Coordination Polymers Coordination polymers [Cd(L)2(NO3)2]n (2) and {[Cd(L)(NO3)2(CH3OH)]·0.5CH3OH}n Silver coordination(3) were obtained polymer by [Ag( theL )NOreaction3]n ( 1of) wascadmium(II) synthesized nitrate from and silver L in nitrate(I) methanol solution at and L in methanolsolvothermal at room temperature conditions (80 (Scheme °C). The1). molar Molar ratio ratio of Ag: reagentsL = 1:1 was was Cd: used,L = but1:2 for 2 and 2:1 the same productfor formed 3. With withthe ratio Ag: LCd:=L 1:2 = or1:12:1. the mixture of crystals of 2 and 3 was obtained.

SchemeScheme 1. Synthesis 1. Synthesis of silver(I) of silver(I)and cadmium(II) and cadmium(II) coordination coordination polymers polymers with 1,3-bis with(1,2,4 1,3-bis(1,2,4-triazol-1--triazol-1-yl)adamantane. yl)adamantane. 2.2. Crystal Structures of the Coordination Polymers Coordination polymers [Cd(L) (NO ) ]n (2) and {[Cd(L)(NO ) (CH OH)]·0.5CH OH}n Coordination polymer2 3 2 1 crystallizes in monoclinic3 2 crystal3 system3, P21/c space group. (3) were obtained by the reaction of cadmium(II) nitrate and L in methanol solution at The elementary◦ unit consists of one Ag(I) ion, one L ligand, and one nitrate ion. Each sil- solvothermal conditionsver(I) ion (80coordinatesC). The three molar L ratioligands of— reagentstwo of wasthem Cd:L via nitrogen = 1:2 for atoms2 and at 2:1 positions 4 of for 3. With the ratio1,2,4- Cd:triazoleL =1:1 rings the and mixture one ligand of crystals via nitrogen of 2 and atoms3 was at obtained. position 2 (Figure 1). Bridging L ligands and Ag(I) ions forms 2D layers parallel to the (-102) crystallographic plane (Figure 2.2. Crystal Structures of the Coordination Polymers 2). The layers are composed from two types of metallocycles—18-membered {Ag2L2} cy- 1 P c Coordinationcles polymer and 30-memberedcrystallizes {Ag in4L4 monoclinic} cycles. Nitrate crystal ions system, are disordered21/ space over group. two positions (Fig- The elementaryure unit S1) consists, in one of of them one Ag(I)(occupancy ion, one 0.53),L ligand, a bridging and coordination one nitrate ion.mode Each is observed with silver(I) ion coordinatesAg–O distances three L ofligands—two 2.640(2) and 2.801(2) of them Å via. For nitrogen the second atoms position at positions (occupancy 4 0.47) the of 1,2,4-triazolecoordination rings and one mode ligand should vianitrogen be considered atoms as at monodentate position 2 (Figure with the1). shortest Bridging Ag–O distance L ligands and Ag(I)of 2.852(3 ions) Å forms. The 2Dobserved layers coordination parallel to the modes (-102) of crystallographicthe nitrate ions are plane consistent with (Figure2 ). TheKleywegt’s layers are geometrical composed fromcriteria two calcu typeslated of from metallocycles—18-membered interatomic distances and angles (Table {Ag2L2} cycles andS1) [35] 30-membered. The bridging {Ag nitrate4L4} cycles.ions join Nitrate the adjacent ions are layers disordered into a 3D over structure two (Figures S2, positions (FigureS3). S1), in one of them (occupancy 0.53), a bridging coordination mode is observed with Ag–O distances of 2.640(2) and 2.801(2) Å. For the second position (occupancy 0.47) the coordination mode should be considered as monodentate with the shortest Ag–O distance of 2.852(3) Å. The observed coordination modes of the nitrate ions are consistent with Kleywegt’s geometrical criteria calculated from interatomic distances and angles (Table S1) [35]. The bridging nitrate ions join the adjacent layers into a 3D structure (Figures S2 and S3). Molecules 2021, 26, 5400 3 of 10 Molecules 2021,, 26,, xx FORFOR PEERPEER REVIEWREVIEW 3 of 10

FigureFigure 1.1. FragmentFragment of of crystal crystal structure structure of of coordination coordination polymer polymer1 showing 1 showing thermal thermal ellipsoids ellipsoids (at 50% (at probability50% probability level) level) and labelsand labels for non-hydrogen for non-hydrogen atoms. atoms Hydrogen.. Hydrogen atoms atoms and and the the second second position position of of nitrate ion are omitted for clarity. Symmetry operations: i (1 − x, 1 − y, 1 − z); ii (2 − x, −0.5 + y, 1.5 nitrateof nitrate ion ion are are omitted omitted for for clarity. clarity Symmetry. Symmetry operations: operations: i (1i (1− −x x,, 1 1− − y,, 1 1 − zz);); ii ii (2 (2 − −x, x−,0.5−0.5 + y, + 1.5y, − z); iii (−1 + x, 1.5 − y, −0.5 + z); iv (1 + x, 1.5 − y, 0.5 + z); v (–x, −0.5 + y, 0.5 − z). 1.5− z)−; iiiz); (− iii1 + (− x1, 1.5 + x −, 1.5y, −−0.5y ,+− z)0.5; iv + (1z );+ ivx, (11.5 + −x y,, 1.5 0.5− + yz),; 0.5v (– +xz, );−0.5 v (– +x y, ,− 0.50.5 − + z)y., 0.5 − z).

Figure 2. Layer of coordination polymer 1 with 18- and 30-membered metallocycles. Hydrogen at- FigureFigure 2.2. LayerLayer ofof coordination coordination polymer polymer1 with1 with 18- 18 and- and 30-membered 30-membered metallocycles. metallocycles. Hydrogen Hydrogen atoms atoms are omitted for clarity. Atom legend: Ag—gray balls; C—dark gray dots; N—blue dots; O—red are omitted for clarity. Atom legend: Ag—gray balls; C—dark gray dots; N—blue dots; O—red dots. dots.

Compound 22 is a 1D coordination coordination polymer polymer,, thethe asymmetric unitunit consists ofof one Cd Cd(II)(II) ion, twoCompound nitrate ions, 2 is a and 1D coordination two L ligands polymer (Figure,3 the). Cd(II) asymmetric ions are unit in aconsists seven-coordinated of one Cd(II) ion, two nitrate ions,, and two L ligands (Figure 3). Cd(II) ions are in a seven-coordinated environment, whichwhich cancan be best described as distorted pentagonal bipyramidal, according toenvironment, calculated minimal which can distortion be best pathsdescribed listed as in distorted Table S2. pentagonal Two equatorial bipyramidal, coordination according places to calculated minimal distortion paths listed in Table S2. Two equatorial coordination areto calculated occupied byminimal nitrogen distor atomstion at paths position listed 4 of in triazole Table rings S2. Two and equatorial the remaining coordination three by places are occupied by nitrogen atoms at position 4 of triazole rings and the remaining oxygenplaces are atoms occupied of nitrate by ionsnitrogen (Figure atoms S4). Accordingat position to 4 Kleywegt’sof triazole rings criteria and (Table the S1remaining), one of three by oxygen atoms of nitrate ions (Figure S4). According to Kleywegt’s criteria (Table thethree nitrate by oxygen ions is atoms coordinated of nitrate in aions monodentate (Figure S4 fashion). According (Cd–O to distance Kleywegt’s 2.388(2) criteria Å), (Table while S1), one of the nitrate ions is coordinated in a monodentate fashion (Cd–O distance theS1), other one isof bidentate the nitrate with ions Cd–O is coordinated distances 2.524(2) in a monodentate and 2.627(2) Å. fashion (Cd–O distance 2.388(2) Å ), while the other is bidentate with Cd–O distances 2.524(2) and 2.627(2) Å ..

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Figure 3.Figure Fragment 3. Fragment of crystalFigure structureof crystal 3. Fragment of structure coordination of crystal of coordination polymer structure 2 showing of polymer coordination thermal 2 showing polymerellipsoids thermal2 showing(at 50% ellipsoids probability thermal ellipsoids(at level) 50% probability (at level) and labels for non-hydrogen atoms. Hydrogen atoms are omitted for clarity. Symmetry operations: i (x + 1, y, z); ii (2 + x, and labels for non50%-hydrogen probability atoms. level) Hydrogen and labels atoms for non-hydrogen are omitted atoms. for clarity. Hydrogen Symmetry atoms are operations omitted for: i ( clarity.x + 1, y, z); ii (2 + x, y, z); iii (−1 + x, y, z). y, z); iii (−1 + x, y, zSymmetry). operations: i (x + 1, y, z); ii (2 + x, y, z); iii (−1 + x, y, z).

TwoTwo Cd(II)Cd(II) ions areare linkedlinked byby twotwo ligandsligands intointo 1D 1D chains chains {Cd(NO {Cd(NO3)32)2(L)(L)22}}nn oriented alongalong crystallographic Two Cd axis (II) a ions(Figure are4 4). ).linked PairsPairs of ofby neighboringneighboring two ligands chains chains into participate participate 1D chains in in {Cd(NO CH CH······O 3)2(L)2}n oriented closeclose contacts along (2.508 (2.508 crystallographic and and 2.598 Å Å)) axisof the a nitrate(Figure ions 4). Pairs and adamantane of neighboring methyne chains groups participate in CH···O (Figure(Figuress S S5close5 and S6 S6).contacts). (2.508 and 2.598 Å ) of the nitrate ions and adamantane methyne groups (Figures S5 and S6).

FigureFigure 4. Chain of coordination polymer 2 2,, viewed along c axis. Atom legend: Cd Cd—yellow—yellow balls; CC—dark—dark gr grayay dots; N N—blue—blue dots; O O—red—red dots; H H—white—white dots. Figure 4. Chain of coordination polymer 2, viewed along c axis. Atom legend: Cd—yellow balls; 3 CompoundCompoundC—dark 3 crystallizes grcrystallizesay dots; N in in— ablue amonoclinic monoclinic dots; O —P2 P2red1/c1 space /cdots; space group,H— group,white the dots.asymmetric the asymmetric unit con- unit tainscontains two twocrystallographically crystallographically inde independentpendent Cd(II) Cd(II) cations, cations, four nitrate four nitrate ions, ions,two ligand two lig- L 2+ molecules,and L molecules, and three and CH three3OH CHmolecules3OH molecules (two of which (two ofare which coordinated are coordinated to Cd2+, Figure to Cd 5)., Compound 3 crystallizes in a monoclinic P21/c space group, the asymmetric unit con- Figure5 ). Cd(II) ions are seven-coordinated and their coordination polyhedra resemble a Cd(II) ionstains are seven two -crystallographicallycoordinated and their inde coordinationpendent polyhedrCd(II) cations,a resemble four a distortednitrate ions, two ligand L pentagonaldistorted pentagonal bipyramid bipyramid (Figure S7 (Figure, Table S S7,2). TableThe equatorial S2). The equatorial coordination coordination places areplaces occu- molecules, and three CH3OH molecules (two of which are coordinated to Cd2+, Figure 5). piedare occupied by four oxygen by four atoms oxygen of atomsthe nitrate of the ions nitrate, and ions, one andposition one position4 nitrogen 4 nitrogenatom of 1,2,4 atom- triazoleof 1,2,4-triazole ring.Cd (II)The ring. ionsaxial The arepositions axialseven positions are-coordinated occupied are occupied by and a 1,2,4 their by-triazole a coordination 1,2,4-triazole nitrogennitrogen atompolyhedr of another atoma resemble of a distorted Lanother molecule Lpentagonal molecule and an oxygen and bipyramid an atom oxygen of (Figure atoma coordinated of aS coordinated7, Table methanol S2) methanol. The molecule. equatorial molecule. Both coordinationof Boththe nitrate of the places are occu- ionsnitrate coordinated ionspied coordinated by to four each tooxygen of each independent of atoms independent of Cd the(II) Cd(II)nitrateions can ions ions be can considered, and be consideredone positionas bidentate as bidentate 4 nitrogen with atom of 1,2,4- thewith shortest the shortesttriazole and the and ring. longest the The longest N axial–O distances N–O positions distances of are2.330(7) ofoccupied 2.330(7) Å and by Å2.602(7) anda 1,2,4 2.602(7) Å- triazole(Table Å S (Table 1nitrogen). Cd S1).(II) atom of another Cd(II) cations are linked by bridging L molecules into 1D chains {Cd(NO3)2(L)(CH3OH)} cations areL linked molecule by bridging and an L oxygen molecules atom into of1D a chains coordinated {Cd(NO 3methanol)2(L)(CH3OH) molecule.} oriented Both of the nitrate oriented along crystallographic axis b (Figure6). The chains are involved in intermolecular along crystallographicions coordinated axis b (Figureto each 6 of). The independent chains are involved Cd(II) ions in intermolecular can be considered CH···O as bidentate with CH···O close contacts between the nitrate ions and 1,2,4-triazole hydrogen atoms at posi- close contacts between the nitrate ions and 1,2,4-triazole hydrogen atoms at position 5 tion 5 (2.699the Å) shortest or between and the the methanol longest moleculesN–O distances and the of 1,2,4-triazole 2.330(7) Å and hydrogen 2.602(7) atoms Å (Table S1). Cd(II) (2.699 Å ) or between the methanol molecules and the 1,2,4-triazole hydrogen atoms (2.694 (2.694 Å, Figurecations6). are These linked contacts by bridging join the chains L molecules into supramolecular into 1D chains 2D {Cd(NO layers oriented3)2(L)(CH3OH)} oriented Å , Figure 6). These contacts join the chains into supramolecular 2D layers oriented parallel parallel toalongab plane crystallographic (Figure S8). axis b (Figure 6). The chains are involved in intermolecular CH···O to ab plane (Figure S8). close contacts between the nitrate ions and 1,2,4-triazole hydrogen atoms at position 5 (2.699 Å ) or between the methanol molecules and the 1,2,4-triazole hydrogen atoms (2.694 Å , Figure 6). These contacts join the chains into supramolecular 2D layers oriented parallel to ab plane (Figure S8).

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FigureFigure 5.5.Fragment Fragment of of crystal crystal structure structure of of coordination coordination polymer polymer3 showing 3 showing thermal thermal ellipsoids ellipsoids (at 50% (at 50% probability level) and labels for non-hydrogen atoms. Hydrogen atoms and uncoordinated probability50% probability level) andlevel) labels and forlabels non-hydrogen for non-hydrogen atoms. Hydrogenatoms. Hydrogen atoms and atoms uncoordinated and uncoordinated CH3OH moleculesCH3OH molecules are omitted are for omitted clarity. for Symmetry clarity. Symmetry operations: operat i (x,iiyon+s: 1, ii z();x,, ii y (+x ,1,y z−);; ii1,ii (zx).,, y − 1, z)..

Figure 6. 3 ··· Figure 6. ChainsChains ofof coordinationcoordinationpolymer polymer 3with with short short CH CH···OO contacts.contacts.. TheThe viewview isisis alongalong thethe cc axis.axis.. OnlyOnly oneonesolvate solvate CHCH33OHOH moleculemolecule isisis shown shownshown for forclarity. clarity.Atom Atom legend: legend: Cd—yellow Cd—yellow balls;balls; C—dark C—dark graygray dots;dots; N—blueN—blue dots;dots; O—redO—red dots; dots;H—white H—white dots. dots. 2.3. Powder X-ray Diffraction, Thermal Analysis, and FT-IR Spectroscopy 2.3.. Powder X-Ray Diffraction,, Thermal Analysis, and FT-IR Spectroscopy The phase and chemical purity of compounds 1–3 were conﬁrmed by powder X-ray The phase and chemical purity of compounds 1–3 were confirmed by powder X-ray diffraction (powder XRD, Figures S9–S11) and elemental (CHN) analyses. diffraction (powder XRD, Figures S9–S11) and elemental (CHN) analyses. Thermal stability of the complexes was evaluated by thermogravimetric analysis Thermal stability of the complexes was evaluated by thermogravimetric analysis (TGA) coupled with differential scanning calorimetry (DSC). Coordination polymer 1 (TGA) coupled with differential scanning calorimetry (DSC).. Coordination polymer 1 shows only a slight weight loss up to 285 ◦C, after which it undergoes a rapid decomposition shows only a slight weight loss up to 285 °C , after which it undergoes a rapid decompo- inshows the range only ofa slight 285–325 weight◦C, followed loss up to by 28 a5 graduate °C , after weightwhich it loss undergoes (Figure S12). a rapid The decompo- residual sition in the range of 285–325 °C, followed by a graduate weight loss (Figure S12). The masssition at in 700 the◦ Crange (24%) of corresponds 285–325 °C well, followed to silver by content a graduate in compound weight loss1 (24.5%), (Figure indicative S12). The residual mass at 700 °C (24%) corresponds well to silver content in compound 1 (24.5%), ofresidual complete mass loss at of 700 nitrate °C (24 ions%) andcorresponds decomposition well to ofsilver the organiccontent ligand.in compound 1 (24.5%), indicative of complete loss of nitrate ions and decomposition of the organic ligand. indicativeCoordination of complete polymer loss of2 is nitrate stable ions up toand 290 decomposition◦C, after which of athe decomposition organic ligand. process Coordination polymer 2 is stable up to 290 °C, after which a decomposition process similarCoordination to the one observed polymer for2 iscompound stable up to1 290takes °C, place after (Figure which a S13). decomposition Thermal behavior process similar to the one observed for compound 1 takes place (Figure S13).. ThermalThermal behaviorbehavior ofof of the coordination polymer 3 is different because of the presence of solvate CH3OH molecules.the coordination It demonstrates polymer 3an is different early weight because loss of aboutthe presence 4% at35–75 of solvate◦C, attributable CH3OH mole- to removalcules. It demonstrates of uncoordinated an early methanol weight molecules loss of about (calculated 4% at 35– weight75 °C, attributable loss 3%). The to removal formed productof uncoordinated is stable in methanol the range molecules of 75–305 (calculated◦C, after which weight it decomposes loss 3%). The in formed two steps—rapid product is

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stable in the range of 75–305 °C, after which it decomposes in two steps—rapid at 305–345 °C (55% weight loss) and gradual up to 685 °C, both attributable to loss of coordinated at 305–345 ◦C (55% weight loss) and gradual up to 685 ◦C, both attributable to loss of methanol, and decomposition of the organic ligand and cadmium nitrate (Figure S14). coordinated methanol, and decomposition of the organic ligand and cadmium nitrate Compounds 1–3 were studied by FT-IR spectroscopy in the solid state (Figures S15– (Figure S14). S18). Bands in the IR spectra of the coordination polymers 1–3 associated with 1,2,4-tria- Compounds 1–3 were studied by FT-IR spectroscopy in the solid state (Figures S15–S18). −1 zoleBands ring in vibrations the IR spectra in the of the range coordination 1507–1517 polymers cm are1 shifted–3 associated to higher with frequencies 1,2,4-triazole com- ring paredvibrations to the in spectrum the range of 1507–1517 the free L cm ligand−1 are consistent shifted to with higher thefrequencies participation compared of the hetero- to the cyclicspectrum rings of in thecoordination. free L ligand consistent with the participation of the heterocyclic rings in coordination.Nitrate ion vibration bands in the spectrum of coordination polymer 1 were found −1 −1 near 1438Nitrate and ion 1337 vibration cm , the bands separation in the spectrumof 101 cm of between coordination them polymeris consistent1 were with found the monodentatenear 1438 and coordination 1337 cm−1, theof the separation nitrate ions. of 101 FT- cmIR −spectra1 between of compounds them is consistent 2 and 3 demon- with the stratemonodentate different coordination patterns in the of theregion nitrate of NO ions.3- vibrations. FT-IR spectra Thus, of compounds bands of asymmetric 2 and 3 demon- and symmetric NO3- stretching vibrations are found- at 1436 and 1283 cm−1 for compound 2 and strate different patterns in the region of NO3 vibrations. Thus, bands of asymmetric and 1448 and 1276 cm- −1 for compound 3 (Figures S16 and S17). Higher−1 separation between symmetric NO3 stretching vibrations are found at 1436 and 1283 cm for compound 2 and these1448 andbands 1276 (172 cm cm−1−1for versu compounds 153 cm3−1(Figures) is consistent S16 and with S17). a more Higher bidentate separation character between of coordinationthese bands (172of nitrate cm−1 ionsversus in compound 153 cm−1) 3 is. consistent with a more bidentate character of coordination of nitrate ions in compound 3. 2.4. Luminescent Properties of the Coordination Polymers 2.4.The Luminescent luminescent Properties properties of the Coordinationof the ligand Polymers L and the coordination polymers 1–3 were studiedThe for luminescent polycrystalline properties samples of in the the ligand solid Lstate.and The the coordinationexcitation and polymers emission1 –spectr3 werea ofstudied the free for ligand polycrystalline contain a samplessingle band in the near solid 350 state. nm Theand excitation410 nm associated and emission with spectra π–π* transitionsof the free in ligand 1,2,4- containtriazole arings single [36] band (Figure near 7a 350). The nm excitation and 410 nmand associated emission spectra with π –ofπ* thetransitions coordination in 1,2,4-triazole polymers rings1–3 are [36 very] (Figure similar,7a). Theconsistent excitation with and the emission intraligand spectra nature of the of thecoordination luminescence. polymers In contrast 1–3 are tovery the spectrum similar, consistent of the free with ligand the intraligandL, two excitation nature bands of the wereluminescence. detected in In the contrast spectra to of the the spectrum coordination of the polymers free ligand 1–3L ,(Figure two excitation 7b,c), the bands lower were en- ergydetected band in demonstrates the spectra of a thebathochromic coordination shift polymers to 370 nm1–3 relatively(Figure7b,c), to the the free lower ligand energy, in addition,band demonstrates high-energy a bathochromicbands appear shift at 270 to 370nm, nm associated relatively with to the n–π free* transitions ligand, in addition,in 1,2,4- triazolehigh-energy rings. bandsThe emission appear band at 270 also nm, undergoes associated a withbathochromicn–π* transitions shift of 40 in nm 1,2,4-triazole upon ex- citationrings. The at 370 emission nm. Excitation band also at undergoes270 nm leads a bathochromic to the appearance shift of of a 40 higher nm upon-energy excitation shoul- derat 370near nm. 400 nm Excitation, probably at associated 270 nm leads with to the the π* appearance–n emission pathway of a higher-energy (Figure 7b) shoulder. Similar photophysicalnear 400 nm, probablybehavior was associated observed with previously the π*–n foremission cadmium pathway complexes (Figure with7b). structur- Similar allyphotophysical similar 1-(1,2,4 behavior-triazol was-1- observedyl)adamantane previously [32]. for cadmium complexes with structurally similar 1-(1,2,4-triazol-1-yl)adamantane [32].

(a) (b) (c)

Figure 7. Normalized excitation and emission spectra of the free ligand L (a), compound 1 (b) and compounds 2, 3 (c). Figure 7. Normalized excitation and emission spectra of the free ligand L (a), compound 1 (b) and compounds 2, 3 (c). 3. Materials and Methods 3.3.1. Materials Synthesis and of theMethods Coordination Polymers 3.1. SynthesisAll reagents of the wereCoordination of reagent Polymers grade and used as received without further puriﬁca- tion. 1,3-Bis(1,2,4-triazol-1-yl)adamantane (L) was synthesized according to a previously reported procedure [37].

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[Ag(L)(NO3)]n (1). Solution of AgNO3 (51 mg, 0.3 mmol) in methanol (2 mL) was added dropwise with stirring to the solution of L (81 mg, 0.3 mmol) in methanol (1 mL). The resulting solution was protected from light and left at room temperature without stirring. The immediately formed colorless precipitate was collected by ﬁltration after 12 h, washed with methanol, and dried to give complex 1 in 77% yield. Anal. Calcd. (%) for C14H18AgN7O3: C 38.20, H 4.12, N 22.27; Found (%): C 38.48, H 4.02, N 22.58. FT-IR (ν, cm−1): 3119 (w), 2932 (w), 2860 (w), 1507 (m), 1438 (w), 1337 (s), 1274 (s), 1139 (s), 1018 (m), 974 (m), 910 (w), 826 (w), 739 (m), 657 (s). Single crystals of compound 1 as thin needles were obtained by layering an aqueous solution of AgNO3 over chloroform solution of L in a narrow test tube. [Cd(L)2(NO3)2]n (2). Solution of Cd(NO3)2·4H2O (6,1 mg, 0.02 mmol) in methanol (1 mL) was added dropwise with stirring to L (10.8 mg, 0.04 mmol) in methanol (1 mL) in a screw-capped glass vial. The resulting solution was put in the oven and heated at 80 ◦C for 24 h. Colorless crystals were obtained, collected by ﬁltration, washed with methanol, and dried to give complex 2 in 49% yield. Anal. Calcd. (%) for C28H36CdN14O6: C 43.28, H 4.67, N 25.23; Found (%): C 43.54, H 4.39, N 25.49. FT-IR (ν, cm−1): 3138 (w), 2943 (w), 2861 (w), 1516 (m), 1437 (s), 1284 (s), 1129 (s), 1035 (s), 984 (s), 858 (m), 817 (m), 739 (m), 660 (s). [Cd(L)(NO3)2(CH3OH)]·0.5CH3OH (3). Cd(NO3)2·4H2O (12.3 mg, 0.04 mmol) in methanol (1 mL) was added dropwise with stirring to L (5.4 mg, 0.02 mmol) in methanol (1 mL). Then the same process was used as for 2 to give complex 3 in 40% yield. Anal. Calcd. (%) for C15.5H24CdN8O7.5: C 33.55, H 4.36, N 20.20; Found (%): C 33.25, H 4.22, N 20.30. FT-IR (ν, cm−1): 3129 (w), 2927 (w), 2870 (w), 1517 (m), 1447 (s), 1274 (s), 1132 (s), 990 (s), 903 (w), 858 (m), 817 (m), 738 (m), 657 (s).

3.2. Characterization Methods Thermogravimetric analysis (TGA) coupled to differential scanning calorimetry (DSC) was carried out with a NETZSCH 449F3 instrument (NETZSCH TAURUS Instruments GmbH, Weimar, Germany) at a heating rate of 10 ◦C/min in a stream of helium, scanning range—30–750 ◦C. IR spectra were recorded on Agilent Cary 630 FT-IR spectrometer (Agi- lent Technologies, Santa Clara, CA, USA) equipped with a diamond ATR (attenuated total reﬂectance) tool (Agilent Technologies, Santa Clara, CA, USA). Elemental analyses were carried out on Carlo Erba CHNS analyser (Carlo Erba, Barcelona, Spain). The photoluminescence spectra were recorded on Horiba Jobin Yvon Fluorolog 3 Photoluminescence (HORIBA Jobin Yvon SAS, Edison, NJ, UAS) Spectrometer, equipped with 450 W xenon lamp, excitation/emission monochromator, and FL-1073 PMT detector. The powder X- ray diffraction data were obtained on a Shimadzu XRD 7000S powder diffractometer (Shimadzu Corporation, Kyoto, Japan) (Co-Kα radiation). Continuous shape measures were calculated by the SHAPE 2.1 program [38] for seven-coordinated reference polyhedra [39].

3.3. X-ray Structure Determination Single-crystal X-ray diffraction data were collected at 150 K (compound 2) or 298 K (compounds 1 and 3) on a Bruker-DUO APEX CCD diffractometer (Bruker Corporation, Billerica, MA, USA) (graphite monochromatized Mo Kα radiation, λ = 0.71073 Å, ϕ and ω scans of narrow frames) equipped with a 4K CCD area detector (Table1). Absorption corrections were applied using the SADABS program [40]. The crystal structures were solved by direct methods and refined by full-matrix least-squares techniques with the use of the SHELXTL package [41] and Olex2 GUI [42]. Atomic thermal displacement parameters for non-hydrogen atoms were refined anisotropically. The positions of H atoms were calculated corresponding to their geometrical conditions and refined using the riding model. Molecules 2021, 26, 5400 8 of 10

Table 1. Crystallographic data of the compounds 1–3.

Compound 1 2 3

Empirical formula C14H18AgN7O3 C28H36CdN14O6 C15.5H24CdN8O7.5 Formula weight 440.22 777.11 554.83 Temperature, K 298(2) 150(2) 298(2) Crystal system monoclinic monoclinic monoclinic Space group P21/c P21/n P21/c a, Å 13.3900(4) 11.3904(13) 14.4331(6) b, Å 9.7545(3) 13.4621(12) 12.1592(6) c, Å 13.0518(4) 20.904(2) 25.3803(12) β, ◦ 110.4360(10) 93.070(4) 104.848(2) Volume, Å3 1597.44(8) 3200.7(6) 4305.4(3) Z 4 4 8 3 ρcalc, g/cm 1.830 1.613 1.712 µ, mm−1 1.294 0.749 1.073 F(000) 888.0 1592.0 2248.0 Crystal size, mm3 0.13 × 0.08 × 0.05 0.4 × 0.08 × 0.05 0.25 × 0.18 × 0.07 2Θ range for data collection, ◦ 3.246 to 48.81 3.6 to 51.39 2.92 to 50.052 −15 ≤ h ≤ 15 −9 ≤ h ≤ 13 −16 ≤ h ≤ 17 Index ranges −11 ≤ k ≤ 11 −15 ≤ k ≤ 16 −14 ≤ k ≤ 14 −15 ≤ l ≤ 15 −25 ≤ l ≤ 24 −29 ≤ l ≤ 30 Reflections collected 16302 18657 53132 2630 [R = 0.0390, 6089 [R = 0.0366, 7600 [R = 0.0458, Independent reflections int int int Rsigma = 0.0298] Rsigma = 0.0463] Rsigma = 0.0310] Data/Restraints/Parameters 2630/50/263 6089/0/442 7600/33/587 Goodness-of-fit on F2 1.047 1.007 1.168 Final R indexes (I ≥ 2σ (I)) R1 = 0.0549, wR2 = 0.1346 R1 = 0.0315, wR2 = 0.0666 R1 = 0.0724, wR2 = 0.1530 Final R indexes (all data) R1 = 0.0774, wR2 = 0.1478 R1 = 0.0465, wR2 = 0.0720 R1 = 0.0980, wR2 = 0.1631 Largest diff. peak/hole, e·Å−3 2.40/−0.97 0.75/−0.46 1.37/−1.04

4. Conclusions In summary, coordination chemistry of a new ligand, 1,3-bis(1,2,4-triazol-1-yl) adamantane, was explored through the examples of silver(I) and cadmium(II) nitrates. Depending on the metal-to-ligand ratio, cadmium formed 1D coordination polymers with chains of different composition, while in the case of silver(I) ions, a 2D coordination polymer was obtained independently of the ratio of the reagents used. All three coordination polymers demonstrated ligand-centered emission.

Supplementary Materials: The following are available online, Figure S1. Disorder of nitrate ions in the structure of the coordination polymer 1 (a) and the asymmetric unit of the coordination polymer 1 showing both positions of the nitrate ions (b), Figure S2. Bridging nitrate ions in the structure of the coordination polymer 1. View along crystallographic axis b, Figure S3. Packing of layers of the coordination polymer 1. View along crystallographic axis b, Figure S4. Coordination polyhedron of Cd(II) ion in the coordination polymer 2, Figure S5. Close CH···O contacts between the chains of the coordination polymer 2, Figure S6. Packing of chains of the coordination polymer 1. View along crystallographic Compound 3 axis a, Figure S7. Coordination polyhedra of two crystallographically independent Cd(II) ions in the coordination polymer 3, Figure S8. Packing of chains of the coordination polymer 3 into supramolecular layers. View along crystallographic axis a, Figure S9. Powder X-ray diffraction plots for the coordination polymer 1, Figure S10. Powder X-ray diffraction plots for the coordination polymer 2, Figure S11. Powder X-ray diffraction plots for the coordination polymer 3, Figure S12. TG and DTA curves for the coordination polymer 1, Figure S13. TG and DTA curves for the coordination polymer 2, Figure S14. TG and DTA curves for the coordination polymer 3, Figure S15. FT-IR spectrum of the coordination polymer 1, Figure S16. FT-IR spectrum of the coordination polymer 2, Figure S17. FT-IR spectrum of the coordination polymer 3, Figure S18. FT-IR spectrum of the ligand L, Table S1. Interatomic distances, angles, and geometrical criteria for nitrate coordination in compounds 1–3, Table S2. Continuous shape measures criteria for seven-coordinated Cd(II) centers in compounds 2 and 3. Molecules 2021, 26, 5400 9 of 10

Author Contributions: Conceptualization, A.S.P.; methodology, A.S.P.; investigation, R.D.M., T.S.S. and A.A.R.; writing—original draft preparation, R.D.M.; writing—review and editing, A.S.P.; super- vision, A.S.P. All authors have read and agreed to the published version of the manuscript. Funding: The research was supported by the Ministry of Science and Higher Education of the Russian Federation, project numbers 121031700321-3 and 121031700313-8. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: CCDC 2099260-2099262 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Center at http://www.ccdc.cam.ac.uk/data_request/cif. Conﬂicts of Interest: The authors declare no conﬂict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results. Sample Availability: Samples of the compounds L, 1-3 are available from the authors.

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