inorganics Article Influence of Substituents in Terephthalate Linker on the Structure of MOFs Obtained from Presynthesized Heterometallic Complex Marina Barsukova 1, Evgeny Dudko 1,2, Denis Samsonenko 1 , Konstantin Kovalenko 1 , Alexey Ryadun 1, Aleksandr Sapianik 1,* and Vladimir Fedin 1 1 Nikolaev Institute of Inorganic Chemistry, 3 Acad. Lavrentiev Ave., 630090 Novosibirsk, Russia; [email protected] (M.B.); [email protected] (E.D.); [email protected] (D.S.); [email protected] (K.K.); [email protected] (A.R.); [email protected] (V.F.) 2 Natural Sciences Department, Novosibirsk State University, 1, Pirogova str., 630090 Novosibirsk, Russia * Correspondence: [email protected] Abstract: The synthesis of new porous materials with desired properties is a challenging task. It becomes especially difficult if you need to combine several metals in one framework to obtain a heterometallic node. The use of presynthesized complexes for obtaining of new heterometallic metal–organic frameworks could be essential to solve the problem of tailored synthesis. In our study we use presynthesized heterometallic pivalate complex [Li2Zn2(piv)6(py)2] to obtain new MOFs with heterometallic core as a node of the framework. We are managed to obtain four new heterometallic MOFs: [H2N(CH3)2]2[Li2Zn2(bdc)4]·CH3CN·DMF (1), [Li2Zn2(H2Br2-bdc)(Br2-bdc)3]·2DMF (2), [H N(CH ) ][LiZn (ndc) ]·CH CN (3) and [{Li Zn (dmf)(py) }{LiZn(dmf) } (NO -bdc) ]·5DMF 2 3 2 2 3 3 2 2 2 2 2 2 6 (4). Moreover three of them contain starting tetranuclear core {Li2Zn2} and saves its geometry. We also demonstrate the influence of substituent in terephthalate ring on preservation of tetranuclear Citation: Barsukova, M.; Dudko, E.; core. For compound 1 it was shown that luminescence of the framework could be quenched when Samsonenko, D.; Kovalenko, K.; Ryadun, A.; Sapianik, A.; Fedin, V. nitrobenzene is included in the pores. Influence of Substituents in Terephthalate Linker on the Structure Keywords: metal–organic frameworks; heterometallic complexes; luminescence of MOFs Obtained from Presynthesized Heterometallic Complex. Inorganics 2021, 9, 4. https://doi.org/10.3390/ 1. Introduction inorganics9010004 Metal–organic frameworks (MOFs) represent a relatively new class of compounds that combine the advantages of inorganic compounds due to the presence of metal cations Received: 25 November 2020 or clusters in the structure, together with almost unlimited possibilities of organic synthesis Accepted: 18 December 2020 due to the use of organic ligands as linkers [1]. The large surface area and possibility Published: 2 January 2021 of inner surface functionalization made MOFs a suitable material for gas storage and separation [2–5]. The use of MOFs as luminescent and electrochemical sensors, conductive Publisher’s Note: MDPI stays neu- materials and heterogeneous catalysts has significantly expanded the field of applications tral with regard to jurisdictional clai- ms in published maps and institutio- and posed new aims for the structural design of such compounds [6–15]. Synthesis of new nal affiliations. porous materials with desired properties is challenging due to the many possible options for how inorganic nodes and organic linkers interact with each other and give the final structure [16]. The task becomes especially difficult if you need to combine several metals in one framework to obtain a heterometallic node [17,18]. The resulting materials are Copyright: © 2021 by the authors. Li- even more specialized for certain applications or can be used as multifunctional materials censee MDPI, Basel, Switzerland. for the simultaneous execution of various tasks [19,20]. Thus using of presynthesized This article is an open access article complexes could be essential to solve the problem of tailored synthesis. There are five main distributed under the terms and con- approaches for obtaining of heterometallic MOFs described in published investigations: ditions of the Creative Commons At- • tribution (CC BY) license (https:// postsynthetic modification of MOFs by the inclusion of metal ions in the pores of creativecommons.org/licenses/by/ the framework [21–23]; 4.0/). Inorganics 2021, 9, 4. https://doi.org/10.3390/inorganics9010004 https://www.mdpi.com/journal/inorganics Inorganics 2021, 9, x FOR PEER REVIEW 2 of 15 Inorganics 2021, 9, 4 2 of 15 • postsynthetic modification of MOFs by the inclusion of metal ions in the pores of the framework [21–23]; • • postsyntheticpostsynthetic modificationmodification ofof MOFsMOFs byby thethe partialpartial oror completecomplete replacementreplacement ofof thethe metalmetal cationscations inin nodesnodes withwith cationscations closeclose inin ionicionic radiusradius [24[24–26];–26]; • • thethe useuse of of salts salts of several of several metals metals in the initialin the reaction initial mixture reaction to obtainmixture heterometal- to obtain licheterometallic MOFs [27–32 MOFs]; [27–32]; • • thethe useuse ofof aa metalloligandmetalloligand containingcontaining aa metalmetal cationcation otherother thanthan thethe structure-formingstructure-forming metalmetal frameworkframework [[33–35];33–35]; • • thethe useuse of of presynthesized presynthesized polynuclear polynuclear heterometallic heterometallic complexes complexes to obtain to obtain MOFs MOFs with awith given a given nodes nodes [36–40 [36–40];]; TheThe lastlast approachapproach lookslooks thethe mostmost promisingpromising forfor obtainingobtaining ofof newnew heterometallicheterometallic MOFsMOFs withwith givengiven geometry.geometry. InIn thisthis casecase thethe synthesissynthesis ofof designeddesigned structurestructure becomesbecomes rationalrational andand predictable.predictable. InIn our our study study we we use use previously previously obtained obtained and describedand described het- erometallicheterometallic pivalate pivalate complex complex [Li 2[LiZn2Zn2(piv)2(piv)6(py)6(py)2]2 to] to obtain obtain new new MOFs MOFs with with given given metal metal corecore asas a node of of the the framework framework [41]. [41]. Terephthalic Terephthalic acid acid and and its itsanalogues analogues with with various var- ioussubstituents substituents in the in benzene the benzene ring ringare areused used as linkers as linkers (Scheme (Scheme 1).1 ).We We investigate investigate the theinfluence influence of the of substituent the substituent on the on formation the formation of structure of structure and changes and changes occurring occurring with the withstarting the startingheterometallic heterometallic core. Using core. this Using approaches this approaches we managed we managed to obtain to obtain four fournew newheterometallic heterometallic MOFs: MOFs: [H [H2N(CH2N(CH3)2]32[Li)2]22Zn[Li2(bdc)Zn2(bdc)4]·CH4]3·CN·DMFCH3CN·DMF (1), ([Li1),2 [LiZn22Zn(H2Br(H22-bdc)Br2- bdc)(Br2-bdc) (Br2-bdc)3]·2DMF3]·2DMF (2), (2[H), [H2N(CH2N(CH3)23][LiZn)2][LiZn2(ndc)2(ndc)3]·CH3]·CH3CN3CN (3) ( 3)and and [{Li[{Li2Zn2Zn22(dmf)(py)(dmf)(py)22}} {LiZn(dmf){LiZn(dmf)22}}22(NO2-bdc)-bdc)66]·5DMF]·5DMF ( (44).). Sorption Sorption and and luminescence properties havehave beenbeen studiedstudied forfor 11 andand 22.. 22−− 2−2− 2− 2− 2− 2− SchemeScheme 1.1. StructuralStructural formulaeformulae ofof bdcbdc ,, Br Br22-bdc-bdc , NO, NO2-bdc2-bdc, and, and ndc ndc dicarboxylatedicarboxylate linkers. linkers. 2.2. ResultsResults Synthesis and Crystal Structures Synthesis and Crystal Structures The compounds [H2N(CH3)2]2[Li2Zn2(bdc)4]·CH3CN·DMF (1), [Li2Zn2(H2Br2-bdc) The compounds [H2N(CH3)2]2[Li2Zn2(bdc)4]·CH3CN·DMF (1), [Li2Zn2(H2Br2-bdc) (Br2-bdc)3]·2DMF (2), [H2N(CH3)2][LiZn2(ndc)3]·CH3CN (3) and [{Li2Zn2(dmf)(py)2} (Br2-bdc)3]·2DMF (2), [H2N(CH3)2][LiZn2(ndc)3]·CH3CN (3) and [{Li2Zn2(dmf)(py)2} {LiZn(dmf)2}2(NO2-bdc)6]·5DMF (4) were obtained under solvothermal conditions via {LiZn(dmf)2}2(NO2-bdc)6]·5DMF (4) were obtained under solvothermal conditions via the the reactions of presynthesized pivalate complex [Li2Zn2(piv)6(py)2] with terephthalic acid reactions of presynthesized pivalate complex [Li2Zn2(piv)6(py)2] with terephthalic acid or or a substituted terephthalic acid in a solvent mixture of acetonitrile and DMF. The pivalate a substituted terephthalic acid in a solvent mixture of acetonitrile and DMF. The pivalate complex was synthesized according to previously published procedure [41]. Obtained crystalscomplex except was synthesized for compound according2 were usedto previously for single crystalpublished XRD procedure to determine [41]. the Obtained crystal structures.crystals except In case for ofcompound compound 2 were2, crystals used for obtained single crystal ina reaction XRD to mixture determine of acetonitrile the crystal andstructures. DMA (insteadIn case of DMF)compound were 2 used, crystals due toobtained the smaller ina reaction size of crystalsmixture obtained of acetonitrile with DMF/acetonitrileand DMA (instead mixtures. of DMF) were used due to the smaller size of crystals obtained with DMF/acetonitrile mixtures. The structure of starting pivalate complex [Li2Zn2(piv)6(py)2] presents a tetranuclear heterometallicThe structure block of consisting starting pivalate of two Li complex+ and two [Li Zn2Zn2+2(piv)cations6(py) all2] in presents a tetrahedral a tetranuclear environ- mentheterometallic (Figure1). Eachblock Znconsisting2+ atom isof bound two toLi+ the and N donortwo Zn of2+ a pyridinecations all ligand in a and tetrahedral to three environment (Figure 1). Each Zn2+ atom is bound to the N donor of a pyridine ligand and O donors of three carboxylate groups, bond distances Zn–OOCO are from 1.9297(18) to + OCO 1.9519(19)to three Å,O Zn–Ndonorspy –2.067(2)of threeÅ. carboxylate Li atoms coordinate groups, bond to four distances O donors fromZn–O four pivalates,are from 1.9297(18) to 1.9519(19) Å, Zn–Npy–2.067(2) Å. Li+ atoms coordinate to four O donors from bond distances Li–OOCO vary from 1.889(5) to 1.985(5) Å. The center of symmetry of the tetranuclear block is at the intersection of the diagonals of the almost square [Li2(µ2-O)2] moiety, and the {Li2Zn2} core has a planar structure. Three bridging pivalates link the Inorganics 2021, 9, x FOR PEER REVIEW 3 of 15 Inorganics 2021, 9, 4 3 of 15 four pivalates, bond distances Li–OOCO vary from 1.889(5) to 1.985(5) Å.