molecules 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/). Molecules 2021, 26, 5400. https://doi.org/10.3390/molecules26175400 https://www.mdpi.com/journal/molecules Molecules 2021, 26, x FOR PEER REVIEW 2 of 10 1,2,4-Triazole cycles and rigid adamantane structures can be combined in bis(1,2,4-tria- zolyl)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 separa- tion [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 potentialMo(IV), applications—gasCu(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 deriva- tives [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 ).