Magneto-Structural Studies of Manganese(II) 2,4′-Benzophenone Dicarboxylate Based Coordination Polymers

Abstract

The role of the N-donor auxiliary ligand in the formation of coordination polymers (CPs) has been examined for a series of Mn(II) aromatic dicarboxylate-based framework systems. The solvothermal reaction of L-shaped dicarboxylate with Mn(II) through a varying N-donor auxiliary ligand resulted in the crystallization of six new multinuclear Mn-based CPs:MnCP6 (where 2,4′-bpdc = benzophenone-2,4′-dicarboxylate, phen = 1,10 phenanthroline, 2,2′-bipy = 2,2′-bipyridine, 4,4′-dimethyl-2,2′-bipy = 4,4′-dimethyl-2,2′-bipyridine, and 5,5′-dimethyl-2,2′-bipy = 5,5′-dimethyl-2,2′-bipyridine). The two 1D CPs, MnCP1 (square pyramidal) and MnCP2 (trigonal prism), respectively, were isolated from reactions in the absence and presence of an auxiliary ligand. The presence of phen led to anhydrous MnCP2 wherein C−H•••O interactions stabilized the 1D chains. The crystal packing in the hydrated MnCP1 is facilitated due to carboxylate oxygens interacting strongly with disordered lattice water. The auxiliary ligand, 2,2′-bipy and its derivatives in a suitable solvent led to the growth of four new solids built of a trimeric manganese cluster. MnCP3 is a layered solid while the methyl substituents on 2,2′-bipy altered the manganese carboxylate extended coordination in a different manner: (i) 4,4′-methyl substitution led to 1D (MnCP4) and 2D network (MnCP5); the bridging within the trimeric unit is also facilitated through in situ formed counter anions formate and acetate groups. (ii) 5,5′-Methyl substitution led to a 1D chain (MnCP6) where the trimeric unit occurred through the interference by another counter anion (chloride). The paper provides a mechanistic pathway for the observed crystal packing in terms of supramolecular condensation of soluble 1:1 manganese dicarboxylate complex species through a combination of coordination and H-bonding interactions. It also highlights how the supramolecular assembly is influenced when another competing soluble manganese complex coprecipitates, thus providing a rationale to the observed composition and coordination framework. All the manganese carboxylates showed antiferromagnetic behavior. The magnetic behavior of the two structurally comparable solids, MnCP1 and MnCP2, were further supported by highlevel first principle-based computations.

Crystallization and Magnetic Behavior of Manganese(II) 4,4′-Benzophenone Dicarboxylates and a Comparison of Its Structural Landscape with 2,4′-Benzophenone Dicarboxylate

“…Unlike simple salt systems, the crystallization phase diagram is difficult to construct to establish the structural landscape of manganese salt–benzophenone dicarboxylate–solvent with or without the presence of an auxiliary ligand. In our work, we employed a systematic synthetic protocol (Table S8) to examine the crystallization behavior of manganese benzophenone dicarboxylates taking two positional isomers, namely 4,4′- H 2 bpdc (described in this work) and 2,4′- H 2 bpdc in the presence of the same set of auxiliary ligands under comparable solvothermal condition. In Scheme , we have shown the various soluble molecular species that are likely to be present in the solution when the reactants are subjected to solvothermal condition.…”

“…Under our reaction condition, the presence of phen favored the formation of the soluble complex species, [Mn­( phen )­(sol) 3 (4,4′- bpdc )] and [Mn­( phen )­(sol) 3 (2,4′- bpdc )], respectively. Both isomers yielded only one solid each containing 1D manganese carboxylate chains but with a difference in composition: the linkage through one carboxylate oxygen (−Mn–O–Mn−) led to [Mn­( phen )­(H 2 O)­(4,4′- bpdc )] in 1 (Figure ), while bridging a pair through carboxylate (−Mn–C–O–C–Mn−) formed [Mn­( phen )­(2,4′- bpdc )] . The solid, [Mn­( phen )­(H 2 O)­(4,4 ′-OBA )], is isostructural with 1 reported here, while [Mn 3 ( phen ) 2 (4,4′- OBA ) 3 ] is a 3D framework built of trimeric Mn-carboxylate unit.…”

“…In the presence of 2,2′- bipy as an auxiliary ligand, both 4,4′- bpdc and 2,4′- bpdc led to crystallization of the solids [Mn 3 (2,2′- bipy ) 2 (4,4′- bpdc ) 3 ] DMA and [Mn 3 (2,2′- bipy )­(DMA) 2 (2,4′- bpdc ) 3 ], respectively. Interestingly, both contain trimeric units that result in 2D sheets.…”

“…{Mn­(sol) 5 ( bpdc )} and {Mn­(2,2′- bipy )­(sol) 3 ( bpdc )} but in different molar ratios 1:2 and 2:1, respectively. The symmetric isomer 4,4′- bpdc yielded three isostructural solids only with the variation in the lattice solvent whereas 2,4′- bpdc formed only one solid; the condensation pathway is different again due to the positioning of the two carboxylate groups (Figure ).…”

“…With the aim of screening every potential crystallizing phase on the use of neutral auxiliary ligands, we employed the high-throughput method. − In an earlier study, we explored the crystallization of manganese­(II) 2,4′-benzophenone dicarboxylate in the presence of selected auxiliary ligands. Here, we have investigated the crystallization behavior of manganese­(II) with 4,4′- H 2 bpdc , a positional isomer of 2,4′-benzophenone dicarboxylic acid (2,4′- H 2 bpdc ) adopting a similar synthetic protocol . The results provided us a platform to compare their structural diversity and magnetic behavior.…”