Two Geometrical Isomers of a 1D Coordination Polymer: Rationalization by Theoretical Calculations and Variation of Electrical Properties with the Change in Binding Mode of Dicarboxylate Linker

Abstract

The joining of bimetallic trinuclear nodes, [(CuL1)2Cd] (where H2L1 = N,N′-bis(α-methylsalicylidene)-1,3-propanediamine) by a spacer, 4,4′-benzenedicarboxylic acid (H2L2), produced two isomeric one-dimensional coordination polymers, having molecular formula {[(CuL1)2CdL2]·H2O} n . Structural characterization revealed that, in complex 1, one of the oxygen atoms of each carboxylate group of the linker [L2]2– coordinates only to the central Cd­(II) atom of the node in η1 fashion. However, in complex 2, both the oxygen atoms of each carboxylate group coordinate to the metal centers, one to Cd­(II) and the other to a terminal Cu­(II) via η2 syn–syn bridging mode. Moreover, the two bridging carboxylate O atoms are mutually cis in 1 while these are trans in 2. These differences resulted in the novel isomeric zigzag (or cis) and linear (or trans) chains of the coordination polymer. DFT calculations revealed that complex 2 is thermodynamically more stable than complex 1 by 4.3 kcal/mol in the gas phase. The electrical characterizations, i.e., impedance, capacitance, and current–voltage (I–V) studies, reveal substantive electrical conductivity for both complexes, but the charge transport properties are higher for 2 in comparison to 1. Both the materials exhibit photoswitching properties as they show increased electrical conductivity under illuminated conditions than under dark conditions. However, complex 2 shows significantly higher photosensitivity (P S = 571.50) compared to 1 (P S = 201.40) and thus has more potentiality toward fabrication of photosensitive devices.

Joining of Trinuclear Heterometallic CuII2–MII (M = Mn, Cd) Nodes by Nicotinate to Form 1D Chains: Magnetic Properties and Catalytic Activities

“…There have been a few reports of multidimensional coordination polymers involving various trinuclear nodes and spacers such as dicyanamide, 4,4′-bipyridine, pyrazine, and dicarboxylic acids. − Among these, dicyanamide often led to the formation of polymers with unpredictable nuclearities and dimensionalities depending upon the stoichiometry of the reactants and methods of preparation . The N-donor ditopic linkers 4,4′-bipyridine and pyrazine have so far been used only to join the Cu 2 Ln nodes, and as expected they link the terminal Cu II atoms of two successive nodes to form 1D polymeric chains. , On the other hand, to date three trinuclear nodes, Cu 2 Co, Cu 2 Mn, and Cu 2 Cd, have been joined by aromatic dicarboxylic acids (isophthalic, terephthalic, and 4,4′-benzenedicarboxylic acids) and in all cases a 1D chain is produced. − The common feature of these chains is that, except in one case, the coordination mode of each carboxylate ion is syn-syn (1 κO :2 κO ′), by which it forms another bridge between the central and terminal metal atoms of the node in addition to two phenoxido bridges. Only in one chain are the carboxylic ligands monodentate, being coordinated to the central Cd II through one of its oxygen atoms .…”

“…A list of these complexes is provided in Table S1 in the Supporting Information. In addition, a few coordination polymers have also been prepared by linking the heterometallic trinuclear nodes [(ML) 2 M′] (where H 2 L is an N 2 O 2 donor ligand as in the present paper) by spacers such as dicyanamide and benzenedicarboxylic acids. − The general procedure for the synthesis of such polymers is to react the neutral di-Schiff base complex of Cu II or Ni II with the salt of a second metal ion in the presence of the linker. The complexes of Cu II and Ni II act as metalloligands, and two such metalloligands coordinate to the other metal ion through phenoxido oxygen atoms, forming trinuclear nodes which are subsequently joined by the linkers to form the polymers. , In the present work, we have followed the same procedure to join Cu II 2 Mn II and Cu II 2 Cd II nodes by an N,O donor linker, nicotinic acid.…”

“…In addition, a few coordination polymers have also been prepared by linking the heterometallic trinuclear nodes [(ML) 2 M′] (where H 2 L is an N 2 O 2 donor ligand as in the present paper) by spacers such as dicyanamide and benzenedicarboxylic acids. − The general procedure for the synthesis of such polymers is to react the neutral di-Schiff base complex of Cu II or Ni II with the salt of a second metal ion in the presence of the linker. The complexes of Cu II and Ni II act as metalloligands, and two such metalloligands coordinate to the other metal ion through phenoxido oxygen atoms, forming trinuclear nodes which are subsequently joined by the linkers to form the polymers. , In the present work, we have followed the same procedure to join Cu II 2 Mn II and Cu II 2 Cd II nodes by an N,O donor linker, nicotinic acid. Interestingly, here on changing the molar ratios of the reactants, we could get two different types of complexes: the one-dimensional polymeric chains {[(CuL) 2 M­(nic)­(H 2 O) 2 ]­(ClO 4 )­(H 2 O)} n ( 1 and 2 ) and the discrete trinuclear complexes [(CuL) 2 M­(nic) 2 ]·2CH 3 OH ( 3 and 4 ) (M = Mn for 1 and 3 and M = Cd for 2 and 4 ).…”

“…This technique has been expanded further by employing oligonuclear complexes as nodes instead of single metal ions. − Polymers consisting of oligoheterometallic nodes are rather scarce, presumably because of the fact that the preformed heterometallic oligomer undergoes dissociation during joining by the spacers. In this regard, the dinuclear complexes of N 2 O 4 donor Schiff base ligands are exceptional, as these are robust enough to be joined by various spacers and thus have been used to construct a variety of CPs. − Recently, we found that the heterometallic trinuclear nodes derived from N 2 O 2 donor Schiff base ligands, although not very stable, can be joined by spacers such as dicyanamide, − pyrazine, benzenedicarboxylic acid, − and 4,4′-bipyridine. , We wished to investigate if such trinuclear nodes can also be joined by pyridinecarboxylic acids.…”

Synthesis, crystal structures and vapor adsorption properties of mercury(II) coordination polymers derived from two dipyridylamide ligands

“…There has been continuing and increasing interest in the design, structural characterization, and properties measurements of coordination polymers (CPs) in the past few decades. [1][2][3][4][5][6] This intriguing class of materials have demonstrated multifunctional properties in diverse applications such as ion exchange, gas storage, molecular separation, photochemistry, heterogeneous catalysis for organic transformations, and more recently as possible sensors for the detection of explosive compounds. [7][8][9][10][11][12][13] The striking aesthetic appeal of their fascinating architectures and topologies of coordination polymers is also an undeniable impetus for continued investigation.…”