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 η2syn–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 (PS = 571.50) compared to 1 (PS = 201.40) and thus has more potentiality toward fabrication of photosensitive devices.