Quasi-Planar Organic Synthon and S···X (X = S or H-C) Contacts in Flat Copper Coordination Chains: Syntheses, Structures and Conductive Behaviour

A new organic building block, TEPB, has been synthesized that comprises three 2‐ethylthio‐substituted pyrimidine groups coupled to one central phenyl ring at the 1‐, 3‐ and 5‐positions. TEPB exhibits a quasi‐planar conformation due to its intramolecular C–H···N hydrogen bonds. The assembly of TEPB with CuI and CuCl2 produced two flat coordination chains 1 and 2, both exhibiting similar assembly hierarchies from chain through 2D layer to 3D architecture. It was found that extensive S···S and C–H···S contacts exist in the 2D layers of 1 and 2, respectively. Between the 2D layers of 2, there are O–H···Cl hydrogen‐bonding interactions between water molecules and coordinated Cl atoms that provide a proton‐transfer network. Complex 2 exhibits a smaller optical band gap (1.11 eV) than 1 (1.93 eV), which has been attributed to d‐electron transition in the copper(II) ion. The d.c. conductivities of 1 and 2 at room temperature were measured to be 2.84 × 10–12 and 2.42 × 10–10 S cm–1, respectively. The a.c. conductivity of 2 obtained at room temperature by the complex impedance technique is about 5.90 × 10–9 S cm–1, which can be attributed largely to proton conduction. Moreover, the a.c. conductivity of 2 decreases almost linearly with increasing temperature, presumably as a result of its temperature‐sensitive O–H···Cl hydrogen‐bonding network that allows for proton conduction. The assembly of quasi‐planar organic synthon TEPB with CuI and CuCl2 produced two flat coordination chain structures (1 and 2) that incorporate S···S and C–H···S contacts in their packing structures. Complex 1 is an insulator, whereas 2 shows conductive properties with an a.c. conductivity of 5.90 × 10–9 S cm–1 at room temperature.