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 CuCl 2 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.