Curved Cyclic Trimers: Orthogonal Cu–Cu Interaction versus Tetrameric Halogen Bonding

Abstract

In this work, two polymorphs and a pseudopolymorph of a trinuclear copper(I) pyrazolate complex, namely, [Cu(L-Br)]3 (L-Br = 4-(4-bromophenyl)-3,5-dimethylpyrazolyl), were isolated. One of them shows remarkable molecular shape curving, which is imposed by short intermolecular CuI–CuI interaction and parallelogram-like Br4 halogen bonding. These two sets of noncovalent interactions propagate along different directions and do not interact directly with each other. Interestingly, these cooperative interactions give rise to an undulating layer in the crystal structure of one polymorph. We used a variety of theoretical methods, such as electron density distribution (e.g., atoms-in-molecules analysis and reduced-density-gradient mapping), molecular orbitals, charge analysis, electrostatic potentials, and Hirshfeld surface analysis, to demonstrate the nature and strength of multiple CuI–CuI and Br···Br bonding qualitatively and quantitatively. Moreover, preliminary calculations based on time-dependent density fu...