Mono vs Double Copper(I) Ring Systems with Cu···H Interactions.

Weak secondary interactions often play a critical role in defining the structural and electronic properties of coordination complexes. Herein, we report a rare Cu···H hydrogen interaction in large copper(I)-thione ring systems. The neutral (APBT)CuI and ionic [(APBT)2Cu]BF4 complexes supported by the APBT ligand have been synthesized and characterized. Single-crystal X-ray diffraction reveals distinct coordination geometries around the copper center in metallacyclic ring systems, adopting a trigonal-planar and a distorted tetrahedral environment. Detailed structural analysis indicates the presence of short intramolecular Cu···H contacts consistent with anagostic interactions, suggesting a potential contribution of weak metal-hydrogen interactions to structural stabilization and molecular packing. Upon complexation, a slight downfield shift of the characteristic protons in 1H NMR spectrum has been observed due to C-H···Cu interactions. A comparative analysis of the two complexes highlights the influence of the metal-ring architecture and spatial confinement on the occurrence and geometry of these weak Cu···H contacts, providing structural insight into their role as secondary interactions in copper(I) complexes.