Anion-Controlled Nuclearity and Metal−Metal Distances in Copper(I)−dppm Complexes (dppm = Bis(diphenylphosphino)methane)

Dicapped triangular copper(I)−dppm complexes Cu 3 (dppm) 3 (μ 3 -X) 2 + (X = Cl, Br, and I) and monocapped Cu 3 (dppm) 3 (μ 3 -OH) 2+ have been prepared by treating the dimeric Cu 2 (dppm) 2 (CH 3 CN) 4 (ClO 4 ) 2 or Cu 2 (dppm) 2 (dmcn) 3 (BF 4 ) 2 (dmcn = dimethylcyanamide) complexes with the corresponding bridging ligand X - . The trimeric complexes Cu 3 (dppm) 3 (μ 3 -OH)(BF 4 ) 2 and Cu 3 (dppm) 3 (μ 3 -Cl) 2 Cl can be converted to dimers Cu 2 (dppm) 2 (dmcn) 3 (BF 4 ) 2 and Cu 2 (dppm) 2 (dmcn)(Cl) 2 by reaction with HBF 4, dmcn, and excess dmcn, respectively. The complexes synthesized by the above means, Cu 3 (dppm) 3 (μ 3 -Cl) 2 ClO 4 ( 1 ), Cu 3 (dppm) 3 (μ 3 -Br) 2 ClO 4 ( 2 )·2THF, Cu 3 (dppm) 3 (μ 3 -I) 2 I· 2CH 2 Cl 2 ·CH 3 OH ( 3 ), and Cu 2 (dppm) 2 (dmcn)(Cl) 2 ·2dmcn ( 4 ) have been characterized by IR, 1 H and 31 P{ 1 H} NMR, and solid-state emission spectroscopy. The solid-state molecular structures of complexes 2, 3, and 4 were determined from single-crystal X-ray diffraction studies. Apart from confirming the nuclearity, the structural information reveals interesting variations in the Cu···Cu distances in dimeric and trimeric complexes. A simple geometric correlation between the Cu−X and Cu···Cu distances is noted in the trimeric complexes with an important exception of the dicapped Cl complex. Ab initio electronic structure calculations of the homo dicapped Cu 3 X 2 + (X= Cl, Br, HO, and HC 2 ) and mixed-capped Cu 3 XY + (X = Cl, Y = HC 2 ) species have been carried out at the MP2 level of theory using valence-DZP-quality basis sets with effective core potentials on copper. The computed Cu···Cu distances reproduce the observed experimental trend. Analyses of the electronic structures of the optimized model Cu 3 X 2 + complexes reveal the electronic tuning of Cu···Cu distances by the capping ligand. The variation of Cu···Cu distances in monobridged dimeric copper(I)−dppm complexes can also be rationalized along similar lines.