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)(mu(3)-X)(2)(+) ( X = Cl, Br, and I) and monocapped Cu-3(dppm)(3)(mu(3)-OH)(2+) have been pre pared by treating the dimeric Cu-2(dppm)(2)(CH3CN)(4)(ClO4)(2) or Cu-2(dppm )(2)(dmcm)(3)(BF4)(2) (dmcn = dimethylcyanamide) complexes with the corresp onding bridging ligand X-. The trimeric complexes Cu-3(dppm)(3)(mu(3)-OH)(B F4)(2) and Cu-3(dppm)(3)(mu(3)-Cl)(2)Cl can be converted to dimers Cu-2(dpp m)(2)(dmcn)(3)(BF4)(2) and Cu-2(dppm)(2)(dmcn)(Cl)(2) by reaction with HBF4 , dmcn, and excess dmcn, respectively. The complexes synthesized by the abo ve means, Cu-3(dppm)(3)(mu(3)-Cl)(2)ClO4 (1), Cu-3(dppm)(3)(mu(3)-Br)(2)ClO 4 (2). 2THF, Cu-3(dppm)(3)(mu(3)-I)(2)I . 2CH(2)Cl(2). CH3OH (3), and Cu-2( dppm)(2)(dmcn)(Cl)(2). 2dmcn (4) have been characterized by IR, H-1 and P-3 1{H-1} NMR, and solid-state emission spectroscopy. The solid-state molecula r structures of complexes 2, 3, and 4 were determined from single-crystal X -ray diffraction studies. Apart from confirming the nuclearity, the structu ral information reveals interesting variations in the Cu ... Cu distances i n dimeric and trimeric complexes. A simple geometric correlation between th e Cu-X and Cu ... Cu distances is noted in the trimeric complexes with an i mportant exception of the dicapped Cl complex. Ab initio electronic structu re calculations of the homo dicapped Cu3X2+ (X= Cl, Br, HO, and HC2) and mi xed-capped Cu3XY+ (X = Cl, Y = HC2) species have been carried out at the MP 2 level of theory using valence-DZP-quality basis sets with effective core potentials on copper. The computed Cu ... Cu distances reproduce the observ ed experimental trend. Analyses of the electronic structures of the optimiz ed model Cu3X2+ complexes reveal the electronic tuning of Cu ... Cu distanc es by the capping ligand. The variation of Cu ... Cu distances in monobridg ed dimeric copper(I)-dppm complexes can also be rationalized along similar lines.