Spectroscopic and Computational Studies on the Trans-μ-1,2-Peroxo-Bridged Dinickel(II) Species [{Ni(tmc)}2(O2)](OTf)2: Nature of End-On Peroxo−Nickel(II) Bonding and Comparison with Peroxo−Copper(II) Bonding

Resonance Raman (rR) spectroscopic and density functional theory (DFT) computational studies on a trans-μ-1,2-peroxo-bridged (Ni2+)2 complex, [{(tmc)Ni2+}2(O2)]2+ (1, tmc = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), are presented and discussed. These studies afford a detailed description of the geometric and electronic structures of the Ni2O2 core in 1 and provide a suitable basis for a quantitative comparison between Ni−peroxo and Cu−peroxo bonding. From a normal coordinate analysis of rR data of 1, values of kNi-O = 1.52 mdyn/A and kO-O = 2.58 mdyn/A are obtained for the Ni−O and O−O stretch force constants, respectively, which are considerably smaller than kCu-O = 2.05 mdyn/A and kO-O = 3.09 mdyn/A reported for a representative trans-μ-1,2-peroxo-bridged (Cu2+)2 complex, [{(TMPA)Cu2+}2(O2)]2+. These differences primarily reflect a strongly reduced covalency of the metal−peroxo bonds in 1 relative to the (Cu2+)2 dimer as a result of the lower effective nuclear charge of Ni2+ than Cu2+. DFT...