Isovalent gold(I), -(II), and -(III) and mixed-valent gold(I)/gold(III) phosphorus ylide complexes. Combined ab initio and density functional study of electronic structures and spectroscopic properties

摘要

The binuclear gold phosphorus ylide complexes [Au-2(I)(CH2PH2CH2)(2)] (1), [(Au2X2)-X-II(CH2PH2CH2)(2)] (X = Cl (2a), Br (2b), I (2c)), [(Au2X4)-X-III(CH2PH2CH2)(2)] (X = Cl (3a), Br (3b)), and [(AuAuX2)-Au-I-X-III-(CH2PH2CH2)(2)] (X = Cl (4a), Br (4b)) were explored using density functional theory and ab initio methods. The use of methods, basis sets, and substituent effects confirmed our calculations. The analyses on their electronic structures reveal that two- and four-electron oxidation from 1 to 2-4 mainly occurs at the gold centers, resulting in their different coordination geometry features and metal-metal interactions as well as spectroscopic properties. Bond-order and frequency calculations provided the evidence for the weak Au-Au bonding interaction in 1, 3, and 4 and an approximate Au-Au single bond in 2. Unrestricted MP2 calculations showed that the triplet excited-state structures of 1, 2a, and 3a are minimum points on the potential energy surface. Upon excitation, the Au-Au distances of 1 and 3a shorten while that of 2a increases. This is closely correlated with the promotion of electrons into the bonding or antibonding orbitals of the gold centers.