Theoretical Studies on Metal−Metal Interaction, Excited States, and Spectroscopic Properties of Binuclear Au−Au, Au−Rh, and Rh−Rh Complexes with Diphosphine Ligands: Buildup of Complexity from Monomers to Dimers

• Published in: Inorganic chemistry 2009-04, Vol.48 (7), p.2844-2854
• Main Authors: Pan, Qing-Jiang, Zhou, Xin, Guo, Yuan-Ru, Fu, Hong-Gang, Zhang, Hong-Xing
• Format: Article
• Language: English
• Subjects: Circular Dichroism; Computer Simulation; Dimerization; Gold - chemistry; Ligands; Models, Chemical; Organometallic Compounds - chemical synthesis; Organometallic Compounds - chemistry; Phosphines - chemistry; Quantum Theory; Rhodium - chemistry
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic801687w

To understand their photocatalytic activity and application in luminescent materials, a series of gold and rhodium phosphine complexes (mononuclear [AuI(PH3)2]+ (1) and [RhI(CNH)2(PH3)2]+ (2); homobinuclear [AuI 2(PH2CH2PH2)2]2+ (3) and [RhI 2(CNH)4(PH2CH2PH2)2]2+ (4); heterobinuclear [AuIRhI(CNH)2(PH2CH2PH2)2]2+ (5), [AuIRhI(CNH)2(PH2NHPH2)2Cl2] (6), and [AuIRhI(CNH)2(PH2NHPH2)2]2+ (7); and oxidized derivatives [AuIIRhII(CNH)2(PH2CH2PH2)2]4+ (8), [AuIIRhII(CNH)2(PH2NHPH2)2Cl3]+ (9), and [AuIIRhII(CNH)2(PH2NHPH2)2]4+ (10)) were investigated using ab initio methods and density functional theory. With the use of the MP2 method, the M−M′ distances in 3−7 were estimated to be in the range of 2.76−3.02 Å, implying the existence of weak metal−metal interaction. This is further evident in the stretching frequencies and bond orders of M−M′. The two-electron oxidation from 5−7 to their respective partners 8−10 was shown to mainly occur in the gold−rhodium centers. Experimental absorption spectra were well reproduced by our time-dependent density functional theory calculations. The metal−metal interaction results in a large shift of d z 2 → p z transition absorptions in binuclear complexes relative to mononuclear analogues and concomitantly produces a low-lying excited state that is responsible for increasing visible-light photocatalytic activities. Upon excitation, the metal-centered transition and the metal-to-metal charge transfer strengthen the metal−metal interaction in triplet excited states for 3−6, while the promotion of electrons into the σ*(d z 2 ) orbital weakens the interaction in 9.