| 19281182 |
Pan QJ, Zhou X, Guo YR, Fu HG, Zhang HX: 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. Inorg Chem. 2009 Apr 6;48(7):2844-54.
To understand their photocatalytic activity and application in luminescent materials, a series of gold and rhodium phosphine complexes (mononuclear [Au (I)(PH (3))(2)](+) (1) and [Rh (I)(CNH)(2)(PH (3))(2)](+) (2); homobinuclear [Au (I)(2)(PH (2) CH (2) PH (2))(2)](2+) (3) and [Rh (I)(2)(CNH)(4)(PH (2) CH (2) PH (2))(2)](2+) (4); heterobinuclear [Au (I) Rh (I)(CNH)(2)(PH (2) CH (2) PH (2))(2)](2+) (5), [Au (I) Rh (I)(CNH)(2)(PH (2) NHPH (2))(2) Cl (2)] (6), and [Au (I) Rh (I)(CNH)(2)(PH (2) NHPH (2))(2)](2+) (7); and oxidized derivatives [Au (II) Rh (II)(CNH)(2)(PH (2) CH (2) PH (2))(2)](4+) (8), [Au (II) Rh (II)(CNH)(2)(PH (2) NHPH (2))(2) Cl (3)](+) (9), and [Au (II) Rh (II)(CNH)(2)(PH (2) NHPH (2))(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 A, 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 sigma*(d (z (2))) orbital weakens the interaction in 9. |
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