title: 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.
abstract: 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.
authors.affiliation: Laboratory of Physical Chemistry, School of Chemistry and Materials Science, Heilongjiang University, Harbin 150080, China.
authors.forename: Qing-Jiang
authors.initials: QJ
authors.lastname: Pan
authors.forename: Xin
authors.initials: X
authors.lastname: Zhou
authors.forename: Yuan-Ru
authors.initials: YR
authors.lastname: Guo
authors.forename: Hong-Gang
authors.initials: HG
authors.lastname: Fu
authors.forename: Hong-Xing
authors.initials: HX
authors.lastname: Zhang
mesh_terms: D002942:Circular Dichroism; D003198:Computer Simulation; D019281:Dimerization; D006046:Gold / Q000737:chemistry*; D008024:Ligands; D008956:Models, Chemical; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010720:Phosphines / Q000737:chemistry*; D011789:Quantum Theory; D012238:Rhodium / Q000737:chemistry*
chemical_list: D008024:Ligands; D009942:Organometallic Compounds; D010720:Phosphines; D006046:Gold; D012238:Rhodium