Benzoquinolateplatinum(II) complexes as building blocks in the synthesis of Pt-Ag extended structures

Resum

The reaction between (NBu 4)[Pt(bzq)(C 6F 5) 2] (1, bzq = 7,8-benzoquinolate) and AgClO 4 in a 1:1 molar ratio, in acetone, gives the polymer [{Pt(bzq)(C 6F 5) 2}Ag] n (2). The reaction of 2 with equimolecular amounts of PPh 3 and SC 4H 8 (tht) produces the bimetallic complexes [{Pt(bzq)(C 6F 5) 2}AgL] (L = PPh 3 (3), tht (4)). For L = py, decomposition takes place and [Pt(bzq)(C 6F 5)py] (5) is obtained. All these complexes have been characterized by X-ray diffraction. The most interesting features of complexes 2-4 is the presence of Pt-Ag bonds, with Pt-Ag distances of ca. 2.75 Å. Besides, the silver centres establish short η 1 bonding interactions with the C ipso of the bzq ligands, with distances Ag-C of ca. 2.45 Å. Complex 2 is a one-dimensional infinite chain in which the fragments "Pt(bzq)(C 6F 5) 2 -" and Ag + alternate. On the other hand, complexes 1 and 3-5 show intermolecular pairing through π⋯π interactions between the aromatic rings of the bzq ligand, having interplanar separations of ca. 3.5 Å. Complex 2 dissolves in donor solvents (acetone, THF) as discrete bimetallic solvated fragments [{Pt(bzq)(C 6F 5) 2}AgS n] (S = solvent), similar to complexes 3 and 4. The persistence of the Pt-Ag bond in 2-4, supported by multinuclear NMR spectroscopy, causes a significant blue-shift in the lowest-lying absorption in relation to 1. This fact is attributed (TD-DFT) to a remarkable modification of the orbitals contributing to the HOMO, which changes the character of the transition from 1LC/ 1MLCT in 1 to admixture 1L′LCT/ 1MLCT in the bimetallic complexes. The low energy feature (490-530 nm) of 2 in solid state is attributed to CT from the Pt fragments to the Ag centers. Complexes 2-4 are only emissive in rigid media (solid and glasses). In the solid state, the metallic chain 2 exhibits a bright orange emission (560 nm, 298 K; 590 nm, 77 K), assigned to an excited state involving charge transfer from the platinum fragment with a remarkable contribution of C 6F 5 (Ar f) rings to the Pt-Ag bond ( 3LMM′CT/ 3L′M′CT). However, 3 and 4 exhibit in solid state at 298 K a vibronic band, which is clearly resolved in two close non-equilibrated bands at 77 K in 3, tentatively ascribed to a mixture of 3MLCT/ 3L′LCT transitions modified by the formation of the Pt-Ag bond. In glassy solution (77 K) 2-4 display a vibronic emission ascribed primarily to 3LC character. © The Royal Society of Chemistry 2012.