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Issue 12, 2012
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Benzoquinolateplatinum(II) complexes as building blocks in the synthesis of Pt–Ag extended structures

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The reaction between (NBu4)[Pt(bzq)(C6F5)2] (1, bzq = 7,8-benzoquinolate) and AgClO4 in a 1 : 1 molar ratio, in acetone, gives the polymer [{Pt(bzq)(C6F5)2}Ag]n (2). The reaction of 2 with equimolecular amounts of PPh3 and SC4H8 (tht) produces the bimetallic complexes [{Pt(bzq)(C6F5)2}AgL] (L = PPh3 (3), tht (4)). For L = py, decomposition takes place and [Pt(bzq)(C6F5)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 η1 bonding interactions with the Cipso 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)(C6F5)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)(C6F5)2}AgSn] (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 C6F5 (Arf) 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.

Graphical abstract: Benzoquinolateplatinum(ii) complexes as building blocks in the synthesis of Pt–Ag extended structures

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The article was received on 06 Oct 2011, accepted on 23 Dec 2011 and first published on 06 Feb 2012

Article type: Paper
DOI: 10.1039/C2DT11885H
Citation: Dalton Trans., 2012,41, 3439-3451
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    Benzoquinolateplatinum(II) complexes as building blocks in the synthesis of Pt–Ag extended structures

    J. Forniés, S. Ibáñez, E. Lalinde, A. Martín, M. T. Moreno and A. C. Tsipis, Dalton Trans., 2012, 41, 3439
    DOI: 10.1039/C2DT11885H

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