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Structural Basis for Unusually Long Wavelength Charge Transfer Transitions in Complexes [MCl(ECH2CH2NMe2)(PR3)] (E = Te, Se; M = Pt, Pd):  Experimental Results and TD-DFT Calculations

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posted on 07.05.2002, 00:00 authored by Sandip Dey, Vimal K. Jain, Axel Knödler, Axel Klein, Wolfgang Kaim, Stanislav Záliš
A series of new complexes, the blue compounds [PdCl(TeCH2CH2NMe2)(PR3)] (PR3 = PEt3, PPrn3, PBun3, PMe2Ph, PMePh2, PPh3, PTol3) and the red [PtCl(TeCH2CH2NMe2)(PR3)] (PR3 = PMe2Ph, PMePh2), were synthesized and studied spectroscopically (1H and 31P NMR, UV/vis) and by cyclic voltammetry. The structures of [PdCl(TeCH2CH2NMe2)(PPrn3)] (2b) [PdCl(TeCH2CH2NMe2)(PMePh2)] (2e), [PtCl(TeCH2CH2NMe2)(PMePh2)] (2i), and the related [PtCl(SeCH2CH2NMe2)(PEt3)] (3) were determined crystallographically, revealing a typical pattern of trans-positioned neutral N and P donor atoms in an approximately square planar setting. The molecules 2b, 2e, and 2i were calculated by TD-DFT methodology to understand the origin of the weak (ε ≈ 200 M-1 cm-1) long-wavelength bands at about 600 nm for Pd/Te complexes such as 2b or 2e, at ca. 460 nm for Pt/Te systems such as 2i, and at about 405 nm for Pt/Se analogues such as 3. These transitions are identified as charge transfer transitions from the selenolato or tellurolato centers to unoccupied orbitals involving mainly the phosphine coligands for the PtII compounds and more delocalized MOs for the PdII analogues. Calculations and electrochemical data were used to rationalize the effects of metal and chalcogen variation.