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Altering the Balance between Ligand-Based Radical Anion Formation and Dechelation in Electrochemically Reduced Binuclear Copper(I) Complexes:  A Resonance Raman Spectroelectrochemical Study

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journal contribution
posted on 07.08.1998, 00:00 by Simon E. Page, Keith C. Gordon, Anthony K. Burrell
The electrochemistry and spectral properties of a series of mono- and binuclear complexes with bridging ligands based on 2,3-di(2-quinolyl)quinoxaline are reported. The ligands are 2,3-di(2-quinolyl)quinoxaline (dqq), 6,7-dimethyl-2,3-di(2-quinolyl)quinoxaline (dqqMe2), and 6,7-dichloro-2,3-di(2-quinolyl)quinoxaline (dqqCl2). The complexes are [Cu(dqq)(PPh3)2]BF4, 1·[BF4]; [Cu(dqqMe2)(PPh3)2]BF4, 2·[BF4]; [Cu(dqqCl2)(PPh3)2]BF4, 3·[BF4]; [(PPh3)2Cu(dqq)Cu(PPh3)2](BF4)2, 4·[BF4]2; [(PPh3)2Cu(dqqMe2)Cu(PPh3)2](BF4)2, 5·[BF4]2; [(PPh3)2Cu(dqqCl2)Cu(PPh3)2](BF4)2, 6·[BF4]2. The mononuclear complexes reduce at the metal and dechelate, as evidenced by UV/vis spectroelectrochemistry. Reduction of the binuclear complexes results in ligand-based radical anion formation for 4 and 6 but decomposition of 5 to 2. The reduction species are identified using resonance Raman spectroscopy. The structures of [Cu(PPh3)2(C26H14Cl2N4)][BF4] (3·[BF4]) and [(Cu(PPh3)2)2(C26H14Cl2N4)][BF4]2·2CH2Cl2 (6·[BF4]2) were determined by single-crystal X-ray diffraction. 3·[BF4] crystallized in the monoclinic space group P1̄ with cell dimensions a = 10.956(2) Å, b = 15.278(3) Å, c = 16.032(3) Å, α = 100.342(8)°, β = 95.291(13)°, γ = 93.968(12)°, Z = 2, ρcalcd = 1.431 g/cm3, and R(Fo) = 0.0589. 6·[BF4]2 crystallized in the monoclinic space group C2/c with cell dimensions a = 21.295(4) Å, b = 24.322(5) Å, c = 20.034(4) Å, β = 112.64(3)°, Z = 8, ρcalcd = 1.486 g/cm3, and R(Fo) = 0.0422.