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|Title:||Effect of an ancillary ligand on single helix-double helix interconversion in copper complexes. Copper(I)-water bond|
Drew, Michael G B
|Keywords:||Coordination chemistry;Copper;Helical compounds|
|Abstract:||Reaction of Cu(ClO4)2.6H2O with the 1:2 condensate of benzildihydrazone and 2-acetylpyridine, in methanol in equimolar ratio yields a green compound which upon recrystallisation from 1:1 CH2Cl2-C6H6 mixture affords [CuL(H2O)](ClO4)2.½C6H6. The complex crystallises in the space group P-1 with a = 8.028(11) Å, b = 12.316(17) Å, c = 18.14(3) Å, = 97.191(10)o, = 94.657(10)o and = 108.039(10)o. It is single helical with the metal having a distorted trigonal bipyramidal N4O coordination sphere. The acid dissociation constant of the Cu(I) complex in CH3CN is 3.34 ± 0.19. The X band EPR spectrum of the compound is rhombic with g1 = 2.43, g2 = 2.10, g3 = 2.02 and A1 = 79.3 x 10-4 cm-1. The Cu(II/I) potential of the complex in CH2Cl2 at a glassy carbon electrode is 0.43 V vs SCE. It is argued that the copper-water bond persists in the corresponding copper(I) species. Its implications on the single helix-double helix interconversion in copper helicates are discussed. DFT calculations at the B3LYP/ 6-311G** level shows that the binding energy of water in the single helical five-coordinate copper(I) species [CuL(H2O)]+ is ~ 40 kJ mol-1.|
|Appears in Collections:||IJC-A Vol.50A(02) [February 2011]|
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