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Title: Effect of an ancillary ligand on single helix-double helix interconversion in copper complexes. Copper(I)-water bond
Authors: De, Senjuti
Chowdhury, Shubhamoy
Drew, Michael G B
Datta, Dipankar
Keywords: Coordination chemistry
Helical compounds
Issue Date: Feb-2011
Publisher: NISCAIR-CSIR, India
Abstract: Reaction of Cu(ClO<sub>4</sub>)<sub>2</sub>.6H<sub>2</sub>O 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 CH<sub>2</sub>Cl<sub>2</sub>-C<sub>6</sub>H<sub>6</sub> mixture affords [CuL(H<sub>2</sub>O)](ClO<sub>4</sub>)<sub>2</sub>.½C<sub>6</sub>H<sub>6</sub>. The complex crystallises in the space group  P-1 with <i style="">a</i> = 8.028(11) Å, <i style="">b</i> = 12.316(17) Å, <i style="">c </i>= 18.14(3) Å, <i><img src='/image/spc_char/alpha.gif' border=0></i> = 97.191(10)<sup>o</sup>, <i><img src='/image/spc_char/beta.gif' border=0></i> = 94.657(10)<sup>o</sup> and <i><img src='/image/spc_char/gamma.gif' border=0></i> = 108.039(10)<sup>o</sup>. It is single helical with the metal having a distorted trigonal bipyramidal N<sub>4</sub>O coordination sphere. The acid dissociation constant of the Cu(I) complex in CH<sub>3</sub>CN is 3.34 ± 0.19. The X band EPR spectrum of the compound is rhombic with <i>g</i><sub>1</sub> = 2.43, <i>g</i><sub>2</sub> = 2.10, <i>g</i><sub>3</sub> = 2.02 and <i style="">A</i><sub>1</sub> = 79.3 x 10<sup>-4</sup> cm<sup>-1</sup>. The Cu(II/I) potential of the complex in CH<sub>2</sub>Cl<sub>2</sub> 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(H<sub>2</sub>O)]<sup>+</sup> is ~ 40 kJ mol<sup>-1</sup>.
Description: 171-175
ISSN: 0975-0975(Online); 0376-4710(Print)
Appears in Collections:IJC-A Vol.50A(02) [February 2011]

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