Very short OHO hydrogen bonds in a binuclear transition-metal complex. Neutron-diffraction study at 120 K of [Co2{H2N(CH2)2OH}3{H2N(CH2)2O}3][ClO4]3·0.5H2O

Abstract

A structural determination of [Co₂{H₂N(CH₂)₂OH}₃{H₂N(CH₂)₂O}₃][ClO₄]₃·O.5H₂O has been carried out at 120 K by neutron diffraction: a= 12.059(9), b= 8.700(7), c= 16.477(14)Å, β= 121.86(3)° space group P2/c, and Z= 2. Binuclear cations made up of tris chelates are linked by very short hydrogen bonds: R(O O)= 2.390(7), r(O–H) 1.195(4); R(O O) 2.429(6), r(O–H)= 1.204(7), 1.228(7)Å. The results show that a previous X-ray diffraction study provided an inadequate description of the structure, since it was unable to resolve disorder of the water molecule(which had been misplaced), of one of the perchlorate groups, and of one of the neutral ligands; the superiority of low-temperature neutron diffraction in the resolution of disorder at this level is demonstrated. The jr. spectrum is discussed in relation to the nature of the proton potential well.