Influence of secondary bonding on the intradimer distance of trichloro(ethane-1,2-diolato-O,O′)tellurate(IV)

Abstract

The structure of ammonium trichloro(ethane-1,2-diolato-O,O′)tellurate(IV) was determined by single-crystal methods: monoclinic, space group P2₁/c(no. 14), a= 10.779(1 ), b= 12.418(2), c= 6.915(1)Å, β= 108.65(1)°. The co-ordination around Te^IV is distorted ψ octahedral with one of the two oxygen atoms lying opposite to the lone pair of Te. Two identical anions form a dimeric unit via a centre of symmetry. A short Te–O intradimeric distance of 2.764(6)Å is about 0.84 Å shorter than the sum of the corresponding van der Waals radii. The structure is compared with that of the corresponding tetraphenylphosphonium salt where the intradimer distance is clearly longer. The size of the cation and the amount of intermolecular interactions seem to be decisive factors in secondary bonding between two anionic units. The electronic properties of the anions in the two salts were investigated by ab initiocalculations and compared with those of the optimised structure of the corresponding monomeric anion. The positive charge of 1.36 electrons at Te is almost invariable. The main interaction within a dimeric unit in the ammonium salt is a donation of an electron pair from oxygen to the antibonding molecular orbital between Te–Cl in the neighbouring anion. The bond between Te and one of the equatorial Cl atoms (opposite to oxygen) is sensitive to dimerisation. The charge density, ionic nature of the bond and bond length increase when the degree of dimerisation increases, whereas the other two Te–Cl bonds are almost insensitive.