Structural and magnetic properties of di-µ-hydroxo-bis[bis(ethylenediamine)chromium(III)] dithionate

Abstract

The crystal and molecular structure of the title complex [{Cr(en)₂(OH)}₂][S₂O₆]₂ has been determined from three dimensional single-crystal X-ray counter data. The complex crystallizes In the orthorhombic space group Pbca with four molecules in a cell of dimensions a= 13.58(1). b= 18.42(2), and c= 10.02(1)Å. The observed and calculated densities are 1.85(2) and 1.851 g cm^–3, respectively. The structure has been refined by full-matrix least-squares techniques to a value of R(on F) 0.049. The complex consists of dimeric [{Cr(en)₂(OH)}₂]⁴⁺ units which are hydrogen bonded to the dithionate anions. The dimeric cation isolated is the meso form, there being a crystallographic inversion centre in the middle of the dimer. The geometry around each chromium(III) centre is approximately octahedral, the Cr–Cr separation and bridging Cr–O–Cr angle being 3.032(3)Å and 100.0(2)°, respectively. The dithionate anion has the staggered conformation [S–S 2.127(3)Å, S–O 1.435(6)–1.460(5)Å]. The hydrogen bonding is extensive, with all the possible donor and acceptor atoms participating. The magnetic susceptibility of a powdered sample of the complex shows a maximum near 7.3 K, indicative of antiferromagnetic coupling between the metal centres. The best fit of the susceptibility data to the Van Vleck equation (modified by the inclusion of biquadratic exchange) yields values for g. J, j, and ΔE(the singlet–triplet splitting) of 1.947 (7), –1.08(2) cm^–1, 0.234(7) cm^–1, and –3.68 cm^–1, respectively.