Magnetic and structural characterization of the chromium(III) dimer sodium diμ-hydroxobis[bis(oxalato)chromate(III)] hexahydrate, Na 4[Cr(C 2O 4) 2OH] 2·6H 2O

• Published in: Inorganica Chimica Acta Vol. 22; pp. 175 - 183
• Main Authors: Scaringe, R.P, Hatfield, W.E, Hodgson, D.J
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 1977
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/S0020-1693(00)90916-2

The crystal and molecular structure of the sodium di-μ-hydroxobis[bis(oxalato)chromate(III)] hexahydrate, Na 4[Cr(C 2) 4) 2·6H 2O [or Na 4[Cr(ox) 2OH] 2·6H 2O], has been determined from three-dimensional X-ray diffraction data collected by counter methods. The material crystallizes in the monoclinic space group P2 1/c with four dimeric formula units in a cell of dimensions a = 19.530(12), b = 9.860(7), c = 12.657(10) Å and β = 106.93(4)°: least-squares refinement of the structure has led to a final R-factor (on F) of 0.061 using 3278 independent intensities. The structure consists of two crystallographically independent dimeric [Cr(ox) 2OH] 4− 2 anions which interact with sodium cations and water molecules in the cell. The geometry around each independent chromium(III) center is roughly octahedral. The bridging unit is strictly planar, there being an inversion center in the middle of each dimer. The CrOCr bridging angles are 99.6(2) and 99.7(2)°, and the CrCr separations are 2.999(3) and 3.001(2) Å. There is extensive hydrogen bonding between the oxalate ligands and the water molecules. The magnetic susceptibility of a single crystal of the complex has been examined in the temperature range 2–70 K, and has been interpreted by means of application of the magnetization expression for coupled pairs of S = 3 2 ions with a small value of ∣J∣. The dimer exhibits a very small exchange interaction, the best fit to the magnetization expression yielding J = −0.31 cm −1 and γ = 0.28; the latter value gives an inter-dimer lattice interaction parameter, J′, of 0.034 cm −1 for the four nearest neighbors.