The Crystal and Molecular Structure of Rubidium Bis(pyridine-2,6-Dicarboxylato)-Chromate(iii)

A three dimensional X-ray structural analysis of rubidium bis (pyridine-2,6-dicarboxylato)chromate(III), Rb[Cr(dipic)2], has been carried out. The structure was refined by full matrix least-squares methods, using 713 observed independent reflections recorded at room temperature, to a conventional weighted R of 0.034. The crystals are tetragonal with a=b=6.950(3) Å, c=29.47(1) Å, space group 14 1/a and Z=4. The point group symmetry of the [Cr(dipic)2]− ion is S4. The Cr–N and Cr–O distances (1.974(4) and 2.000(3) Å respectively) noticeably differ from the usual values in aminoacid chromium(III) complexes. The π bonding effect of the pyridine nitrogen atom corroborates the previous spectral studies on the sodium salt of this complex. The lability of [Cr(dipic)2]− in acid solution has been tentatively explained on the basis of the relatively severe strain within the complex ion.