CRYSTAL AND MOLECULAR-STRUCTURE OF TRIS[TETRA-MU-FORMATO-DIAQUODICHROMIUM(II)] DECAHYDRATE - CASE OF AN UNUSUALLY GOOD FALSE MINIMUM IN A STRUCTURE SOLUTION

The title compound, [Cr2(OCH)4(H2O2]3·10H2O, crystallizes from a dilute aqueous solution of chromium(II) formate in the tetragonal space group I41/acd. The unit cell has the dimensions a=17.929 (3) Å, c=25.198 (3) Å, V=8100 (4) Å3, dx=1.87 g/cm3, and Z=8 for the formula given. The 48 chromium atoms in the unit cell are all present in Cr2(O2CH)4(H2O)2 units and these are of two crystallographically independent types having Cr-Cr distances of 2.373 (2) and 2.360 (2) Å, while the respective Cr-Oax distances are 2.268 (4) and 2.210 (6) Å. The structure initially refined to a false minimum (R1=0.0551, R2=0.0805), but this was recognized because of unreasonable values of some internuclear distances. A structure with reasonable values of these bond lengths and significantly lower residuals (R1=0.0505, R2=0.0684) was found to be stable under refinement and is reported in detail. © 1978, American Chemical Society. All rights reserved.