The prepns. and x-ray crystallog. studies are reported on 5 Cr2[RNC(O)R']4L2-type compds. (R = Ph, 2,6-Me2C6H3, 4-(Me2N)C6H4: R' = Me, NHPh: L = THF). The studies were done to det. the response of the Cr-Cr bond to the introduction and variation of axial ligands. The structures are reported for Cr2[4-Me2NC6H4NC(O)Me]4.THF (I), Cr2[2,6-Me2C6H3NC(O)Me]4.3THF (II), Cr2[2,6-Me2C6H3NC(O)Me]4.THF.PhMe (III), Cr2[PhNC(NHPh)O]4.2THF.C6H14 (IV), and Cr2[2,6-Me2C6H3NC(O)Me].3py (V) and the Cr-Cr bond length are 2.006(2), 2.221(3), 2.023(1), 2.246(2), and 2.354(5)\AA, resp. The Cr-Cr bond length is a sensitive function of both the no. of axial ligands present and the donor ability of the axial ligands. Each THF mol. in the axial position causes an $\sim$0.18-\AA increase in the length of the Cr-Cr bond. Each length also increases by $\sim$0.12 \AA upon replacing 2 axial THF ligands by 2 pyridine ligands. The basic crystallog. data on the 5 compds. are as follows: I, space group C2/c, a 21.254(4), b 10.990(2), c 20.733(4) \AA, b 110.64 (2)°, Z = 4; II, Pbcn, a 16.775 (2), b 19.736(3), c 19.739(2) \AA, Z = 4; III, Pbcn, a 16.806(2), b 19.311(3), c 14.887(3) \AA, Z = 4; IV, Pccn, a 24.813(5), b 13.408(3), c 18.631(3) \AA, Z = 4; V, P21/n, a 17.374(4), b 12.836(4), c 23.603(6) \AA, Z = 4. These structures are compared with those of some 30 other quadrupoly bonded dichromium compds. with bridging ligand chains of the types of O-C-O, N-C-O, N-C-N, N-N-N, C-C-O, and C-P-C, and certain trends in the Cr-Cr distance as these ligand types are changed are noted. [on SciFinder(R)]
