Diphosphazane derivatives of [Co4(CO)12]: Crystal and molecular structure of [CO4(μ-CO)3-(CO)7[μ-(C6H5O)2PN(C2H5)P(OC6H5)2]]

New diphosphazane derivatives of [Co4(CO)12] of stoicheiometry [Co4(CO)10[μ-(RO)2PN(Et)P(OR)2]] and [Co4(CO)8[μ-(RO)2PN(Et)P(OR)2]2] (R = Me, CH2, Ph, and Prsup(i) have been synthesized by reaction of the ligand with [Co4(CO)12] in the appropriate molar ratio. These compounds have been characterized spectroscopically and, in the case of [Co4(CO)10[μ-(PhO)2PN(Et)P(OPh)2]], by a complete single crystal X-ray structure determination. The latter crystallizes in the space group P21/c with a 21,61(1); b 10,609(5); c 18,87(1) A; β 112,68(5)0; V3991 A3; and Z = 4. Diffraction data were collected on a Phillips PW1100 automated diffractometer using graphite-monochromated Mo-Ksub(α) radiation, and the structure was refined to a conventional R 0,066 and Rsub(w) 0,058 for 2927 independent reflections with 1 > 2 omicron(l). The structure is derived from the Csub(3v) structure of [Co4(CO)12] itself. The three bridging CO groups along one triangular set of edges is retained, but the bridging diphosphazane ligand replaces and apical CO group on each of two basal cobalt atoms. Infrared and 31P[1H] n.m.r. spectroscopic evidence suggests that this isomer is the dominant species in solution for all the [Co4(CO)10[μ-(RO)2PN(Et)P(OR)2]] complexes. The solution structures of the tetrasubstituted [Co4(CO)8[μ-(RO)2PN(Et)P(OR)2]2] derivatives are also briefly discussed