100 trans-TRICHLOROBIS[DIETHYL(PHENYL)PHOSPHINEIHYDROXORHENIUM(IV) magnetic moment. As we did not succeed in locating the H atom, we do not know whether the zr bond is actually formed by the dxy or dx~ AO's, although the observed deformations in the coordination polyhedron seem to indicate that the last AO is more probably used. In fact the greater repulsion exerted by oxygen towards the P atoms, which could not be explained by the balance of the intramolecular contacts, can be understood in terms of increased angular space occupied by the zcMO in the P(1)-Re-P(2) plane. A comparison of the Re-P and Re-CI distances observed in the present compound with those found in oxo complexes of Re v is reported in Table 4. The mean Re-P distance of 2.47 A agrees well with that observed in the other molecules studied, with the exception of [ReOC12(PPh3)(acac)l, where this distance was found significantly shorter (2.43 A). The Re-CI distances deserve more attention. Data of Table 4 show that Re-CI distances are systematically longer when the C1 atom is trans to a ligand known to exert a relevant trans influence (like thiourea or PRa) and that a similar lengthening of the Re-CI bond trans to the multiply bonded O atom is observed in the compound under examination. However, whether or not such an effect can be interpreted in terms of trans weakening remains controversial, as Bright & Ibers (1969)believe that the weakening of bonds trans to multiply bonded nitrido or imino ligands is essentially caused by steric repulsion of other ligands, while Shustorovich, Porai- Koshits & Buslaev (1975) uphold with theoretical arguments and structural data the point of view of a true trans influence exerted by a multiple metal-ligand bond. The authors thank Professor L. Magon (University of Ferrara, Italy) for helpful discussions and Mr G. Bertocchi for technical assistance. This work has been financially supported by the CNR (Rome). References BOMBIERI, G., MAZZI, U., GILLI, G. & HERN~,NDEZ-CANO, F. (1978). J. Organomet. Chem. 159, 53-62. BONDI, A. (1964). J. Phys. Chem. 68, 441-451. BRIGHT, D. & IBERS,J. A. (1969). Inorg. Chem. 8, 709-716. CHATT, J., GARFORTH, J. D., JOHNSON, N. P. & ROWE, G. A. (1964). J. Chem. Soc. pp. 601-606. CHAT'r, J. & ROWE, G. A. (1962). J. Chem. Soc. pp. 4019-4033. EHRLICH, H. W. W. & OWSTON,P. G. (1963). J. Chem. Soc. pp. 4368-4372. FLETCHER, R. S. & SKAPSKI, A. C. (1972). J. Chem. Soc. Dalton Trans. pp. 1073-1078. GIGLIO, E. (1969). Nature (London), 222, 339-341. HAMXLTON, W. C. (1959). Acta Cryst. 12, 609-610. HURSTHOUSE, M. B., JAYAWEERA, S. A. S. & QUICK, A. (1979). J. Chem. Soc. Dalton Trans. pp. 279-282. International Tables for X-ray Crystallography (1974). Vol. IV. Birmingham: Kynoch Press. JOHNSON, C. K. (1971). ORTEP. Report ORNL-3794, revised. Oak Ridge National Laboratory, Tennessee. LIS, T. (1977). Acta Cryst. B33, 944-946. LOCK, C. J. L. & CHE'NG WAN (1975). Can. J. Chem. 53, 1548-1553. SHELDRICK, G. M. (1976). SHELX 76. A program for crystal structure determination. Univ. of Cambridge, England. SHUSTOROVICH, E. M., PORAI-KOSHITS, M. A. & BUSLAEV, Yu. A. (1975). Coord. Chem. Rev. 17, 1-98. Acta Cryst. (1982). B38, 100-104 S tructure of Chlorobis(N-methylsalicylideneiminato)oxorhenium(V) BY G. GILLI, M. SACERDOTI AND V. BERTOLASI Centro di Strutturistica Diffrattometrica, Universitd di Ferrara, Italy AND R. RossI Istituto Chimico, Universitt~ di Ferrara, Italy (Received 28 August 1980; accepted 27 May 1981) Abstract C16H16C1N2OaRe, M r = 505.9, is monoclinic, space group I2/c; a = 20.731(4), b = 11.949(3), c = 13.578 (3)/k, fl = 94.13 (2) ° , Z = 8, D C = 2.00 Mg 0567-740[~/82/010100-05 $01.00 m -3, g(Mo K-fi) = 7.08 mm-L The crystal structure has been determined and refined to an R value of 0.028 for 2767 observed reflections. The coordination around the Re atom is approximately octahedral. The two biden- tate ligands are mutually orthogonal and the oxygen of © 1982 International Union of Crystallography