Vol. 4 , No. 1, January 1965
COMPOUNDS CONTAINING THE TRIRHENIUM NONABROMIDE GROUP 59
Solvent interactions and/or Jahn-Teller distortions would be expected to lift the orbital degeneracies of these configurations and reduce the orbital contributions to the g values. It should be pointed out that these configurations would be expected to lead to extremely short spin-lattice relaxation times if the e* orbitals were made up of a large contribution from metal dorbitals. However, since the paramagnetic resonance results indicate that if these configurations are correct, these orbitals have very little admixture of metal orbitals, the situation might be analogous to the effect of orbital degeneracy in the benzenez0 and cyclooctatetraeneZ1 negative ions. I n these cases the spinlattice relaxation is only slightly enhanced in C,&and not significantly in CsHg-. The principal objection to the configurations is that the monoanions are diamagnetic rather than having S = 1. However, if the e* orbitals are strongly delocalized on the ligands, electron repulsion terms may be relatively unimportant. Consequently, lower symmetry electrostatic fields from solvent interactions might remove the orbital degeneracy of e* sufficiently to yield a singlet ground state for the monoanions. (20) M. G. Townsend and S. I. Weissman, J . Chem. Phys., 82, 309 (1960); H. M. McConnell and A. D. McLachlan, ibid., 84, 1 (1961). (21) A. D. McLachlan and L. C. Snyder, ibid., 86, 1159 (1962).
Finally, we have examined the e.p.r. spectrum of tris(dipyridyl)vanadium, [V(dipy)3].l 3 This complex is known to have trigonal symmetry.22 Its g value has been measured previously. 2 3 Tris(dipyridy1) complexes are generally considered to contain the metal in its lowest formal valence state consistent with the total charge on the complex; in this case the metal has been considered as V(0) (d6).l3~l4OrgeP has discussed the ]* electronic configurations of certain [ M ( d i ~ y ) ~complexes and has suggested the (ea*)4 configuration (in our notationz) for [ T i ( d i ~ y ) ~ ]The . (e,*)4(al*)1 configuration for [V(dipy)3] is unlikely by the arguments already given.2 The e.p.r. results for this complex are quite similar to those for the other vanadium complexes studied. We infer that the odd electron in [V(dipy)s] is likewise strongly delocalized on the ligand and suggest that the electronic structure may be analogous t o that for [vs&~(c&)~]. Acknowledgment.-Financial support by the National Science Foundation (Grants GP-596 and GP957), the Advanced Research Projects Agency (Contract SD-88), and the Milton Fund of Harvard University are gratefully acknowledged. (22) G. Albrecht, 2.Chem., 3,182 (1963). (23) B. Elschner and S. Herzog, Arch. Sci. (Geneva), 11, 160 (1958).
CONTRIBUTION FROM THE DEPARTMENT OF CHEMISTRY MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE, MASSACHUSETTS
The Preparation and Characterization of Compounds Containing both Hexabromorhena te (IV) and the Trirhenium Nonabromide Group1 BY F. A. COTTON
AND
S. J. LIPPARD2
Received August 25, 1964 From solutions of rhenium(II1) bromide in concentrated aqueous HBr, compounds with the general formula M2RerBrlb (M = quinolinium, pyridinium, or tetraethylammonium ion) have been isolated. Evidently there is oxidation of some Re(II1) to Re(IV), and, by using equimolar quantities of ResBrg and [ReBr~l z-, the quinolinium compound can be obtained more directly. A single crystal X-ray diffraction investigation shows the presence of ResBrs groups and ReBro groups in the quinolinium compound. The visible spectra of the MzRerBrl:, compounds indicate that ReaBr9 and [ReBro]2 - are present. From the X-ray work, the dimensions of the ResBrg group have been established and it is clear that this group is structurally homologous to the ReaCls group which is known to occur in numerous compounds derived directly from rhenium(II1) chloride and in rhenium( 111) chloride itself.
Introduction Recent studies in this3-7 and other829 laboratories (1) Supported by the U. S. Atomic Energy Commission. ( 2 ) National Science Foundation Predoctoral Fellow (1962-present); Woodrow Wilson Honorary Fellow (1962-1963). (3) J. A Bertrand, F. A. Cotton, and W. A. Dollase, I n o w . Chew., 2, 1166 (1963). (4)'F. A. Cotton and B. F. G. Johnson, ibid., 3, 780 (1964). ( 5 ) F. A. Cotton and J. T. Mague, Proc. Chem. Soc., 233 (1964); Inorg. Chem., 8 , 1402 (1964). (6) F A. Cotton and J. T. Mague, ibid., 8 , 1094 (1964). (7) F. A. Cotton, N. F. Curtis, C . B. Harris, B. F. G. Johnson, S. J. Lippard, J. T. Mague, W. R. Robinson, and J. S. Wood, Science, 146, 1305 (1964). (8) W. T. Robinson, J. E. Fergusson, and B. R. Penfold, Pvoc. Chem. Soc., 116 (1963).
have shown that compounds derived from the chloride and bromide of rhenium (111)have remarkable chemical and structural properties. The chloro compounds have been most but the existence of the diverse species Re3Br9Ls,RezBrs2-, ReBr4-, and [ R ~ B ~ ~ ( H ~has o ) ~been ] - briefly reported.7,g8. A
-
(9) J. E. Fergusson, B R. Penfold, and W. T. Robinson, h'ature, 201, 181 (1964). (Sa) NOTE ADDEDI N PRooF.-In a preliminary communication [F. A. Cotton and S. J. Lippard, J . A m . C h ~ mSOC., . 86, 4497 (196411 the preparation of a number of derivatives of ResBre has been described and spectroscopic evidence presented to justify their formulation as ResBrs derivatives. In another preliminary communication [J. E. Fergusson and B. R . Robinson, Proc. Chem. Soc., 189 (1964)l the isolation of compounds which probably contain [ReaBrlol- and [ReaBriopyzl- ions has been reported.
AND S. J. LIPPARD 60 F. A. COTTON
Inorganic Chemistry
Anal. Calcd. for C1sHl&~l
