INFRARED SPECTRA LASER RAMAN SPECTRA, AND FORCE CONSTANTS OF METAL-HEXAHALO SPECIES R2M4X6, RMVX6 [R=(C2H5)4N OR CS - M4=TI, ZR, OR HF - MV=NB OR TA - X=CL OR BR], AND WCL6

The infrared and laser Raman spectra of a series of metal-hexahalo species of groups IV-VI have been recorded in the range 700-70 cm-1. The compounds are R2MX6 [R = (C2H6)4N or Cs; M = Ti, Zr, orHf; X = Cl or Br], RMX6 [R = (C2H5)4N or Cs; M = Nb or Ta; X = Cl or Br], and WCl6. Assignments for the three Raman-active and two infraredactive fundamentals are made; in addition the value for the inactive fundamental v6 (t2u) has in some cases been deduced from infraredactive combination bands. Force constants for the hexahalo species have been calculated on the assumption both of a modified Urey-Bradley force field (MUBFF) and of a generalized valence force field (GVFF). The value for v6 could thus be calculated and compared with the value deduced from combination bands. For both force fields the average value of the bond stretching force constants for the quadrivalent ions lies below that for quinquevalent ions, which in turn lies below that for WCl6. For example, on the basis of the MUBFF, Kav for the MCl2-6 ions is ∼1.0 mdyn/Å, for the MCl-6 ions it is ∼1.3 mdyn/Å, and for WCl6 it is ∼1.6 mdyn/Å. This increase in K with increase in the oxidation state of the metal is consistent with previous findings on other complex ions. In addition, KMOI > KMBr in all cases for a given central metal atom. The expected isotopic structure of the alg mode of an MCl6 molecule is calculated, but could not, in practice, be resolved for either the TiCl2-6 or the TaCl-6 ions. © 1969, American Chemical Society. All rights reserved.