PREPARATION, CRYSTAL-STRUCTURES, VIBRATIO NAL-SPECTRA, AND NORMAL-COORDINATE ANALYSIS OF TRANS-(PNP)[TCCL4(PY)(2)] AND TRANS-(PNP)[TCBR4(PY)(2)]

By reaction of (PNP)(2)[TcX(6)] with pyridine in the presence of [BH4] (-) (PNP)[TcX(4)(Py)(2)], X = Cl, Br, are formed. X-ray structure dete rminations on single crystals of these isotypic Tc-III complexes (mono clinic, space group P2(1)/n, Z = 2, for X = Cl: a = 13.676(4), b = 9.1 02(3), c = 17.144(2) Angstrom, beta = 91.159(1)degrees; for X = Br: a = 13.972(2), b = 9.146(3), c = 17.285(4) Angstrom, beta = 90.789(2)deg rees) result in the averaged bond distances Tc-Cl: 2.386, Tc-Br: 2.519 , Tc-N: 2.132(3) (X = Cl) and 2.143(4) Angstrom (X = Br). The two pyri dine rings are coplanar and vertical to the X-Tc-X-axes, forming angle s of 42.28 degrees (X = Cl) and 43.11 degrees (X = Br). Using the mole cular parameters of the X-ray structure determination and assuming D-2 h point symmetry, the IR and Raman spectra are assigned by normal coor dinate analysis based on a modified valence force field. Good agreemen t between observed and calculated frequencies is obtained with the val ence force constants f(d)(TcCl) = 1.45, f(d)(TcBr) = 1.035, f(d)(TcN) = 1.37 (X = Cl) and 1.45 mdyn/ Angstrom (X = Br), respectively.