CRYSTAL-STRUCTURES, VIBRATIONAL-SPECTRA A ND NORMAL-COORDINATE ANALYSES OF TRANS-[PTX(2)(ACAC)(2)], X=CL,BR,I,SCN

The crystal structures of trans-[PtCl2(acac)(2)] (monoclinic, space gr oup P2(1)/c, a=7.616(5), b=12.759(5), c=7.892(5) Angstrom, beta=118.45 9(5)degrees, Z=2), trans-[PtBr2(acac)(2)] (triclinic, space group <P(1 )over bar>; a=7.502(5), b=7.665(5), c =8.155(5) Angstrom, alpha=114.50 8(5), beta=94.537(5), gamma=117.669(5)degrees, Z=1) and trans-[Pt(SCN) 2(acac)(2)] (triclinic, spare group <P(1)over bar>, a=7.095(10), b=7.9 393(10), c=7.963(10),c=7.9631 Angstrom, alpha=114.051(10), beta=100.95 5(10), gamma=100.573(10)degrees, Z=1) have been determined by single c rystal X-ray diffraction analysis. The crystal structure of trans-[PtI 2(acac)(2)] is known from the literature. To enhance the spectroscopic resolution, the IR and Raman spectra of the four complexes have been measured at low temperature (10 K). Using the X-ray data, normal coord inate analyses based on a modified valence force field have been perfo rmed and the normal modes of vibration for the octahedral skeleton [Pt X(2)O(4)] have been assigned. With a set of 19 or 23 force constants t aking into account the inner-ligand vibrations a good agreement betwee n observed and calculated frequencies has been achieved. The valence f orce constants are e.g. f(d) (PtCl)=2.16, f(d) (PtBr)=1.45, f(d) (PtI) =1.01, f(d) (PtS)=1.80 mdyn/Angstrom, and f(d) (PtO) ranges from 1.89 to 1.91 mdyn/Angstrom.