COMPARISON OF THE PROPERTIES OF SNCL3- AND SNBR3- COMPLEXES OF PLATINUM(II)

The complexes M(3)[Pt(SnX(3))(5)] (M = Bu(4)N(+), PhCH(2)PPh(3)(+); X = Cl, Br), cis-M(2)[PtX(2)(SnX(3))(2)] (M = Bu(4)N(+), PhCH(2)PPh(3)(), CH(3)PPh(3)(+), Pr4N+; X = Cl, Br), and [PhCH(2)PPh(3)](2)[PtBr3(Sn Br3)] have been prepared and characterized by Sn-119 and Pt-195 NMR, f ar-infrared, and electronic absorption and emission spectroscopies. In acetone solutions the [Pt(SnX(3))(5)](3-) ions retain their trigonal bipyramidal structures but are stereochemically nonrigid as evidenced by Sn-119 and Pt-195 NMR spectroscopy. For [Pt(SnCl3)(5)](3-) spin cor relation is preserved between 183 and 363 K establishing that the nonr igidity is due to intramolecular tin site exchange, probably via Berry pseudorotation. Whereas, [Pt(SnCl3)(5)](3-) does not undergo loss of SnCl3- or SnCl2 to form either [Pt(SnCl3)(4)](2-) or [PtCl2(SnCl3)(2)] (2-), [Pt(SnBr3)(5)](3-) is not stable in acetone solution in the abse nce of excess SnBr2 and forms [PtBr2(SnBr3)(2)](2-) and [PtBr3(SnBr3)] (2-) by loss of SnBr2. Similarly, [PtCl2(SnCl3)(2)](2-) is stable in a cetone at ambient temperatures but disproportionates at elevated tempe ratures and [PtBr2(SnBr3)(2)](2-) loses SnBr2 in acetone to form [PtBr 3(SnBr3)](2-). The crystal structures of methyltriphenylphosphonium ci s-dibromobis(tribromostannyl)platinate(II) and benzyltriphenylphosphon ium tribromo(tribromostannyl)platinate(II) have been determined. Both compounds crystallize in the triclinic space group P (1) over bar in u nit cells with a 12.293(16) Angstrom, b 12.868(6) Angstrom, c = 25.047 (8) Angstrom, alpha = 96.11(3)degrees, beta = 91.06(3)degrees, gamma = 116.53(3)degrees, rho(calc) = 2.30 g cm(-3), Z = 3 and with a = 11.04 6(7) Angstrom, b = 14.164(9) Angstrom, c = 22.549(10) Angstrom, alpha = 89.44(4)degrees, beta = 83.32(5)degrees, gamma = 68.31(5)degrees, rh o(calc) = 1.893 g cm(-3), Z = 2, respectively. Least-squares refinemen ts converged at R = 0.057 and 0.099 for 4048 and 4666;independent obse rved reflections with I/sigma(I) > 3.0 and I/sigma(I) > 2.0, respectiv ely. For the-former, the asymmetric unit contains 1.5 cis-[PtBr2(SnBr3 )(2)](2-) ions, 0.5 of which is disordered in such a way as to be pseu docentrosymmetric. This disordering involves a half-occupied PtBr2 uni t appearing on either side of the center. Simultaneously, one bromine from each SnBr3 ligand changes sides while the other two bromines appe ar in average positions with very small displacements between their po sitions. The Pt-Sn distance in [PtBr3(SnBr3)](2-) (2.486(3) Angstrom) is slightly shorter than that in cis-[PtBr2(SnBr3)(2)](2-) (2.4955(3) Angstrom, average), and both are significantly longer than that previo usly found in cis-[PtCl2(SnCl3)(2)](2-) (2. 3556 Angstrom, average), w hich is not consistent with the relative magnitudes of the (1)J(Pt-195 -Sn-119) coupling constants (28 487, 25 720, and 27 627 Hz, respective ly). From our electronic absorption and emission studies of the Pt-SnX (3)(-) complexes, we conclude that (a) the low-energy transitions are d-d transitions analogous to those found in [PtX(4)](2-) systems, (b) the SnCl3- ligand is a stronger sigma donor than SnBr3-, (c) the tripl et state from which the emission occurs is split by spin-orbit couplin g into different spin-orbit states, (d) a forbidden spin-orbit state m ust lie at or near the bottom of the spin-orbit manifold, (e) the soli d state crystal environment perturbs the platinum-tin halide electroni c states, and (f) dispersion of the samples in solvents changes this p erturbation, which can be rationalized in terms of an in-plane distort ion of the square planar platinum coordination sphere.