Crystal Structures, Spectroscopic Analysis, and Normal Coordinate Analysis of (n-Bu4N)2[M(ECN)4]; M = Pd, Pt; E = S, Se

Abstract

The reaction of (NH4)2[PdCl4] or K2[PtCl4] with KSCN or KSeCN in aqueous solutions yields the complex anions [Pd(SCN)4]2-, [Pt(SCN)4]2- and [Pt(SeCN)4]2-, which are converted into (n-Bu4N) salts with (n-Bu4N)HSO4. (n-Bu4N)2[Pd(SeCN)4] is formed by treatment of (n-Bu4N)2[PdCl4] with (n-Bu4N)SeCN in acetone. X-ray structure determinations on single crystals of (n-Bu4N)2[Pd(SCN)4] (monoclinic, space group P21/n, a = 13.088(3), b = 12.481(2), c = 13.574(3) Å, β = 91.494(15)°, Z = 2), (n-Bu4N)2[Pd(SeCN)4] (monoclinic, space group P21/n, a = 13.171(2), b = 12.644(2), c = 13.560(2) Å, β = 91.430(11)°, Z = 2) and (n-Bu4N)2[Pt(SeCN)4] (monoclinic, space group P21/n, a = 13.167(2), b = 12.641(1), c = 13.563(2) Å, β = 91.516(18)°, Z = 2) reveal, that the compounds crystallize isotypically and the complex anions are centrosymmetric and approximate planar. In the Raman spectra the metal ligand stretching modes of (n-Bu4N)2[Pd(SCN)4] (1) and (n-Bu4N)2[Pt(SCN)4] (3) are observed in the range of 260-303 cm-1 and of (n-Bu4N)2[Pd(SeCN)4] (2) and (n-Bu4N)2[Pt(SeCN)4] (4) in the range of 171-195 cm-1. The IR and Raman spectra are assigned by normal coordinate analysis using the molecular parameters of the X-ray determination. The valence force constants are fd(PdS) = 1.17, fd(PdSe) = 1.17, fd(PtS) = 1.44 and fd(PtSe) = 1.42 mdyn/Å. The 77Se NMR resonances are 23 for 2, -3 for 4 and the 195Pt NMR resonances 549 for 3 and 130 ppm for 4.