Preparation and spectral characterization of cadmium(II) thiocyanate complexes of tricyclohexyl-, triphenyl- and tri-m-tolylphosphines and the crystal and molecular structure of the tri-m-tolylphosphine complex

Article abstract of DOI:10.1021/ic50225a064

The complexes Cd(SCN)₂PR₃, where R = cyclohexyl, phenyl, or m-tolyl, have been isolated from the reaction of Cd(SCN)₂ with the phosphine. Phosphorus-31 NMR, infrared, and Raman spectra of the complexes have been examined, and the structure of the tri-m-tolylphosphine complex has been determined by a single-crystal X-ray diffraction study. No satellites due to ¹¹¹Cd/¹¹³Cd-³¹P spin-spin couplings are observed in the ³¹P NMR spectra even at 183 K. The vibrational spectra of the complexes are consistent with a polymeric structure involving bridging thiocyanates and five-coordinate cadmium. The crystals of the m-tolyl compound Cd(SCN)₂(P(C₇H₇)₃) belong to the monoclinic space group P2₁/c, with a = 10.866 (7) ?, b = 10.203 (3) ?, c = 20.077 (6) ?, β = 101.14 (4)°, and Z = 4. The structure was solved by the heavy-atom method and refined by least-squares procedures on 1965 nonzero reflections. The final R factor was 0.038. Infinite chains of five-coordinated Cd atoms and bridging SCN groups extend along the b direction in the crystal. The metal shows a distorted trigonal-bipyramid geometry with the equatorial positions being occupied by the phosphine (Cd-P = 2.584 (2) ?), an S-bonded SCN group (Cd-S = 2.595 (2) ?), and the N end of a symmetry-equivalent SCN group (Cd-N = 2.256 (6) ?). The remaining SCN group bridges axial positions along the chain by forming weaker bonds (Cd-S = 2.792 (2) ?, Cd-N = 2.297 (6) ?). The unusual distribution of soft S atoms and hard N atoms in both the axial and equatorial positions undoubtedly results from the intermediate softness of cadmium, since the strongly bonding equatorial sites are filled only by soft P and S atoms in the similar mercury complexes.