Binary Transition Metal Dinitrogen Complexes. Part II. Matrix Infrared and Raman Spectra, Structure, and Bonding of Pt(N2)n (where n = 1–3)

Abstract

The products of the cocondensation reactions of Pt atoms with N2 at 4.2–10 °K are investigated by matrix isolation infrared and Raman spectroscopy and are shown to be binary dinitrogen complexes of the form Pt(N2)n. Examination of the reaction products in pure 14N2, in 14N2/15N2, in dilute 14N2/Ar, in 14N2/15N2/Ar as well as 14N2/14N/15N/15N2/Ar matrices establishes the stoichiometries of the complexes to be n = 1–3. Structural assignments can be made for the complexes Pt(N2) and Pt(N2)3 which contain end-on bonded dinitrogen and are found to be similar to the corresponding dinitrogen and carbonyl complexes of nickel and palladium. Pt(N2)2 appears to be the exception in this series of complexes, for which side-on bonded dinitrogen is proposed.On the basis of the Cotton–Kraihanzel force field of approximation and the isotope intensity sum rules, isotopic frequencies are computed for the NN stretching modes of the individual complexes and isotopic absorption intensities for Pt(N2)3 and are found to be in close agreement with the observed values. In the case of Pt(N2), the scrambled 14N15N isotope data establish that the dinitrogen ligand is bonded to the Pt atom in an end-on fashion. On the basis of its unusual spectroscopic behavior Pt(N2)2 is proposed to have sideways bonded dinitrogen ligands. Pt(N2)3 in solid α-N2 is found to be slightly distorted from a regular triangular planar molecule but appears to be regular D3h in solid argon. Calculations show that a substitutional site symmetry of C2 for Pt(N2)3 satisfactorily accounts for all the spectral lines observed for the complex in nitrogen. Comparisons are made within the group of binary dinitrogen complexes M(N2)n where n = 1–3 and with the corresponding binary carbonyl complexes M(CO)n. The relationship between the dinitrogen complexes NiN2, PdN2, and PtN2 and nitrogen chemisorbed on those same metals is discussed.