Solid-State NMR, X-Ray Diffraction, and Theoretical Studies of Neutral Mononuclear Molecular Bis(triphenylphosphine)silver(i) Mono-Carboxylate and -Nitrate Systems

Abstract

Neutral mononuclear molecular silver(i) carboxylate complexes of the form [(Ph3P)2Ag(O2XY)] with O2XY = O2CCH2Ph, O2CCHPh2, O2CC(CH3)3, O2CCH2C(CH3)3, and O2CCF3 (compounds 1-4 and 5β) have been investigated in the solid state using single-crystal X-ray structure determinations, 1D 31P CPMAS NMR and 2D 31P-31P CPCOSY NMR measurements, and ab initio computational modelling. The results show that these complexes contain P2AgO2 molecular cores with four-coordinate silver in which the carboxylate ligands are weakly bound to the silver atoms via the two oxygen atoms giving rise to unsymmetrical chelate units. Crystal structure determinations and solid-state NMR spectra have also been analysed for the mononuclear molecular silver(i) nitrate complex [(Ph3P)2Ag(O2NO)] (9α) and two polymorphs of its toluene monosolvate (11α, β). In 9α, the two PPh3 ligands are of the same chirality, whereas in 11α, β, they are opposed. The crystalline environments in the polymorphs have been explored by way of Hirshfeld surface analyses, after quantum-mechanical isolated-molecule calculations had shown that although the molecular energies of the experimental geometries of 9α, and 11α, β are significantly different from each other and from the energies of the optimized geometries, the latter, in contrast, do not differ significantly from each other despite the conformational isomerism. It has further been shown using 9α as an example that the energy dependence on variation of the P-Ag-P angle over a range of ∼15° is only ∼5 kJ mol-1. All this indicates that the forces arising from crystal packing result in significant perturbations in the experimental geometries, but do not alter the stereoisomerism caused by the donor atom array around the Ag atom. In the NMR study, a strong inverse correlation has been found between 1J(107/109Ag,31P) and the Ag-P bond length across all carboxylate and nitrate compounds.