H(3)P···AgI: generation by laser-ablation and characterization by rotational spectroscopy and ab initio calculations

The new compound H(3)P···AgI has been synthesized in the gas phase by means of the reaction of laser-ablated silver metal with a pulse of gas consisting of a dilute mixture of ICF(3) and PH(3) in argon. Ground-state rotational spectra were detected and assigned for the two isotopologues H(3)P···(107)AgI and H(3)P···(109)AgI in their natural abundance by means of a chirped-pulse, Fourier-transform, microwave spectrometer. Both isotopologues exhibit rotational spectra of the symmetric-top type, analysis of which led to accurate values of the rotational constant B (0), the quartic centrifugal distortion constants D ( J ) and D ( JK ), and the iodine nuclear quadrupole coupling constant χ ( aa )(I) = eQq ( aa ). Ab initio calculations at the explicitly-correlated level of theory CCSD(T)(F12*)/aug-cc-pVDZ confirmed that the atoms P···Ag–I lie on the C (3) axis in that order. The experimental rotational constants were interpreted to give the bond lengths r (0)(P···Ag) = 2.3488(20) Å and r (0)(Ag–I) = 2.5483(1) Å, in good agreement with the equilibrium lengths of 2.3387 Å and 2.5537 Å, respectively, obtained in the ab initio calculations. Measures of the strength of the interaction of PH(3) and AgI (the dissociation energy D (e) for the process H(3)P···AgI = H(3)P + AgI and the intermolecular stretching force constant F (P···Ag)) are presented and are interpreted to show that the order of binding strength is H(3)P···HI < H(3)P···ICl < H(3)P···AgI for these metal-bonded molecules and their halogen-bonded and hydrogen-bonded analogues.