A computational study on [(PH2X)2]·+ homodimers involving intermolecular two-center three-electron bonds

A computational study at CCSD(T) theoretical level has been carried out on radical cation [(PHX)] homodimers. Four stable minima configurations have been found for seven substituted phosphine derivatives, X = H, CH, CCH, NC, OH, F and Cl. The most stable minimum presents an intermolecular two-center three-electron P···P bond except for X = CCH. The other three minima correspond to an alternative P···P pnicogen bonded complex, to a P···X contact and the last one to the complex resulting from a proton transfer, PHX:PHX. The complexes obtained have been compared with those of the corresponding neutral ones, (PHX), and the analogous protonated ones, PHX:PHX, recently described in the literature. The spin and charge densities of the complexes have been examined. The electronic characteristics of the complexes have been analyzed with the NBO and AIM methods. The results obtained for the spin density, charge and NBO are coherent for all the complexes.This work has been supported by the Spanish Ministerio de Economı´a y Competitividad (CTQ2012-35513-C02-02) and Comunidad Auto´noma de Madrid (S2013/MIT-2841, Fotocarbon). Computer, storage and other resources from the CTI (CSIC) are gratefully acknowledged. One of us (M.M.-L.) thanks the Ministerio de Economı´a y Competitividad for her contract.Peer Reviewe