Mechanochemical and solution synthesis, and crystal structures and IR and solid-state (CPMAS) NMR spectroscopy of some bis(triphenylphosphine) silver(I) mono- and di-hydrogencitrate systems

The complex [(Ph3P)(2)Ag(H(2)cit)]center dot EtOH (1; H(2)cit(-) = dihydrogencitrate = C6H7O7-) contains [(Ph3P)(2)Ag(H(2)cit)] molecules in which the silver atom is coordinated to two PPh3 molecules and the two oxygen atoms of one of the 'terminal'/1-carboxylate groups of the dihydrogencitrate group. The molecules form centrosymmetric hydrogen-bonded dimers in the solid. In [{(Ph3P)(2)Ag}(2)(Hcit)], (2), unsymmetrical deprotonation of the citrate grouping is found, from the 1- and 3- (i.e. terminal and central) carboxylates: [(Ph3P)(2)Ag(O2CCH2C(OH) (CH2COOH)CO2)Ag(PPh3)(2)]. The above complexes, as well as [(Ph3P)(3)Ag(H(2)cit)] (3) were prepared via conventional solution methods, involving the reaction of trisilver(I) citrate, citric acid and triphenylphosphine, and by a mechanochemical method involving the reaction of silver(I) oxide, citric acid and triphenylphosphine. IR studies of 1-3 show the presence of coordinated carboxylate and free carboxylic acid groups in the mono- and di-hydrogencitrate ligands, and the formation of 2 from 1 shows that dihydrogencitrate deprotonation can occur upon dissolution of 1 in protic solvents. High-field (9.40 T) P-31 CPMAS NMR spectra were recorded and analysed, yielding heteronuclear (1)J(Ag-107/109, P-31) and homonuclear (2)J(P-31,P-31) spin-spin coupling constants.