The influence of alkane spacer of bis(diphenylphosphino)alkanes on the nuclearity of silver(I): Syntheses and structures of P,P′-bridged clusters and coordination polymers involving dithiophosphates

The effect of the length of alkane spacer in diphosphines on the nuclearity of Ag(I) complexes containing dialkyl dithiophosphates (dtp) ligands has been investigated. 1,1-Bis(diphenylphosphino)methane (dppm) yielded tetranuclear [Ag4(dppm)2{S2P(OEt)2}4] (1), [Ag4(dppm)2{S2P(OiPr)2}4] (3), trinuclear [Ag3(dppm)3{S2P(OEt)2}2](PF6) (2), and a dinuclear [Ag2(dppm)2{S2P(OiPr)}](PF6) (4). The increase in spacer length from one methylene in dppm to two in 1,2-bis(diphenylphosphino)ethane (dppe) resulted in the formation of polymeric, [Ag(dppe){S2P(OR)2}]∞ (R = Et, 5a and 5a′; iPr, 5b), and [Ag4(μ3-Cl)(dppe)1.5{S2P(OR)2}3]∞ (R = Et, 6a; iPr, 6b). Compounds 5a, 5b, 6a and 6b were reported earlier [C.W. Liu, B.-J. Liaw, L.-S. Liou, J.-C. Wang, Chem. Commun. (2005) 1983]. Further increase in the chain length to four methylene units in 1,4-bis(diphenylphosphino)butane (dppb) yielded dppb-bridged polymers, [Ag(dppb){S2P(OEt)2}]∞ (7) and [Ag2(dppb){S2P(OEt)2}2]∞ (8). In all the polynuclear compounds, diphosphines acted as P,P′-bridging ligands, while the dtp ligands (S,S′-donors) adopted varieties of coordination patterns: S,S′-chelating (5, 7), S,S′-bridging (4), bimetallic-triconnective, μ2:η2,η1 (1, 3, 8), bimetallic-diconnective, μ2:η2 (2, 3) and trimetallic-triconnective, μ3:η2,η1 (6). Some of the complexes exhibit argentophilicity with Ag⋯Ag distances in the range, 2.918–3.360 Å. Concomitant bridging of two silver atoms either by dppm and dtp ligands (1, 3 and 4) or two dtp ligands (8) lead to close silver-silver contacts. The diphosphines (dppe and dppb) with longer spacer appeared to favor 1D or 2D polymers due to the flexibility of the spacer within the diphosphine unit by adopting anti conformation as opposed to syn conformation of the dppm linker is revealed in complexes.