Multi-modal bridging ligands; effects of ligand functionality, anion and crystallisation solvent in silver(I) co-ordination polymers

The influence of solvent and anion on the formation of co-ordination polymers of silver(I) and the multi-modal ligands 2,2'-bipyrazine (bpyz) and pyrazino[2,3-f]quinoxaline (pyq) has been studied. Reaction of AgX (X=BF4- or PF6-) with bpyz or pyq in MeNO2 affords three-dimensional co-ordination networks, {[Ag(bpyz)]X}(infinity) or {[Ag(pyq)]X}(infinity). Whereas {[Ag(bpyz)]X}(infinity) form diamond-like networks, which adopt a chiral structure due to the different bridging modes of the bpyz ligand, {[Ag(pyq)]X}(infinity) form unusual achiral three-dimensional frameworks which are constructed from bridged [Ag(pyq)](infinity) tubes. In the case of {[Ag(bpyz)]X}(infinity) an increase in anion volume from BF4- to PF6- leads to a corresponding increase in helix volume and concomitant contraction of the helical pitch of the diamondoid framework. The use of co-ordinating solvents of crystallisation in the reactions of AgBF4 with bpyz results in the formation of an undulating two-dimensional sheet, {[Ag(bpyz)(MeCN)]BF4}(infinity), when MeCN replaces MeNO2, or a one-dimensional polymer {[Ag-2(bpyz)(2)(PhCN)][BF4](2)}(infinity), when PhCN is used. Reaction of AgBF4 with pyq in either MeCN or PhCN affords the discrete molecular complex [Ag(pyq)(2)]BF4 in which only the chelating donors of the pyq ligand are co-ordinated to the silver(I) ion. [Ag(pyq)(2)]BF4 exhibits dimorphism with the two structures observed differing in the nature of their pi-pi interactions.