Hexafluorosilicate and tetrafluoroborate coordination to lead(II) di- and tri-imine complexes – Unusual fluoroanion coordination modes

Abstract

Lead(II) tetrafluoroborate and hexafluorosilicate complexes with 2,2′-bipyridyl, 1,10-phenathroline and 2,2′:6′,2″-terpyridyl have been prepared from the ligand and lead salt in aqueous/MeCN. Crystal structures are reported for [Pb(bipy)2(SiF6)], [Pb(phen)2(SiF6)] and [Pb(bipy)2(BF4)2] which are dinuclear with each lead coordinated “cis” to the two diimines and with the bridging fluoroanions completing eight or nine-coordination. [Pb(phen)2(BF4)2] is eight-coordinate and mononuclear with “cis” diimines and two κ2-BF4− groups. [Pb(phen)2(H2O)2(SiF6)] is also mononuclear with a κ2-SiF62− group and two coordinated water molecules. Reaction of Pb(BF4)2 with 2,2′:6′,2″-terpyridyl gave only [Pb(terpy)3][BF4]2, but Pb(SiF6) produced [Pb(terpy)(H2O)(SiF6)], which is a chain polymer with bridging SiF62− groups and significant π-stacking of the imine rings. The work has identified a number of coordination modes of the SiF62− anion, which has been little used in coordination chemistry but proves to be versatile and also stable (to decomposition/hydrolysis).