Examination of cobalt, nickel, copper and zinc(ii) complex geometry and binding affinity in aqueous media using simple pyridylsulfonamide ligandsElectronic supplementary information (ESI) available: experimental details for [M(L2)2], [M(L3)2] and [M(L4)2] (M = Zn, Cu, Ni, Co); species distribution plots. See http://www.rsc.org/suppdata/nj/b2/b206279h/