Crystal structures of three copper(II)–2,2′-bipyridine (bpy) compounds, [Cu(bpy)<sub>2</sub>(H<sub>2</sub>O)][SiF<sub>6</sub>]·4H<sub>2</sub>O, [Cu(bpy)<sub>2</sub>(TaF<sub>6</sub>)<sub>2</sub>] and [Cu(bpy)<sub>3</sub>][TaF<sub>6</sub>]<sub>2</sub> and a related coordination polymer, [Cu(bpy)(H<sub>2</sub>O)<sub>2</sub>SnF<sub>6</sub>]<sub> <i>n</i> </sub>
Acta crystallographica. Section E, Crystallographic communications