Syntheses and crystal structures of three novel oxalate coordination compounds: Rb(2)Co(C(2)O(4))(2)·4H(2)O, Rb(2)CoCl(2)(C(2)O(4)) and K(2)Li(2)Cu(C(2)O(4))(3)·2H(2)O

Single crystals of three novel transition-metal oxalates, dirubidium di­aqua­dioxalatocobalt(II) dihydrate or dirubidium cobalt(II) bis­(oxalate) tetra­hydrate, Rb(2)[Co(C(2)O(4))(2)(H(2)O)(2)]·2H(2)O, (I), catena-poly[dirubidium [[di­chlorido­cobalt(II)]-μ-oxalato]] or dirubidium cobalt(II) dichloride oxalate, {Rb(2)[CoCl(2)(C(2)O(4))]}( n ), (II), and poly[dipotassium [tri-μ-oxalato-copper(II)dilithium] dihydrate] or dipotassium dilithium copper(II) tris­(oxalate) dihydrate, {K(2)[Li(2)Cu(C(2)O(4))(3)]·2H(2)O}( n ), (III), have been grown under hydro­thermal conditions and their crystal structures determined using single-crystal X-ray diffraction. The structure of (I) exhibits isolated octa­hedral [Co(C(2)O(4))(2)(H(2)O)(2)] units, whereas (II) consists of trans chains of Co(2+) ions bridged by bidentate oxalato ligands and (III) displays a novel tri-periodic network of Li(+) and Cu(2+) ions linked by oxalato bridging ligands.