Crystal structure of dodecaaqua-tetra-μ3-carbonato-hexa(N,N,N',N'- tetramethylethylenediamine)hexanickel(II) hemiheptabromide hemihydroxide, [{Ni2(C6H16N2)2(H2O)4(CO3)1.33}3][Br]3.5[OH]0.5