-We report the synthesis and crystal structures of two transition metal-based coordination polymers comprising ligand molecules not included in the original reaction mixtures but instead formed in situ during hydrothermal treatment, Zinc meso-iminodisuccinate hydrate (I), Zn-2(C8H7NO8)center dot 0.57H(2)O, formed from zinc acetate and L-aspartic acid, and tetraaquanickel(II) 5,10-dioxo-5,10-dihydro-4,9-dioxa-pyrene-2,7-dicarboxylate (II), Ni(H2O)(4)(C16H4O8), formed from nickel acetate and 5-hydroxyisophthalic acid. We show that the formation of I takes place via a fumaric acid intermediate, while the formation of II requires the formation of a new C-C bond. The structure of I consists of weakly interacting sheets, while the structure of II consists of strongly hydrogen-bonded chains. Crystal data: for I, P2(1)/n (14), a = 10.073 angstrom, b = 9.894 angstrom, c = 12.053 angstrom, beta = 105.605 degrees, V = 1156.87(13) angstrom(3), Z = 4; for II, P (1) over bar (2), a = 5.011 angstrom, b = 6.526 angstrom, c = 12.305 angstrom, alpha = 76.868 degrees, beta = 84.988 degrees, gamma = 87.619 degrees, V = 390.3(4) angstrom(3), Z = 1.