Crystal engineering of molecular to nonmolecular metal malonates in the presence of piperazine: Role of metal ions in tuning architectures

Mote, Kaustubh ; Thomas, Jency ; Ramanan, Arunachalam


Growth of transition metal malonate (mal) based solids from aqueous solution is investigated in the presence of piperazine (pip). Reaction under ambient conditions favored the growth of [{M(mal)2(H2O)2}{H2pip}] (M: Ni, 1; M: Co, 2), [{Cu(mal)2(H2O)2}{H2pip}].2H2O (3), and, [Zn(mal)(pip)(H2O)] (4). While 1-3 are molecular solids, 4 is a 2-D coordination polymer. In the case of cobalt, higher acidic condition favored the formation of a molecular organic-inorganic salt, [(H2pip){CoCl4}] (5). The same reaction under a different crystallization condition, i.e., lesser polar solvent and slightly higher temperature (solvothermal) led to a 2-D coordination polymer [{Co(mal)(H2O)(Hpip)}]Cl (6). A retrosynthesis approach has been employed to interpret the crystallization reaction and compare the supramolecular reactivity of aggregating metal tectons in engineering the molecules to form either a molecular solid or coordination polymer.


Crystallization, Transition metal ions, Malonate, Piperazine, Nickel, Cobalt, Copper, Zinc

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