Three new coordination polymers based on the combination of rctt-1,2,3,4-cyclobutanetretracarboxylic acid (rctt-H4Cbtc) and trans-1,2-bis(4-pyridyl)ethane (4,4'-bpe) and Zn and Ni metal centers were synthesized under hydrothermal conditions and structurally characterized either by X-ray Single Crystal or Powder Diffraction: [Zn2(4,4'-bpe)(rctt-Cbtc)(OH2)]n·4H2O (1), [Zn(4,4'-bpe)0.5(rctt-Cbtc)0.5(OH2)]n (2) and [Ni2(4,4'-bpe)2(rctt-Cbtc)(OH2)6] (3). The crystal structure of 1 formed a 3-D coordination polymer. A similar building unit is found in 2 but forming part of a polymeric 2-D array, where the bipyridine displays a gauche conformation in contrast to the anti conformation found for 1. In 3, the change of Zn by Ni as a node produces a novel supramolecular array based on an 1-D coordination polymer, which is constructed from chains bearing 4,4'-bpe in an anti configuration. A sequential hydrothermal transformation was observed between 1 and 2 in the range of 80 and 120 °C, respectively. An increase of time or temperature of reaction favored the formation of 2 below 140 °C. Solid phases 1 and 2 are metastable above 140 °C. A novel unidentified phase is observed at 180 °C, starting from the same chemical precursors in a similar molar ratio. DFT calculations corroborate the experimental observations; compound 2 is a few more stable than 1. The energy lost when water leaves the Zn atom is partially compensated by the O atom of the rctt-Cbtc ligand and could induce the formation of compound 2.

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