Unexpected formation of two different coordination polymers from the reaction of Zn(HCOO)2·2H2O with 1,2-bis(4-pyridyl)ethylene

Zn(HCOO)2·2H2O reacts with 1,2-bis(4-pyridyl)ethylene (bpe) yielding two new coordination polymers [Zn4(HCOO)8(bpe)2(H2O)]? (1) and [Zn2(HCOO)4(bpe)]? (2) which were structurally characterized by IR spectroscopy and single crystal X-ray diffraction study. The hydrate species 1 is a 3D polymer where four different zinc sites are present, the first of them, four-coordinated, being linked by three bridging formate and one bridging bpe, the second six-coordinated, with a ZnNO5 coordination environment, almost regular, due to three bridging formate groups and one monodentate formate, one water molecule and one bpe. The third zinc center in 1 is always tetrahedral with three bridging formate ligands and one bridging bpe whereas the fourth Zn site is coordinated by five bridging formate ligands and one bridging bpe. The anhydrous species 2, obtained upon recrystallisation from DMF at 278 K is a zig-zag 1D polymer with a tetrahedral N2O2 zinc coordination environment due to two monodentate formate groups and two bridging bpe. Thermal analysis of 1 show a weight loss due to water elimination followed by formate and bpe decomposition, whereas in the case of 2 only a decomposition between 210 and 240 °C was observed.