Coordination polymers based on trinuclear heterometallic pivalates and polypyridines: Synthesis, structure, sorption and magnetic properties

It was shown that interaction of trinuclear pivalates Fe2MO(Piv)(6)(Hpiv)(3) (M = Ni-II or Co-II, Piv = (CH3)(3)CCO2 ) with pyridine-containing ligands - trans-bis-1,2-(4-pyridyl)ethylene (trans-dpe), bis-1,3-(4-pyridyl)propane (py(2)Pn) resulted in formation of 2D porous coordination polymers [Fe2NiO(Piv)(6)-(trans-dpe)(1.5)](n) (1), [Fe2CoO(Piv)(6)(trans-dpe)(1.5)](n) (2) and 1D polymers [{Fe2CoO(Piv)(6)(cis-dpe)}(2)(trans-dpe)](n) (3), [Fe2NiO(Piv)(6)(py(2)Pn)(DMF)](n) (4), where cis-dpe is cis-bis-1,2-(4-pyridyl)ethylene, formed due to in situ isomerization of trans-dpe. Interaction of Fe2NiO(Piv)(6)(Hpiv)(3) with bis-2,3-(4-pyridyl)-2,3-dihydroxybutane led to in situ destruction of this ligand and isolation of trinuclear complex Fe2NiO(Piv)(6)(pyCOCH(3))(3) (5). X-ray structures of all five complexes were determined; compounds 1 and 2 were found to be isostructural. It was shown that crystal structures of [Fe2MO(Piv)(6)(trans-dpe)(1.5)](n) complexes significantly changed at temperature variation. Sorption capacity of 1 and 2 on N-2, H-2 at 78 K (total volume of pores V-T less than 0.045 cm(3)/g) was much lower than sorption capacity on methanol and ethanol at 293 K (V-T from 0.16 cm(3)/g to 0.37 cm(3)/g), which can be explained by flexibility of crystal structure of these coordination polymers. Magnetic properties of 1 and 2 were simulated taking into account exchange interactions between metal ions and zero-field splitting of NiII or CoII. Exchange coupling between trinuclear units Fe2MO(Piv)(6) was negligibly small. (C) 2011 Elsevier B. V. All rights reserved.