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

Abstract It was shown that interaction of trinuclear pivalates Fe 2 MO(Piv) 6 (Hpiv) 3 (M = Ni II or Co II , Piv = (CH 3 ) 3 CCO 2 − ) 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 [Fe 2 NiO(Piv) 6 ( trans -dpe) 1.5 ] n ( 1 ), [Fe 2 CoO(Piv) 6 ( trans -dpe) 1.5 ] n ( 2 ) and 1D polymers [{Fe 2 CoO(Piv) 6 ( cis -dpe)} 2 ( trans- dpe)] n ( 3 ), [Fe 2 NiO(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 Fe 2 NiO(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 Fe 2 NiO(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 [Fe 2 MO(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 Ni II or Co II . Exchange coupling between trinuclear units Fe 2 MO(Piv) 6 was negligibly small.