Influence of the Synthesis Conditions and the Presence of Guest Molecules on the Structures of Coordination Polymers [Fe₂MO(Piv)₆(L)_x]_n (L = 4,4′-Bipyridine, Bis(4-Pyridyl)ethane) with the Labile Crystal Lattice

Coordination polymers [Fe₂MO(Piv)₆(L¹)_x]_n · nSolv (L¹ = 1,2-bis(4-pyridyl)ethane, M = Ni (I), Co (II), x = 1.5; M = Cо (III), x = 2) are synthesized. Depending on the synthesis conditions, compounds II (cross diffusion of reactants) or III (fast mixing of reactant solutions) of different compositions are formed. It is shown by X-ray diffraction analysis (CIF files CCDC 1550804 (I) and 1550805 (III)) that compound I is a porous coordination polymer built of parallel 2D layers and compound III is a 1D coordination polymer. The crystals of complexes I and II are isostructural. The mutual arrangement of the 2D layers in compound II depends on the solvent in which this coordination polymer is formed. The desolvation of polymers I and II leads to the collapse of the crystal lattice. Unlike the complexes with L¹, [Fe₂NiO(Piv)₆(L²)_1.5]_n · nSolv (IV · nSolv) is formed in the case of 4,4'-bipyridine (L²), regardless of the solvent nature, and its crystal lattice is formed by interpenetrating 2D layers. The mutual arrangement of the 2D layers in the crystal lattice of compound IV varies with the solvent used for the synthesis of this coordination polymer or for the resolvation of a sample of polymer IV. It is found that the parameters of the ⁵⁷Fe Mössbauer spectra for compounds IV and IV · nDEF (DEF is N,N-diethylformamide) differ, which can be explained by a decrease in the symmetry of the coordination environment of the Fe³⁺ ions when the pores are filled with DEF molecules.