2D Porous Honeycomb Polymers versus Discrete Nanocubes from Trigonal Trinuclear Complexes and Ligands with Variable Topology

Trinuclear building block {Fe₂NiO(Piv)₆} (Piv=pivalate), which possessed pseudo‐D_3h symmetry, was linked by two ligands, pseudo‐D_3h ligand tris‐(4‐pyridyl)pyridine (L1) and C_2v ligand 4‐(N,N‐dimethylamino)phenyl‐2,6‐bis(4‐pyridyl)pyridine (L2) into two products with different topologies: 2D coordination polymer [Fe₂NiO(Piv)₆(L1)]_n (1), and discrete molecule [{Fe₂NiO(Piv)₆}₈{L2}₁₂], which had a nanocube structure (2). In compound 1, trinuclear {Fe₂NiO(Piv)₆} blocks were linked through ligand L1 into layers with honeycomb topology. In compound 2, eight trinuclear blocks were located in the vertices of the nanocube, with each L2 ligand linked to two {Fe₂NiO(Piv)₆} units. In the crystal structure, these nanocubes formed infinite catenated chains. Analysis of possible structures that could be assembled from these building blocks showed that compounds 1 and 2 corresponded to their respective predicted topologies. Compound [1⋅solvent] possessed a porous structure, in which the voids were filled by solvent molecules (DMF or DMSO). This structure was retained following desolvation, and compound 1 absorbed significant quantities of N₂ and H₂ at 78 K (S_BET=730 m² g⁻¹, H₂ sorption capacity: 0.9 % by weight at 865 Torr). Desolvation of [2⋅solvent] led to disorder of its crystal structure, and compound 2 only adsorbed negligible quantities of N₂ but adsorbed 0.27 % H₂ (by weight) at 855 Torr and 78 K. The magnetic properties of these complexes (temperature dependence of molar magnetic susceptibility) were governed by the magnetic properties of the trinuclear “building block”.