Incomplete Spin Crossover versus Antiferromagnetic Behavior Exhibited in Three-Dimensional Porous Fe(II)-Bis(tetrazolate) Frameworks

Two three-dimensional (3D) Fe­(II) porous metal–organic frameworks (MOFs) [Fe2(H0.67bdt)3]·13H2O (1·13H2O) and [Fe3(ox)­(H0.67bdt)3(H2O)2]·solvent (2·solvent) (H2bdt = 5,5′-(1,4-phenylene)­bis­(1H-tetrazole); H2ox = oxalic acid; solvent = 10H2O and 9CH3OH for 2·9MeOH and 6H2O and 5C4H9OH for 2·5n-BuOH) were solvothermally synthesized and characterized. The X-ray structure analysis reveals that complex 1·13H2O is constructed from one-dimensional (1D) {Fe­(tz)3}n (tz = tetrazolate) chains which are linked through the phenyl tethers of the bdt ligands into a 3D microporous framework. In the case of complex 2·solvent, the linear trinuclear [Fe3(tz)6] units are linked by ox2– bridges to form 1D {Fe3(tz)6(ox)}n chains, which are also extended into a 3D microporous framework linked by the bdt ligands. Their frameworks can be simplified as the same topological network (46,66,83)­(42,63,8). The substructure of the 1D {Fe­(tz)3}n chain in 1·13H2O consists of spin-crossover (SCO) active Fe1 ions and low spin (LS) Fe2 ions alternately, while the trinuclear unit in 2·solvent contains a partial high spin (HS) Fe1 ion and two terminal HS Fe2 ions. Magnetic susceptibility measurements reveal that complex 1·13H2O presents an incomplete gradual SCO behavior. Although complex 2·solvent also has the SCO active Fe1 ions, the spin state change is extremely small and the antiferromagnetic property is primarily observed.