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.

两种三维（3D）Fe(II)多孔金属有机框架（metal–organic frameworks，MOFs）[Fe₂(H₀.₆₇bdt)₃]·13H₂O（1·13H₂O）与[Fe₃(ox)(H₀.₆₇bdt)₃(H₂O)₂]·溶剂（2·溶剂），其中H₂bdt = 5,5'-(1,4-亚苯基)二(1H-四唑)；H₂ox = 草酸；2·9MeOH的溶剂组分为10H₂O与9CH₃OH，2·5n-BuOH的溶剂组分为6H₂O与5C₄H₉OH，二者通过溶剂热法合成并完成表征。X射线衍射结构分析表明，配合物1·13H₂O由一维（1D）{Fe(tz)₃}ₙ（tz = 四唑根）链构成，该链通过bdt配体的苯基连接臂相互连接，形成三维微孔框架。对于配合物2·溶剂，其线性三核[Fe₃(tz)₆]结构单元通过ox²⁻桥联形成一维{Fe₃(tz)₆(ox)}ₙ链，该链同样通过bdt配体拓展为三维微孔框架。二者的框架均可简化为同一拓扑网络(46,66,83)­(42,63,8)。配合物1·13H₂O中一维{Fe(tz)₃}ₙ链的亚结构由自旋交叉（SCO）活性Fe1离子与低自旋（LS）Fe2离子交替排布；而配合物2·溶剂的三核结构单元则包含一个部分高自旋（HS）Fe1离子与两个端基高自旋（HS）Fe2离子。磁化率测试结果显示，配合物1·13H₂O表现出不完全的渐变形自旋交叉行为。尽管配合物2·溶剂同样含有SCO活性Fe1离子，但其自旋态变化幅度极小，主要呈现反铁磁特性。