Assembly of Iron(II)-Triazole Polymers from 1D Chains to 3D Interpenetrated Frameworks: Syntheses, Structures, and Magnetic Properties

By the reactions of FeX₂ with α,ω-bis(1,2,4-triazol-1-yl)alkane ligands (X = ClO₄⁻, BF₄⁻, NCS⁻, and NCSe⁻), a series of novel iron(II) coordination polymers have been synthesized and characterized. Complexes [Fe(btp)₃](ClO₄)₂ (1a), [Fe(btp)₃](BF₄)₂ (1b), and [Fe(btp)₂(NCS)₂] (2) (btp = 1,3-bis(1,2,4-triazol-1-yl)propane) are infinite 1D-linear chains. [Fe(btb)₃](ClO₄)₂ (3a) and [Fe(btb)₃](BF₄)₂ (3b) (btb = 1,4-bis(1,2,4-triazol-1-yl)butane) are 3-fold interpenetrated α-polonium cubic frameworks. The two sorts of btb ligands with different conformations alternately link to the Fe(II) centers in [Fe(btb)₂(NCS)₂]·H₂O (4) to form a 3D interpenetrating architecture of CdSO₄-like topology. When NCSe⁻ instead of NCS⁻ was used as the framework-regulator, a 2D grid layer [Fe(btb)₂(NCSe)₂]·2H₂O (5) was obtained. The counteranions, spacer length, and conformation of the α,ω-bis(1,2,4-triazol-1-yl)alkane ligands are responsible for the assembled topological architectures. Magnetic studies indicate that all of these iron(II) polymers retain a high-spin ground state upon cooling from 300 to 4 K.