Crystal Structure, Magnetic Properties, and ⁵⁷Fe Mössbauer Spectroscopy of the Two-Dimensional Coordination Polymers [M(1,2-bis(1,2,4-triazol-4-yl)ethane)₂(NCS)₂] (M^II = Fe, Co)

Abstract

New coordination polymers of the formula [M(btre)(2)(NCS)(2)] (btre = 1,2-bis(1,2,4-triazol-4-yl)ethane; M(II) = Fe, Co) have been synthesized, and their crystal structures have been determined at 293 K by X-ray analysis. The Fe(II) compound (C(7)H(8)FeN(7)S(2)) crystallizes in the monoclinic space group P2(1)/n, a = 12.439(5) A, b = 8.941(2) A, c = 9.321(3) A, beta = 90.88(2) degrees , V = 1036.6(6) A(3), Z = 2, 3791 reflections [I > 3sigma(I)], R(F) = 0.036, wR2 = 0.123. The Co(II) compound is isostructural to the Fe(II) compound. The crystal structure consists of a 2D sheet in which the metal ions are linked by bis monodentate (N1, N1') 1,2,4-triazole ligands. The structure is stabilized by pi-bond interactions between two adjacent sheets and by S...S interactions. Temperature-dependent SQUID, (57)Fe Mössbauer, and X-ray diffraction measurements indicate that [Fe(btre)(2)(NCS)(2)] retains a HS ground state upon cooling from 293 K down to 8 K. The surprising absence of spin-crossover behavior for this Fe(II)-1,2,4-triazole polymeric coordination compound that has been confirmed by pressure experiments up to approximately 12 kbar and by light irradiation experiments at 10 K is discussed on the basis of its structural features. Insight into the origin of the cooperative effects of the spin transition in [Fe(btr)(2)(NCS)(2)].H(2)O (btr = 4,4'-bis-1,2,4-triazole) is also given thanks to a re-evaluation of its distortion parameters in the high- and low-spin states.

Assembly of two ferrous coordination polymers with triazole derivative: Syntheses, structures and magnetic properties

“…The similar magnetic behavior has also been found in other Fe(II) complexes with bis-1,2,4-triazole ligands [21], which indicate that the magnitudes of the ligand field in these coordination modes are weak, and against to show detectable thermal spin-crossover behaviors. For the aim to obtain spincrossover complexes in this system, the ligands with stronger ligand field such as cyanogen should be introduced, and this work is underway in our lab.…”

Spin State Crossover, Vibrational, Computational, and Structural Studies of FeII 1‐Isopropyl‐1H‐tetrazole Derivatives

“…The impact of intermolecular interactions involving the thiocyanate ligands in the crystal lattice on SCO cooperativity has been discussed . In the case of the two‐dimensional coordination polymer [Fe(btre) 2 (NCSe) 2 ] [btre = 1,2‐bis(1,2,4‐triazol‐4‐yl)ethane], interchalcogen interactions (of the Se ··· Se type) were found to be so strong that SCO was no longer detected . In the present work, we came to the conclusion that (1) typically, the Fe–N–C (NCS) angle changes by 10° on the LS–HS transition, (2) the weak intra‐ and intermolecular interactions of the thiocyanate anion with the other molecular fragments are decisive for the value of the above angle – one may infer that such interactions result in a more cooperative spin transition if they are of intermolecular nature.…”

Spin state switching in iron coordination compounds

“…(right) χ M T versus T showing a square-shaped hysteresis loop on cooling. The structural distortion parameter Σ remains the same in the HS and LS states revealing that the local symmetry is not modified by the spin state change [330]. …”