Crystal structure, magnetic properties, and 57Fe Mossbauer spectroscopy of the two-dimensional coordination polymers [M(1,2-bis(1,2,4-triazol-4-yl)ethane)2(NCS)2] (MII=Fe, Co)

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 Fell compound (C7H8FeN7S2) crystallizes in the monoclinic space group P2(1)/n, a = 12.439(5) angstrom, b = 8.941(2) angstrom, c = 9.321(3) angstrom, beta = 90.88(2)degrees, V= 1036.6(6) angstrom(3), Z= 2, 3791 reflections [l > 3 sigma(l)], R-F = 0.036, wR2 = 0.123. The Coll compound is isostructural to the Fell 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 (SS)-S-... interactions. Temperature-dependent SQUID, Fe-57 Mossbauer, 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 similar to 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)]center dot H2O (btr = 4,4'-bis-1,2,4-triazole) is also given thanks to a reevaluation of its distortion parameters in the high- and low-spin states.