Two-step spin crossover in the mononuclear iron(ii) complex [FeII(L)2(NCS)2] (L = 2,5-di-(2-pyridyl)-1,3,4-thiadiazole)

Abstract

The first iron(ii) complex of 2,5-di-(2-pyridyl)-1,3,4-thiadiazole (L), namely [Fe(II)(L)(2)(NCS)(2)], has been synthesised and studied by magnetic susceptibility measurements, Mössbauer spectroscopy and X-ray diffraction. It has been found to undergo thermally-induced spin crossover featuring two well-separated, abrupt steps at T(1/2)(1) = 167 K and T(1/2)(2) = 112 K.

Multimetastability, phototrapping, and thermal trapping of a metastable commensurate superstructure in a FeIIspin-crossover compound

“…10 Although the vast majority of thermal spin transitions proceed in a single step, there has been an increasing number of two-step transitions reported for polymeric, [11][12][13][14][15][16][17] polynuclear, [18][19][20][21][22][23][24] or mononuclear SCO systems. [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] Such transitions result most frequently from the existence of two crystallographically (symmetrically) independent SCO Fe I I sites with slightly different coordination environments, leading to dissimilar transition temperatures delimiting a plateau (or shoulder), which usually occurs with an approximately equal populations of HS and LS species. Alternatively, the subtle interplay between short-range correlations and long-range interactions may be such that intermediate phases with remarkable structural topologies, characterized by well-ordered patterns of HS and LS Fe I I molecular species, may be stabilized in a more or less wide temperature range, providing a two-step character.…”

Symmetry Breaking in Iron(II) Spin-Crossover Molecular Crystals

“…There are two distinct situations that account for stepwise transitions. One is observed when different SCO sites, characterized by distinct transition temperatures (T 1/2 or T c ), are present in the solid [10][11][12][13][14][15][16][17]. The other arises from subtle balances between different elastic interactions in the crystal lattice, which spontaneously generate two or more The crystal structures of the anhydrous and the hydrate species (x = 0, 1/3) were investigated at 200 K, 130 K and 90 K. At 200 K, the crystals are monoclinic (space group C2/c, (Z = 8)) and contain one crystallographically independent Fe II site, which is HS.…”

Unexpected Coordination Behaviour of 3,5‐Di(2‐pyridyl)‐1,2,4‐oxadiazole

“…Complexes of the type [Fe II (L) 2 (NCX) 2 ] (X = S, Se or BH 3 ) [1][2][3][4] of these ligands often exhibit the spin-crossover [7][8][9][10][11] and LIESST [12][13][14][15][16] phenomena. Recently we have studied the coordination behaviour of 2,5-di(2-pyridyl)-1,3,4-oxadiazole (L O ), [3] 2,5-di(2-pyridyl)-1,3,4-thiadiazole (L S ) [1,2] and 2,5-di(2-pyridyl)-1,3,4-selenadiazole (L Se ) [3] (Scheme 1), identifying several spin-crossover complexes. To further examine this series of complexes we expanded our studies to ligands of the type 3,5-di(2-pyridyl)-1,2,4-chalcadiazoles.…”

“…2,5-Di(2-pyridyl)-1,3,4-chalcadiazoles [1][2][3] and related 2-pyridyl-substituted [1,2,4]triazolo [4,3-a]pyridines [4][5][6] have been shown to be effective bidentate chelating ligands for the synthesis of 3d transition metal complexes with interesting structures and properties. Complexes of the type [Fe II (L) 2 (NCX) 2 ] (X = S, Se or BH 3 ) [1][2][3][4] of these ligands often exhibit the spin-crossover [7][8][9][10][11] and LIESST [12][13][14][15][16] phenomena.…”