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The FeII ion in [Fe(NCS)2(4,4′-bis-1,2,4-triazole)2](H2O) has distorted tetragonal symmetry with two trans-oriented NCS− ligands. It shows a very abrupt high-spin α low-spin transition at 123.5 K on cooling and 144.5 K on warming. The compound is rather stable in vacuo at room temperature; however, samples which have passed the spin transition once lose their water of hydration above 240 K in vacuo. The dehydrated substance does not show a spin transition; it is high spin in the whole temperature range. Mossbauer ligand-field spectra and magnetic behaviour of both the hydrated and non-hydrated compounds are discussed. The spin transition has been followed by EPR measurements with the aid of traces of Cu2+ ions which could be substituted for Fe2+ in the tetragonal structure. In the high-spin phase the EPR signal is very broad and featureless; in the diamagnetic low-spin phase it is very sharp and resolved in hyperfine and superhyperfine structures. This unusual method to follow the spin transition was shown to be quite generally applicable. In the crystal structure of Fe(NCS)2(C4H4N6)2(H2O) the distances FENCS are 2.125(3) A, and FeN(ligand) 2.180(3) and 2.188(2) A. The water molecule is connected to the non-coordinating ligand N-atom by hydrogen bonding.

The synthesis, characterization and X-ray structure determination of [Cu 3 (metz) 6 (H 2 O) 4 ] (CF 3 SO 3 ) 6 (H 2 O) 4 is described. The compound crystallizes in the space group R , with a = b = 14.075(3) and c = 34.655(8) A. The complex cation consists of linear trinuclear clusters positioned on the crystallographic three-fold axis, and in which the Cu atoms are bridged by triple N 1 ,N 2 -coordinating triazole ligands. The terminal copper atoms are in addition coordinated by two water molecules, and thus have a distorted tetragonal pyramidal geometry. The central copper ion is located at a three-fold inversion center and thus should exhibit dynamic Jahn-Teller behaviour. In the crystal one observes the average of three such trimers related by the three-fold axis, and due to this disorder and also to that in the triflate anions, the structure could be refined only to R = 0.17 ( R w = 0.20). The infrared and ligand-field spectroscopic data and magnetic susceptibility are in agreement with the observed structure.

The synthesis of a new class of two-dimensional triazole compounds is described, including the crystal structure of [Co(NCS)2(btr)2]H2O [btr stands for 4,4′-bis-1,2,4-triazole (C4H4N6)]. Crystals are monoclinic, space group C2/c, a = 11.159(1) A, b = 13.047(4) A, c = 12.993(3) A, β = 91.81(2)°, Z = 4. The structure has been solved by Fourier and direct methods and refined by full-matrix least squares to R = 0.0229, Rw = 0.0283. The structure consists of layers of six-coordinated cobalt atoms, each having two trans-oriented N-bonded thiocyanate groups [CoNCS 2.098(2) A] and linked together in the equatorial plane by single bridges of btr to a two-dimensional network. The btr ligand coordinates through its N(1) and N(1′) atoms [CoN 2.128(1) and 2.142(1) A]. The intralayer CoCo distance is 9.207(2) A, and the inter-layer CoCo distance is 8.584(1) A. The magnetic susceptibilities of the compound and of the isostructural nickel and iron compounds are discussed. The iron compound exhibits a high-spin-low-spin crossover at liquid-nitrogen temperatures, as shown by magnetic susceptibility.

The spectroscopic and magnetic properties are described of coordination compounds with asymmetric 3,4-diakyl substituted 1,2,4-triazoles. The ligands 3-methyl-4-ethyl-1,2,4-traizole and 3-methyl-4-t-butyl-1,2,4-triazole have been investigated. Using M(CF 3 SO 3 ) 2 (M = Mn, Co, Ni, Cu, Zn) compounds have been obtained with a linear trinuclear structure, in which the metal ions are linked to each other by two pairs of three bridging triazoles. The coordination sphere around the terminal ligands is completed by monodentate ligands and/or water molecules. The structure has been confirmed by an X-ray structure determination of [Co 3 (metz) 6 (H 2 O) 6 ][Co 3 (metz) 8 (H 2 O) 4 ](CF 3 SO 3 ) 12 (H 2 O) 8 . this compound crystallizes in the space group P 1 with lattice constants a = 13.793(4), b = 14.401(3), c = 23.258(4) A, α = 80.58(2), β = 83.23(2) and γ = 64.33(2)°. The unit cell contains two independent trinuclear clusters of different composition. These two clusters have the same overall structure. Differences are related to the presence of monodentately coordinating ligands as well as to the position of the C3-methyl substituent. The complete refinement of this structure was obstructed by disorder problems in the anions and the non-coordinating water molecules. The magnetic susceptibilities of the compounds have been recorded and could be fitted to theoretical expressions for linear trimers. The compound [Ni 2 - (mtbtz) 5 (H 2 O) 4 ](CF 3 SO 3 ) 4 (H 2 O) 4 appears to be a dimeric species as concluded from its magnetic behaviour.

Le compose du titre cristallise dans le systeme orthorhombique avec le groupe d'espace Pbca. Affinement de la structure jusqu'a 0,063. Les atomes Mn sont entoures octaedriquement par 2 moles d'eau orientees en trans et 4 atomes N du coordinat