Low-spin state structure of [Fe(chloroethyltetrazole)6](BF4)2 obtained from synchrotron powder diffraction data.

The complex [Fe(teec)6](BF4)2 (teec = chloroethyltetrazole) shows a two-step complete spin-crossover transition in the temperature range 300-90 K. Time-resolved synchrotron powder diffraction experiments have been carried out in this temperature range, and crystal structure models have been obtained from the powder patterns by using the parallel tempering technique. Of these models, the low-spin state structure at 90 K has been refined completely with Rietveld refinement. Its structural characteristics are discussed in relation to the high-spin state model and other spin-crossover compounds. The complex shows a remarkable anisotropic unit-cell parameter contraction that is dependent on the applied cooling rate. In addition, the possible important implications for the interpretation of spin-crossover behavior in terms of structural changes are discussed.

Tetrakis[1-(3-chloropropyl)-1,2,4-triazole-kappaN4]bis(tetrafluoroborato-kappaF)copper(II).

In the title complex, [Cu(BF(4))(2)(1tpc)(4)] [1tpc is 1-(3-chloropropyl)-1,2,4-triazole, C(5)H(8)ClN(3)], the copper(II) centres reside in a tetragonally distorted octahedral coordination environment. Four 1tpc ligands are coordinated to the metal atom via the N4 atom of the triazole rings in a square-planar arrangement, with Cu-N bond lengths in the range 2.002 (2)-2.019 (2) A. Two tetrafluoroborate anions, in the axial positions above and below the square plane, are weakly coordinated to the copper(II) centre, with Cu-F distances of 2.4009 (18) and 2.5096 (18) A.

Strongly isolated ferromagnetic layers in poly-trans-mu-dichloro- and poly-trans-mu-dibromobis(1-(2-chloroethyl)-tetrazole-N4)copper(II) complexes.

Two new isostructural compounds, dichlorobis(1-(2-chloroethyl)tetrazole)copper(II) (1) and dibromobis(1-(2-chloroethyl)tetrazole)copper(II) (2), have been prepared. The synthesis, characterization, and spectral and magnetic properties as well as the crystal and molecular structures of 1 and 2 have been studied. Both complexes form two-dimensional, distorted square grid planes of copper and halides, distinctly separated by layers of tetrazole ligands. The differential (ac) magnetic susceptibility, chi = (deltaM/deltaH)(T), and magnetization M(H) of both complexes have been studied as a function of temperature and field. The compounds possess a ferromagnetic interaction within the isolated copper-halide layers (J/k(B) = 8.0 K, J/k(B) = 10.2 K, respectively, for the chloride and the bromide, and T(c) = 4.75 K, T(c) = 8.01 K). The magnetic coupling J'/k(B) between the different layers is found to be very weak (|J'/J|

Structures of Fe(II) spin-crossover complexes from synchrotron powder-diffraction data.

Crystal structure determination and analysis have been carried out for the two spin-crossover compounds [Fe(teeX)(6)](BF(4))(2) (teeX is haloethyltetrazole; X = I: teei; X = Br: teeb), in both their high-spin (near 300 K) and their low-spin states (T = 90 K), using high-resolution powder-diffraction data collected at the ESRF (Grenoble, France) and SPring8 (Japan) synchrotron radiation facilities. The structures of teei have been solved using various direct-space structure determination techniques (grid search, genetic algorithm and parallel tempering) and refined with the Rietveld method using geometrical restraints. In the case of teeb, a structural model was found but a full refinement was not successful because of the presence of a significant amount of an amorphous component. Analysis of the structures (space group P2(1)/c, Z = 2) and diffraction data, and the absence of phase transitions, show the overall structural similarity of these compounds and lead to the conclusion that the gradual spin-crossovers are likely to be accompanied by small structural changes only.