SYNTHESIS, CRYSTAL-STRUCTURE, EXAFS, AND MAGNETIC-PROPERTIES OF 2-HYDROXYETHYL)-1,2,4-TRIAZOLE-N-1,N-2)COPPER(II)] DIPERCHLORATE TRIHYDRATE- RELEVANCE WITH THE STRUCTURE OF THE IRON(II) 1,2,4-TRIAZOLE SPIN TRANSITION MOLECULAR MATERIALS

[Cu(hyetrz)(3)](ClO4)(2) . 3H(2)O (hyetrz = 4-(2-hydroxyethyl)-1,2,4-t riazole) represents the first structurally characterized metal(II) cha in compound containing triple N-1,N-2-1,2,4-triazole bridges. The stru cture has been solved at 298 K by single-crystal X-ray analysis. 2-hyd roxyethyl)-1,2,4-triazole-N-1,N-2)copper(II)] diperchlorate trihydrate (C12H27N9Cl2O14CU) crystallizes in the monoclinic space group P2(1)/n , a = 13.877(3) Angstrom, b = 23.023(5) Angstrom, c = 15.351(2) Angstr om, beta = 91.10(2)degrees, Z = 8 (Cu(II) units). The Cu(II) ions are linked by triple N-1,N-2-1,2,4-triazole bridges yielding a slightly al ternating chain with Cu1-Cu2 = 3.853(2) Angstrom and Cu2-Cu3 = 3.829(2 ) Angstrom. The EXAFS results are consistent with the crystal structur e. At 30 K, the EXAFS signature of the multiple scattering path Cu1-Cu 2-Cu3 is clearly observed, confirming that such exceptional long dista nce EXAFS signals can be used to detect metal alignments in inorganic long chains when crystal structures are not available. The thermal beh avior of this multiple scattering signal was compared to those of simi lar Fe(II) low-spin compounds, and the observed differences have been discussed by comparing their electronic (dynamic Jahn-Teller effect) a nd vibrational properties. The Cu(II) ions are weakly antiferromagneti cally coupled with J = -1.18(2) cm(-1) (based on the Hamiltonian, H = -J[Sigma(i)S(i) . Si+1]). The nature and the magnitude of the antiferr omagnetic exchange have been discussed on the basis of the structural features.