Magnetic Studies on &mgr;-Azido Polynuclear Nickel(II) Compounds with the 222-tet Ligand. Crystal Structure of (&mgr;-N(3))(2)[Ni(222-tet)](2)(BPh(4))(2) (222-tet = Triethylenetetramine) and EXAFS Structural Characterization of the Triangular Compounds (&mgr;-N(3))(3)[Ni(222-tet)](3)(X)(3) (X = PF(6)(-), ClO(4)(-)).
The nickel(II) dinuclear 1,3-azido-bridged compound (&mgr;-N(3))(2)[Ni(222-tet)](2)(BPh(4))(2) (1) and the trinuclear compounds (&mgr;-N(3))(3)[Ni(3)(222-tet)(3)](PF(6))(3) (2) and (&mgr;-N(3))(3)[Ni(3)(222-tet)(3)](ClO(4))(3) (3) were synthesized and characterized. 222-tet is the tetraaminate ligand triethylenetetramine. The crystal structure of 1 was solved by X-ray diffraction. 1 crystallizes in the monoclinic system: space group P2(1)/n, a = 10.639(4) Å, b = 19.770(7) Å, c = 13.609(6) Å, beta = 97.78(3) degrees, Z = 2, formula C(60)H(76)B(2)N(14)Ni(2). In the absence of single crystals of 2 and 3, we carried out an EXAFS study of 1-3 at the nickel K-edge, using compound 1 as a model, in order to obtain structural information for compounds 2 and 3. The analysis of XANES and EXAFS spectra of compounds 1-3 reveals the occurrence of azido-bridged trinuclear nickel(II) compounds for 2 and 3 with Ni-Ni separations of 5.16 and 5.12 Å, respectively. Each nickel(II) atom is placed in an octahedral NiN(6) environment: four nitrogen atoms of the amine and two nitrogen atoms of two azido bridges. The magnetic properties of the three compounds were studied by susceptibility measurements at variable temperatures (300-4 K). From the spin Hamiltonian H = -JS(1)S(2), the calculated J value for 1 is -83.6 cm(-)(1), in good agreement with the expected value. From the spin Hamiltonian H = -J(1,2)(S(1)S(2) + S(1)S(3)) - J(3)(S(2)S(3)), the obtained J values are J(1,2) = -72(3) cm(-)(1), J(3) = -36(3) cm(-)(1) for 2 and J(1,2) = -60.3(3) cm(-)(1), J(3) = -29.4(2) cm(-)(1) for 3.
Escuer
Albert
A
Departament de Química Inorgànica, Universitat de Barcelona, Diagonal 647, Barcelona 08028, Spain, Departament de Química Inorgànica, Facultat de Química, Universitat de València, Dr. Moliner 50, 46100 Burjassot, València, Spain, and Institut für Physikalische und Theoretische Chemie, Technische Universität Graz, A-8010 Graz, Austria.
Castro
Isabel
I
Mautner
Franz
F
El Fallah
Mohamed Salah
MS
Vicente
Ramon
R