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.