Four new nickel(II) polynuclear end-on azide-bridged compounds : [{Ni(en)(2)}(2)(mu-N-3)(2)](ClO4)(2) (1), [{Ni(en)(mu-N-3)(2)}(n)] (2), [{Ni(tn)(mu-N-3)(2)}(n)] (3), and [{Ni(Me(2)tn)(mu-N-3)(2)}(n)] (4) were synthesized and characterized; en is ethylenediamine, tn is 1,3-diaminopropane, and Me(2)tn is 2,2’-dimethyl-1,3-diaminopropane. The crystal structures of 1, 2, and 3 have been solved. Complex 1 crystallizes in the monoclinic system, space group P2(1)/n, with fw = 640.76, a = 8.450(1) Angstrom, b = 13.234(2) Angstrom, c 11.750(2) Angstrom, beta = 103.67(1)degrees, V = 1276.7 Angstrom(3), Z = 2, R = 0.060, and R(w) = 0.063. Complex 2 crystallizes in the triclinic system, space group P $$($) over bar 1, with fw = 202.51, a 16.675(6) Angstrom, b = 12.458(4) Angstrom, c = 5.538(2) Angstrom, alpha = 98.84(2)degrees, beta = 90.04(3)degrees, gamma = 108.67(4)degrees, V = 1075(1) Angstrom(3), Z = 3, R = 0.066, and R(w) = 0.066. Complex 3 crystallizes in the monoclinic system, space group P2(1)/c, with fw = 216.9, a = 12.956(5) Angstrom, b = 22.408(7) Angstrom, c = 5.695(3) Angstrom, beta = 103.82(3)degrees, V = 1605.(2), Z = 8, and R = 0.112. In the three complexes, the nickel atom is placed in a distorted octahedral environment : in complex 1 each nickel(II) is surrounded by two ethylenediamine ligands and two bridging end-on azido ligands. In complexes 2 and 3 each nickel(II) is surrounded by only one amine (en or tn) and four bridging end-on azido ligands, giving a neutral stoichiometry. The Ni-Ni distances are 3.369 Angstrom for 1, 3.190 Angstrom for 2, and 3.312 Angstrom for 3. The magnetic properties of the four compounds have been studied by means of susceptibility measurements vs temperature. For the 1-D systems 2-4 magnetization measurements vs applied field, for several temperatures, have also been carried out. The T-chi M vs T plots for 1-4 show the typical shapes for ferromagnetically coupled nickel(II) polynuclear complexes. By using the spin Hamiltonian -2J Sigma SiSj, J values for 1-4 were 21.7, 11.9, 19.8, and 16.9 cm(-1), respectively. Introducing the single-ion zero field splitting parameter (D) in the Hamiltonian causes J parameters to vary slightly but the accuracy of this paprameter is discussed. Magnetization measurements for 2 and 3 indicate long-range antiferromagnetic order at low temperatures (metamagnetism).