SYNTHESIS, CRYSTAL-STRUCTURE, AND MAGNETIC-PROPERTIES OF [NI(N3)2(2,2-DIMETHYLPROPANE-1,3-DIAMINE)]N, AN INFINITE BIDIMENSIONAL ANTIFERROMAGNETIC POLYMER PRESENTING WEAK 3-D FERROMAGNETISM

The reaction between aqueous solutions of Ni(ClO4)2, NaN3 and 2,2-dime thylpropane-1,3-diamine (Me2tn) gives blue-green crystals of the title compound which presents N3- in a new coordination mode. The new compl ex (C5H14N8Ni)n crystallizes in the monoclinic system, space group P2( 1)/c, with a = 12.649(3) angstrom, b = 7.031(2) angstrom, c = 12.114(3 ) angstrom, beta = 112.39(2)degrees, V = 996.1(8) angstrom3, Z = 4, R = 0.059, and R(w) = 0.059. The Ni(II) atoms are octahedrally coordinat ed by two nitrogen atoms of the amine ligand, one N3 terminal ligand a nd three other bridging N3- ligands shared by three Ni(II) atoms, givi ng the stoichiometry [Ni(N3)(N3)3/3(Me2tn)]. Each bridging azido ligan d coordinates two Ni(II) ions in end-on mode but, at the same time, th is azido ligand coordinates the neighboring Ni(II) in an end-to-end mo de. This new and unexpected coordination mode of the azido ligand stab ilizes a bidimensional polymer made of mu-(1,1-N3)2Ni2 units linked to gether by the bridging azides, thus creating a kind of metallomacrocyc le which repeats throughout the layer. Magnetic measurements from room temperature down to 60 K show a typical 2D antiferromagnetic behavior ; at around 60 K an abrupt field-dependent peak of susceptibility is o bserved, indicating a long-range magnetic ordering with a net magnetic moment (canting). Magnetization curves at low temperature clearly con firm the presence of weak ferromagnetism. The canted spin structure is analyzed in view of the structure and the single-ion anisotropy of th e Ni(II) ion.