M-2(N-3)(4)(hmt)(H2O) (M = Co2+ and Ni2+, hmt = hexamethylenetetramine): mixed azide-hmt bridged 3D metal frameworks with long-range magnetic ordering

Two mixed azide-hmt bridged compounds were obtained with neutral 3D networks, Co-2(N-3)(4)(hmt)(H2O) (1) and Ni-2(N-3)(4)(hmt)(H2O) ((2)), hmt hexamethylenetetramine. In 1, the azide ions present three kinds of coordination modes in the connection of two unique Co2+ ions. Each Co1 is connected by trans-EE-azide ions and hmt into extended (4,4) layers, and each Co2 is connected by EO-azide ions into dimers which are located between the neighboring (4,4) layers. The cis-EE-azide ions connect the dimers to the neighboring layers to form rare 3D networks. The Col(2+) and Co2(2+) ions have four and three connections through azide bridges to the neighboring Co2+ ions, respectively. Twisted torsion angles of cis/trans-EE azide bridges are observed in 1, with a value of 83.39 and 117.43 degrees, respectively. The Ni analogue 2 is isostructural with 1 revealed by IR, elemental analysis and Powder X-ray diffraction. Magnetic investigation shows that 1 is a weak ferromagnet below T-c = 15.0 K, with a large coercivity of 1 T at 2 K, while 2 is a soft ferromagnet below T-c = 10.0 K.