Syntheses of Two New 1D and 3D Networks of Cu(ll) and Co(ll) Using Malonate and Urotropine as Bridging Ligands: Crystal Structures and Magnetic Studies

Two new metal-organic based polymeric complexes, [Cu4(O2CCHzCO2)4(L)]-7H2O (1) and [Co2(O2CCH2CO2)2(L)]2H2O (2) [L = hexamethylenetetramine (urotropine)], have been synthesized and characterized by X-ray crystal structure determination and magnetic studies. Complex 1 is a ID coordination polymer comprising a carboxylato bridged Cu4 moiety linked by a tetradentate bridging urotropine. Complex 2 is a 3D coordination polymer made of pseudo-two-dimensional layers of Co(ll) ions linked by malonate anions in syn-anti conformation which are bridged by bidentate urotropine in frans fashion. Complex 1 crystallizes in the orthorhombic system, space group Pmmn, with a = 14.80(2) A, b = 14.54(2) A, c = 7.325(10) A, beta = 90°, and Z = 4. Complex 2 crystallizes in the orthorhombic system, space group lmnm2, a = 7.584(11) A, b = 15.80(2) A, c = 6.939(13) A, 13 = 90.10°(1), and Z = 4. Variable temperature (300-2 K) magnetic behavior reveals the existence of ferro- and antiferromagnetic interactions in 1 and only antiferromagnetic interactions in 2. The best fitted parameters for complex 1 are J = 13.5 cm^-1, J = -18.1 cm^-1, and g= 2.14 considering only intra-Cu4 interactions through carboxylate and urotropine pathways. In case of complex 2, the fit of the magnetic data considering intralayer interaction through carboxylate pathway as well as interlayer interaction via urotropine pathway gave no satisfactory result at this moment using any model known due to considerable orbital contribution of Co(ll) ions to the magnetic moment and its complicated structure. Assuming isolated Co(ll) ions (without any coupling, J = 0) the shape of the XMT curve fits well with experimental data except at very low temperatures.