Crystal Engineering and Magnetostructural Properties of Newly Designed Azide/Acetate-Bridged Mn12 Coordination Polymers

Crystal engineering of the coordination polymers where polynuclear clusters are building blocks constitutes an emerging class of chemistry. The fine-tuning of the structural motifs leads to interesting and varying magnetic properties. Owing to such properties, two rare mu(6)-oxo centered mixed-valent, azide or acetate-bridged coordination polymers viz, [{(Mn2Mn10Na2)-Mn-II-Na-III(mu(6)-O)(2)(N-3)(10)(NO3)(H2O)(4)(thme)(8)}center dot 3-(Et3NH)](n) (1) and [{(Mn3Mn9Na7)-Mn-II-Na-III(mu(2)-O)(2)(mu(6)-O)(2)(O)(5)-(CH3O)(CH3CO2)(11)(thmp)(8)}center dot(4)(O)](n), (2), with retention of a Mn-12 metallic core in both polymers are obtained using tripodal polyalcohol 1,1,1-tris (hydroxymethyl) ethane (H(3)thme) and 1,1,1-tris (hydroxymethyl)propane (H(3)thmp) ligands, respectively. X-ray analysis shows that 1 is a one-dimensional coordination polymer where Mn-12 units are propagating by bridging azide function. 1 shows the underlying net of 2,2,3C6 topological type. 2 forms a cyclic ring as a result of repeating Mn-12 igzag chains bridging by sodium and H2O. The topology of 2 results in a 31-nodal underlying 3,3,3,3,4,4,4,4,4,4,4,4,4,4,4,5,5,5,5,5,5,6,6,6,6,6,6,6,6,7,7-c net with a point symbol of the net of {3.4.5}(2)-{3.4(7).5(2)}(2){3(2).4(10).5(2).6} {3(2).4(10).5(3)}(4){3(2).4(3).5.20(3).21}{3(2).4(3).5}(6){3(2).4(4)}(2){3(2).4(6).5(2).6(3).7.8}{3(2).4(6).5(2)}{3(4).4(4).5(2)}{3(4).4(6).5(4).6(4).7(2..)8}(2){4(12).5(2).6}(2)-{4(2).6}(2){4(3)}{4(5).5}(3){4(5).6}{4(6).6(3).8}. In 1, a magnetic study ascertains the presence of antiferromagnetic interaction and shows single molecule magnet-like behavior with an energy barrier of 75.5 K. However, 2 exhibited strong antiferromagnetic interaction in dc studies. The super-paramagnetic-like slow relaxation of its magnetization was not observed for 2 in out-of-phase ac magnetic susceptibility due to the absence of a large enough energy barrier. Magnetization versus an applied dc field exhibited a hysteresis loop at 2 K with a coercivity of 1069.10 Oe and remanent magnetization of 0.374 NB in 1, while 2 has no coercivity in the hysteresis loop even at the lowest temperature (2.0 K), and no saturation was observed up to 7.0 T field supporting antiferromagnetic interactions present in the polymer.