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 μ6-oxo centered mixed-valent, azide or acetate-bridged coordination polymers viz, [{MnII2MnIII10Na2­(μ6-O)2(N3)10(NO3)­(H2O)4(thme)8}­·3­(Et3NH)]n (1) and [{MnII3MnIII9Na7­(μ2-O)2(μ6-O)2(O)5­(CH3O)­(CH3CO2)11­(thmp)8}­·4­(O)]n (2), with retention of a Mn12 metallic core in both polymers are obtained using tripodal polyalcohol 1,1,1-tris (hydroxymethyl)­ethane (H3thme) and 1,1,1-tris (hydroxymethyl)­propane (H3thmp) ligands, respectively. X-ray analysis shows that 1 is a one-dimensional coordination polymer where Mn12 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 Mn12 zigzag 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{3.47.52}2­{32.410.52.6}­{32.410.53}4­{32.43.5.203.21}­{32.43.5}6­{32.44}2­{32.46.52.63.7.8}­{32.46.52}­{34.44.52}­{34.46.54.64.72.8}2­{412.52.6}2­{42.6}2­{43}­{45.5}3­{45.6}­{46.63.8}. 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 μB 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