Windmill Co4{Co4(μ4-O)} with 16 Divergent Branches Forming a Family of Metal-Organic Frameworks: Organic Metrics Control Topology, Gas Sorption, and Magnetism

A series of highly connected metal-organic frameworks (MOFs), [Co-8(O)(OH)(4)(H2O)(4)(ina)(8)](NO3)(2)center dot 2C(2)H(5)OH center dot 4H(2)O (1), [Co-8(O)(OH)(4)(H2O)(4)(pba)(8)](NO3)(2)center dot 8C(2)H(5)OH center dot 28H(2)O (2), and [Co-8(O)(OH)(4)(H2O)(4)(pbba)(8)](NO3)(2)center dot guest (3), in which ina=isonicotinate, pba=4-pyridylbenzoate, and pbba=4-(pyridine-4-yl) phenylbenzoate, is reported. These MOFs contain a new secondary building unit (SBU), with a square Co-4(m(4)-O) central unit having the rare mu(4)-O2- motif, which is decorated by the other four peripheral cobalt atoms through mu(3)-OH in a windmill-like shape. This SBU holds 16 divergent connecting organic ligands, pyridyl-carboxylates, to form three different frameworks. The high porosity of desolvated 2 is shown by the efficient gas absorption of N-2, CO2, CH4, and H-2. In addition, 1 and 2 exhibit unusual canted antiferromagnetic behavior with spin-glass-like relaxation, with blocking temperatures that are fairly high, 20 K (1) and 10 K (2), for cobalt materials. The relationship between the metal clusters and linkers has been studied, in which the size and rotational degrees of freedom of the ligands are found to control the topology, gas sorption, and magnetic properties.