A Cu(II) Metal Organic Framework with a Tetranuclear Core: Structure, Magnetism, and Supercapacitor Activity

A Cu(II) coordinated metal-organic framework, {[Cu-4(BTC)(2)(4-APy)(2)(mu(3)-OH)(2)]middot[(CH3OH)(0.5)](2)middot(H2O)(2)}(n) (CuMOF), has been synthesized by the solvo-diffusion of Cu(NO3)(2) to an alcoholic solution of 4-aminopyridine (4-APy) and 1,3,5-benzenetricarboxylic acid (H3BTC) in equimolar proportion. A single-crystal X-ray structure determination suggests that the four-Cu(II)-connected motif ([Cu-II](4)) via edge sharing of two Cu-3-O cores and bridging by six acetato functions of the BTC3- connector generates two five-coordinated distorted-square-pyramidal CuO5 units and two distorted-square-planar CuO4 units; the Cu(II) knot in the latter one (CuO4) is coordinated by pyridyl-N of 4-APy. The remaining donor centers of acetato-O of BTC3- bind adjacent [Cu-II](4) core to form an infinite 3D network structure. The coordination of CH3OH and H2O forms different hydrogen bonds to make a strong superstructure. A surface morphology determination shows a nanoflower pattern. The hybrid material Cu-MOF exhibits a very high specific capacitance, 547 F g(-1), at a scan rate of 2 mV s(-1) with excellent recycling stability (retains 97.4% after 5000 cycles). The chi T-M value for Cu-MOF at 300 K is 1.735 cm(3) mol(-1) K for four copper(II) ions, which is as expected for four isolated copper(II) ions with g = 2.15. The chi T-M values are almost constant until ca. 55 K, and then chi T-M decreases sharply, giving a minimum value of 0.753 cm3 K mol(-1) at 2 K.