A Cu(II) Metal Organic Framework with a Tetranuclear Core: Structure, Magnetism, and Supercapacitor Activity
Srikanta Jana, Samik Saha, Angeera Chandra, Salah El Fallah, Sachindranath Das, Chittaranjan Sinha
Abstract
A Cu(II) coordinated metal–organic framework, {[Cu4(BTC)2(4-APy)2(μ3-OH)2]·[(CH3OH)0.5]2·(H2O)2}n (Cu-MOF), 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 ([CuII]4) via edge sharing of two Cu3–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 [CuII]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 χMT value for Cu-MOF at 300 K is 1.735 cm3 mol–1 K for four copper(II) ions, which is as expected for four isolated copper(II) ions with g = 2.15. The χMT values are almost constant until ca. 55 K, and then χMT decreases sharply, giving a minimum value of 0.753 cm3 K mol–1 at 2 K.