Metal-organic structures with formate and sulfate anions: Synthesis, crystallographic studies and hydrogen storage by PM7 and ONIOM

Abstract

Six coordination complexes: {[H2NMe2][Co(CHO2)3]}n (1), [Co(bpy)(CHO2)2]n (2), [Cu(dmf)(CHO2)2]2 (3), {[H2NMe2][Cu(CHO2)3]}n (4), [H2NMe2]4[Fe4O2(dmf)4(SO4)6] (5) and [Co3(bpy)(SO4)3]n (6) have been efficaciously synthesized using solvothermal techniques and slow evaporation. Two compounds (5 and 6) containing the sulfate anion (SO42−) with iron (III) and cobalt (II) had never been described in the Cambridge Structural Database. In all complexes, the transition metal is hexacoordinated with a distorted octahedral geometry and displays a three-dimensional supramolecular architecture through hydrogen bonding interactions [NH⋯O]. Formate (CHO2−) and sulfate (SO42−) anions were very important to the assembly of the three-dimensional MOFs and can be regarded as the template for all structures. All metal-organic complexes were identified by single-crystal X-ray diffraction, elemental composition and Fourier-transform infrared spectroscopy. In this paper, we propose the PM7 and ONIOM calculations as two effective methods in the determination of hydrogen storage. The weight percentage (wt %) of the hydrogen stored in the small cavities of the PCPs studied were: (1) 1.03 wt %, (4) 1.01 wt %, (6) 0.28 wt %.