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

Six coordination complexes: {[H 2 NMe 2 ][Co(CHO 2) 3 ]} n (1), [Co(bpy)(CHO 2) 2 ] n (2), [Cu(dmf)(CHO 2) 2 ] 2 (3), {[H 2 NMe 2 ][Cu(CHO 2) 3 ]} n (4), [H 2 NMe 2 ] 4 [Fe 4 O 2 (dmf) 4 (SO 4) 6 ] (5) and [Co 3 (bpy)(SO 4) 3 ] n (6) have been efficaciously synthesized using solvothermal techniques and slow evaporation. Two compounds (5 and 6) containing the sulfate anion (SO 4 2−) 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 [N H⋯O]. Formate (CHO 2 −) and sulfate (SO 4 2−) 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 %. Image 1 • Small anions produce interesting and variable crystalline structures. • Formate and sulfate are very important templates in supramolecular architecture. • Hydrogen bonds between the layers with the anions extend the 3D arrays. • Hydrogen storage capacity was determined by PM7 and ONIOM methods. • PM7 consumes less computing time than other methods. [ABSTRACT FROM AUTHOR]