CH3-Tagged Bis(pyrazolato)-Based Coordination Polymers and Metal-Organic Frameworks: An Experimental and Theoretical Insight

The novel coordination polymers M(Me2BPZ) (M = Co, Zn; H2Me2BPZ = 3,3′-dimethyl-1H,1′H-4,4′-bipyrazole), M(H2Me2BPZ)(CH3COO)2(H2O)2 (M = Co, Ni), and Cu(H2Me2BPZ)(Cl)2 were isolated along conventional or solvothermal routes. Their crystal structure was unveiled by powder X-ray diffraction (PXRD), while their thermal stability was assessed by coupling thermogravimetric analysis to variable-temperature PXRD. The textural properties of the M(Me2BPZ) (M = Co, Zn) compounds, featuring three-dimensional open frameworks with one-dimensional channels, were assessed by N2 and CO2 adsorption at 77 and 273 K, respectively, and compared to those of the nonmethylated isostructural counterparts M(BPZ) (M = Co, Zn; H2BPZ = 1H,1′H-4,4′-bipyrazole). The positive effect of the methyl groups in CO2 adsorption, suggested by the adsorption energy trend [Eads(M(Me2BPZ)) > Eads(M(BPZ))] and substantiated by theoretical calculations at the B3LYP-D3 level coupled to topological analyses, is counterbalanced by the higher steric hindrance of Me2BPZ2- vs BPZ2-, finally reducing the amount of gas adsorbed by the M(Me2BPZ) couple vs the M(BPZ) one.