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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. [ABSTRACT FROM AUTHOR]

The metal-organic frameworks (MOFs) M(BPZNO 2 ) (M=Co, Cu, Zn; H 2 BPZNO 2 =3-nitro-4,4'-bipyrazole) were prepared through solvothermal routes and were fully investigated in the solid state. They showed good thermal stability both under a N 2 atmosphere and in air, with decomposition temperatures peaking up to 663 K for Zn(BPZNO 2 ). Their crystal structure is characterized by 3D networks with square (M=Co, Zn) or rhombic (M=Cu) channels decorated by polar NO 2 groups. As revealed by N 2 adsorption at 77 K, they are micro-mesoporous materials with BET specific surface areas ranging from 400 to 900 m 2  g -1 . Remarkably, under the mild conditions of 298 K and 1.2 bar, Zn(BPZNO 2 ) adsorbs 21.8 wt % CO 2 (4.95 mmol g -1 ). It shows a Henry CO 2 /N 2 selectivity of 15 and an ideal adsorbed solution theory (IAST) selectivity of 12 at p=1 bar. As a CO 2 adsorbent, this compound is the best-performing MOF to date among those bearing a nitro group as a unique chemical tag. High-resolution powder X-ray diffraction at 298 K and different CO 2 loadings revealed, for the first time in a NO 2 -functionalized MOF, the insurgence of primary host-guest interactions involving the C(3)-NO 2 moiety of the framework and the oxygen atoms of carbon dioxide, as confirmed by Grand Canonical Monte Carlo simulations. This interaction mode is markedly different from that observed in NH 2 -functionalized MOFs, for which the carbon atom of CO 2 is involved., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)