Porous 10- and 12-vertex (bi)-p-dicarba-closo-boranedicarboxylates of cobalt and their gas adsorptive properties

Abstract

Two new porous coordination polymers, [Co3(μ3-OH)(Bcb10DC)2.5(DEF)3(EtOH)1.5(H2O)0.5] · DEF · EtOH (3b) and [Co2(Bcb12DC)2(DMF)4(EtOH)] · 2EtOH (4) based on 10- and 12-vertex p-bicarboranedicarboxylic acids, 1,1′-bi-(1,10-dicarba-closo-decaborane)-10,10′-dicarboxylic acid (H2Bcb10DC) and 1,1′-bi-(1,12-dicarba-closo-decaborane)-12,12′-dicarboxylic acid (H2Bcb12DC) were synthesized. Their properties were compared with the two known analogues based on shorter ligand-homologues, [Co(cb10DC)(DMF)] (1) and [Co4(OH)2(cb12DC)3(DMF)2(H2O)4] · 3DMF · EtOH (2). The structure of 3b is based on a trinuclear cluster and has a 3D structure with a 5-c bnn underlying net, while 4 is based on a binuclear cluster and composed of stacked 2D sql layers. Activated 3′ with altered structure has SBET(N2) of 1012 m2 g−1 and 4′ with mostly retained structure 920 m2 g−1. Gas adsorption by 3′ and 4′ at 1 bar is: 80.1 cm3 g-1 (0.72%wt) and 81.3 cm3 g-1 (0.73%wt) H2 at 77 K; 16.7 and 21.9 cm3 g-1 CO2 at 273 K; 6.2 and 10.0 cm3 g-1 of CH4 at 273 K. The isosteric heat of adsorption Qst at zero coverage are respectively: 5.0 and 4.5 kJ mol−1 for H2, 16.7 and 21.9 for CO2; 6.2 and 10.0 for CH4. 2′ with ∼645 m2 g−1 (calc. 883 m2g−1) has the highest mass-specific H2 adsorption, >30% than other compounds, while Qst is close to 1′ and slightly higher than for 3′ and 4´. Adsorption of CO2 and CH4 and Qst are ∼1.5–2 times lower for 3′ and 4′ compared to 1′ and 2´. The surface area specific adsorption of H2, CO2 and CH4 is the highest for 1´. The CO2/CH4 IAST selectivities (0.15/0.85; 1 bar, 298 K) are in 2–4.5 range. 3′ and 4′ retain a significant part of porosity after soaking in water unlike 1′ and 2´.