Highly Selective CO₂ Uptake in Uninodal 6-Connected “mmo” Nets Based upon MO₄²– (M = Cr, Mo) Pillars

A novel 4(8).6(7) topology metal-organic material (MOM) platform of formula [M(bpe)(2)(M'O(4))] (M = Co or Ni; bpe = 1,2-bis(4-pyridyl)ethene; M' = Mo or Cr) has been synthesized and evaluated in the context of gas sorption. These MOMs have been assigned RCSR code mmo and are uninodal 6-connected nets. [Ni(bpe)(2)(MoO(4))], MOOFOUR-1-Ni, and its chromate analogue, CROFOUR-1-Ni, exhibit high CO(2) affinity and selectivity, especially at low loading. This behavior can be attributed to exceptionally high isosteric heats of adsorption (Q(st)) of CO(2) in MOOFOUR-1-Ni and CROFOUR-1-Ni of ∼56 and ∼50 kJ/mol, respectively, at zero loading. These results were validated by molecular simulations which indicate that the electrostatics of these inorganic anions affords attractions toward CO(2) that are comparable to those of unsaturated metal centers.