Formation of a mixed-valence Cu(i)/Cu(ii) metal–organic framework with the full light spectrum and high selectivity of CO(2) photoreduction into CH(4)

Based upon the hetero-N,O ligand of pyrimidine-5-carboxylic acid (Hpmc), a new semiconductive Cu(i)/Cu(ii) mixed-valence MOF with the full light spectrum and a novel topology of {4(3)·6(12)·8(6)}(2){4(3)·6(3)}(2){6(3)}(6){6(4)·8(2)}(3), {(Cu(4)I(4))(2.5)[Cu(3)(μ(4)-O) (μ(3)-I) (pmc)(3)(Dabco)(3)]·2.5DMF·2MeCN}(∞) (NJU-Bai61, NJU-Bai for Nanjing University Bai group; Dabco = 1,4-diazabicyclo [2.2.2] octane), was synthesized stepwise. NJU-Bai61 exhibits good water/pH stabilities and a relatively large CO(2) adsorption capacity (29.82 cm(3) g(−1) at 1 atm, 273 K) and could photocatalyze the reduction of CO(2) into CH(4) without additional photosensitizers and cocatalysts and with a high CH(4) production rate (15.75 μmol g(−1) h(−1)) and a CH(4) selectivity of 72.8%. The CH(4) selectivity is the highest among the reported MOFs in aqueous solution. Experimental data and theoretical calculations further revealed that the Cu(4)I(4) cluster may adsorb light to generate photoelectrons and transfer them to its Cu(3)OI(CO(2))(3) cluster, and the Cu(3)OI(CO(2))(3) cluster could provide active sites to adsorb and reduce CO(2) and deliver sufficient electrons for CO(2) to produce CH(4). This is the first time that the old Cu(i)(x)X(y)L(z) coordination polymers' application has been extended for the photoreduction of CO(2) to CH(4) and this opens up a new platform for the effective photoreduction of CO(2) to CH(4).