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

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 . A Cu( i )/Cu( ii ) MOF with a full light spectrum was synthesized, exhibiting a photocatalytic CO 2 -to-CH 4 selectivity of 72.8% in aqueous solution.