Synthesis and structural characterization of the formato bridged Cu(II) cubane: Crystallographic evidence of atmospheric CO2 fixation as formate in a tertranuclear Cu(II) cluster, .

a b s t r a c t
Fixation of atmospheric carbon-di-oxide (CO2) by metal complexes continuously receives a great deal of attention from the viewpoint of environmental concerns. Herein, a novel tetranuclear copper (II) clus�ter [Cu4 μ3-(mph)4 μ2-(HCO2)2] (ClO4)2.CH2Cl2 (1), synthesized using Methyl(6-hydroxymethyl)picolinate ligand (Hmhp) and Cu(ClO4)2·6H2O in the presence of triethylamine base, is reported where atmospheric CO2 is serendipitously trapped in the form of formato-bridging ligand. The single X-ray structural eluci�dation of the complex 1 reveals a Cu4O4 cubane cluster stabilized by four peripheral mhp ligands, all of which display μ3-η1: η1: η3 binding mode (each bridging ligand link three Cu (II) ions). Moreover, the cubane core was supported by two bridging formate groups, resulted from the reduction of atmospheric
CO2. The two formate ions exhibit μ2-η1: η1 binding mode, bridges two Cu(II) atoms. All the Cu(II) ions in the cubane core possess distorted octahedral coordination geometry (CuN1O5). Based on the observed Cu···Cu interactions in the Cu4O4 cubane core, 1 can be categorized under [2+2+2] type of classification.
In addition to the synthesis and characterization of 1, a mechanistic hypothesis for the reduction of at�mospheric CO2 to formate is also proposed to highlight the future potential of similar complexes in CO2 fixation/conversion