Synthesis, Structural Characterization, Hirschfeld Surface Analysis and Photocatalytic CO₂ Reduction Activity of a New Dinuclear Gd(III) Complex with 6-Phenylpyridine-2-Carboxylic Acid and 1,10-Phenanthroline Ligands

A new dinuclear Gd(III) complex was synthesized and named [Gd2(L)4(Phen)2(H2O)2(DMF)2]·2H2O·2Cl (1). Here, L is the 6-phenylpyridine-2-carboxylate anion, Phen represents 1,10-phenanthroline, DMF is called N,N-dimethylformamide, and Cl− is the chloride anion, which is characterized by IR and single crystal X-ray diffraction analysis. The structural analysis reveals that complex (1) is a cation–anion complex, and each Gd(III) ion is eight-coordinated with four O atoms (O1, O5, O2a, O4a, or O1a, O2, O4, O5a) of four different bidentate L ligands, two O atoms (O6, or O6a) of DMF molecules, two N atoms (N1, N2, or N1a, N2a) of Phen ligands, and two O atoms (O3 or O3a) of coordinated water molecules. Complex (1) forms the three-dimensional π–π stacking network structure with cavities occupied by chloride anions and uncoordinated water molecules. The Hirschfeld surface of the complex (1) shows that the H···H contacts represented the largest contribution (48.5%) to the Hirschfeld surface, followed by C···H/H···C and O···H/H···O contacts with contributions of 27.2% and 6.0%, respectively. To understand the electronic structure of the complex (1), the DFT calculations have been performed. The photocatalytic CO2 reduction activity shows complex (1) has excellent catalytic activity with yields of 22.1 μmol/g (CO) and 6.0 μmol/g (CH4) after three hours. And the selectivity of CO can achieve 78.5%