Synthesis, structure, and oxygen reduction reaction of three copper complexes supported by ethylenediamine derivatives with outer-sphere oxoboron clusters

Three copper complex borates, [Cu(en) 2 ]·[B 4 O 5 (OH) 4 ]·2H 3 BO 3 ( 1 , en  = ethylenediamine), [Cu(Eten) 2 ]·[B 5 O 6 (OH) 4 ] 2 ( 2 , Eten =  N -ethyl ethylenediamine) and [Cu(Dmen) 2 ]·[B 10 O 13 (OH) 6 ] ( 3, Dmen =  N,N -dimethyl ethylenediamine) have been successfully synthesized and structurally characterized by single-crystal X-ray diffraction, PXRD, and FTIR. Their oxoboron clusters are [B 4 O 5 (OH) 4 ] 2− , [B 5 O 6 (OH) 4 ] − and [B 10 O 13 (OH) 6 ] 2− , respectively. Copper ion was used as the central atom, ethylenediamine and its derivatives were selected as ligand. The structure of oxoboron clusters in 1 , 2 and 3 can be modulated through varying ethylenediamine derivative ligand, as well as temperature and pressure of reaction system. These copper complex borates exhibited open framework formed by the interconnection of hydrogen bonds of oxoboron clusters. Moreover, the oxygen reduction reaction activity of these borate-based catalysts was investigated. The half-wave potential values of the products after heating   1 – 3   with carbon at 600 °C (1/C-600, 2/C-600 and 3/C-600) were 0.817, 0.80 and 0.73 V, respectively.