Structural Regulation and Oxygen Reduction Reaction Activity of [Co(bpy)₂BO₂(OH)] and [Cu(bpy)(OH)]^2– Complex Templated Borates

Abstract

Two templated borates, [Co(bpy)2­BO2­(OH)]·[B5­O6­(OH)4]·H3­BO3·H3O·H2O (1) and [Cu(bpy)(OH)]2·[B5­O6­(OH)4]2·H2O (2), have been synthesized successfully and characterized by single-crystal X-ray diffraction, powder X-ray diffraction, and Fourier transform infrared. The [Co(bpy)2BO2(OH)] complex in 1 shows a very rare coordination mode between Co2+ and BO2(OH)2–. The structures of 1 and 2 can be adjusted by changing the reagent. The oxygen reduction reaction activity of these Co- and Cu-based catalysts was studied. The E 1/2 values of Co–C-750 and Cu–C-750 are 0.864 and 0.837 V, respectively.

Chelated O2BOH2– or Chelated O2CO2–: An Isoelectronic Conundrum

“…We obtained a pink crystalline material from the above synthesis, which looked similar to that reported by Pan and co-workers . The only difference was that our product took slightly longer (11 days) to crystallize in reasonable amounts.…”

“…Conspicuously absent from this list are oxyanions derived from deprotonation of boric acid, H 3 BO 3 , with discrete transition metal complexes containing these ligands being rare. Therefore, the recent report by Pan and co-workers of only the second structurally characterized example of chelated hydrogenborate in the Co­(II) complex [Co­(bipy) 2 O 2 BOH]·[B 5 O 6 (OH) 4 ]·H 3 BO 3 ·H 3 O·H 2 O (bipy = 2,2′-bipyridine) was of interest, given our extensive work on the coordination chemistry of oxyanions. − However, several features of the reported synthesis and characterization led us to question the identity of the isolated complex. First, the reaction was carried out under aerobic conditions; air oxidation of solutions of Co­(II) in the presence of amine ligands is often facile, and while Co­(II) complexes containing two bipy ligands have been isolated under aerobic conditions, , oxidation to Co­(III) cannot be excluded.…”

“…The X-ray structure of the complex cation in [Co­(bipy) 2 (O 2 CO)]·[B 5 O 6 (OH) 4 ]·H 3 BO 3 ·2H 2 O is shown in Figure , and listings of all data are given in Tables S1–S6. It should be noted that the unit cell parameters obtained by us are identical to those of Pan and co-workers . The structure consists of a central Co­(III) ion chelated to two bipy ligands and a carbonato ligand in a slightly distorted octahedral geometry.…”

“…The complex [Co(bipy) 2 (O 2 CO)]·[B 5 O 6 (OH) 4 ]·H 3 BO 3 ·2H 2 O was prepared under aerobic conditions as described by Pan and co-workers (see Supporting Information, page S2), and X-ray quality crystals were obtained directly from the reaction mixture …”

“…We also rerefined the original data from the deposited CIF and observed that replacement of the B atom with a C atom gave improved figures of merit. R1 after merging and wR2 were 0.0520 and 0.1275, respectively, for the carbonate complex, while these were 0.0537 and 0.1367 for the borate complex . To confirm, or otherwise, the presence of H 3 O + , all the H atoms of the purported hydronium ion were deleted, and inspection of the resulting Fourier map following refinement gave evidence for the presence of only two H atoms in the vicinity of the O atom, strongly suggesting that this is a water molecule.…”