Oxidopolyborate anions templated by transition-metal complex cations: Self-assembled syntheses and structural studies (XRD) of [Co(NH3)6]2[B4O5(OH)4]3·11H2O, [Ni(phen)3][B7O9(OH)5].9.5H2O and [Zn(dac)2(H2O)2][B7O9(OH)5]·H2O

The crystal structure and oxygen reduction reaction of Ni(II)-complex templated borate-sulfate and borate

Three nickel borate compounds, [Ni(1-MI)₆]·[B(OH)₃]₄·SO₄ (1-MI = 1-methylimidazole) (1), [Ni(H₂O)₃(1-MI)₃]·[B₅O₆(OH)₄]₂ (2) and [Ni(DMA3)]·[B₆O₇(OH)₆]·3.5H₂O (DMA3 = N,N-dimethylethylenediamine) (3), have been synthesized. It is noteworthy that the structures of 1 and 2 can be adjusted by varying the ratio of amine. Compound 3 has shown an unexpected example of unique water clusters in its structure. The three frameworks exhibit different interlinkage modes, resulting in channels varying in their size and shape. These compounds have been characterized by FTIR, UV-vis and PXRD. In addition, 1, 2, and 3 exhibited different wide band gaps (4.4 eV for 1, 4.5 eV for 2 and 4.4 eV for 3), and ORR activities with a half-wave potential of 0.78 V for 1, 0.74 V for 2 and 0.79 V for 3.

Oxidoborates Templated by Cationic Nickel(II) Complexes and Self-Assembled from B(OH)3

Several oxidoborates, self-assembled from B(OH)3 and templated by cationic Ni(II) coordination compounds, were synthesized by crystallization from aqueous solution. These include the ionic compounds trans-[Ni(NH3)4(H2O)2][B4O5(OH)4].H2O (1), s-[Ni(dien)2][B5O6(OH)4]2 (dien = N-(2-aminoethyl)-1,2-ethanediamine (2), trans-[Ni(dmen)2(H2O)2] [B5O6(OH)4]2.2H2O (dmen = N,N-dimethyl-1,2-diaminoethane) (3), [Ni(HEen)2][B5O6(OH)4]2 (HEen = N-(2-hydroxyethyl)-1,2-diaminoethane) (4), [Ni(AEN)][B5O6(OH)4].H2O (AEN = 1-(3-azapropyl) -2,4-dimethyl-1,5,8-triazaocta-2,4-dienato(1-)) (5), trans-[Ni(dach)2(H2O)2][Ni(dach)2] [B7O9(OH)5]2.4H2O (dach = 1,2-diaminocyclohexane) (6), and the neutral species trans-[Ni(en)(H2O)2{B6O7(OH)6}].H2O (7) (en = 1,2-diaminoethane), and [Ni(dmen)(H2O){B6O7(OH)6}].5H2O (8). Compounds 1–8 were characterized by single-crystal XRD studies and by IR spectroscopy and 2, 4–7 were also characterized by thermal (TGA/DSC) methods and powder XDR studies. The solid-state structures of all compounds show extensive stabilizing H-bond interactions, important for their formation, and also display a range of gross structural features: 1 has an insular tetraborate(2-) anion, 2–5 have insular pentaborate(1-) anions, 6 has an insular heptaborate(2-) anion (‘O+’ isomer), whilst 7 and 8 have hexaborate(2-) anions directly coordinated to their Ni(II) centers, as bidentate or tridentate ligands, respectively. The Ni(II) centers are either octahedral (1–4, 7, 8) or square-planar (5), and compound 6 has both octahedral and square-planar metal geometries present within the structure as a double salt. Magnetic susceptibility measurements were undertaken on all compounds.