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The new oxidopolyborate salts [Co(NH3)6]2[B4O5(OH)4]3.11H2O (1), [Ni(phen)3][B7O9(OH)5].9.5H2O (2), and [Zn(dac)2(H2O)2][B7O9(OH)5].H2O (3), were crystallized, in moderate yields, from aqueous solutions containing B(OH)3 and the hydroxide salt of the corresponding cationic metal complex (prepared in situ) in moderate yields. Complexes 1-3, characterized by spectroscopic (NMR, IR) and thermal (TGA) methods and by single-crystal XRD studies, were obtained through cation-templated self-assembly reactions. Compound 1 contains insular tetraborate(2-) anions (4-1:2 + 2T) and 2 and 3 both contain insular heptaborate(2-) anions (‘O+’ isomer, 6:(3+ 3T) + ). The X-ray structures show that in all three compounds the polyborate anions are H-bonded together into extended networks, and there are multiple cation-anion H-bond interactions present in 1 and 3. Compound 2 has cation-cation -stacking interactions. These interactions are likely to be responsible for templating the observed structures. Thermal decomposition of 1-3 in air yielded amorphous anhydrous borates of composition CoB6O10.5, NiB7O11.5 and ZnB7O11.5, respectively.


  • Heptaborate(2-), Oxidoborate, Tetraborate(2-), Transition-metal complex, XRD study
Original languageEnglish
JournalJournal of Molecular Structure
Issue number127071
Early online date13 Sep 2019
Publication statusPublished - 15 Jan 2020
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