Zn−OH₂ and Zn−OH Complexes with Hydroborate-Derived Tripod Ligands: A Comprehensive Study

The complete array of those hydrotris(pyrazolyl/thioimidazolyl)borate ligands that were developed and used in the author's laboratories, with N3, N2S, NS2, and S3 donor sets, was scanned for their ability to form Zn−OH2 and Zn−OH complexes. The coordination motifs found were Zn−OH2, Zn−OH, Zn−OH−Zn, and Zn−O2H3−Zn. Of these, the well-established Zn−OH motif was complemented with novel species bearing N3, NS2, and S3 tripods. The Zn−OH2 motif was observed only with pyrazolylborate ligands and only in unusual situations with coordination numbers higher than 4 for zinc. The new Zn−OH−Zn motif was realized for three different pyrazolylborates, for one NS2 tripod, and for two S3 tripods. Finally, it was verified that the Zn−O2H3−Zn motif again occurs only with pyrazolylborate ligands. The new complexes were identified by a total of 11 structure determinations.