Reactions of the pyrazolylborates KTp‘ with
Zn(ClO4)2 and KOH in a 2:2:1 ratio yield
the complexes
[Tp‘2Zn2O2H3]ClO4
(1) for Tp‘ =
hydrotris(3-R-5-methylpyrazolyl)borate with R =
p-isopropylphenyl (a), 3-pyridyl
(b), and 3-(6-methyl)pyridyl (c). Their
structure determinations have revealed a Zn-OH-H···OH-Zn
array (i.e., a
bridging H3O2
- ligand) in the
dinuclear complex cations. The zinc ions in complex 1a
are in a distorted tetrahedral
ZnN3O environment, and those in 1b and
1c are in a distorted trigonal bipyramidal ZnN4O
environment due to
additional coordination of one pyridyl nitrogen from the opposing Tp‘
ligand. In 1b, one Zn-OH function is
involved
in a hydrogen bridge to a cocrystallized methanol molecule. The
complexes represent a mode of stabilization for
the zinc−aqua function in the cationic Tp‘Zn-OH2 species,
and they are intermediates in the formation of the stable
Tp‘Zn-OH complexes. It is suggested that the
Zn-O2H3-Zn unit is present as a structural and
possibly functional
motif in oligozinc enzymes like phospholipase C or P1
nuclease.