Structural Features of Lithium Organoborates

The NMR and crystallographic characterization of lithium bis[salicylato(2-)]borate, Li(BSB), and
lithium bis[1,2-benzenediolato(2-)-O,O‘]borate, Li(BBB), are reported. The single-strand polymer {(MeCN)2 Li(BSB)}∞
crystallizes from a saturated solution of Li(BSB) in ethanenitrile and consists of μ2-{(MeCN)2Li}+ cations bridging
the exocyclic oxygen atoms of two [BSB]- anions. Crystallization of Li(BSB) from tetrahydrofuran produces {(THF)2Li(BSB)}∞, which has essentially the same structure as {(MeCN)2Li(BSB)}∞. In contrast, crystals of Li(BBB) grown
from THF/diethyl ether or THF/toluene mixtures (1:1) contain adventitious water and form a hydrogen-bonded,
three-dimensional lattice comprising {(H2O)2(THF)Li(BBB)} units. This novel structural motif contains the first
example of lithium bound to one THF and two water molecules, and also exhibits hydrogen bonding between the
water and the THF. Ab initio calculations suggest that the Li−OBBB bond in {(H2O)2(THF)Li(BBB)}∞, while still
predominantly ionic in character, is more covalent than an analogous Na−OBBB bond. Crystallization of Li(BBB)
from ethanenitrile produces {[(H2O)(MeCN)Li(BBB)]2}∞, which contains the first example of lithium bound to one
MeCN and one water molecule. In this case, hydrogen bonding occurs between dimeric {(H2O)(MeCN)Li(BBB)}2
units to form two-dimensional sheets in the ab crystal plane.