Crystal chemistry of tetraradial species. Part 7. Lithium tetrakis(1-imidazolyl)-borate solvate, Liiv[Liiv(H2O)(MeOH)]-[B(C3H3N2)4]2•MeOH, a 3-dimensional polymer; with observations on the geometry of imidazole rings

Abstract

The title compound is a 3-dimensional polymer with a completely ordered triclinic structure [Formula: see text] a = 12.380(2) Å, b = 14.434(2) Å, c = 9.683(3) Å, α = 90.36(2)°, β = 105.44(2)°, γ = 90.75(2)°, Z = 2). Every B atom is tetrahedrally coordinated by N(1) atoms of the imidazole rings, every Li(1) atom is tetrahedrally coordinated by N(3) atoms, and every Li(2) atom is coordinated by two N(3) and two oxygen atoms, one from the H2O molecule and one from a MeOH molecule. The imidazole rings connected by the B—N(1) and Li—N(3) bonds thus generate a 3-dimensional covalent polymeric network. The MeOH molecules of coordination are hydrogen-bonded to unengaged N(3) atoms, thereby supplementing the covalent bonding system. The H2O molecules are hydrogen-bonded to the MeOH molecules of solvation to form centrosymmetric [Ow … OMeOH]2 rings, which in turn are connected to the covalent network by OMeOH—H … N(3) bonds to the remaining unengaged N(3) atoms. Every atom in the structure except the H(C) hydrogens is thus involved in the 3-dimensional bond system. The excellent consistency of the bond lengths and endocyclic bond angles [Formula: see text] in the eight imidazole rings of the title compound has provided an opportunity for investigating the effect of substitution on the geometry of the imidazole ring in a sample of 17 substituted imidazoles. While the bond lengths have been found at most weakly correlated, the multilinear correlations of the [Formula: see text] in this sample are highly significant. Among the substituents the NO2, group is the most ipso- [Formula: see text] -expanding and the anionic B (in the title compound) the most ipso- [Formula: see text] -contracting. Protonation or deprotonation at the N atoms affect the ipso C—N—C angles considerably. Limited comparisons are drawn with the results of the classical investigations by Domenicano et al. on the effect of substitution on the geometry of the benzene ring. Keywords: hydrogen bond, imidazole, lithium compounds, polymers, tetrahedral boron ions.