Synthesis, structure and research on quasi-aromaticity of a new organically templated aluminoborate: [NH0.5C4H4NH0.5][AlB12O14(OH)12

Abstract

► The research on quasi-aromaticity of [AlB 12 O 14 (OH) 12 ] − is firstly brought up. ► Three isolated p bonds changing into a large p bond is confirmed by NICS. ► How 3 p bonds forming into a large p bond is explained by Mulliken charges. ► Presence of ring currents or quasi-aromaticity is validated by 2D IR COS. By employing hydrothermal method, we identify a new organically templated aluminoborate [NH 0.5 C 4 H 4 NH 0.5 ][AlB 12 O 14 (OH) 12 ] which is structurally determined by single crystal X-ray diffraction and characterized by simulated and experimental IR, 2D IR COS (two-dimensional infrared correlation spectroscopy), NICS (nucleus-independent chemical shifts) and Mulliken charges calculations. Although the cluster anions [AlB 12 O 14 (OH) 12 ] − is identical to the counterpart of compound reported by Lin et al. at 2008, we firstly bring up its quasi-aromaticity, discuss and confirm it by NICS, Mulliken charges calculations and magnetic-induced 2D IR COS, and conclude that three isolated and non-coplanar four-center six-electron π bonds of cluster could cooperate and interact with each other to form a closed conjugated large π orbital system, endowing the cluster anions with quasi-aromaticity. Thus, a one-dimensional chain is constructed by π – π stacked interaction between quasi-aromatic clusters and aromatic pyrazine along [ 1 0 ¯ 1 ] direction. The title compound crystallizes in monoclinic space group C2/c with a = 18.397(4), b = 12.0670(16), c = 11.075(2) Å, α = 90.00, β = 116.483(11), γ = 90.00°, Z = 4, V = 2200.6(7) Å, R = 0.0442 and wR = 0.1128 for 2689 observed reflections.