Alkali-metal complexes with neutral molecular receptors containing nitrogen donor atoms: a crystallographic and multinuclear magnetic resonance study

Abstract

The pyrazole-functionalized macrocyclic ligands 1,4,7-tris(pyrazol-1-ylmethyl)-1,4,7-triaza-cyclononane L¹ and 1,4,7,10-tetrakis(pyrazol-1-ylmethyl)-1,4,7,10-tetraazacyclododecane L² form stable complexes of formula [ML]BPh₄(M = Li or Na, L = L¹ or L²) with alkali-metal cations. The crystal and molecular structure of [LiL¹]BPh₄ has been determined by X-ray diffraction: space group P, a= 11.985(5), b= 18.596(6), c= 20.932(4)Å, α= 110.96(3), β= 91.38(3) and γ= 108.63(3)°. The metal ion is in a six-co-ordinated environment formed by the nitrogen atoms of the macrocyclic frame and by the unsubstituted nitrogen atoms of the pendant pyrazole groups. This structure is compared with that previously reported for [NaL²]BPh₄ which contains eight-co-ordinated sodium. The ¹H, ¹³C, ⁷Li and ²³Na NMR spectral data for the compounds in solution are presented.