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.