A. Bencini, A. Bianchi, S. Chimichi
Sep 1, 1991
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0
Influential Citations
27
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Journal
Inorganic Chemistry
Abstract
The synthesis and characterization of the new azamacrocycle 4,10,15-trimethyl-1,4,7,10,15-pentaazabicyclo[5.5.5]heptadecane (L) are reported. The stepwise basicity constants have been determined by potentiometry (25C, NaCl 0.15 mol dm[sup [minus]3]). L behaves as biprotic base: log K[sub 1] = 11.8; log K[sub 2] = 10.0. The molecular structure of the monoprotonated salt [HL][BPh[sub 4]] has been determined by single-crystal X-ray analysis. The structure of [HL]+ shows the five nitrogen atoms in endo configuration, indicating that the proton is inside the cage cavity. Geometrical considerations indicate that the proton is bound to the bridgehead nitrogen atom N(2). The cage L selectivity encapsulates Li+, and the equilibrium for the formation of the inclusion complex [LiL]+ has been investigated by potentiometry (log K = 5.5) and [sup 7]Li NMR techniques. The molecular structure of the complex [LiL][BPh[sub 4]] has been determined by single-crystal X-ray analysis. Li+ is wholly enclosed in the cage cavity adopting a regular bipyramidal geometry with the Li-N distances for the 2.01-2.08-[angstrom] range. Cu(II) is also encapsulated by L; the electronic spectra of the complex show essentially the same features in the solid state and in solution and are diagnostic of a five-coordinate trigonal-bipyramidal structure.