SELECTIVE LITHIUM ENCAPSULATION IN AQUEOUS-SOLUTION BY THE NEW CAGE 4,10-DIMETHYL-1,4,7,10,15-PENTAAZABICYCLO[5.5.5]HEPTADECANE (L) - SYNTHESIS, CHARACTERIZATION, AND STRUCTURAL ASPECTS - CRYSTAL-STRUCTURES OF [LIL][CLO4] AND [CUL]BR2.3H2O

Synthesis and characterization of the new azamacrobicycle 4,10-dimethyl-1,4,7,10,15-pentaazabicyclo[5.5.5]heptadecane (L) are reported. The stepwise basicity constants have been determined by potentiometry (25 °C, 0.15 mol dm-3 NaCl). The azacage L behaves as a strong base (log K1 = 12.48) in the first protonation step, as a much weaker base in the second step (log K2 = 9.05), and as a very weak base in the last step (log K3 < 1). The cage selectively encapsulates Li+, and the inclusion [LiL]+ complex formation equilibrium has been investigated by potentiometry (log K = 4.8) and 7Li NMR techniques. The molecular structure of the complex [LiL][ClO4] has been determined by single-crystal X-ray analysis. The compound crystallizes in a monoclinic unit cell (space group P21/n) with lattice constants a = 15.046 (11) Å, b = 8.893 (4) Å, c = 15.305 (8) Å, and 0 = 113.58 (4)°, with Z = 4. Least-squares refinement converged at R = 0.065 for 1385 observed reflections of I > 3σ(I). Li+ is wholly enclosed in the cage cavity and adopts a five-coordinate geometry, with a short Li-N mean distance of 2.04 Å. The molecular structure of the complex [CuL] [Br2]•3H2O has been determined by single-crystal X-ray analysis. The compound crystallises in an orthorhombic unit cell (space group Cmc21) with lattice constants a = 11.629 (1) Å, b = 13.031 (1) Å, and c = 14.702 (1) Å, with Z = 4. Least-squares refinement converged at R = 0.068 for 542 observed reflections of I > 3σ(I). The Cu2+ is enclosed by the cage and is five-coordinated, adopting a trigonal-bipyramidal coordination geometry. The electronic spectra of the copper complex show essentially the same features in the solid state and in solution and are diagnostic of five-coordinate trigonal-bipyramidal structures. © 1990, American Chemical Society. All rights reserved.