SYNTHESIS, OPTICAL RESOLUTION, AND X-RAY CRYSTAL-STRUCTURE OF A HELICAL HEXAAZAMACROCYCLIC ZINC COMPLEX

The synthesis and structural characterization of the zinc complex of a n 18-membered macrocyclic ligand containing four saturated amines and two pyridine groups are described. The compound is formulated as 7,23, 24-hexaazatricyclo[17.3.1.1(8,12)]tetracosa-1 (23),8,10,12(24),19,21-h exaene)zinc(2+) trifluoromethanesulfonate, [Zn-(pyo2[18]dieneN6)](CF3S O3)2. The proton-NMR spectrum of the complex is consistent with D2 sym metry in which the ligand is hexacoordinated in a meridional wrap with the pyridine groups twisted relative to each other and the -CH2NHC2H4 NHCH2- groups forming helical linkages connecting the pyridine groups. Well defined multiplets in the NMR spectra were analyzed by spin simu lation, and the resulting dihedral angles were in agreement with those determined in the solid-state by X-ray crystallography. The complex w as inert to both NH and metal ion exchange in aqueous solution. The ri ght- and left- handed helical enantiomers were resolved by formation o f diastereomers with (+)-tartrate. The CD spectra gave positive and ne gative Cotton effects at 262 nm corresponding to the pyridine pi to pi transition. [Zn(pyo2[18]dieneN6)](CF3SO3)2 (ZnC20N6H26S2O6F6) crysta llizes in the orthorhombic space group Imcb (Ibam) with Z = 4, a = 15. 851(4) angstrom , b = 18.391(5) angstrom , c = 9.325(5) angstrom , and V = 2718.4(17) angstrom3. X-ray crystallographic results showed that the complex has 222 (D2) symmetry in the solid state, which is the sam e structure as found in solution.