STRUCTURE AND STABILITY OF SOME COMPLEXES OF LARIAT ETHERS WITH STERICALLY-HINDERED PYRIDYL GROUPS AS PENDENT DONORS

Synthesis of the ligands OMPY2-K22 (N,N'-bis(omicron-methyl-alpha-pyridylmethylene)-1,10-diaza-4,7,13,16-tetraoxacyclooctadecane) and CMPY2-K22 (N,N'-bis(1-methyl-alpha-pyridylmethylene)-1,10-diaza-4,7,13,16-tetraoxacyclooctadecane) is described. Formation constants with Cu(II), Zn(II), Cd(II), Sr(II), Ba(II), La(III), and Pb(II) are reported. The crystal structures of [K(OMPY2-K22)] I and [Na(CMPY2-K22)] I are reported. [K(OMPY2-K22)] I crystallizes as tetragonal, space group P4(1)2(1)2, with a = 12,726(3), c = 37,503(5) angstrom, Z = 8, V = 6066,31 angstrom 3. The final conventional R was 0,044. The potassium is eight coordinate, with a mean K-O length of 2,85 angstrom, and mean K-N lengths to the ring nitrogens of 3,07 angstrom, and to the pyridyl nitrogens of 2,95 angstrom. [Na(CMPY-K22)] I is triclinic, space group P1BAR, with a = 9,216(1), b = 17,279(3), c = 18,480(2) angstrom, alpha = 81,73(1), beta = 81,68(1), gamma = 81,43(1)-degrees, Z = 4, V = 2856,69 angstrom 3. The final conventional R was 0,062. The sodium is eight coordinate, with a mean Na-O length of 2,60 angstrom, and mean Na-N lengths of 2,73 (ring N) and 2,55 angstrom (pyridyl N). The formation constants for OMPY2-K22 and CMPY2-K22 show considerable decrease in complex stability as compared to the parent ligand without omicron-methyl or C-methyl substituents, and these decreases are discussed in relation to the considerable M-N and M-O bond lengthening observed in the reported crystal structures.