Solution studies of the cobalt(II) N-rac- and N-meso-CoL2+ isomers and molecular and crystal structures of the low-spin, five-coordinate cobalt(II) macrocyclic complexes N-rac-[CoL(H2O)](ClO4)2·0.6H 2O (1) and N-rac-CoL(OClO3)ClO4 (2) (L = 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene)

David J. Szalda, Carolyn L. Schwarz, John F. Endicott, Etsuko Fujita, Carol Creutz

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Abstract

The title cobalt(II) complexes were prepared from the reaction of CoL(Cl)H2O2+ with Cr2+(aq) in 1.0 M HClO4, and crystals of 1 and 2 were obtained from acetone. Structures were determined from single-crystal X-ray diffraction data collected with use of Cu Ka radiation. Crystallographic data: 1, N-rac-[CoL(H2O)](ClO4)2·0.6H 2O, Pbcn, a = 15.654 (4) Å, b = 14.623 (2) Å, c = 55.221 (11) Å, V = 12640 (7) Å3, Z = 20 (R = 0.113, Rw = 0.135); 2, N-rac-[CoL(OClO3)]ClO4, P21/c, a = 10.336 (3) Å, b = 17.094 (1) Å, c = 13.890 (2) Å, β = 105.59 (2)°, V = 2363 (1) Å3, Z = 4 (R = 0.061, Rw = 0.087). Both 1 and 2 contain a five-coordinate cobalt(II) center with the four nitrogen atoms of N-rac-L forming the base of a square pyramid and axial water (1, Co-OH2 = 2.25 (5) Å) or axial perchlorate ion (2, Co-OClO3 = 2.305 (5) Å) forming the apex of the square pyramid. Studies of N-rac- and N-meso-CoL2+ in solution (perchlorate salts) are described: the lowest energy d-d band (1400-1700 nm, depending upon solvent) provides a probe of the isomeric composition of the solutions, since this band is 2-3 times more intense for the N-rac than for the N-meso isomer. Equilibration of the two isomers is slow at room temperature (-7 s-1) in organic solvents and in acidic aqueous solutions; it is, however, rapid in alkaline media, and the N-rac isomer is favored at equilibrium.

Original languageEnglish
Pages (from-to)3214-3219
Number of pages6
JournalInorganic Chemistry
Volume28
Issue number16
Publication statusPublished - 1989

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ASJC Scopus subject areas

  • Inorganic Chemistry

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