Potentiometric titrations and nickel(II) complexes of four topologically constrained tetraazamacrocycles
UNSPECIFIED (2001) Potentiometric titrations and nickel(II) complexes of four topologically constrained tetraazamacrocycles. SUPRAMOLECULAR CHEMISTRY, 13 (2). pp. 261-276. ISSN 1061-0278Full text not available from this repository.
The novel high spin Ni2+ complexes of the topologically constrained tetraazamacrocycles (1-4) [4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane (1); 4,10-dimethyl-1,4,7,10-tetraazabicyclo[6.5.2]pentadecane (2); 4,10-dimethyl-1,4,7,10-tetraazabicyclo[5.5.2]tetradecane (3); racemic-4,5,7,7,11,12,14, 14-octamethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane (4)] show striking properties. Potentiometric titrations of the ligands 2 and 4 revealed them to be proton sponges, as reported earlier for 1 . Ligand 3 is less basic, losing its last proton with a pK = 11.3(2). Despite high proton affinities, complexation reactions in the absence of protons successfully yielded Ni2+ complexes in all cases. The X-ray crystal structures of Ni(1)(acac)(+), Ni(3)(acac)+ and Ni(1)(OH2)(2)(2+) demonstrate that the ligands 2 enforce a distorted octahedral geometry on Ni2+ with two cis sites occupied by other ligands. Magnetic measurements and electronic spectroscopy on the corresponding Ni(L)Cl-2. (L = 1 - 3) complexes reveal that all are high spin and six-coordinate with typical magnetic moments. In contrast, [Ni(4)Cl+] is five-coordinate with a slightly higher magnetic moment and its own characteristic electronic spectrum. The extra methyl groups on ligand 4 define a shallow cavity, sterically allowing only one chloride ligand to bind to the nickel(II) ion.
|Item Type:||Journal Article|
|Subjects:||Q Science > QD Chemistry|
|Journal or Publication Title:||SUPRAMOLECULAR CHEMISTRY|
|Publisher:||GORDON BREACH PUBLISHING, TAYLOR & FRANCIS GROUP|
|Number of Pages:||16|
|Page Range:||pp. 261-276|
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