The preparation of the new
ligand 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane, (-N(Me)-(CH2)2-)4
(= L), and the complexes [NiL] (ClO4)2,
[NiL(OCHNMe2)] (ClO4)2,
[NiLN3] ClO4, [CuL] (ClO4)2,
and [NiY] (ClO4)2, where Y =
(-N(Me)(CH2)2N(Me)(CH2)3-)2,
1,4,8,11-tetra-methyl-1,4,8,11-tetraazacyclotetradecane, are described. The
magnetic moments of the nickel((11) species are reported, and the labile
low-spin/high spin equilibria characterizing the
[NiLI2+ and [NiY]2+ systems
over a range of temperatures and ionic strengths in aqueous solution are
discussed. The spectrophotometric titration of the aqua ligands in [NiLH2O]2+,
[CuLH2O]2+, and [NiYH2O]2+ against
sodium hydroxide yields pKa values of 10.2
� 0.2, 12.0 � 0.3 and 10.7 � 0.2, respectively, and a study, using Job's method
of continuous variations, of the formation of azide
species shows [NiLN3]+ and [NiYN3]+
to be formed predominantly in aqueous solution.