- Synthesis and Co-ordination Chemistry of Two Penta-azamacrocycles containing a 1,4-Piperazine Backbone. Crystal Structure Determinations of 6,12-Dioxo-1,5,13,17,22-penta-azatricyclo7,11>docosa-7(22),8,10-triene and 1,5,13,17,22-Penta-azatricyclo7,11>docosa-...
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Two closely related pyridine-containing penta-azamacrocycles with a 1,4-piperazine backbone have been prepared, and the co-ordination chemistry of one of them 7,11>docosa-7(22),8,10-triene, L2> with nickel(II), copper(II), and zinc(II) investigated.L2 was obtained in low yield from the related diamide macrocycle 6,12-dioxo-1,5,13,17,22-penta-azatricyclo7,11>docosa-7(22),8,10-triene, L1, by reduction with BH3.thf (thf = tetrahydrofuran).The crystal structure of L1 shows that the 1,4-piperazine backbone adopts a chair conformation, with the lone pairs of the two 1,4-piperazine N atoms pointing in opposite directions, unfavorable for chelation.Complexes of L1 could not be isolated.Complexes of L2 with Ni(2+), Cu(2+), and Zn(2+) were readily obtained, and the crystal structure of 2)>2 shows the 1,4-piperazine is in the boat conformation required for chelation.The Ni(2+) is co-ordinated to all five N atoms of the macrocycle in a symmetric, but distorted, trigonal-bipyramidal geometry, with the pyridine ring at right angles to the plane of the carbon framework of the 1,4-piperazine backbone.The pyridine and two 1,4-piperazine N atoms are equatorial, and the other two N atoms axial; the Ni-N bond lengths are in the ranges 2.16 - 2.18 Angstroem (axial) and 2.02 - 2.08 Angstroem (equatorial), with the Ni-pyridine-N bond length being the shortest.The 13C n.m.r. spectrum of the Zn(2+) complex is consistent with the same symmetric structure as the Ni(2+) complex.
- Alcock, Nathaniel W.,Moore, Peter,Reader, C. James,Roe, S. Mark
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p. 2959 - 2964
(2007/10/02)
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