Macrocyclic Ligand Design. Structure—Function Relationships Underlying the Interaction of Substituted Derivatives of Oxygen-Nitrogen Macrocycles with Selected Transition and Post Transition Metal Ions

Abstract

The effect of methyl substitution on 15- and 17-membered macrocycles (incorporating N2O2- and N3O2-donors, respectively) on their interaction with cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II) and lead(II) has been investigated. The results are compared with those obtained for the corresponding complexes of the unsubstituted (parent) rings. Binding constants for the formation of the metal complexes have been determined potentiometrically in 95% methanol (I = 0·1; Et4NClO4). An X-ray crystallographic study of [NiL(H2O)] (ClO4)2 (where L is the dimethyl derivative of a 17-membered, N3O2-donor macrocycle) confirms that the nickel ion is six-coordinate, with the complex cation exhibiting a distorted octahedral geometry defined by all five donor atoms of the O2N3-macrocycle (in its meso form) and the oxygen of the water molecule. In this structure the macrocyclic backbone incorporating the N3-donor fragment is arranged facially. Molecular mechanics modelling of this complex predicts that the observed facial configuration will be favoured over an alternative facial arrangement or a meridional one.

Spectroscopic and computational investigation of three Cys-to-Ser mutants of nickel superoxide dismutase: insight into the roles played by the Cys2 and Cys6 active-site residues

“…The optimized Ni–N bond distances for this model agree well with those observed in related high-spinNi 2+ complexes [84, 110, 112–114]. However, the optimized Ni–O bond distances deviate significantly from those reported for structurally similar Ni 2+ complexes, in particular the Ni–O H 2 O bond length [84, 110, 112–114, 117]. Although the Ni–O H 2 O bond distance is longer than expected (approximately 2.6 Å), it is important to note that a similarly long Ni–O H 2 O bond was obtained upon geometry optimization of the H134A urease active-site model (vide supra).…”

“…Importantly, the average Ni–N/O distance in the DFT-optimized structure (2.14 Å) agrees very well with the distance determined by the EXAFS analysis. The optimized Ni–N distances for the H134A urease active-site model are also in good agreement with those reported for structurally similar, synthetic high-spin Ni 2+ complexes, whereas the Ni–O bond lengths are overestimated by approximately 0.14–0.2 Å [84, 86, 109–114]. …”

“…Consistent with the MCD data, DFT predicts a distorted O h Ni 2+ center for the six-coordinate C2S/C6S 6-c model. The optimized Ni–N bond distances for this model agree well with those observed in related high-spinNi 2+ complexes [84, 110, 112–114]. However, the optimized Ni–O bond distances deviate significantly from those reported for structurally similar Ni 2+ complexes, in particular the Ni–O H 2 O bond length [84, 110, 112–114, 117].…”

Synthesis and Characterisation of Macrocyclic Copper(II) Complexes Containing N3O4 Donor Sets

“…The study of the complexation capability of Cu(II) towards oxaazamacrocyclic ligands derived from diketo-or diformylprecursors and the appropriate aliphatic or aromatic diamine precursors, often by a template procedure, have been previously reported. [5][6][7][8][9][10][11][12][13][14][15][16][17] Previously, we have reported a number of copper(II) Schiff base polyazamacrocyclic complexes with and without pendant arms by a template procedure. [18][19][20][21] We report here the synthesis and characterisation of two new potentially heptadentate (N 3 O 4 ) Schiff base macrocyclic copper(II) complexes, 1 and 2, derived from cyclocondensation of 2,6-bis(2-formylphenoxymethyl)pyridine with 1,2-bis(2′aminophenoxy)benzene (L 1 ) or 1,2-bis(2′-aminophenoxy)-4tert-butylbenzene (L 2 ) (Fig.…”