A continuous shape measures analysis of the coordination polyhedra of a host of transition metal complexes with bi- and multidentate ligands discloses the distortion pathway associated with each particular topology of the chelate rings formed. The basic parameter that controls the degree of distortion is the metal-donor atom bond distance that induces nonideal bond angles due to the rigidity of the ligands. Thus, the degree of distortion within each family of complexes depends on the atomic size, on which the high- or low-spin state has a large effect. Special attention is therefore paid to several spin-crossover systems and to the enhanced distortions that go along with the transition from low- to high-spin state affected by temperature, light, or pressure. Several families of complexes show deviations from the expected distortion pathways in the high-spin state that can be associated to the onset of intermolecular interactions such as secondary coordination of counterions or solvent molecules. Also, significant displacement of counterions in an extended solid may result from the changes in metal-ligand bond distances when ligands are involved in intermolecular hydrogen bonding.

Distortion Pathways of Transition Metal Coordination Polyhedra Induced by Chelating Topology.

Comparison of the structures of four monomanganese (and one monoiron) complexes of ligands with the identical donor [N3(O–)3] set reveals that geometry determines the redox state of the cation.

Geometric control of manganese redox state

A new manganese(II) complex, Mn(II)−tris[2-[N-(2-pyridylmethyl)amino]ethyl]bishexafluorophosphate (Mn−TPAA), has been synthesized, its X-ray crystal structure resolved, and its superoxide stoichiometric scavenging activity established. The complex has been formed with the tripodal potentially heptadentate ligand TPAA which turns out to be the single ligand coordinated to the metal ion and therefore achieves the seven coordination. The complex crystallizes in the space group P212121, a = 19.654(9) A, b = 15.416(5) A, c = 10.425(4) A, with four formula units per unit cell. The manganese is bonded to three pyridine nitrogen atoms, to three amine groups, and to the tripodal bridging nitrogen N. The reactivity toward superoxide has been investigated using the indirect xanthine−xanthine oxidase−cytochrome c method, the electrochemical reaction of in-situ generated superoxide, and γ and pulse radiolysis measurements. From the cytochrome c assay, it has been found that the IC50 value is equal to 4.4 μM. From elec...

A Seven-Coordinate Manganese(II) Complex Formed with a Single Tripodal Heptadentate Ligand as a New Superoxide Scavenger

Subtle differences in metal-ligand bond lengths between a series of [M(4)L(6)](4-) tetrahedral cages, where M = Fe(II), Co(II), or Ni(II), were observed to result in substantial differences in affinity for hydrophobic guests in water Changing the metal ion from iron(II) to cobalt(II) or nickel(II) increases the size of the interior cavity of the cage and allows encapsulation of larger guest molecules NMR spectroscopy was used to study the recognition properties of the iron(II) and cobalt(II) cages towards small hydrophobic guests in water, and single-crystal X-ray diffraction was used to study the solid-state complexes of the iron(II) and nickel(II) cages

Size-selective encapsulation of hydrophobic guests by self-assembled M4L6 cobalt and nickel cages.

Reactions of the LCrIII unit with an in situ prepared M(PyA)3n- ion, where L represents 1,4,7-trimethyl-1,4,7-triazacyclononane and PyA- is the monoanion of pyridine-2-aldoxime, yield heterodinucle...

Tris(pyridinealdoximato)metal Complexes as Ligands for the Synthesis of Asymmetric Heterodinuclear CrIIIM Species [M = Zn(II), Cu(II), Ni(II), Fe(II), Mn(II), Cr(II), Co(III)]: A Magneto−Structural Study

The variable coordination chemistry of a potentially heptadentate ligand with a series of 3d transition metal ions. The chemistry and structures of [M(py3tren)]2+, where M(II) Mn, Fe, Co, Ni, Cu, and Zn and (py3tren) N{CH2CH2C(H)(C5H4N)}3

Carlo Mealli

Papers

The variable coordination chemistry of a potentially heptadentate ligand with a series of 3d transition metal ions. The chemistry and structures of [M(py3tren)]2+, where M(II) Mn, Fe, Co, Ni, Cu, and Zn and (py3tren) N{CH2CH2C(H)(C5H4N)}3