The Syntheses and Characterization of Binuclear Clathrochelate Complexes

Author: Marritt, William Alan

Year: 1983

Degree: Dissertation (Ph.D.)

Advisor: Grubbs, Robert H.

Committee Members: Bercaw, John E.; Gray, Harry B.; Gagne, Robert R.; Grubbs, Robert H.

Option: Chemistry

DOI: 10.7907/xpqf-ns89

Abstract

A series of binuclear clathrochelate complexes, MA(II)MB(II)L+, have been synthesized and characterized for the purpose of examining electrostatic, magnetic, and electronic delocalization effects in binuclear complexes. The clathrochelating ligand, L3-, is a bicyclic Schiff-base compound derived from 3 equiv of 2-hydroxy-5-methylisophthalaldehyde and 2 equiv of 2,2',2"-triaminotriethylamine (tren). The following MA(II)MB(II)L+ complexes were prepared by combinations of metal-ion template, metathesis, and insertion reactions: homonuclear complexes with MA = MB = Mn, Fe, Co, Cu, Zn, and Cd; heteronuclear complexes with MA = Mn, MB = Co, Ni, Zn, Cd, and Mg; MA = Fe, MB = Mn, Co, Ni, Cu, Zn, Cd, and Mg; MA = Cu, MB = Mn, Co, Ni, Zn, Cd, and Mg. In addition, syntheses and characterization are reported for the binuclear Cu(II)Cu(II)LH2+ complex and mononuclear complexes of the non-deprotonated ligand, MLH3n+, with M = Na(I), Mn(II), Mn(III), Fe(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and Mg(II).

The MA redox potentials of the Mn(III)/Mn(II), Fe(III)/Fe(II), and Cu(II)/Cu(I) couples were determined by cyclic voltammetry and differential pulse voltammetry for three series containing both homonuclear and heteronuclear complexes, Mn(II)MB(II)L+, Fe(II)MB(II)L+, and Cu(II)MB(II)L+. Within experimental error, the average of the MA redox potentials for each series of heteronuclear complexes was the same as that for the corresponding homonuclear complex. This result suggests that there is no measurable stabilization of Mn(III)Mn(II)L2+, Fe(III)Fe(II)L2+, and Cu(I)Cu(II)L with respect to mixed-valent heteronuclear analogues.

The magnetic properties of a series of four homonuclear MA(II)MB(II)L+ complexes were examined by variable temperature susceptibility measurements (MA = MB = Mn, Fe, Co, and Cu). In all cases, weak antiferromagnetic coupling between the metal centers was observed (-33.5 cm-1 < J < -0.8 cm-1). The weakness is attributed to limited overlap of metal orbitals with those of the bridging atoms.

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