The Syntheses and Characterization of Binuclear Clathrochelate Complexes

Citation

Marritt, William Alan (1983) The Syntheses and Characterization of Binuclear Clathrochelate Complexes. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/xpqf-ns89. https://resolver.caltech.edu/CaltechTHESIS:10302018-160040560

Abstract

A series of binuclear clathrochelate complexes, M_A(II)M_B(II)L⁺, have been synthesized and characterized for the purpose of examining electrostatic, magnetic, and electronic delocalization effects in binuclear complexes. The clathrochelating ligand, L^3-, 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 M_A(II)M_B(II)L⁺ complexes were prepared by combinations of metal-ion template, metathesis, and insertion reactions: homonuclear complexes with M_A = M_B = Mn, Fe, Co, Cu, Zn, and Cd; heteronuclear complexes with M_A = Mn, M_B = Co, Ni, Zn, Cd, and Mg; M_A = Fe, M_B = Mn, Co, Ni, Cu, Zn, Cd, and Mg; M_A = Cu, M_B = 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 M_A 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)M_B(II)L⁺, Fe(II)M_B(II)L⁺, and Cu(II)M_B(II)L⁺. Within experimental error, the average of the M_A 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 M_A(II)M_B(II)L⁺ complexes were examined by variable temperature susceptibility measurements (M_A = M_B = 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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