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Thermochemical Bond Energy Studies Of Various Transitional-Metal Bis-Beta-Diketone Compounds And Their Inner Orbital Splittings By Bomb Calorimetry

Author

Charles Irvin Drew, University of the Pacific

Date of Award

1971

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Graduate School

First Advisor

Richard P. Dodge

First Committee Member

Paul H. Gross

Second Committee Member

RIchard L. Perry

Third Committee Member

Celestia Potts

Fourth Committee Member

John R. Tyssdall

Abstract

The thermochemical technique of static bomb calorimetry was used to determine the heats of combustion for some twenty chelated metal complexes. Studied were the first row transitional metals (Mn⁺² through Zn⁺²) bis-beta diketone complexes of acetylacetome and their related ligands and the acetyl ·· acetonates of Pd⁺², Pt⁺², Be⁺², Ce⁺³, Tl⁺¹, and Zr⁺⁴.

Solid purified samples of from 1 to 2 grams were combusted in a pressurized oxygen atmosphere to the reaction products H₂0 (1), C0₂ (g) and metallic oxides. The temperature change for the exothermic reactions was standardized with benzoic acid to give the enthalpy of combustion in kcal/mol. The majority of the data for the combustion reaction are in error of 1/2 of 1% or less.

The heat of combustion data were used in a suitable Born-Haber thermochemical cycle to determine the average bond energy for the metal to ligand bond. The bond cleavage can be expressed in either terms of an ionic or a coordinated bond break, known as hererelytic and hemolytic cleavage respectively, depending on the choice of the thermochemical cycle. The hemolytic bond energy cycle is suitable for the calculation of the average bond energy.

For the acetylacetonate complexes of Mn⁺² through Zn⁺², the heterolytic thermochemical cycle was used. Thus, the heterolytic bond energies obtained are shown to vary with the electronic configuration of the central metal. These variations are predicted by crystal field theory.

A plot of the total heterolytic bond energies versus atomic number will, with a knowledge of the spin state of the metal ions, give an estimation of 10Dq values for the complexes. For the complexes investigated, 10Dq values are in good agreement with those obtained by the more accurate spectroscopic method.

A second series of compounds investigated consisted of various ligands similar to acetylacetone. The copper and nickel complexes were synthesized with benzoylacetone, dibenzoylmethane and salicylaldehyde. lt was expected that a pattern of decreasing bond energy could he found by the systematic replacement of first one and then the other methyl groups by a phenyl group (the substituent effect). No clear pattern emerged.

This investigation provides the framework for future investigations to give a more quantitative understanding of metal chelated complexes and their metal-ligand bond energies.

Pages

94

Recommended Citation

Drew, Charles Irvin. (1971). Thermochemical Bond Energy Studies Of Various Transitional-Metal Bis-Beta-Diketone Compounds And Their Inner Orbital Splittings By Bomb Calorimetry. University of the Pacific, Dissertation. https://scholarlycommons.pacific.edu/uop_etds/3521