STABILITIES OF TRIVALENT METAL COMPLEXES WITH BETA-DIKETONES

172 Pages·6.516 MB·English

by  COOPERSTEIN, RAYMOND

The Pennsylvania State College
The Graduate School
Department of Chemistry
Stabilities of Trivalent Metal Complexes with
Beta-diketones
A thesis
*>7
Raymond Cooperstein
Submitted in partial fulfillment
of the requirements
for the degree of
Doctor of Philosophy
January, 1952
Approved;
Department of Chemistry
Head of' the Department
TABLE OP CONTENTS
Page
I Introduction 1
A. Discussion of type of work done in the past. 1
B. Statement of objectives of thesis. 3
II General theory of step equilibria.
8
1. Complex formation is stepwise.
8
. Symbols and definition of terms. 10
2
3. Mathematical development of equations used In
calculations.
11
III The coordination process. 16
IV Experimental procedure. 18
V Preparation of reagents. 22
A. Buffer solutions. 22
B. Metal salt solutions. 22
C. Acids. 31a
D. Ligands. 31a
E. Solvents. 31a
VI Experimental section. 32
A. Dissociation constants of the betja-dike tones. 32
... 1. Acetylacetone. 33
2. Benzoylacetone. 34
3. Dithenoylmethane. 34
4. Graphical determination of mid-point of
plateau. 36
366703
TABLE OF CONTENTS
(continued)
Page
Vi Experimental section
B. Beta-diketone chelation titrations with,
aluminum salts. 38
C. Beta-diketone chelation titrations with
gallium chloride. 42
D. Beta-diketone chelation titrations with
indium salts.
43
E. Beta-diketone chelation titrations with
scandium salts. 44
F. Beta-diketone chelation titrations with
chromium salts. 48
G. Beta-diketone chelation titrations with
ferric salts. 50
H. Beta-diketone chelation titrations with
ruthenium and rhodium(III) chloride. 51
I. Beta-diketone chelation titrations with
lanthanum and cerium salts. 54
J. Preparation of metal acetylacetonates by
homogeneous precipitation. 56
VII Discussion of Results. 70
VIII Summary. 98
IX References. 100
X Appendix A.
XI Appendix B.
ACKNOWLEDGMENT
The author wishes to express his appreciation to
Dr. W. C. Fernelius, whose discerning knowledge and assis­
tance gave this work its direction and whose encouragement
made its problems resolvable.
In addition, the author desires to acknowledge the
cooperation of his fellow workers, who were always willing
to help.
The author’s gratitude Is also extended to the Atomic
Energy Commission, whose grant helped make this work possible
DEDICATION
To my family, without whose willingness to make sacri­
fices, nothing would have been possible.
I INTRODUCTION
Investigation of coordination compounds has, until
recently, been directed mainly to their preparation and
structure and to their use in analysis. Most studies have
been carried out largely with solid substances and the problems
arising out of their differing stabilities - their varying
ease of formation, decomposition or disproportdonation - have
been complicated by the very fact that solid lattices rather
than individual molecules have been under Investigation.
Although this work led in a general way to a better under­
standing of those factors which influence the stability of
complexes, this approach produced no direct Information re­
garding the affinity between the central atom of the compound
and the molecules or ions bound to it.
For data of greater variety and more quantitative character,
it became necessary to turn to solution chemistry. By quanti­
tative studies of the formation of the complex ions in solution
It is possible to make a more direct comparison of the tendency
of the various metal Ions to form complexes under comparable
conditions. For lattice forces do not operate In solution and
one can almost completely eliminate the influence of the ions
which are only building stones In the crystal lattice without
being direct constituents of the complexes themselves.
The first thorough investigations in this field were Ini­
tiated by Abegg, BodlSnder and their students^*^*^ at the turn
of the century. As a rule, Abegg and Bodlfinder only determined
2
the overall complexity constant:
Kjq - LMAjJ_______
<M) (A)n
for the complex MAn which predominated at high concentrations
of the coordinated ligand A. In thi? expression (M) denotes
the concentration of the free metal ion and (A) the concen­
tration of the free ligand* Prom their data they found that*
in general, the stability of the complexes increased with an
increase in the electronegativity of the metal ion*
The work of N. Bjerrum and that of his son J* Bjerrum^
gave a tremendous impetus to solution chemistry, for it
demonstrated that the formation of complex ions always occurs
stepwise and that it was experimentally possible to study and
measure the equilibrium constants of complexes existing together
in various proportions In aqueous solution* Moreover, it is
possible to make quantitative studies of complexes which can­
not be isolated In a pure state - inasmuch as they can exist
only In solution and In equilibrium with other complexes.
Bjerrum’s treatise "Metal Ammine Formation in Aqueous
Solution"^ showed that one can determine the formation con­
stants of metal Ions with ligands that are either acidic or
basic in nature by the measurement of the hydrogen ion acti­
vity in aqueous solutions containing a known amount of metal
ion and coordinating agent. Since then, rather extensive
investigations have been carried out using mono- and poly-
3
amines and derivatives of salicylaldehyde as lIgands8,9,
4 *5,6,7
This work has revealed that there is a general order of stabi­
lities for the divalent metal ions of the first transition
series in complexes which is preserved although the ligand is
varied. The question then arises; can a similar order of
stabilities be observed for the trivalent ions? If such an
order does exist, what is its variation from ion to ion?
Present Investigation
The present survey was undertaken to discover, among
other things, whether a wide variation in stabilities occurs
with complexes formed by the coordination of a series of tri­
valent metal ions with beta-dlketones. If this was the case,
it would be of interest to see how the stabilities vary with
the position of the metal In the Periodic Table, since this
Is a function of the electronic structure of the metal. The
effect of variation of the anion present in the solution on
the type of complex produced and Its stability, was another
point of Interest to be studied. Still other factors to be
investigated were: (a) what effect variations in solvent
composition have on these stabilities; (b) whether a better
procedure for the. preparation of metallic acetylacetonates
could be devised; (c) the extent to which complex formation
is Influenced by temperature.
Just as a knowledge of the dissociation constants of
acids and bases has done much to systematize our understanding
4
of the behavior of these substances, so a knowledge of stab­
ility constants may be expected to throw light on the behavi­
or of metal complexes in quantitative analysis and in ion
exchange separations.'*'^
The major portion of the work undertaken here concerns
itself with a study of the coordinating ability of acetyl-
acetone toward three t^pes of trivalent ion salts, namely
those having the inert gas configuration, transition elements
and inner transition elements.
Table I summarises the conditions under which the various
titrations were performed.
5
Table I
Summary of titrations performed.
Conditions:
Initial volume of solutions 100 ml.
Temperature 30°C
concentration 0.01 M
Ligand concentration 0.06 M
Neutral salt 0.05 M
Excess salt
Titrant, NaOH solutions 1.00 M
Metal Salt Solvent Chelating Agents
A1C1, H20 Acetylacetone
50-50 HgO-dioxane it
w
ai(no3 )3 HgO
n
50-50 HgO-dioxane
w
A1(C104 )3 H20
50-50 H 0-dioxane n , Benzoylaeetone
2
25-75 HgO-dioxane n , Benzoylacetone,
Dithenoylmethane
GaCl, h Acetylacetone
20
50-50 HgO-dioxane it
InCl, He° n
50-50 HgO-dioxane