Palladium (II), and Rhodium (III) Chelates of Aspartic and Glutamic Acid

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Palladium (II), and Rhodium (III) Chelates of Aspartic and Glutamic Acid University of the Pacific Scholarly Commons University of the Pacific Theses and Dissertations Graduate School 1964 A study of the platinum (II), palladium (II), and rhodium (III) chelates of aspartic and glutamic acid Cecilia Elizabeth Luschak University of the Pacific Follow this and additional works at: https://scholarlycommons.pacific.edu/uop_etds Part of the Chemistry Commons Recommended Citation Luschak, Cecilia Elizabeth. (1964). A study of the platinum (II), palladium (II), and rhodium (III) chelates of aspartic and glutamic acid. University of the Pacific, Thesis. https://scholarlycommons.pacific.edu/ uop_etds/1559 This Thesis is brought to you for free and open access by the Graduate School at Scholarly Commons. It has been accepted for inclusion in University of the Pacific Theses and Dissertations by an authorized administrator of Scholarly Commons. For more information, please contact [email protected]. A s TunY oF THE PLAT.tNu~ u'i). -PALLADi uM tn> • .AND RHODIUM (Ill) CHELATES OF ASPARTIC AND GLUTAMIC ACID A Thes is P 1·esented to the Faculty of the Gr aduate School Univer s ity of the Pacific In Partial F ulfillment of the Requirements for the Degree Master of Science by Cecilia Elizabetn L uschak J anuary 1964 This dissertation is approved for recommendation to the Graduate Council. Department Chairman or Dean: Dissertation Committee: , Chairman Dated ~ TABLE OF CONTENTS CHAPTER PAGE I. INTRODUCTION . 1 II. THEORY •••• 3 1. Chel a t ing Tendencies of Aspartic a nd Glutamic Ac id . 3 2. The Coordina tion of Palladium , P la tin um , and Rho di um . • • • . 5 3. P l a tinum and P a lladium 6 A. The Val enc e B ond Method . 6 B. The Mol e cul ar O r bita l Approac h . 7 C. The Crysta l F iel d Theo ry •• 7 D. The Val ence B ond Theory a nd Rhodi um (III) 11 E . The Mol e c ul a r Orbital Theory and Rho dium (III) . 12 F. The Crys ta l Fiel d Theory a nd Rhodium (III) 12 4. L igan d F iel d Theo ry • • • • 13 5. Coval e ncy • • • • • • • • • • . 14 6. C r ys ta l F iel d Spectra of Rhodi um (III) • . 15 iii CHAPTER PAGE "1 . Charge Transfer Spectra ••••• . 16 8. pH Dependence of the Reactions 16 9. The Preparat ion of Potassium Tetrachl oroplatinate • • . 17 III. EXPERIMENTAL • . • • • • • • • • • • • 19 1. Synthesis of the Chelates • • •• . 19 A. Bisaspartatopl atinum (II) 19 B. .B1sglutamatoplatinum (II) ••• . 21 C . Biaglutamatopalladium (II) •• • 22 D. Bisaspartatopalladium (It) • . 24 2. Stereochemistry of the P latinum (II) and + - P alladium--(11) Chelati)s . -.-.~ . • 3. Pol ymeriz;a.tlon •••••••••••• 27 4. Synthesis of Bisglutama torhodium (III) and Bis aspa.rtatorhodium (III) 28 5. Stereochemistry of the Rhodium (Ill) Chel ates • 30 IV. SPECTRA ••••••• . 32 1. E xperimental . 33 2. Infrared Spech·a . • • • • • • • • • • 33 V. SUMMARY ••••••••• . 39 B IBLIOGRAPHY • • • • • • • • • • • • • • • • • • • • • • 4 1 APPENDI X . • . • . • . • . • • . 44 L IST OF TABLES T ABLE P AGE 1 Infrared Spectra Assignments for Glutamic and Aspar tic Acid . • • • • • • • • • • • • • • . 36 11 Absorbance Obtained in the Infrared Spectra of Aspartic Acid • • • • • • • • . • • • • • 37 Ill Abso1•bance Obta ined in tl1e Infr ared Spect ra of Glutamic Acid • • • • • . • • • . • • • • 3 7 LIST OF F IGURES F IGURE PAGE 1 Bonding Orbital s of Palladium and P l atinum . 6 2 Splitting of the d - Orbital s in Squar e-planar Compl exes of Platinum (II) and Palladium (II). 8 3 Bisglutamatopalladium (II) . • • • • • • . • 23 4 General Structure for the Palladium (II) a1td P l a tinum (11) Chel ate s of Aspartic and Glutamic Acids • • • • . • • • 27 5 General Struc ture for the Dimer 28 6 P ossi bl e Structures fo r the Rhodium (III) Chel a.tea • • • • . • • • • . • • • 30 7 ·tnfrare<.l Spectra o1Aspartic Acid . " . 45 8 Infrared Spectra of Glutamic Acid . • 46 9 Infrared Spect ra. of Bisaspar tatopl atinum (II) • • • 47 10 Infrared Spectra of Bisglutamatopl atinum (II) • 48 11 Inf r ared Spectra o( Bisglutamatopalladium (U) ••• 49 12 Infrared Spectra of Bisaspartatopa.lladium (II) fr om Method I • • • • • • • • • • • • • • • • • • 50 13 Infrared Spectra of Bisaspa1·tatopalladium (II) from Method 11 • • • • . • • • • . • • • • • • • • 51 14 Ul traviolet Spectra of Bieglutamatopalladium (II) .. 5l 15 Ultr aviolet Spe,~tra of Bioaapartatop3.1ladium (II) •. 52 ACKNO WLEDGMENTS The writer wishes to express her oincere t hanks to Dr. Hers c h(~ l Frye, who directed the r esearch and acted as Chairman of the Thesis Committee. She is al s o especially grateful to Dr. Emerson G. Cobb and Dr. Milton E • .F'ulle1· for their inspiration, encouragement, and guidanc e during the course of study. CHAPTER I INTRODUCTION It is fairly well known tha t alpha-amino dicarboxylic a cids combine quite readily with basic metal ions s uch as t he a lkaline earths. The lite r a ture indicates that considerabl e s tudy has been done in this area (Lumb and Martell, 1953). F urther s tudies have shown tha t ther e is also considerable a ffinity fol· the tra ns ition el ements and a good number of these have been investigated (Nyberg, Cefola atld Sabine, 1959). The nature of the problem includes the synt hesis and c ha1·a cterization of six platinum metal chelates of two alpha - amino dicarboxylic a cids, namely aspartic and glutamic a cids. The metal ions upon which the investigation is focused are platinum (II), palladium (II), a nd rhodium (III). Sever al of these are reported as having been prepared (Volshtein and Anokhova, 1959; Spacu and Sc her zer, 1962). The series is incompl e te, however, and little study has been done correl a ting the stabilities a nd tre nds of the compl exes as a function of the metal ion and carbon chain l e ngth of the ligand acid m olecule . Hence, t he ultimate a im of the investigation is to s tudy the tendence of c hel a tion as the ca r bon c hain l engt h of the alpha- amino dicarboxylic a cid increases and also to study the stability of the 2 chelates as the central metal ion is varied. Because there are numerous problems involved here, the investigation extends somewhat beyond the scope of a Master's research. Therefore the investigation is limited 011ly to aspartic and glutamic acid. The methods of synthesis for the palladium, platinum, and rhodium chelatea oi aapa1·tic and glutamic acids were studied and outlined. After synthesis, the means which were employed for characterization included elemental analysis, molecular weight determination, and infrared and ultraviolet spectra. CHAPTER II THEORY 1. Cb.elating Tendencies of Glutamic and Aspa1·tic Aci~ Both aspartic and glutam ic acid have three functional g roups which could feasibly combine with metal a toms: two c ar boxylic a cid groups and an amino g roup. If this is actually the case. they would be considered tridentates. Ste ric considerations indicate that this is quite unlikely, however. The lite1·ature (Volehte in and Anokhova, 1959• Spacu and Sche rzer, 1962) also indicates that these alpha~ amino dicarboxylic acids appear as bidentates, forming inner complexes when com bining with metals of the second and third transition series. ~ence , it is "13xpected that-aspartic-and glutamic acid behave as bidentates in inner complexes of palladium (11) and platimtm (II). F urthermore, the bonds between the metal ion and ligand would m ost likely occur betwe en the metal ion and amino group, and between the metal ion and alpha ... carboxyl group. As a r esult. a five member ed r ing would be formed. This ring may be closed by t he formation of coval ent linkages or coordinate bonds , or by the combination of the two (Gilreath, 1958). The coval ent bonding is produced by the r epl acement of a proton in the acidic carhoxyl group on the aspartic and glutamic acids. 'I' he COOrdinate linkagt.S- uwithOtlt the 4 replacement of hydrogen--are formed by the donation of an electrotl pair f1•om the amino group. This is shown by: 0 II C - 0 ~ c II 0 In case t here is bond formation invol ving the amino group and the beta-carboxyl group, a seven membered ring would arise. This seems leas likely on stability grounds. In general, chelates fo~ming five ot· six mexnbered rings are the moat staale; from this it follows that the beta-carboxyl group does not participate in chelate formation, and one would expect the resulting inner chelate to have acid character. It is perhaps worthwhile noting that this allows for the possibility of salt formation with the beta - cal.~ boxyl group. In studying tbe chelating tendencies of aspartic and glutamic acids, Lumb and Martell ( 19 53) found that the a s par tate ion has a higher affinity for the less basic metal ions, while ghttamate ion is more effective in complexing the more basic m etal ions. They conclude that for most divalent m etal ions, binding with aspartate will be greater th.an with glutarnate. 5 The participation of the beta- carboxyl g roup in binding the metal ion is also ruled out by them . E ven thougb the additional carboxylate ion is probably not involved in the metal-chelate bonds, it has an indirect influe nce on the s tability of tl1e chelate ring (l.umb and Martell, 1953). The gene1·ally greater stability of the aspartate chelateB indicates that t he inductive effect of the negative beta­ carboxyl group leuds s tability to the a tructure by increasing the basicity of the donor g roups towards the metal ion. In the analogous glutamate structure thio inductive effect would be considerably weaker.
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