Investigation of the Distribution of Cupric Ion in Various Metal Oxinates by Electron Paramagnetic Resonance SHIZUO FUJIWARA and KO20 NAGASHIMA' Departmenf o f Chemisfry, Faculty o f Science, the University of Tokyo, Hongo, Tokyo, lapan
b An electron
paramagnetic resonance spectrum with hyperfine structure (hfs) due to copper nuclei was observed in some metal oxinate precipitates to which copper had been added, while in others only a single broad absorption was found. This appearance of hfs was used to determine whether the added copper was homogeneously distributed throughout the precipitate. It was found that Zn, Cd, Hg, and Mg oxinates form a homogeneous solid solution with Cu oxinate, while Ca, Sr, Ba, Pb, and Ag oxinates do not. Instead, these latter elements form two-phase precipitates. Be and AI oxinates form two-phase precipitates composed of Cu oxinate and Be, or AI oxinate containing small amounts of Cu. An x-ray powder analysis confirmed the above results.
I
report ( I ) , the use of electron paramagnetic resonance (EPR) in det,ermining the distribution of paramagnetic ions in solids was introduced with a discussion of the distribution of &In ions in CaC03. In this report, the distribution of Cu ions in various metal oxinates is discussed. Oxine, 8-hydroxyquinoline, is an important organic reagent as a metal ion precipitant and as a means of extraction prior to the spectrophotometric determination of metals. There are many reports on the use of osine in analytical chemistry (3, IO). Also, the relation between structure and precipitating procedure of cupric oxinate has been fully studied (4,12, IS). However, no report was found in the literature on the study of mixed crystals of Cu-metal oxinate by EPR. A copper chelate, suc,h as a Cu-amino acid complex (aqueous solution), gives four Cu hyperfine lines, and solids containing Cu-amino acid complexes exhibit EPR spectra which contain hyperfine structure (hfs), and sometimes super hfs (due to the interaction of I i 1 4 and Cu). The EPR spectrum of Cu oxinate in an organic solvent (16) and that in a frozen solution at liquid nitrogen N A PREVIOUS
1 Present address, Department of Chemistry, Tokyo Kyoiku University, Hunkyoku, Tokyo, Japan.
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ANALYTICAL CHEMISTRY
temperature have been discussed (2). Magnetic data for cupric oxinate dihydrate were determined on samples prepared by diluting isotopically pure Cue3 oxinate dihydrate with isomorphous zinc oxinate dihydrate (6). I n this report, we will discuss the EPR spectra of precipitates which are formed when oxine is added to a metal ion solution containing a small amount of C U + ion. ~ Cu hfs was observed for some precipitates, such as (Zn-Cu) oxinate, and not for others, such as (Ca-Cu) oxinate. The structures of metal oxinates, such as those of Zn and Cu, have been determined ('7-9) and it is established that the metal ions are located in sites about 5 A. apart from each other. Dipolar broadening by the nearest neighbors has an overwhelming effect in erasing the hyperfine structure. Exchange interactions among the C u f 2 ions, which can be produced in the coagulates of cupric oxinate, also smear out the hyperfine structure. Those two factors are the only reasonable mechanisms to account for the disappearance of hyperfine structure of the spectrum. Hence, a single line with a broad line width, which is very similar to that of many cupric salts, contains Cu+* ions which are closely packed-Le., in this case, the Cu-oxinate and the other metal-oxinate form different phases in the solid system. Whereas, a spectrum with hfs means that in the solid, Cuoxinate molecules are well separated and dipolar interactions are not sufficient to destroy the magnetic behavior of each Cu+* ion-Le., the Cu-oxinate molecules must be homogeneously d i s tributed throughout the solid, which means the formation of a mixed crystal. Mixed crystal formation is usually studied by means of x-rays. However, many metal oxinates are isostructural with Cu-oxinate, with similar lattice parameters (7-9). An x-ray analysis in such a case is obviously difficult. EXPERIMENTAL
Reagent grade chlorides, or nitrates of Cu, Zn, Cd, Hg(II), Ca, Ba, and other metals were dissolved in water, and concentrations were determined by titration with standard EDTA. Reagent grade Reagents.
oxine was dissolved in 3N acetic acid, or in ethanol. Solutions of 2.5% were used. Oxine was reacted with acetic anhydride for the preparation of acetoxine. The product was purified by recrystallizing from an isopropyl-ethern-heptane solution (II), and was dissolved in acetone a t a concentration of 2.5%. Apparatus. The E P R spectrometer used throughout this investigation is Model J E S 118 (X-band) manufactured by the Japan Electron Optics Co. Precipitation Procedure. Three different procedures, described below, were used in preparing the precipitate. USUAL PROCEDURE IN CHEMICAL ANALYSIS.Solutions, containing about 0.1 gram of metal ion with 1 atomic per cent of Cu, were diluted to about 500 ml., and warmed to 70'-80' C. A slight excess of an alcoholic solution of oxine was added, and the pH was adjusted with a buffer solution to allow the precipitation of the oxinate. The buffers used were acetic acid and sodium acetate for Zn, Cd, Hg, etc., and ammonium hydroxide-chloride for Mg, Cs, Sr, and Ba. The solutions were kept warm for a while, filtered, and the precipitates washed with warm water. According to Sekido (IS), cupric oxinate prepared by the above procedure is a mixture of two crystalline forms, monoclinic and tetragonal. ROOMTEMPERATURE PRECIPITATION TECHNIQUE. To a solution containing metal ion and cupric ion, an equivalent amount of oxine (solution) was added, and precipitation was completed by the addition of the appropriate buffer solution, without warming. Cu-oxinate, formed a t room temperature, consists of monoclinic crystals (IS). An x-ray powder analysis of Zn, Cd, Hg, and Mg-ouinates containing small amounts of Cu, prepared by the above procedure, showed structures similar to that of monoclinic Cu-oxinate. PRECIPITATION FROM A HOMOGENEOUS SOLUTION.To a solution containing metal ion and cupric ion, an acetone solution containing an equivalent amount of acetoxine was added. The pH was adjusted by the addition of the appropriate buffer solution, and the temperature was raised, and kept a t about 70" C. Usually precipitation appeared in several minutes, and was complete within 2 hours. 4 n x-ray powder analysis of these Zn, Cd, Hg, and Mg-oxinates containing Cu showed diffractions similar to that of monoclinic Cu-ouinate.
Figure 1.
EPR spectra of (Cu-Zn) oxinate precipitates containing various amounts of Cu Arrows indicate DPPH
Samples. Metal oxinate precipitates of Zn, Cd, Hg, and M g containing 1 , 3, 5, 7, 10, 15, and 20 atomic per cents of Cu, those of Ca, Si-, and Ba containing 3 and 10 atomic per cents of Cu, and those of Ag, Be, Al, Ga, I n , Y, Ce, Ni, and Co containing 3y0 Cu were prepared by the room temperature technique. Some were also prepared by the usual method. Precipitates of Zn, Cd, Hg, Mg, Ca, and Ba containing 3 and 10% Cu were prepared by the homogeneous precipitation technique. RESULTS AND DISCUSSION
Precipitates Giving EPR hfs. A typical example of spectra with hfs Zn oxinate with various amounts of Cu+* ions is shown in Figure 1. Up to about 20y0 Cu, hfs is clearly observable. This type of spectrum was obtained from the precipitates of the oxinates of Zn, Cd, Hg, and Mg which contained Cu, and were prepared by the first two methods. This shows, as mentioned before, the formation of a mixed crystal, or sclid solution of the above metals and Cu oxinates. The oxinates of Zn and Cd containing more than 7% Cu (sometimes) gave a spectrum of the type shown in Figure 2. This spectrum may be taken as a superposition of the spectra shown in Figures 1 and 3, namely the spectrum given by homogeneously and inhomogeneously distributed CufZions. Formation of this type of precipitate is attributed to the change in the conditions under which it is formed, because homogeneous precipitates, even 3y0 in Cu, gave spectra of the type shown in Figure 2 . I n these systems, the distribution coefficient, 1,defined as ?, = [log(l -fraction of Cu pptd.)]/[log(l -fraction of a metai pptd.)] is probably not equal to
Figure 2. oxinate
EPR spectrum of (Cu-Zn)
The arrow indicates DPPH
place either at the beginning, or at the end of the precipitating reaction. If the concentration of Cu is high in a metal oxinate, it gives an EPR spectrum similar to that of the pure Cu-oxinate. Magnetic parameters calculated using Zn-Cu-oxinates are given in Table I, together with those obtained for Cuoxinates (2, 6) and other Cu-compounds by other workers (26). I n calculating gl, the 80and AOvalues of Cu-oxinate were taken as 2.128 and 0.0068 cm.-l, respectively. These values were obtained from the central point and the separation of the quartet structure of the spectrum, respectively, which was taken for the Cu-oxinate dissolved in acetic acid. The All , A,, 811 , and gI values obtained from other metal Cuoxinates agree with the above values within the experimental error. CY*, a parameter of the covalency of the linkage between Cu and coordinated atoms introduced by Kivelson and Neiman (6), was calculated to be 0.84 by applying their equation, cy2
unity. Thus, it is quite possible that, with a homogeneous distribution of Cu in the solid, a concentration of Cu takes Table I.
=
+ (811 ("7)
(where P
= 2-yPoPN
+
- 2) (81 - 2)
+ 0.04
(7-90= 3.5 X
Values of g and A
Cu oxinateO (in Zn oxinate) This work Reference (6)
Cu oxinate in a frozen Cu-dimethyl Cu-salicylsolution(%) glyoxime (16) aldoxime (16)
2 . 12Sb 2.08 2.11 2.042 2.05 2.06 2.034 2.066 f 0.006 2.317 2.287 f 0.004 2.172 2.15 2.22 0.0025 0.0015 0.002 0.0030 f 0.0010 A , (cm.-') 0.0014 0.0171 f 0.0005 0.0162 0.0144 0.0163 A,, (cm.-I) 0.0164 gl, giI , and A are calculated using go. Values determined by direct measurements are gL 2.074, g,, 2.274, A,, 0.0164-l and m a = 0.810. A value determined for acetic acid solution of cupric oxinate.
go 91, Q ,
VOL. 38,
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10-2cm.-1 for CufZ ion). The value is very close to that given by Kokoszka et al. (6), a2= 0.820, and to those given by Kivelson and Neiman for cupric complexes-e. g., a 2 = 0.84 for EDTACu, 0.76 for 1-10 phenanthroline-Cuand shows the covalent nature of the bonding. Figures 4 and 5 show the E P R spectra of Hg-Cu-, and Mg-Cu-oxinate measured a t liquid nitrogen temperature. Both hfs, and super hfs is observed, the latter being due to the interaction of the unpaired electron of the Cu atom with the nitrogen atom. Chemically, it may be important that there is some difference between the two spectra. The difference suggests an environmental effect upon the magnetic behavior of the Cuoxinate molecule, and will be discussed in afuture publication. Precipitates Which Give Broad EPR Spectra. An EPR spectrum, typical of Ca-Cu-oxinate, is shown in Figure 3. Precipitates of Ca, Sr, Ba, Pb, and Ag-oxinate containing various amounts of Cu exhibit this type of spectrum, regardless of the technique used in preparation. The shape and g-values (g = 2.120) are identical with those of pure Cu-oxinate. This shows that in these oxinate precipitations, the Cu-oxinate and the other metaloxinate-e.g., Ca-oxinate-exist in different phases-Le., the precipitate is a mixture of crystalline C& and Cuoxinate. The Be, Al, Y, and Ce-oxinates containing 3% Cu exhibit slightly complicated spectra. These spectra consist of superpositions of a single, broad absorption, and a spectrum with hfs, suggesting
.
I
\II ,I y i
I
i
.:'
.,
..
i
.
:
:.
i._._-. ; . . I
,
.
:
!
!
(Cu/Ca = 10/90) The arrow indicates DPPH
limited solubilities of Cu in these oxinates. X-Ray Powder Analysis. X-Ray powder studies were carried out on a number of samples to establish the formation of mixed crystals. The main x-ray powder diffraction lines of Ca-(lO% Cu)-oxinate, and Be(3% Cu)-oxinate, both prepared by the room temperature technique, showed lines obviously belonging to the strongest diffraction of Cu-oxinate. This shows that the precipitates are mixtures of Ca- and Cu-oxinate, and
Be- (probably with a small amount of dissolved Cu), and Cu-oxinate, which are different from Ca-oxinate, precipitated from a homogeneous solution. The main x-ray powder diffractions of Zn-oxinate, Zn-(3% Cu)-oxinate, Zn-(15% Cu)-oxinate, and Cu-oxinate, all prepared by the room temperature technique, agree well and coincide with those indexed by Sekido (14). The similarities in the diffraction patterns of Zn- and Cu-oxinate make it difficult to discern a mixed crystal. Practically no difference was observed between the diffractions of Zn-oxinate and those of Zn-(15(ro Cu)-oxinate. Two conclusions may be drawn from this result: Cuand Zn-oxinate form a mixed crystal, or the superimposed spectra of Cu- and Zn-oxinate are being observed. X-ray powder diffractions of Mgoxinate, Mg-(3% Cu)-oxinate, and Mg(15% Cu)-oxinate, all prepared by the room temperature technique, showed similarity. However, the similarities in the diffractions of the end members prohibit any study of the formation of a mixed crystal in this system. Similar results were obtained for the Cd-Cu- and Hg-Cu-oxinate systems. The above results do not positively indicate the existence of a mixed crystal for Zn-, hIg-, Cd-, and Hg-Cu-oxinate; however, they do not deny the formation. Heat Treatment of Some Precipitates. To show that the x-ray powder diffraction patterns of Zn-Cuoxinate are not a superposition of Zn- and Cu-oxinate diffractions, the following experiments were undertaken. According to Sekido (14), when heated, Zn oxinate changes into the unhydrated form via an (x-ray) amorphous state. He suggested the following
Figure 4. EPR spectrum of (Cu-Hg) oxinate precipitate
Figure 5. EPR spectrum of (Cu-Mg) oxinate precipitate
(Cu/Hg = 3 / 9 7 ) a t liquid nitrogen temperature
(Cu/Mg = 1 / 9 9 ) a t liquid nitrogen temperature
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ANALYTICAL CHEMISTRY
oxinate precipitate and Mg-(lO% Cu)reasons. The coordination number of oxinate precipitate were heated and is 6, the Zn+2 in Zn(CQH60N)~.2Hz0 examined with x-rays. It waa clearly coordination polyhedron being octaheseen by the x-ray patterns that the dral; and in the unhydrated form, Znabove precipitates are almost com(C&ON)z, the coordination number of pletely amorphous after 2 hours of Zn+2 is 4, the coordination polyhedron heating at 150’ C. No diffraction from being tetrahedral. Therefore, when Cu-oxinate waa detected for the sample hydrated Zn-oxinate is heated, it treated at that temperature, suggesting changes form via an (x-ray) amorphous Cu+* ions are homogeneously distribstate. The same is true of Mg-oxinate. uted in the crystals. I n the case of Cu-oxinate, the lowtemperature form, C U ( C Q H ~ O N ) ~ - ~ H Z O (coordination number 6, octahedral), ACKNOWLEDGMENT changes directly to the high-temperaThe authors express their thanks to ture form, Cu(CaH60N)~(coordination Toshikatsu Sugiura and Nobutaka number 4,planar), upon heating without Yoshikuni for their help in the experipassing through an (x-ray) amorphous mental work. state. Therefore, if part of the copper in the Zn-Cu-oxinate precipitate exists as a coagulate in the cu(C6H~oN)z. LITERATURE CITED 2Hz0 state, it might be detected after (1)Fujiwara, S., ANAL. CHEM.36, 2259 the whole precipitate has been heated to ( 1964). 150’ C. or higher, and the Zn-oxinate is (2) Gersmann, H. R., Swalen, J. D., in the amorphous state. J. Chem. Phys. 36, 3221 (1962). (3) Hollingshead, R. G. W., “Oxine and According to the above, Zn-(lO% Cu)-
its Derivatives,” Vol. I, 11, 1954, III, IV, 1956 Butterworth, London. (4) Ishibashi, M.,Suito, E., Sekido, E., Ni p o n Kagaku Zasshi 78, 1784 (1957).
8.
(5) ivelson, D., Neiman, R., J. Chem. Phys. 35, 149 (1961). (6) Kokoszka, G. F.,Allen, H. C., Jr., Gordon, G., Zbid 42, 3730 (L)(1965). (7) Kruh, R., Dwyggns, C. W., J. Am. Chem. SOC.77, 806 (1955). (8)Merritt, L. L., Jr., ANAL.CHEM.25, 718 (1953). (9) Merritt, L. L., Jr., Cady, R. T., Mundy, B. W., Acta Cryst. 7, 473 (1954). (10) Motojima, K., “Shinbunsekikagakukoza,” Vol. 6, Kyoritsu, Tokyo, 1959. (11) Salesin, E. D.,Gordon, L., Talanta 4, 75 (1960). (12) Sekido, E.,Nippon Kagaku Zasshi 78, 1788 (1957). (13) Zbid., p. 1791. (14) Sekido, E.,Zbid., 80, 379 (1959). (15) Toyoda, K., Ochiai, K., Proc. Znt. Symp. Mol. Struct., Spectry. D211, Tokvo. -, 1962. - - - ~ (16)-%iersema, A. K., Windle, J. J., J. Phys. Chem. 68, 2316 (1964).
RECEIVEDfor review March 28, 1966. Accepted June 23, 1966.
Determination of Molecular Structure of Hydrocarbon Olefins by High Resolution Nuclear Magnetic Resonance FERDINAND C. STEHLING and KENNETH W. BARTZ Esso Research and Engineering
Co., Baytown, Texas
Comprehensive correlations of NMR chemical shifts, spin coupling constants, and characteristic spectral patterns derived from the spectra of 60 aliphatic hydrocarbon mono-olefins are presented. Examples of the use of these correlations in the proof of structure of oligomers of mono-olefins and polymers of di-olefins are given. Information concerning monomer sequence distribution and reactivity ratios for isobutylene-isoprene copolymers can b e derived from the detailed interpretation of the spectra of such copolymers.
T
HE PROOF of molecular structure of unknown compounds by high resolution NMR is greatly facilitated by a knowledge of chemical shifts and coupling constants obtained from compounds with related structures. I n the course of the analysis of some olefinic hydrocarbons it was found that the chemical shift and spin coupling constant data available in the literature were often insufficient for positive identification of an unknown compound. Some chemical shift data for
alkenes, alkadienes, and cycloalkenes have been presented previously by Chamberlain (6), Tiers (16), Reddy and Goldstein ( l a ) , and Francis and Archer (9). A comprehensive listing of chemical shifts and spin coupling constants in vinyl compounds has been given by Brugel et al. (6), and spin coupling constants of olefinic compounds have been given by Schaeffer (13) and Bothner-By et al. (4). We have now obtained the spectra of about 60 aliphatic hydrocarbon monoolefins of known structure and have summarized the data in the form of chemical shift charts and a spin coupling constant table. Characteristic NMR spectral patterns encountered in these compounds are also presented. The manner in which chemical shift correlations are applied in structural determinations has been described in detail by Chamberlain, and some applications of spin coupling constants have been discussed by Jackman (11). The utility of characteristic spectral patterns in structure determinations has been demonstrated by Rartz and Chamberlain (3). The data presented here have been very useful in establishing the structure
of oligomers of mono-olefins and high polymers of di-olefins. Several examples are given. EXPERIMENTAL
Procedure. SAMPLES. Spectra of approximately 60 pure aliphatic mono-olefinic hydrocarbons secured from the American Petroleum Institute or synthesized in this laboratory were run on a Varian A-60 high resolution NMR spectrometer. Care was taken to ensure the accuracy of the chemical shift scale by daily calibration using the audio sideband method or by running a sample whose chemical shifts had been previously ascertained using the sideband method. Chemical shifts were reproducible within 0.01 p.p.m. The samples upon which the chemical shift correlations are based were run as the neat liquid or in carbon tetrachloride solution (5 to 50 volume hydrocarbon) with approximately 1% tetramethylsilane (TJIS) added as an internal standard. The unknown samples whcse structures were determined in this study were (1) a dimer of 3-methylbutene-1 that was separated from other reaction products by gas-liquid chromatography (GLC), (2) a dimer of 2-methylpentene-1 that was also purified by GLC, VOL 38, NO. 1 1 , OCTOBER 1966
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