A1 COMPLEXES IN SOLUTION AS STUDIED BY 27AlNMR
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Dr. G. H. Nancollas, State University of New York a t Buffalo, for advice in constructing the calorimeter;
and the National Aeronautic and Space Administration for a fellowship to D. P. F.
Aluminum Complexes in Solution as Studied by Aluminum-27 Nuclear Magnetic Resonance by Hiroki Haraguchi and Shizuo Fujiwara Department of Chemistry, Faculty of Science, The University of Tokyo, Bunkyo-ku, Tokyo, 218, Japan (Received April 3,1969)
Aluminum-27 magnetic resonance of various aluminum complexes has been observed in solution. Aluminum27 in octahedral complexes shows chemical shifts about 100 ppm higher than *'A1 in tetrahedral complexes. Each type of complex shows a slightly different chemical shift depending upon ligand atoms directly bonded to the metal. Iodo complexes of the type A1Ld are exceptional, showing chemical shifts similar to octahedral complexes. Mixed complexes of the type AlX3L (X = C1, Br; L = (C2H&O, Cd&) give signals a t fields intermediate between octahedral and tetrahedral ones. The line widths are mainly determined by the quadrupole interactions and reflect the symmetry of complexes in solution. Chemical shifts are used along with line widths to identify the chemical species produced by dissolving anhydrous aluminum halides in various organic solvents. I n addition, a sequence of the affinities of the ligands to the aluminum ion has been determined as follows: CzHaNCS> CeH6CN> CH2=CHCN > CH3CN. H 2 0 > CzH60H,C3H70H>> C1, Br, I
2
Introduction Aluminum-27 nuclear magnetic resonance (nmr) has been used to investigate aluminum complexes in solution. l-5 O'Reilly interpreted the structure of several complexes in solution, using line width data. Recently, various octahedral and tetrahedral aluminum complexes have been proved to exist in solution by 'H and ?'A1 nmre6-l0 However, the chemical-shift data have not been used for discussions of the symmetry of the chemical species which exist in solution. I n the present work, chemical shifts and line widths are measured for aluminum complexes in various solvents. These data are used along with those reported previously to discuss the symmetry and structure of aluminum complexes in solution. Experimental Section Spectra of 27Alnmr were observed at 6.1403 and 13.557 MHz using a bridge-type spectrometer constructed in this laboratory. Magnetic field strength was measured by proton resonance, and the sweep field was calibrated using a side-band technique. A slightly acidic aqueous solution of aluminum perchlorate was employed as an external standard of the chemical shift. All measurements were carried out at 2.5'. All chemicals used are of reagent grade. Trisacetylacetonatoaluminum, Al(acac)a, and potassium tri-
oxalatoaluminate were prepared by the usual methods,11*12 and they were recrystallized from benzene and water, respectively. Hexaaquoaluminum ion was obtained by dissolving aluminum salts in the acidified water of pH -1. An aqueous solution of aluminate ion was prepared by mixing an aqueous solution of aluminum sulfate with an excess amount of potassium hydroxide. Aluminum isopropoxide, Al(i-PrO)s, was dissolved in n-hexane, and lithium aluminum hydride in diethyl ether. Other samples referred to in Table I were prepared by dissolving anhydrous aluminum (1) D.E.O'Reilly, J. Chem. Phys., 32, 1007 (1960). (2) H.E.Swift, C. P. Poole, Jr., and J. F. Itael, Jr., J. Phys. Chem., 68, 2509 (1964). (3) E.M.Dicalro and H. E. Swift, ibid., 68,651 (1964). (4) C.P.Poole, Jr., H. E. Swift, and J. F. Itzel, Jr., J. Chem. Phys., 42,2676 (1965). (6) H. E. Swift and J. F. Itzel, Jr., Inorg. Chem., 5, 2048 (1966). (6) M'. G. Mouvius and N. A. Matwiyoff, Inorg. Chem., 6, 847 (1967). (7) 8. Thomas and W. L. Reynolds, J. Chem. Phys., 44,3148 (1966). (8) A. Fratiello, R. E. Lee, V. M. Nishida, and R. E. Shuster, ibid., 47,4951 (1967). (9) J. F. Hon, Mol. Phye., 15,57 (1968). (10) R. C. Kidd and D. R. Truax, J . Amer. Chem. SOC.,90, 6867 (1968). (11)Inorg. Hun., 1, 36 (1936). (12) Inorg. Syn.,2, 226 (1946). Volume 78,Number 10 October 1969
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HIROKI HARAGUCHI AND SHIZUO FUJIWARA
Table I : The Results of Z'Al Nmr Chemical Shift and Line Width Complex
Solvent (oonon)
AlL6 Type Complex Acidic aq soln (0.2-1 M ) Benzene (satd) Water (satd) n-Hexane (satd) benzene Ethanol (0.3-1 M ) n-Propanol (0.3-1 M ) Acetonitrile" Acrylonitrile' Benzonitrile" Ethyl isothiocyanate' LiAlH4 A1(OH ), AlzCla
AlBr4-
A& Type Complex Diethyl ether (satd) Alkaline water ( 0 . 5 M ) Diethyl ether (2 M ) Tetrahydrofuran Ethyl isothiocyanate Diethyl ether (1.5 M ) Diethyl ether (1.5 M ) Acetonitrile' Acrylonitrile Acetonitrile' Acrylonitrile Benzonitrile Ethyl isothiocyanate Acetonitrile' Acrylonitrile Benzonitrile Ethyl isothiocyanate Diethyl ether (cf. case 11) Diethyl ether (cf. case 11) Benzene (satd) Benzene (satd) Tetrahydrofuran (satd) Tetrahydrofuran (satd) Acetyl chloride (satd) Benzoyl chloride (satd) Thionyl chloride (satd) n-Heptane (N 1 M )
Chemicala
Line width,b
shift, ppm
Hz
O(ref) NO N O -0 N O -0 34 33 46 -20
- 100
-80 - 105 -95
40 93 125 90 70 70 73 83 100 58 420 60-100 126
-40 - 102
104 81 33
- 80
35
28
58
- 50
- 77
160 210 510 800 1550 1700 166 2000
< - 150
500 2750
-47
- 75
23
- 97
a The chemical shifts are defined asfollows: S = [ ( H o- H,)/H,] X loB(ppm) where H,is the magnetic resonance field (5532.56 G at 6.1403 MHz) for Al(H@)eS+,and H,is the resonance field for the complexes for which S is given. Estimated accuracy, &3 ppm. The line widths refer to the values after field inhomogeneity correction. Estimated accuracy, A 5 Hz. 'Concentrations of these samples are shown in Table 11.
'
halides in the solvents 1 i ~ t e d . l ~Concentrations of these samples are given in Table I.
Results and Discussion The aluminum-27 chemical shifts and the line widths observed are summarized in Table I. As can be seen from Table I, the hexacoordinated complexes of the type AlLa, where L is the ligand, give chemical shifts which are rather different from those for tetracoordinated complexes, AlL4, ie., -21-36 ppm for AIL6 and - 150 to -80 ppm for AlL4. However, chemical shifts for AIL4-type iodo complexes are exceptional, and are The Journal of Physical Chemistry
-40 to 30 ppm. Chemical shifts for several mixed complexes of the type AlLSL', where L refers to C1, Br, and I, and L' to (CzH&O, CaH6,and C4H80,are -75 to 25 ppm. There is a small but significant difference in the chemical shifts among Aloe, AlNs, and AlSe type complexes. Since the line width for the system studied in the present investigation is mainly determined by the quadrupole interaction, l4 it may be qualitatively ex(13) Contamination of impurities such as water and peroxides in the organic solvents is assumed negligible, because no proton resonance signals which correspond to these impurities have been observed.
A1 COMPLEXES IN SOLUTION AS STUDIED BY 27AlNMR
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Table I1 : Z'Al Nmr Results for the Solutions of Aluminum Halides in Acetonitrile, Acrylonitrile, Benzonitrile, and Ethyl Isothiocyanate Compound
AlCla
AIBrs
Solvent (concn)
Acetonitrile ( 1 - ~ 2M) Acrylonitrile (-1.5 M ) Benzonitrile ( ~ 1 . M) 5 Ethyl isothiocyanate (satd ~2 M) Acetonitrile ( ~ 1 .M 5) Acrylonitrile (-1.5 M) Benzonitrile (Nl.5M ) Ethyl isothiocyanate (-1.5 M) Acetonitrile (satd) Acrylonitrile (satd) Benaonitrile (satd) E thy1 is0thiocyanat e (satd)
Complexes obsvd in s o h
Al(CH3CN)s' + AlClrAl(CHz=CHCN)s'+ AIClrA1(CaHaCN)aS+ AlClrA1,Cla AliCla
Chemical shift, ppm
25
- 108 33
- 105 32 - 103 - 105 1105
A1(CHaCN)sS+ AIBrrAI(CHB=CHCN)E' A1Br4AlBr4-
+
AlBr4Al(CHaCN)aa+ A&Al(CH*=CHCN)s* + A&A1(CsH&N)sa + A114 A1(CzHaNCS)a8+ A&AMe
34
Line width,
Hz
225 33 70 32 155 (30)' 200' 100
Intensitya ratio
-1/5 -J1/10
. . .b
...
