FAR-INFRARED SPECTRAOF TETRAHALO METALCOMPLEXES
Jan. 5 , 1964 [CONTRIBUTION FROM
THE ISTITUTO DI
CHIMICA GENERALE E
INORGANICA,
UNIVERSITA'
DI
17
FIRENZE,FIRENZE, ITALY]
Far-Infrared Spectra of Some Tetrahalo Metal Complexes BY A. SABATINI AND L. SACCONI RECEIVED AUGUST30, 1963 The far-infrared spectra (400-70 cm - l ) of twenty-seven tetrahedral tetrahalogenmetallates( 11), R 2 [ M X 4 ] ( R = univalent organiccation, M = M n ( I I ) , F e ( I I ) , C o ( I I ) , Ni(II), C u ( I I ) , Z n ( I I ) , X = C1-, Br-, I - ) , have been examined In the chloro and bromo compounds t h e two infrared active fundamental vibrations of the FP species ( v g and v 4 ) were observed, whereas in the iodo cornpounds only the vg appeared in the spectra Owing t o the distorted symmetry, a splitting of the absorption hands was observed in the copper(I1) compounds The vibration frequencies of the [ZnCI4]2 - and [ZnBr4]% - ions have been calculated using a simplified ionic model The agreement between the calculated and observed frequencies is satisfactory
Introduction During the last few years a considerable number of salts of tetrahedral tetrahalogenmetallates, R2 [MXI] (R = univalent organic cation; M = bivalent first row transition metal; X = C1-, Br-, and I-), have been prepared and characterized. 1 , 2 Extensive studies of their magnetic and spectral properties, as well as some X-rays investigations, have also been recently reported. We have now measured the far-infrared spectra of a series of these complex salts (with R = tetramethylammonium, (Me4?J)+, tetraethylammonium, (Et4N)+, and tetra-n-propylammonium, (nP r 4 N ) + ; M(I1) = Mn, Fe, Co, Ni, Cu, Zn; X = C1-, Br-, I - ) , with the aim to observe their vibrational frequencies and to determine, if possible, which of the complex anions have a regular and which a distorted tetrahedral configuration. When the present research was nearly completed, two papers appeared which reported the infrared spectra of ~ inorganic complex halides down to 190 ~ m . - l , and assigned the metal-chlorine and metal-bromine stretching vibrations. In our investigation, extended down to 70 cm.-l, we were able to observe also the metaliodine stretching vibrations, as well as the X-M-X bending vibrations. In addition, we calculated the vibrational frequencies of the [ZnCl4I2- and [ZnBr4I2ions on the basis of an ionic model involving nonpolarizable charged spheres interacting with repulsive forces of the Lennard-Jones type. Experimental The tetramethyl- and tetraethylammonium salts were prepared according to the literature',%by mixing anhydrous ethanol solutions of the metal halides and tetraalkylammonium halides. The tetra-n-propylammonium salts, which in general cannot be easily crystallized from their ethanol solutions, were prepared using isoamyl alcohol or sec-octyl alcohol as solvents, except for (n-Pr4X)2[ZnBr4] which separated from ethahol, and for (nPr4N)2[FeBr4] and (n-Pr4N)z[Fe14]which were obtained from their ethanol solutions by dilution with ethyl acetate in a nitrogen atmosphere. The compounds (Me4N)z[NiC14] and (n-Pr4N)~[CuBra]could not be obtained in a sufficiently pure state. The analytical data for the investigated compounds are listed in Table I . T h e infrared spectra were taken with a Perkin-Elmer 301 double beam spectrophotometer, employing h'ujol mulls supported on polyethylene windows. The 4OC-70 cm.-' region was investigated.
Results and Discussion The frequencies of the absorption bands of the complex salts R2[MX4]are listed in Table 11. The spectra of the corresponding tetraalkylammonium halides, RX, were also measured for comparison and are listed in Table 111. The absorptions observed in the spectra of (1) N . S . Gill and R . S . Nyholm, J . Chcm. S O C . 3997 , (1959). (2) N. S . Gill, ibid., 3.512 (1961); C. Furlani and G. Morpurgo, 2 . physik. Chem. (Frankfurt), 18, 93 (1961); D.M.L. Goodgame, M. Goodgame, and F. A. Cotton, J . A m . Chem. S O C . 89, , 4161 (1961); F. A. Cotton, D. M. 1,. Goodgame, and M. Goodgame, i b i d . , 8S,4690 (1961). (3) B. Morosin and E. C. Lingafelter, Acta Cryst., 19, 611 (1959); B. Morosin and E . C. Lingafelter, J . Phys. Chent., 66, 50 (1961). (4) R.J . H . Clark and T. M . Dunn. J . Chem. Soc., 1198 (1963); D. M. Adams, J , C h a t t , J , M. Davidson, and J. Gerrat, i b i d . , 2189 (1963)
TABLE I ANALYTICAL DATA -Metal, Calcd
15 16 16 17 18 12 12 12 12 13 13 8 8 9 9 9 10 7 7 7 7 8 5 5 6 6 6
92 15 89 97 39 01 19 78 73 63 97 65 i8 22 18 87 13 35 46 84 83 63 87 96 27 25 92
RFound
-Halogen, %- -Nitrogen, %Calcd. Found Calcd. Found
15 80 16 31 16 79 17 89 18 49 11 92 12 17 12 76 12 i 2 13 46 13 80 8 55 8 37 9 03 9 13 9 88 10 04 7 15 7 30 7 74 7 68 8 51 5 85 5 81 6 13 6 48 6 84
41.10 41.00 40.63 40.10 39.89 31.02 30.96 30.75 30.76 30.44 30.32 50.33 50.25 50.02 50.04 41.66 49.52 42.78 42.72 42.55 42.56 42.19 54.28 54.22 54.05 54.06 53.68
41.01 40.81 40.49 40.03 39.75 31.10 30.89 30.66 30.64 30 19 30.27 50 30 50.34 49.90 49.81 49.52 49.30, 42.30 42.35 42.47 42.05 42.09 54.38 54.54 53.90 53.61 53.58
6.13
6.30
6.07 6.08 6 . 0 1 5.89 5.99 5 96 4.41 4.20 4.38 4.21 4 . 3 9 4.23 4.34
4.40
the tetraalkylammonium halides, RX, cannot correspond to internal vibrations of the organic cations, for they are considerably shifted toward lower wave numbers as the atomic weight of the halide ion increases. We attribute these absorptions to lattice modes. The frequencies listed in Table I1 are assigned to vibrations of the tetrahalogenmetallate ions, as confirmed by the fact that salts of the same anion with different cations have approximately the same absorptions. To predict the number of infrared active fundamental vibrations of molecules or ions in crystals, it is sufficient in general to know the space group of the crystals and the number of molecules per unit ceN5 Of all the compounds investigated by us, only (Me4N)*[COCI~],(Me4N)2[CuC14], and (Me4N)2[ZnClr] have known crystal structure^.^ They belong to the space group Di!-Pnma, with four molecules per unit cell. The site symmetry a t the metal ion is C,. The [CoC14I2- and [ZnClrI2- ions have an almost perfect tetrahedral structure, the four M-Cl distances being identical within experimental accuracy, and the bond angles being very close to the tetrahedral value of 109' 28'. The [ C U C ~ ~ion, ] ~ -on the other hand, is a flattened tetrahedron, the four Cu-Cl distances being almost (5) D.F. Hornig, J . Chem. Phyc. 16, 1063 (1948); H . Winston and R . S. Halford, ibid., 17,607 (1941);
A. SABATINI AND L. SACCONI
18
TABLE I1 FAR-INFRARED ABSORPTION FREQUENCIES (CM. -I) Compound
Assignment
Mn
va (M-CI stretching)
(MeJWMCLI
Fe
OF
Vol. 86
Rz[MXa] COMPOUNDS
co
Ni
cu
281 s 237 m 145 w 128 vw
284 s
284 s
296 s
123 m
126 m
131 m
(CI-M-CI bending) or lattice vibration
79 w
81 w
85 w
va (M-CI stretching)
284 s
286 s
297 s
289 s
v( (CI-M-C1 bending)
118 m
119 m
130 m
112 m
vz (CI-M-C1 bending)
78 w
77 w
82 w
79 m
v4 v2
(CI-M-CI bending)
83W 267 s 248 sh 136 sh 118 m 77 w
Zn
276 s 133 m 84 w
277 s 130 m 80 w
or lattice vibration va (M-Br stretching)
V,
221 s
(Br-M-Br bending)
85 m
va (M-Br stretching)
216 s
219 s 84m 215 s
231 sh 224 s
216 s 174 m
207 s
91 m
83 m
85 w
92 m
230 sh 222 s
228 sh 219 s
231 s
206 sh 199 s
(n-PrLWMBrd v4
( n - PrdN )2 I MI41
81 m
(Br-M-Br bending)
v8 (M-I stretching)
185 s
TABLE 111 FAR-INFRARED ABSORPTION FREQUENCIES (CM. - l ) TETRAALKYLAMMONIUM HALIDES
OF
(Me4N)CI
(Me4N)Br
(EtrNICI
(Et4N)Br
(n-PrcN)Br
(n-PrrN)I
115 m 83m
98m
