STEREOCHEMISTRY OF AMINEOXIDEMETALCOMPLEXES1535
Vol. 7 , No. 9, September 1968
1995 (m), and 1985 (w) cm-', which resemble the carbonyl bands for 1. An absorption a t 721 cm-' is assignable to the N-S stretching band. Two absorptions a t 755 and 682 cm-' are the CH out-of-plane deformation bands for the monosubstituted benzene. I n the far-infrared region were observed absorptions a t
CONTRIBUTION
642 (m), 617 is), 583 (s), 561 (s), -475 (w, b), 445 (w), and 397 (w, b ) cm-'.
Acknowledgments*-we are indebted to Fuji PhotoFilm CO.for partial financial support.
DEPARTMENTS O F CHEMISTRY O F THE UNIVERSITY O F MANCHESTER INSTITUTE O F SCIEh'CE TECHNOLOGY, MANCHESTER, ENGLAND, A N D YORKUNIVERSITY, DOWNSVIEW, ONTARIO, CANADA
FROM THE
AND
Some Aspects of the Stereochemistry of Amine Oxide Metal Complexes BY W. BYERS,'" A. B. P. LEVER,lb AND R. V. PARISH1*
Received April 11, 1968 Vibrational and electronic spectra and magnetic d a t a are correlated to show that complexes of the type M(R-PyO)~n+(C1Od), (R-PyO = pyridine N-oxide or a substituted derivative) do not have octahedral (Oh) symmetry. Similarly the copper com plexes C U ( R - P ~ O ) ~ ( C I O do~ )not ~ have D4h symmetry. T h e argument employs d a t a from the literature as well as some novel vibrational (infrared) and low-temperature electronic spectroscopic data. A new five-coordinate derivative Co(2CH3PyO)s(C104)2 (2-CH3Py0 = 2-picoline K-oxide) is characterized.
Complexes of type MLsn+, where L is a polyatomic monodentate ligand, generally have electronic, vibrational, and magnetic properties close to those anticipated for an octahedral complex even though such a molecule will not, in general, belong to the point group O h . 2 The efective symmetry of the molecule is determined not only by the geometric site symmetry of the ion but also by the electronic symmetry, governed by the degree of interaction between the metal ion wave functions and the ligand wave functions. This is particularly marked with bidentate ligands where the properties of species such as MLsn+, where L is an unsaturated molecule such as bipyridyl, deviate considerably from octahedral behavior ;3 with saturated systems such as ethylenediamine, the deviation is very much ~ m a l l e r . ~Pyridine ,~ N-oxide and its substituted derivatives are known to react with a wide range of metal ions forming complexes of considerable current i n t e r e ~ t . ~ ~ ~ This ligand appears to be one of the very few monodentate ligands whose hexakis complexes have properties indicative of a marked variation from regular octahedral symmetry. This variation from the expected octahedral behavior is the main topic of discussion in this paper During the course of our investigation a novel five-coordinate cobalt(I1) complex of 2picoline N-oxide was synthesized. This is also discussed.
(1) (a) Department of Chemistry, University of Manchester I n s t i t u t e of Science a n d Technology, Manchester, England; (b) Department of Chemist r y , York University, Downsview, Ontario, Canada. (2) C. K. Jgrgensen, "Absorption Spectra a n d Chemical Bonding i n M e t a l Compounds," Pergamon Press, Inc., New York, N. Y . , 1960; C. K. Jdrgensen, Advan. Chem. Phys., 5 , 33 (1963). (3) K . A. Palmer a n d T.S. Piper, Inovg. Chenz., 6 , 364 (1966). (4) R . Dingle, Chem. Commun., 304 (1965). (5) K . G . Garvey, J. H. Kelson, a n d R. 0. Kagsdale, Coovd. Chem. Reu., in press. (6) M . Orchin and P . J. Schmidt, ibid., i n press.
Experimental Section Electronic diffuse reflectance spectra were recorded with a Beckman DK2A instrument. T h e low-temperature transmittance spectra were obtained, b y the method outlined b y Rowley and Drago,' using a Cary 14 instrument. Vibrational spectra were recorded with Perkin-Elmer Models 21 and 257 spectrophotometers. Magnetic moments were determined using the Gouy method with a 1.5-in. pole piece Newport electromagnet. Mercury tetrathiocyanatocobaItate(I1) was used as calibrant. T h e new complexes reported in this paper were prepared by the following general technique. T h e metal salt (1 g ) and the ligand (1 g ) were each dissolved in hot alcohol (20 ml). T h e solutions were filtered and mixed. T h e mixture was then kept a t 0' for 24 hr. T h e products were recrystallized from the same solvent, washed with diethyl ether, and dried under reduced pressure. Table I lists the analytical data and also the alcohol (methanol or ethanol) used for each synthesis. In the case of the complex F ~ ( ~ - N O Z P ~ O ) ~ (1Cg~ each O~)Z of the metal salt and ligand were refluxed in ethanol (10 ml) for 5 min. Note: This complex may detonate and care should be taken in handling it. T h e other complexes described here were not observed to be liable to explosion. T h e unusually intense color of this complex and of the corresponding manganese(I1) complex is due t o the presence of a relatively low-energy charge-transfer band and t o the absorption of the -NO2 group. T h e detailed nature of the charge-transfer absorption in pyridine N-oxide metal complexes, which has been briefly commented upon,* is the subject of a future paper.g T h e five-coordinate complex Co(2-CH3Py0).,(CIO4)~ was prepared using a total of 25 ml rather than 40 ml of solvent as in the general method. Prolonged cooling a t 0" is required t o induce crystallization. This cobalt complex has a conductivity of 207 mhos mol-' cm-2 a t an approximately 5 X 10-5 M concentration in nitromethane. This may be compared with the conductivities of (CzH5)4NCBr- and C O ( ~ - C H ~ P ~ O ) ~ ( C ~ O ~ ) ~ being 127 and 206 mhos mol-' cm-z a t similar temperature and concentration, in nitromethane. A value of about 200 mhos mol-'
L). A. Kowley a n d R . S. Drago, I?zovg. Chem., 6, 1092 (1967). ( 8 ) W. Byers a n d A. B. P. Lever, 153rd National Meeting of t h e Arneiican Chemical Society, Miami Beach, F l a . , April 1967, Abstract L106. (9) W. Byers, A. B. P. Lever, a n d R. V. Parish, t o be submitted for publication.
(7)
1836 W. BTERS,A. B P.LEVER,.IND K.V.PARISH
Jnoqiinic Chemistry
TABLE I EXPERIMEUTAL AND ANALYTICAL DATA
___ ? C_-__
Solvent"
COIO~
Calcd
Found
t/G AT----,
Cyo H .-__
,c
Complex"
Calcd
Found
Calcd
~..
,
mcthj~
~
Found
Calcd
I'ound
Pink 40.7 41 0 5.4 3 . 7 9.5 9.7 Pink 47.4 4T 1 4.6 9.3 6 7 ij,ii 4.8 9 25 1.iolet 45.0 35.5 4 4 5 0 8.i5 8.9 7 35 T,:3 40.8 4.3 8.0 8 25 9.1 9 2 40.8 4.4 Blue Blue 44 1 44.8 4 8 4.9 7.4 7.4 8 4 8.4 C U ( Z , ~ , ~ - ( C H ~ ) ~ P ~ O ) ~ ( CB~ O , IGreen )~ 47 5 47.2 5 4 5.7 6.9 6.6 7.8 '7 7 Mi1 (4-SOgPyO)e(C104)2 d Bright red 32.6 32.6 2.2 2.4 15.3 15.1 5,0 5 1 ?vIn(4-CH3PyO)B(C104)2 A Yellow 4i.5 47.6 4 4 4 7 9 25 51.5 3.8 ti.1 Fe(4-SO2PyO je(C104)2 A Black 32.8 32.6 2.7 2.7 15.9 15,8 Xbbreviations: 2-CHIPy0, 2-picoline S-oxide; 3 - c H ~ P y 0 ,3-picoline S-oxide: 4-CH8PyO. 4-picoline S-oxide A-CH,Ol'yO. 4-methoxypyridine S-oxide; 4-SOzPy0, 4-nitropyridiiie S-oxide; 2,6-(CH1)zPy0, 2,B-Iutidine S-oxide; 2,4,6-(CHJ)jI'yO, 2,4,6-collidine K-oxide, Solvent used in preparation: A , ethanol; B, methanol. A c o (PYO) a 1 2 X Co(3-CH3Py0)6(C104)2 A COI2-CHgPy0)5( C10.i): C U ( ~ - C H ~ P ~ O ) ~ ( C ~ O ~ )B~ C ~ i 2 , 6 -CHI)zPyO)&(Cl01)a ( B
~
c i ~ i -a~t infinite dilution in nitroinethdrie is fully consistent the presence of a 1 1 electrolyte.'"
M it11
Results and Discussion Six-Coordinate Complexes. Electronic Spectra.The complexes (PyO)&fn+would have O h symmetry if only the metal to oxygen bonds are considered. However the electronic spectra of the chromium(lII), nickel(II), and cobalt(I1) complexes provide definitive evidence of symmetry lower than Oh. The first absorption band in complexes of Cr(II1) and Ni(I1) corresponding to the transition TLg+ A, is split into a t least two components (Table 11) revealing that the TABLEI1 ELECTROXIC SPECTROSCOPIC DATA'$(24,000-4000 Complex
Temp. 'C ,---Electronic
spectra, cm-1-
15.150, (17,700), (21,300), 23,260 - 196 15,400, 1 i , 6 5 0 ,22,200, 23,250 Co(PyO)a(Cloa)l.h (7250), 8300, 17.700, (18,390), (20,410) -1Y6 7280, 8333, 17,950, 18,870, 20,000 (7250), 8600, 18,600, (21,300) Co (8-CH~PyO)s(CIO~)r (74001, 8475, (12,5001, 14,200 Ni(4-CH3PyO)a(ClOi)z" - 196 (72801, 8060, 9000,(12,330), 13,800, 14,500 Cu(P,.O)a(CIOa)2~ (9615), 12,230 -196 10,150 12.900 Cu(Pyo)a(CIo&)?~ 14,800 b d CU(~-CH~P~O)I(CIO~)? 14,900b Cu(2,6-(CH3)2PyO)r(ClO~)~ 15.550 b Cu(2,~,6-(CH3)aPyO)4iClOi). 16,700 b Fe(l-NO~Py0)6(CIO~)? 7700,9100 Co(2-CH3PyO)s(C10a)~r (11,430), 12,660 i,lU), 1E,100 (561, (20,000) -196 (11,480), 12,i'30, (15,330 w ) , 18,590, (26,670) \ CI-(P?.0)8(Cloa)8h
0 Room-temperature data were recorded as diffuse reflectance spectra; low-temperature data mere obtained by transmittance through S u j o l mulls. * Agreement with previously reported" room-temperature data is good. Shoulders in parentheses. In CHISOy. b = broad.
degeneracy of the T2gstate has been lifted, almost certainly by a lower symmetry component of the ligand field. The splitting, which had been noted previously" but not discussed, is resolved into two distinct peaks a t - 196'~ The second absorption band, Tl,(F) + As,in Oh,is also split (Figure 1). TVe have already observed that monodentate poly(10) A. B. P. Lever, J. Lewis, and I
