Volume 17 Number 12
Inorganic Chemistry
December 1978
0 Copyright 1978 by the American Chemical Society
Contribution from The School of Chemistry, University of Melbourne, Parkville 3052, Australia
Characterization of Binuclear ,u-Peroxo and p-Superoxo Cobalt(111) Amine Complexes from Raman Spectroscopy COLIN G. BARRACLOUGH, GEOFFREY A. LAWRANCE,* and PETER A. LAY Received February 21, 1978
The Raman spectra of a range of binuclear p-peroxo and p-superoxo cobalt(II1) complexes with principally amine donor ligands in other coordination sites have been measured in the characteristic 0-0 stretching regions. Monobridged ,u-peroxo complexes exhibit a strong resonance Raman band in solution or as solid-state pressed disks at 800 A 10 cm-I and monobridged psuperoxo complexes a band at 1120 f 10 cm-I in solution. These vo2 are generally far stronger than other vibrations of the complexes. Binuclear dicobalt complexes with a second phydroxo or p-amido bridge in addition to the p-peroxo or p-superoxo bridge exhibit relatively weak and generally broad vot bands. Dibridged pperoxo complexes exhibit the 02- stretch at 812 f 5 cm-' in solution and 820 i 10 cm-' in the solid state, while dibridged p-superoxo complexes exhibit the 02-stretch at 1075 f 10 cm-I. The observation of strong Raman bands near 795 cm-I for complexes of the macrocyclic (Me6[14ldiene) and 5,12-dimethyltetraamines 5,7,7,12,14,14-hexamethyl-l,4,8,11-tetraazacyclotetradeca-4,11-diene 1,4,8,1l-tetraazacyclotetradeca-4,11-diene (Me2[14ldiene) supports their characterization as monobridged p-peroxodicobalt(II1) complexes and indicates that Raman spectroscopy is useful in the characterization of new binuclear dioxygen complexes.
Introduction Reports of the presence of coordinated peroxide (Oz2-)or superoxide (01)in several oxygen-transport proteins detected by the application of Raman and infrared (IR) spectroscopic techniques have appeared in recent years.'-) Suggestions of oxygen bridging of metal centers in hemocyanin and hemerythrin4 has prompted investigations of the vibrational spectra of readily prepared binuclear cobalt(II1) amine complexes with peroxo and superoxo bridges, since these may be appropriate simple model compounds for complex biological systems. Assignment of the 0-0 stretching frequency has not been clearly established in the I R spectra of p-peroxo-dicobalt c ~ m p l e x e s ~but - ~ is generally accepted to lie in the 800900-cm-' range. Subsequently, however, strong characteristic frequencies in the Raman spectra of both p-peroxo- (near 800 cm-') and p-superoxo- (near 1100 cm-I) dicobalt compounds with ammine, polyamine, and cyanide ligands have been reported.8-'0 Further, we have recently reported the observation of a strong 0-0 stretch in the Raman spectrum near 800 cm-I of a p-peroxo-dicobalt complex with a macrocyclic tetraamine." The reactivity of molecular oxygen with cobalt(I1) complexes has been extensively studied and Solutions of simple cobalt(I1) salts and amine ligands readily oxidize a t room temperature producing characteristically brown p-peroxo binuclear cobalt(II1) complexes. A wide range of monobridged complexes L5Co-02-CoL5"+(n = 4 for neutral ligands L) and dibridged complexes
X
(m = 3 for neutral ligands L) with additional'p-hydroxo or 0020-1669/78/ 1317-3317$01.OO/O
p-amido bridges have been reported. Further oxidation of these diamagnetic p-peroxo-dicobalt complexes with oxidants such as C12 or Ce4+ produces an analogous range of paramagnetic p-superoxo-dicobalt complexes. Despite the extensive chemistry reported for these complexes, only a limited number of dioxygen complexes have been studied by Raman spectroscopy.8-' Since bridged dioxygen complexes would seem to be readily characterized by the observation of an 0-0stretch in their Raman spectra, we have measured the Raman spectra of a large number of aminedioxygendicobalt complexes in t h e characteristic 0-0 stretching regions in both solution and solid states. We present the results of our investigation in this report.
Experimental Section Preparation of Complexes. Monobridged p-peroxo-dicobalt complexes of the general formula L5Co-02-CoL5"+ were prepared (NH,),(dien),25 by previously published methods for L5 = (NH3)5,22-24 (NH~)(!J:)z?~(NHd(tn)~?'(NH3)(bn)2?5( ~ n ) ( d i e n ) ?(tn)(dien),25 ~,~~ (dien) 2, (bn) (dien) ,25 (NH,) (trien),26 (NH,) (en) 2,27(tetren) ,27 (OH2)(Me2[14]diene),25 (SCN)(Me2[14]diene),25 (",)(Me6[ 14]diene),z5(DMF)(salen),% hi^)^,^^ and ( h m ) , ? ~ Common ~~ ligand abbreviations are used.31 Dibridged p-hydroxo-p-peroxo complexes of the general formula L4Co-(O2)(0H)-CoL?+ were prepared by previously published and (tn)2.2s methods for L4 = (NH3)4,32(en)2,33 The p-superoxo analogues of several of the p-peroxo-dicobalt complexes were prepared in solution but not isolated, as previously de~cribed:~by oxidation in dilute perchloric acid solution with chlorine. Measurement of Raman Spectra. Raman spectra were measured with a Spex Ramalog 5 laser spectrophotometer using Ar+ excitation generally at the 5145-A excitation over the region 700-1200 cm-I. The sample as either a pressed disk or an aqueous solution was spun at approximately 1200 rpm in a rotating disk holder or glass solution cell, respectively, to minimize decomposition by the laser beam. Solution samples of p-peroxo-dicobalt complexes of typically 5-mM concentration were prepared and chilled in ice prior to spectroscopic
0 1978 American Chemical Society
3318 Inorganic Chemistry, Vol. 17, No. 12, 1978
Barraclough, Lawrance, and Lay Table I. Solid-state Raman Ozz- Stretching Frequency of pPeroxo Cobalt(II1) Amine Complexes L, Co-0, -CoL, 4t Monobridged Complexesa* anion
dispersant KBr Na, SO, solidC
KBr
NaNO, NaNO, KBr KC10, KBr KBr KBr KC10, KBr KC10, KBr
I
900
BOOcm"
703
Figure 1. Solid-state Raman spectra of [ (NH3)5Co-02-Co(NH3)J(S04), dispersed in (a) KBr and (b) Na2S04.
KBr measurement. The depolarization ratio (pi) for each complex was measured as the ratio of parallel and perpendicular polarized spectrum intensity (I,,/IL). The parallel-polarized and perpendicular-polarized spectrum was measured in turn, followed again by the parallel-polarized spectrum as a check for decomposition. Peak size was estimated by both peak height and peak area, the value of pi calculated by each process being in agreement to less than 5%. To allow for any observed decomposition an estimate of peak size under parallel polarization was obtained by averaging the two measurements obtained. Since decomposition was usually not marked, it was estimated that pi is generally correct to within 1OOh. Spurious reflections from the solution cell were eliminated by first aligning the cell and recording a baseline with water only present. Spectra of complexes containing coordinated ammonia were measured in concentrated 7 or 15 M aqueous ammonia to limit ammine hydrolysis. Solid samples of pperoxo-dicobalt complexes were prepared as pressed disks with either KBr or a simple salt of the anion of the complex under study as dispersant. A ratio of dispersant to complex of approximately 1:2by weight was commonly employed. For selected compounds, a pseudo p1 was measured in a like manner to that described above for solution samples. Spectra of relatively unstable g-superoxo complexes in solution ( 5 mM) were measured in 0.3-M perchloric acid solution to prevent decomposition to peroxo complexes. All solutions were chilled in ice prior to spectroscopic study.
KC10, KBr KBr KC10, KBr KClO, KBr KC10, KBr KBr
0-0 str,
cm-' 808,833 808 808 808 830sh 802' 806 810 sh, 829 80gd 786 811 813 815 805d
805 809 808 804 810 803 800 805 803 80 3 800 805 800
KBr KBr KC10, KBr
801d 806 803
KBr KC10, KBr
796 795 795
KBr KBr
800 br 80 3
799
C O L , ~ *Dibridged Complexesa$
L,Co \
/ A
Results p-Peroxo Complexes. All dicobalt amine complexes known to contain a single peroxo bridge exhibited a strong Raman band in the solid-state spectra in the region 800 f 15 cm-' (Table I), assigned to 0:- ~tretching,~," which was by far the strongest observed band for all complexes studied. The recently prepared dicobalt complexes of the macrocyclic tetraamine ligands Me2[14ldiene and Me6[14ldiene exhibit strong Raman bands a t 795 cm-', consistent with their earlier formulation25 as monobridged p-peroxo-dicobalt complexes. The solid-state spectrum of p-peroxo-decaamminedicobalt(II1) in the 0;- stretching region exhibits a remarkable dependence on dispersant. The sulfate salt dispersed in KBr exhibits two strong bands a t 808 and 833 cm-' (Figure l ) , although only a single band a t 808 cm-' has been reported for the isolated solids9 However, the sulfate salt dispersed in N a 2 S 0 4shows only one band a t 808 cm-'. This behavior was also observed for the nitrate and perchlorate salts dispersed in KBr or N a N 0 3 and KC104, respectively, and implies a specific interaction in the KBr environment. N o similar dispersant dependence was observed for other amine complexes. Measurement of peak area of the OZ2-stretch relative to vl(SOd2-)for added Na2S04 in the disk spectrum of complexes with L5 = (NH,),, (NH3)(trien), and (OH,)-
str? cm-' ( N 0 , ) 3 ~ N H , N 0 , ~ 1 / 2 H z 0KBr 826 (NH,), OH' solidC 793, 820 NHL (NO,),'HiO ("314 785, 820 (en), KBr OH- (S,O&NO,)~H,O Na,S,O, 794 sh, 828 a Art 5145-8 excitation line. sh = shoulder; br = broad. Data from ref 9. Measured also with 4880-A excitation line. e Absorbances relatively weak and broad. L,
x-
A
0-0
anion
dispersant
Me2[14]diene) for spectra recorded a t both 5145 and 4880 indicates the peroxo stretching mode undergoes intensity enhancement as the excitation wavelength is decreased from 5145 to 4880 A. For each complex the relative intensity of the peak at 4880-A excitation lies in the range 1.2-1.5 ( f O . l ) relative to unit intensity a t 5145-A excitation. Minor decomposition during measurement does not allow for accurate enhancement ratios to be determined. This enhancement behavior has been reported previously for L, = (NH,), and suggests that the 022stretching mode is in resonance with the 0," Co(II1) charge-transfer absorption band observedz5 near 300 nm for monobridged complexes. Solution Raman spectra of p-peroxo-dicobalt complexes exhibit a strong band in the region 800 f 10 cm-' for monobridged complexes and a relatively weak broad band in the
-
p-Peroxo and p-Superoxo Cobalt Amine Complexes Table 11. Solution Raman 0,'- Stretching Frequency of p-Peroxo Cobalt(II1) Amine Complexes L,CO-~,-COL,~+ Monobridged Complexes' LS anion 0-0 str, cm-' p1 (",Is NO; 800b 0.40 ("315 SO,'802b ("3)s SCN800 brb (NH 3 ) ,(die4 C10; 800b 0.37 (NH3)(pn), C10; 790 brb 0.32 (NH ,)(en) , C10; 802b 0.30 (NH3)(tn), C10; 810b 0.34 (pn)(dien) C10,800 0.39 (en)(dien) c10,- 799 0.37 (tn)(dien) C10; 802 0.32 (dien) , C10; 808 0.35 (tetren) C10,800' 0.37' (OH,)(Me, [ 14ldiene) C10; 796 0.35 NO; 807 0.30 (his), c1800 0.30 (hm), L,Co
I
0, \
\
I
COL,~'Dibridged Complexes
X
Xanion 0-0 str, cm-' p1 L4 (en), OHc10,810 br -0.5 (pn), OH(S,0,2-)(NO;) 812 brd (tn), OHc10,815 br -0.5 (NH,), NH; C1810 v bre a Measured at 5145-8 excitation in aqueous solution. Aqueous concentrated ammonia solution. 'Also measured at 4880-8 excitation with equivalent results. Fluorescence interference did not permit measurement of p1. e Very broad resonance did not permit measurement of 01.
Table 111. Raman 02Stretching Frequency of p-Superoxo Cobalt(II1) Amine Complexes L,CO-O,-COL,~+ Mononuclear Complexesa J3anion 0-0 str, cm-' ref (NH,),(dien) C10; 1124 b (NH,)(pn), C10,1125 b (en)( dien) c10,1120 b (tn)(dien) C10,1123 ( p i = 0.33) b (tetren) c10,1121 b (his), NO; 1118 b 1120 9 ("3)s NO; 1122' 8 ("3)s so,,lll0C 8 (hm), c11125 b
Inorganic Chemistry, Vol. 17, No. 12, 1978 3319
I
u 11w 1100 10LOCrn~ Figure 2. Raman spectra of (a) [(dien)(en)Co-0,-Co(en)(dien)](C104)4dispersed in a KBr disk, (b) [(dien)(pn)Co-O,-Co(pn)(dien)] (C104)4 in aqueous solution, (c) [ (en)2Co-(02)(OH)-Co(en)2](S206)(N0,) dispersed in a KBr disk, (d) [(tn)$o-(02)(0H)-C0(tn),](C10.,)~ in aqueous solution, and (e) [(dien)(tn)Co-02-Co(tn)(dien)] (C104)5superoxo complex in aqueous 0.3 M HC104.
Figure 3. The dihedral angle w in dioxygendicobalt complexes.
0, stretching mode at 1120 f 10 cm-I. Dibridged complexes exhibit a relatively weak resonance in the region 1075 f 5 cm-I in the solid state, although the resonance could not be readily detected in solution due partly to fluorescence interference. Data for the spectra of the p-superoxo complexes studied are collected in Table 111. Marked differences in the average position of the 0, stretch for monobridged (1120 cm-') and dibridged (1075 cm-I) p-superoxo-dicobalt complexes as well as for the 022- stretch for monobridged (800 cm-') and dibridged (812 cm-') pperoxo-dicobalt complexes occur. Moreover, the intensity of the 02-or 02- stretch is markedly reduced when a second hydroxo or amido bridge is present generally. Typical Raman spectra of both p-superoxo and p-peroxo complexes are illustrated in Figure 2.
Discussion I
\
L,Co
CoLd4+Dibridged Complexes
'x' LA ("31.4
X-
anion
";
so,,-
str, cm-' ref 1080' 8 1072' 8
0-0
c1NH; c10,d b (en), OHa Measured with 5145-8 excitation in 0.3-M aqueous HClO, generally. This work. 'Solid-state spectrum. No resonance peak detected in attempted solution spectrum. ("31,
region 812 f 5 cm-' for dibridged complexes with a hydroxo or amido bridge in addition to the peroxo bridge. The monobridged complexes show a pI between 0.3 and 0.4, while a higher value is obtained in the case of the dibridged complexes of approximately 0.5. Data for the solution spectra are collected in Table 11. p-Superoxo Complexes. Raman spectra of a number of monobridged p-superoxo-dicobalt complexes prepared in solution exhibit a moderately strong resonance assigned to the
Dioxygendicobalt complexes generally adopt configuration 1 for monobridged complexes and configuration 2 for dibridged p
o ,0 -
L
5
,o-0 C ' OL,
4c0\,/
L 5co
1
2
complexes in both peroxo and superoxo forms. Crystal structure determinations of a range of such complexes have been reported and confirm these general configuration^.^^^^^^^^^^ From the determined structures of the simple monobridged p-peroxo- and p-superoxo-decaamminedicobalt(II1) sulfate c ~ m p l e x e s certain , ~ ~ ~ ~obvious ~ differences are apparent. The Co-0 and 0-0 bond lengths vary from 188.2 and 147 pm, respectively, in the peroxo complex to 189.4 and 131 pm, respectively, in the superoxo complex. The observed dihedral angle w , defined as the angle between the Co-0-0 and 0-0-Co' planes (Figure 3), is 146' in the peroxo complex and 175' in the superoxo complex. The Co-0-0 angle is similar for both monobridged complexes, however, being 112O
3320 Inorganic Chemistry, Vol. 17, No. 12, 1978
Barraclough, Lawrance, and Lay
Table IV. Crystallographic Data for Binuclear Dioxygenaminecobalt(II1) Complexes Co-0,, p m
w , deg
LCo-O-0, deg
ref
p-Peroxo Complexes 188 147 183 147 190 149 191 134 193 145 196 131 187 146 186 147 187 146
145.8 180 180 110.1 149 122 62.7 60.7 60.7
112 112 110 120 118 118 110 110 109
22 24 34 35 36 37 38 33 39
p-Superoxo Complexes 189 132 189 131 187 132 188 135 187 134
180 175 0 23.4 22.0
117 117 121 119 120
40 41 42 43 33
Table V. General Absorption Spectral Data for Binuclear Dioxygenaminecobalt(II1) Complexes' complex type monobridged p-peroxo dibridged p-peroxo monobridged p-superoxo dibr idged p-super ox o
0-0, pm
absorption maximab
300 ? 5 (3.8 i. 0.2), 4 3 0 i 20 (2.8 t 0.1)' 352 t 5 (3.7 t 0 . 0 , 500 + 20 (2.6 i. 0.1)' 306 i. 8 (4.2 t 0.15), 468 i. 8 (2.6 i. O . l ) , 705 t 15 (3.05 i 0.15) ca. 300, 4 8 5 t 8 (2.6 t O.l), 6 8 0 + 20 (2.6 + 0.15)
'Data from ref 1 9 and ref 25 and references therein. Averaged band maxima (nm) with averaged extinction coefficients (log e , M" cm-I). ' Shoulder.
-
of monobridged p-peroxo-dicobalt amine complexes, the 022Co(1lI) charge-transfer absorption maximum is observed at 300 f 5 nm, while dibridged complexes generally have maxima a t 352 f 5 nm1.19~25 Average band positions and extinction coefficients of complexes of the type reported here are collected in Table V. A molecular orbital description for the analogous copper-oxygen complexes has been given44and the likely vibronic interaction discussed. The depolarization ratio of observed for the 022stretching frequency is consistent with the idea of a mechanism such as vibronic coupling greatly increasing one component of the polarizability tensor. The standard formula for pI is45
+ 4/32)
(1)
+ ayy) + %A
(2)
= 3/32/(45d
where in the peroxo complex and 117' in the superoxo complex. Structural information available for dioxygendicobalt amine complexes is collected in Table IV. The observed dihedral angle w in solid H 2 0 2 is 90' (C2 symmetry), consistent with the calculated minimum conformational energy of the 022bridge.34 The calculated maximum conformational energy in H202occurs for w = 180°, but this latter conformation appears to be preferred for ionic dicobalt complexes (Table IV). This observation has been interpreted as indicating that electrostatic repulsion of the highly charged metal chromophores is the dominant effect,34 since reduction of effective charge about each cobalt center when anionic ligands are present35or when extensive hydrogen bonding occurszz allows the adoption of a structure with w approaching 90'. For dibridged complexes, the angle w is reduced below 90' as a result of conformational restrictions from inclusion of a second hydroxo or amido bridge. A decrease in bond order and a corresponding increase in bond length are observed from dioxygen (0,)to superoxide (02-) and peroxide (0,2-).20 The Oz molecule of bond order 2 has a bond length of 121 pm, and the 0-0 stretching frequency occurs at 1580 cm-'. The 02-superoxide has a bond order of 1.5 and a bond length of 133 pm in KO2 with an 0-0 stretching frequency a t 1097 cm-' in LiO,. For the peroxide (O;-) of bond order 1, the bond length in BaO, is 149 pm with the 0-0 stretch in L i 2 0 2observed a t 802 cm-'. For ionic binuclear cobalt dioxygen complexes, the average bond length in the p-superoxo-dicobalt complexes is 132 pm compared with 147 pm in the p-peroxo-dicobalt complexes. Assigned 0-0 stretching frequencies lie near 1100 and 800 cm-', respectiveIy.8-1 The resonance Raman effect suggests that the 0,2-stretch is vibronically coupled with the 022- Co(1II) charge-transfer absorption in the monobridged complexes. For a wide range
-
=
1/3(%,
and
P2 = '/2[(%
-- aJ2 +
(ayy),-
%A2 +
(QZZ
- %)2
6(@,2 + Qyz2 +
+
%71 (3)
in which a y = ijth component of the polarizability tensor. It can be seen that, if one of the diagonal tensor components, say aZz, is made very large relative to all other aj,, then pi This expression for pl is for normal Raman scattering. The possibility of an antisymmetric Raman scattering tensor for the resonance Raman spectra cannot be ignored but there is no sign of an inverse polarization ratio. Because of the available structural data for p-peroxo-dicobalt complexes in the solid state, pseudo pI values for several complexes dispersed in pressed disks were measured in an attempt to seek some correlation of measured w and pI values. It has been suggested that polarization data for polycrystalline samples was not useful due to reflections and other optical effects,46 although the possibility of obtaining quantitative polarization data from very fine powders has been ~uggested.4~ For the finely ground pressed disks studied, pseudo pi values in the range 0.48-0.84 were measured. Effects of reflections, which lead to values of p, > 3/4 in certain cases, were assumed constant since several measurements of each compound in different dispersants produced practically identical pl values. No apparent relationship of w and pI was observed. For example, the sulfate and thiocyanate salts of (NH,)&o02-Co(NH3)54+exhibited similar pseudo pl values of 0.84 and 0.78 for measured w of 146 and 180°, respectively, while (en)(dien)C~-O~-Co(dien)(en)~+ with p1 of 0.65 did not differ from (en)zCo-(0,)(OH)-Co(en)23+ with p1 of 0.67, though w varied from 180 to 63', respectively. The solid-state pI values
-
p-Peroxo and p-Superoxo Cobalt Amine Complexes are high compared with those measured in solution and indicate that attempts to elucidate structural information from solid-state polarization data in this case are invalid. Small but significant differences in peak maxima of pperoxo and p-peroxo-p-hydroxo or p-peroxo-y-amido complexes are observed in both solution and solid-state Raman. The dibridged complex band in the 0-0 stretching region was generally relatively weak and broad, with two distinct maxima apparent in certain solid-state spectra (Table I). Previously, the 022stretch for dibridged complexes was assigned as occurring near 790 cm-' on the basis of a peak at 793 cm-' for (NH3)4Co-(02)(NH2)-Co(NH3)43+ and a peak at 790 cm-I for a solution believed to contain (hm),Co-(0,)( 0 H ) - C 0 ( h r n ) ~ ~ + .From I R deuteration studies of similar complexes, however, an 022- stretch was assigned in the 820-830-cm-' region.32 The observation in the solution spectra of one peak near 812 cm-I and of a peqk in the 820-830-cm-' region in the solid state for dibridged complexes reported here suggests that the 022stretch can be best assigned near 820 cm-'. The band sometimes observed near 790 cm-I is presumably an amine ligand band. Monobridged complexes containing ammonia ligands are known to undergo hydrolysis with the formation of an additional p-hydroxo bridge.26 When several p-peroxo complexes of this type were dissolved in water and their Raman spectra recorded at discrete time intervals, a decrease in peak intensity and a shift to higher frequency of the maxima initially near 800 cm-I was observed. This is consistent with p-hydroxo bridge formation and with assignment of the 022- stretch in the dibridged complexes in the region near 820 cm-I. The p-superoxo complexes also exhibited characteristic stretching regions for the monobridged (1 120 cm-') and dibridged (1080 cm-I) species. The hm complex prepared in solution as a p-peroxo complex exhibited a relatively strong peak near 800 cm-I, most consistent with its formulation as a monobridged rather than a dibridged compound. Oxidation to a p-superoxo complex produced a compound exhibiting an 022stretch at 1125 cm-I, analogous to a range of characterized monobridged compounds, supporting assignment of the initial p-peroxo complex as a monobridged rather than dibridged species. The unique behavior of the p-peroxo-decaamminedicobalt(II1) cation's pressed-disk Raman spectrum may be interpreted in two ways. Crystal structural evidence indicates that the symmetry of the complex can be dependent on the c o ~ n t e r a n i o n .Criteria ~ ~ ~ ~ ~for anion-exchange reactions in solid pressed disks have been investigated recently48 and it is reasonable to suppose that bromide ion could supplant the original anion of the polycrystallites partially, The subsequent generation of two different dioxygen environments in the disk could then produce two different resonances. Alternatively, bromide ion may partially replace labile ammine ligands directly in the first coordination sphere. The resultant change in charge of the dicobalt complex cation may influence the 0;- stretching frequency. It has been observed that the peak at higher frequency increases at the expense of the peak a t lower frequency as the relative amount of KBr in the disk increases, but this would be consistent with both proposals. The observations for this complex highlight the fact that the voz is not derived from a "pure" 0-0 stretching vibration and that the mass of the metal and other ligands, as well as the overall symmetry of the complex, must play some role in determining the observed frequency.20 No doublet peaks in KBr disks were observed for other amine complexes even where some coordinated ammonia was present. The characterization of new p-peroxo and p-superoxo complexes of cobalt which are monobridged from the observation of a strong resonance Raman band near 800 and
Inorganic Chemistry, Vol. 17, No. 12, 1978 3321 1 120 cm-I, respectively, has been illustrated in the case of the p-peroxo macrocyclic complexes with Mez[ 14ldiene or Me6[14]diene ligands reported in this study. The 0-0 stretch is generally far stronger than other bands of the monobridged complexes. Known dibridged complexes exhibit weaker and generally broader Raman bands which do not seem to be vibronically coupled as they do not exhibit a detectable resonance Raman effect. While they can be readily distinguished from monobridged complexes, making structural assignments of dibridged complexes on the basis of a weak or undetectable Raman 0-0 stretch alone is hazardous. However, the dibridged dicobalt amine complexes also usually exhibit a strong charge-transfer absorbance near 350 nm, significantly different from the maxima near 300 nm for monobridged amine complexes (Table V). The monobridged p-peroxo complexes appear to adopt an analogous structure to that in the dioxygen complex containing copper protein oxyhemocyanin. Three structures have been considered for dioxygen bridging in oxyhemocyanin, 3, 4, or 5.49-51Structure 4 was discounted on the basis of excessive
c"/o-o\cu 3
P
cu--- ---c" 0
4
cu/
o-oo/cu 5
steric interaction and structure 3 because it was not consistent with the observation of a resonance Raman effect in the protein 0-0 stretch.51 The favored structure (5) is analogous to that known in the dicobalt complexes and supports their value as possible structural models for certain dioxygen-complexing proteins. Acknowledgment. We thank the University of Melbourne and the Australian Research Grants Committee for support for instrumentation and Mr. M. E. Beyer for technical assistance. Registry No. ( [(NH3)sCo]202)(S04)2, 23103-43-7;([(NHJsCO],O2)(NO3)4, 16632-71-6;([(NH3)5CO]202)(C104)4,67393-25-3; ~[(NH~)~COI,OZ)(SCN)~, 18496-85-0; ( [(NH3)~(dien)Col2O,)(Clo4)4, 67421-42-5;( [(NH3)(pn)2Co]20z}(C104)4, 36502-63-3;( [(NH3)(en)2Col2O~l(C104)4,36573-37-2; ( [(NH,)(en)2Col2021(N03)(C104)3, 49736-97-2;([(NHs)(tn)2Co]202)(C104)4, 67393-27-5;([(NH3)(bn)2Co]202)(C104)4, 67393-29-7;{[(pn)(dien)C~]~O~)(ClO~)~, 49728-66-7; ( [(en)(dien)C~]~O~)(ClO~)~, 36502-65-5; ([(tn)(dien)CO]~O~)(C~O~)~, 49728-67-8; ([(bn)(dien)C~],O~)(ClO~)~, 67421-40-3; { [(dien),Co]2O2)(C1O4)467393, 18-4;([(NH3)(trien)Co]202)(C104)4, 36502-64-4;([(tetren)C~]~O~)(ClO~)~, 36502-66-6;( [(OHz)(Me2[ 14]diene)C0]~0~)(ClO~)~, 58880-98-1;( [(SCN-)(Mez[14ldiene)CO]~O~}(C~O~)~, 67393-20-8; {[(",)(Me,[ 14]diene)C0]~0~)(C10~)~, 67393-22-0; {[(DMP)(salen)Col2O2}, 36300-65-9;([(his)zCo1202)(Nod,,37238-70-3;[(NH~)~CO(~,)(~H)CO(NH~)~I(N~~) 67393-24-2;[(NH~)~CO(OZ)(NH~)CO(NH,),I(NO,)~, 31085-11-7; [(en)zCo(02)(OH)Co(en)z](S206)(N03), 58692-02-7; ( [(hm)2Co]z0,)C14,67393-13-9;[(en)zCo(Oz)(OH)Co(en)z] 24925-38-0;[(pn)2Co(02)(OH)Co(pn)z] (Sz0,)(N03),67393-15-1; [ (tn)zCo(0,) (OH)Co(tn)2] (C104) 3 , 6739 3 - 1 6-2; [ (NH3)4C O ( O ~ ) ( N H ~ ) C O ( N H ~67393-17-3; ) ~ ] C ~ ~ , ([(NH3)2(dien)Co]202}(C104)5, 12556-79-5;([(NH3)(pn)2Co]20z)(C104)5, 67478-44-8; ([(en)(dien)C~]~O~)(ClO~)~, 12563-59-6; ( [(tn)(dien)C~]~O~)(ClO~)~, 67478-45-9; ([(tetren)C~]~O,)(ClO~)~, 12568-13-7;( [(hm)2Co]202)C1s, (C104)4, 67478-43-7. 67421-36-7;[(en)zCo(02)(OH)Co(en)z]
References and Notes (1) J. S.Loehr, T. B. Freedman, and T. M. Loehr, Biochem. Biophys. Res. Commun., 56, 510 (1974). (2) C. H. Barlow, J. C. Maxwell, W. J Wallace, and W. S. Caughey, Biochem. Biophys. Res. Commun., 55, 91 (1973). (3) J. B. R. Dum, D.F. Shriver, and I . M Klotz, Proc. Natl. Acad. Sci. U.S.A., 70, 2582 (1973). (4) H. B. Gray, Adv. Chem. Ser., No. 100, 365 (1971). (5) S. Bagger and K. Gibson, Acta Chem. Scand., 26, 3788 (1972). (6) A. G. Sykes and J. A Weil, Prog. Inorg. Chem., 13, 1 (1970). (7) M. Mori, J A. Weil, and M. Ishiguro, J. Am. Chem. SOC.,90,615 (1968). (8) T. Shibahara, J . Chem. SOC.,Chem. Commun., 864 (1973).
Lawrance, Stranks, and Suvachittanont
3322 Inorganic Chemistry, Vol. 17, No. 12, 1978 (9) T. B. Freedman, C. M. Yoshida, and T. M. Loehr, J . Chem. Soc., Chem. Commun., 1016 (1974). (10) T. C. Strekas and T. G. Spiro, Inorg. Chem., 14, 1421 (1975). (1 1) C. G. Barraclough and G. A. Lawrance, Inorg. Nucl. Chem. Lett., 12, 133 (1976). (12) L. H. Voigt, H. Faigbaum, and S. Wimberley, Chem. Rev., 63,269 (1963). (1 3) E. Bayer and P. Schretzmann, Struct. Bonding (Berlin), 2,18 1 (1967). (14) S. Fallab, Angew. Chem., 6, 496 (1967). (15) E.-I. Ochiai, J . Inorg. Nucl. Chem., 37, 1503 (1975). (16) R. G.Wilkins, Adu. Chem. Ser., No. 100, 111 (1971). (17) F. Basolo, B. M. Hoffman, and J. A. Ibers, Act. Chem. Res., 8, 384 (1975). (18) A. V. Savitskii and V. I . Nelyublin, Russ. Chem. Reu. (Engl. Transl.), 44, 110 (1975). (19) G. McLendon and A. E. Martell, Coord. Chem. Reu., 19, 1 (1976). (20) L. Vaska, Acc. Chem. Res., 9, 175 (1976). (21) M. R. Paris and D. Aymes, Bull. Soc. Chim. Fr., 1431 (1976). (22) W. P. Schaefer, Inorg. Chem., 7, 725 (1968). (23) R. Davies, M. Mori, A. G.Sykes, and J. A. Weil, Inorg. Synth., 12, 197 (1970). (24) F. R. Fronczek, W. P. Schaefer, and R. E. Marsh, Acta Crystallogr., Secr. E , 30, 117 (1974). (25) G. A. Lawrance and P. A. Lay, J . Inorg. iVucl. Chem., in press. (26) Y. Sasaki, J. Fujita, and K. Saito, Bull. Chem. Soc. Jpn., 44,3373 (1971). (27) D. L. Duffy, D. A. House, and J. A. Weil, J . Inorg. Nucl. Chem., 31, 2053 (1969). (28) C. Floriani and F. Calderazzo, J . Chem. SOC.A , 946 (1969). (29) M. Woods, J. A. Wei1,and J. K. Kinnaud, Inorg. Chem., 11,1713 (1972). (30) M. S. Michailidis and R. B. Martin, J . Am. Chem. Soc., 91,4683 (1969). (3 1) Ligand abbreviations: en = 1,2-diaminoethane, tn = 1,3-diaminopropane, pn = 1,2-diaminopropane, bn = 1,4-diaminobutane, dien = diethylenetriamine, trien = triethylenediamine, tetren = tetraethylenepentamine, Mez[14ldiene = 5,7-dimethyl-1,4,8,1l-tetraazacyclotetradeca-4,1I-diene, Me6[14ldiene = 5,7,7,12,14,14-hexamethyI1,4,8,1l-tetraazacyclo-
(32) (33) (34) (35)
tetradeca-4,1l-diene, salen = bis(salicylaldehyde)ethylenediimine, his = histidine, hm = histamine. M. Mori, J. A. Weil, and M. Ishiguro, J. Am. Chem. Soc., 90,615 (1968). V. Thewalt and G. Strickmeier, Z . Anorg. Allg. Chem., 419, 163 (1976). J. R. Fritch, G. C. Christoph, and W. P. Schaefer, Inorg. Chem., 12, 2170 (1973). M. Calligaus, G. Nardis, L. Randaccio, and H. Ripamonti, J . Chem. Snc. ... A. 1069 (19701. L . A. Lindblom, W.’P. Schaefer, and R. E. Marsh, Acta Crystallogr., Sect. B, 27, 1461 (1976). B. C. Wang and W. P. Schaefer, Science, 166, 1404 (1969). U. Thewalt, Z . Anorg. Allg. Chem., 393, 1 (1972). M. Zehnder. U. Thewalt. and S. Fallab. Helu. Chim. Acta, 59. 2290 (1976). R. E. Marsh and W. P. Schaefer, Acta Crystallogr., Sect. B, 24, 246 (1968). R. E. Marsh and W. P. Schaefer, Acta Crystallogr., 21, 246 (1966). C. G. Christoph, R . E. Marsh, and W. P. Schaefer, Inorg. Chem., 8, 291 (1969). U. Thewalt and R. E. Marsh, Inorg. Chem., 11, 351 (1972). T. B. Freedman, J. S. Loehr, and T. M. Loehr, J . A m . Chem. Soc., 98, 2809 (1976). T. G. Spiro and T. C. Strekas, Proc. Nail. Acad. Sci. U.S.A., 69,2622 (1972). E. Stager, Raman Spectrosc., 2, 200 (1970). R. S. Tobias, Raman EfJ,2, 419 (1973). J. W. Milne, Spectrochim. Acta, 22, 1347 (1974). T. J. Thaman, J. S . Loehr, and T. M. Loehr, J . A m . Chem. Soc., 99, 4187 (1977). J. A. Larrabee, T. G. Spiro, N. S. Ferris, W. H. Woodruff, W. A. Maltese, and M.S. Kerr, J . A m . Chem. Soc., 99, 1979 (1977). T. B. Freeman, J. S. Loehr, and T. M. Loehr, J . A m . Chem. Soc., 98, 2809 (1976). ~~
(36) (37) (38) (39) . , (40) (41) (42) (43) (44) (45) (46) (47) (48)
(49) (50)
(51)
Contribution from the Department of Inorganic Chemistry, University of Melbourne, Parkville 3052, Australia
Volumes of Activation for Racemization of Mixed 1,lO-Phenanthroline and 2,2’-Bipyridyl Complexes of Nickel(I1) from High-pressure Solution Kinetics GEOFFREY A. LAWRANCE,*’ DONALD R. STRANKS, and SURAPONG SUVACHITTANONT Received June 9, 1978
The effect of pressure on the rates of racemization of Ni(~hen)~(bpy)~+ and Ni(phen)(bpy)F in solution has been evaluated. Reactions of Ni(~hen)~(bpy)’+ exhibit only a minor pressure dependence of the rate, with a volume of activation ( A P ) of +0.6 cm3 mol-’ and -0.1 cm3 mol-’ for racemization in 0.01 and 1.0 M aqueous HCI, respectively. Aquation of Ni(~hen)~(bpy)’+ in 1.0M aqueous HCI exhibits no measurable pressure dependence, with AV = 0.0 cm3mol-’. Racemization of Ni(~hen)(bpy),~+ proceeds with a minor acceleration upon the application of pressure, with A P = -1.9 cm3mol-’ and A v ‘ = -5.2 cm3 mol-’ in 0.01 and 1 .O M aqueous HCI, respectively. Variation of AV with acidity observed suggests an acid-dependent pathway is the dominant mechanism at high acidity but is not important at low acidity. A common mechanistic pathway for racemization and aquation of these complexes is favored since reported rates, enthalpies, entropies, and volumes of activation are very similar. A one-ended dissociatiw mechanism via a half-bonded bpy ligand is consistent with experimental AV data.
Introduction Kinetic studies of racemization and aquation reactions of nickel(I1) complexes have attracted continuing interest2 Extensive kinetic studies of 1,lO-phenanthroline (phen) and 2,2’-bipyridyl (bpy) complexes of nickel(I1) and other metal ions have been r e p ~ r t e d . ~The . ~ rates of dissociation, racemization, and labeled ligand exchange in N i ( ~ h e n ) ~have ~+ been shown to be very ~ i m i l a r ,providing ~,~ consistent evidence for an intermolecular mechanism with rate-determining release of a chelated phen ligand. In nonaqueous solvents, exchange rates are also the same as the rates of racemization in the same solvents for N i ( ~ h e n ) ~although ~ + , ~ rates of racemization and associated activation parameters show a solvent d e p e n d e n ~ e , ~ ? ~ indicating that solvent-mplex interactions may be significant. While racemization of Ni(bpy),2+ also appears to proceed via an intermolecular mechanism, the rate of racemization and also aquation is much faster than that observed for N i ( ~ h e n ) ~ ~ + and further exhibits acid-dependence and specific-ion 0020-1669178113 17-3322$01.OO/O
The mixed complexes Ni(~hen)~(bpy)*’ and Ni(~hen)(bpy),~+ have also been subject to kinetic i n v e ~ t i g a t i o n and , ~ racemization and aquation appear to proceed by a mechanism analogous to that proposed for Ni(bpy)32+, involving a half-bonded bpy molecule in the transition state. Chelated bpy (1) is capable of rotation about the internal C(2)-C(2’) bond joining the pyridine residues, a process which is forbidden by the fused ring system in chelated phen (2).
1
2
One-ended dissociation in complexes with chelated bpy can readily proceed via rotation of one pyridine residue about the C(2)-C(2’) bond while the second ring remains fixed. A one-ended dissociative process may occur for chelated phen,
0 1978 American Chemical Society
