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New solvatochromic inorganic complexes
SpecmxhimicaAcra.Vol. Printed in Great Britain
47A.b.R.pp.985-989. 1991
0584.8539/91 53.00+0.00 @ 1991 Pergamon Press pie
New solvatochromic inorganic complexes A. AL-ALOUSY and J. BURGESS* Chemistry Department, University of Leicester, Leicester LEl 7RR, UK
and A. SAMOTUS and J. SZKLARZEWICZ Faculty of Chemistry, Jagieilonian University, Krakow, Poland (Received 12 December 1990; in final form 12 February 1991; accepted 13 February 1991)
AMract-The solvatochromic behaviours of his-cyclopentadienyi titanium(W) dithiocyanate and of the hexacyanobis-2,2’-bipyridyltungstate(IV) and tricyano-2,2’-bipyridyloxotungstate(IV) anions are described. The solvent sensitivities of these complexes are compared with those of biscyanobis-2,2’-bipyridyliron(I1) and other ~tabl~hed inorganic ~fvat~hromic species.
INTRODUCTION
THE first
report of solvatochromic behaviour for inorganic complexes is thought (11to be that of Bos et al. [2] in 1939. Many years later the classic paper by BJERRUM etaf.[3] laid the foundations for the study of several classes of solvatochromic inorganic complexes [4], especially molybdenum(O)-tetracarbonyl-diimine [5] and iron(diimine-cyanide [6] ternary complexes. In recent years a number of such compounds have been reported, most of which have exhibited solvatochromism of MLCT bands, the charge-transfer being from a metal in the $ configuration. We have recently been investigating solvatochromic behaviour of compounds of elements to the left of the d-block of the Periodic Table, and here describe the ~lvatochromism of titanium(IV) (d”), chromium(II1) (d3; very briefly), and tungsten(IV) (&) complexes. All the complexes with which we are concerned here interact with their environment through hydrogen bond interactions involving protons in the solvent molecules and the oxygen or nitrogen of carbonyl or cyanide groups. The effects of these interactions are transmitted to and across the metal atom, affecting the metal-diimine z-bonding and associated chargetransfer frequency. This central role for hydrogen bonding, here and in organic solvatochromic compounds, is reflected in correlations with solvent acceptor numbers, AN [7]. We are not concerned here with the other type of solvatochromic inorganic complex, e.g. the e~ane-I,2~iimine-~-diketone copper(U) derivative fCu(acac)(tmen)]’ [8], where the electron-donor properties of the solvent are paramount, and correlations are with solvent donor numbers, DN [l].
EXPERIMENTAL
Bi~clo~ntadienyl titanium(IV) thiocyanate ~~(Cs~s)*(NCS~*J was prepared and characterized as described previously [9], as were the tetraphenylphosphonium and tetraphenylarsonitim salts of the tungsten(IV) anions [W(CN),(bipy)]*- and [WO(CN)3(bipy)]- [lo, 111. Refluxing K~~~r(~N)s(NO~] with the Schiff base 1, itself prepared from Z,~ia~~ip~dine and methylamine, for 10h gave an impure sample of [Cr(CN),(LLL)],LLL = 1. it did not prove possible to get an analytically pure sample of this compound; the relatively low solvent sensitivity exhibited by * Author to whom correspondence should be addressed. WA) 47111-A
985
A. AL-ALOUSK et
986 Table 1. Solvent effects on charge-transfer
al.
bands of [Cr(CN,)(LLL)]-,
[Ti(cp),(NCS)r],
[W(CN),(bipy)]*-
and [WOWWbipy)l-
E$
Solvent Water 1,ZEthanediol 1,4-Butanediol Methanol 1,2_Pentanediol 2-Methoxyethanol Ethanol 2-Butoxyethanol I-Butanol 2-Propanol Propylene carbonate Nitromethane Acetonitrile Dimethyl sulphoxide Acetone Nitrobenzene Dichloromethane Dimethylformamide 1,l-Dichloroethane Chloroform Benzene Toluene Carbon tetrachloride *From t Value $ From !t From
[Ti(cph(NCSM
WOWWWy)l- FWW@-W
17 700$
15 OOO§
22 830
16 180 16 340$:
14 6006
22 730
I6 260$
I4 5006
22 620 23000
16260 15460 15800 15 150$ 14 930 14 750
14 270 I4 160 14200 14 1008 13890 13 6008 13 720
14 580
13 8008
63.1 56.3
(52.W 55.5 54.1 52.3 51.9 50.2 50.2 48.6 46.6 46.3 46.0 45.0 42.0 42.0 41.1 41.0 39.4 39.1 34.5 33.8 32.5
PWNMbW12-
23000 23090
20 770 20 390 20 370 20 310 20 260 20 290 20 280 20 280 20 240 20 040
20 410 20 620 20000
22 470 20 530
22 370 19490 22 170 22 120 21830
Ref. [12]. for 1,3_butanediol. Ref. [lo]. Ref. [Ill.
the impure
sample
(see
below) discouraged us from expending disproportionate effort on this
compound. *
All spectra were run on a Shimadzu UV-160 spectrophotometer, whose wavelength calibration was checked periodically against a didymium glass filter. This instrument reads in wavelengths, which were converted into wavenumbers for inclusion in the Table above. The uncertainties on measured wavelengths are f 0.5 nm.
RESULTS AND DISCUSSION
Wavenumbers
of maximum absorption for the lowest energy charge-transfer bands of PWAWW andWO%@ipy)12-are given in Table 1. This Table also includes data for the [WO(CN),(bipy)]anion, though in this case wavelengths are given not for the lowest energy charge-transfer band (which has considerable d-d character) but for the next band of slightly higher energy which shows greater solvatochromic shifts. Preliminary results for other chromium compounds can be obtained from the authors. * Further details of the preparhiion and solvatochromism the authors (J.B.).
of this, and related species, can be obtained from
New solvatochromic inorganic complexes
987
f I
c
1
40
20
E,I kcal mol -’-
Fig. 1. Correlation of frequencies of maximum absorption for the main charge-transfer band of Ti(cph(NC& with solvent ET values (0 hydraxylic solvents; 0 non-hydroxylic solvents).
Titanium (IV) complex
Wavenumbers of maximum absorption for the charge-transfer (LMCT) band of [Ti(cp)* (NCS)J are plotted against solvent Er values in Fig. 1. The I& scale is probably the most extensive and widely used of empirical measures of solvent polarity. It is based on the solvatochromic characteristics of Reichardt’s “I& (30)” betaine [12], whose charge-transfer band is remarkably sensitive to solvation and solvent nature. As so often for inorganic complexes, correlation of Y, with ET for this titanium complex shows two different correlation lines, for hydroxylic and non-hydroxylic solvents [6,13]. The novel feature is that the two lines are not only of markedly different slopes, but they actually cross. Different lines for hydroxylic and non-hydroxylic solvents merely emphasize the differences in hydrogen-bonding properties between this titanium(IV) complex and the organic betaine used as the reference for the ET scale [13]. Direct comparisons of the solvent sensitivity of [Ti(cp)z(NCS)z]and other solvatochromic inorganic species can be made simply by plotting v,,,, values for the titanium(IV) compound against the respective Y,, values for the other compound. This is shown, for comparison with [Mo(CO),(bipy)], in Fig. 2. Again there are two lines, here attributable in the main to differences in hydrogen bonding to thiocyanate and to carbonyl. The slope of the correlation line for non-hydroxylic solvents is a little over 0.4, for the three alcohols rather less than 0.3. Comparison with the much-studied iron(I1) compounds
21000~
(
)
20000
22000
Y WcGO)4~bipy)) Fig. 2. Interrelation between frequencies of maximum absorption for charge-transfer with Ti(cp)2(NCS)2 and Mo(CO),(bipy) (0 hydroxylic solvents; 0 non-hydroxylic solvents).
A. At_-A~ousv et al.
988
17000 -
t
V I.= W (CN),(bipyf 18000 -
v... Fe(CN),(bipy),
-
Fig. 3. Correlation of frequencies of maximum absorption for the principle charge-transfer band of the [W(CN),(bipy)]*- anion with respective values for Fe(CN)r(bipy),.
[Fe(CN),(bipy)z] and [Fe(CN)z(phen),] is difficult due to the low solubility of these complexes in many of the solvents in which the titanium(IV) compound is soluble. However the limited comparison possible for alcohol solvents indicates a relative solvent sensitivity of about 0.3 for [Ti(cp)l(NCS)J. Thus this titanium(IV) complex is a much less sensitive solvatochromic probe of its solvent environment than these molybdenum(0) and iron(U) complexes. It therefore seems unlikely that it will prove useful in this role, except perhaps in media with significant content of aromatic hydrocarbons, where the cyclopentadienyl groups may confer a useful degree of solubility. Tungsten(W)
complexes
Figure 3 includes published and additional (Table 1) data on solvatochromism of the WCW~(bW12-anion. Both hydroxylic and non-hydroxylic solvents lie on the correlation line, whose slope of 1.2 indicates modestly greater solvent sensitivity than that of [Fe(CN)2(bipy)2]. In fact the solvent sensitivity of [W(CN),(bipy)12- is approximately equal to that of the molybdenum(O) complex [Mo(CO),(LLL)], LLL = 1, which is 1.5 (relative to [Fe(CN),(bipy),]) [14,15]. In Fig. 4 wavenumbers of maximum absorption for the oxotungsten(IV) complex [WO(CN),(bipy)]are plotted against respective values for the [W(CN),(bipy)12- anion. It is apparent that there are two correlation lines,
l5ooo
-
t V
c”..
IWOVGN~3(bipy)lcm“
t4OQC
lScQc
V... [W(CN)l(bipyl
I’-/cd
-c
Fig. 4. Correlation of frequencies of maximum absorption for the principle charge-transfer band of the (WO(CN),(bipy)]- anion with respective values for the [W(CN),(bipy)]*- anion (0 hydroxylic solvents; 0 non-hydroxylic solvents).
New solvatochromic inorganic complexes
989
for hydroxylic and for non-hydroxylic solvents. What is more, the two lines intersect (cf. the titanium complex, above). The very different trends in Fig. 4 for the two types of solvents can be attributed with some confidence to the possibility of hydrogen bonding to the oxide ligand in [WO(CN)3(bipy)]‘. The slope of the correlation line in nonhydroxylic media is approximately 0.7. Thus here, as for ternary iron(I1) complexes, solvent sensitivities decrease as the number of cyanide ligands decreases. The decrease here on going from six to three cyanide ligands is comparable with that on going from tetracyanodiimineiron(I1) anions to their dicyano-bis-diimineiron(I1) analogues [15]. K,[W(CN),(bipy)] is freely soluble in water, while (Ph$), [W(CN),(bipy)] is soluble in alcohols and in many other organic solvents. Perhaps surprisingly it is extremely sparingly soluble in paraffins, carbon tetrachloride, and toluene (though it is soluble in polar nitrobenzene). With its fairly high solvent sensitivity, we expect this anion to prove a useful indicator of solvation and local environment in WCW~@im)1*water-rich media, including micellar systems and such “organized media”. A combination of this complex and the titanium(IV) complex discussed above, with their complementary solubility properties, may well prove invaluable in probing solvation in microemulsions of the common and important water-alkoxyethanol-hydrocarbon type. Chromium(IZI) complexes
In contrast to [W(CN)6(bipy)]2-, the tricyanochromium(III)-Schiff base complexes examined in a preliminary manner in the course of our search for new solvatochromic complexes showed a disappointingly low solvent sensitivity. The complex derived from methylamine has only half the solvent sensitivity of (Fe(CN),(bipy),], and offers no compensating advantages. Analogous complexes from hydrazine and from taurine had very broad charge-transfer bands with maxima too flat and broad for solvatochromic probing; the analogous complex from sulphanilic acid showed negligible solubility in the majority of solvents examined. Acknowledgememtv-We are grateful to ALISON WAITS for carrying out much of the preliminary investigation into the chromium complexes, and to the Royal Society for Grants-in-aid towards the purchase of one of the spectrophotometers used in the initial stages of this project.
REFERENCES R. W. Soukup and R. Schmid, .I. Chem. Educ. 62,459 (1985). J. G. Bos, I. Lifschitz and K. M. Dijkema, 2.. Anorg. Aflg. Chem. 242.97 (1939). J. Bjerrum, A. W. Adamson and 0. Bostrup, Acta Chem. Stand. 10,329 (1956). H. Bock and H. tom Dieck, Angew. Chem., fnt. Ed. Engl. 5, 520 (1966); C/rem. Ber. 100,228 (1%7). H. A. Sinn, PhD Thesis, Darmstadt, F. R. G. (1966); H. Saito, J. Fujita and K. Saito, Bull. Chem. Sot. Japan 41,863 (1968); H. tom Dieck and I. W. Renk, Angew. Chem., Int. Ed. Engl. 9,793 (1970). [6] J. Burgess, Spectrochim. Acta 26A, 1369, 1957 (1970); H. Kobayashi, B. V. Aganvala and Y. Kaizu, Bull. Chem. Sot. Japan 48,465 (1975). [7] U. Mayer, V. Gutmann and W. Gerger, Mona&h. Chem. 106, 1235 (1975); V. Gutmann, Monatsh. Chem. 119, 1251 (1988). [S] K. Sone and Y. Fukuda, Bull. Chem. Sot. Japan 45,465 (1972). [9] Razak bin Ah, J. Burgess and A. T. Casey, J. Organomet. Chem. 362, 305 (1989). [lo] J. Szklarzewicz and A. Samotus, TransitionMet. Chem. 13.69 (1988). [ll] A. Samotus, J. Szklarzewicz and N. W. Alcock, fnorg. Chim. Acta 172, 129 (1990); J. Szklarzewicz, A. Samotus, N. W. Alcock and M. Mall, J. Chem. Sot., Dalton Trans. 2959 (1990). [12] C. Reichardt, Liisungsmitteleffeekte in der Organischen Chemie. Verlag Chemie, Weinheim (1968); C. Reichardt and E. Harbusch-Gornert, Annalen 721 (1983). [13] J. Burgess, J. G. Chambers and R. I. Haines, TransitionMet. Chem. 6, 145 (1981). [14] Razak bin Ah, J. Burgess, M. Kotowski and R. van Eldik, TransitionMet. Chem. 12, 230 (1987). [15] M. Kotowski, R. van Eldik, Razak bin Ali, J. Burgess and S. Radulovic. Inorg. Chim. Acta 131, 225 (1987). [l] [2] [3] [4] [S]
47A.b.R.pp.985-989. 1991
0584.8539/91 53.00+0.00 @ 1991 Pergamon Press pie
New solvatochromic inorganic complexes A. AL-ALOUSY and J. BURGESS* Chemistry Department, University of Leicester, Leicester LEl 7RR, UK
and A. SAMOTUS and J. SZKLARZEWICZ Faculty of Chemistry, Jagieilonian University, Krakow, Poland (Received 12 December 1990; in final form 12 February 1991; accepted 13 February 1991)
AMract-The solvatochromic behaviours of his-cyclopentadienyi titanium(W) dithiocyanate and of the hexacyanobis-2,2’-bipyridyltungstate(IV) and tricyano-2,2’-bipyridyloxotungstate(IV) anions are described. The solvent sensitivities of these complexes are compared with those of biscyanobis-2,2’-bipyridyliron(I1) and other ~tabl~hed inorganic ~fvat~hromic species.
INTRODUCTION
THE first
report of solvatochromic behaviour for inorganic complexes is thought (11to be that of Bos et al. [2] in 1939. Many years later the classic paper by BJERRUM etaf.[3] laid the foundations for the study of several classes of solvatochromic inorganic complexes [4], especially molybdenum(O)-tetracarbonyl-diimine [5] and iron(diimine-cyanide [6] ternary complexes. In recent years a number of such compounds have been reported, most of which have exhibited solvatochromism of MLCT bands, the charge-transfer being from a metal in the $ configuration. We have recently been investigating solvatochromic behaviour of compounds of elements to the left of the d-block of the Periodic Table, and here describe the ~lvatochromism of titanium(IV) (d”), chromium(II1) (d3; very briefly), and tungsten(IV) (&) complexes. All the complexes with which we are concerned here interact with their environment through hydrogen bond interactions involving protons in the solvent molecules and the oxygen or nitrogen of carbonyl or cyanide groups. The effects of these interactions are transmitted to and across the metal atom, affecting the metal-diimine z-bonding and associated chargetransfer frequency. This central role for hydrogen bonding, here and in organic solvatochromic compounds, is reflected in correlations with solvent acceptor numbers, AN [7]. We are not concerned here with the other type of solvatochromic inorganic complex, e.g. the e~ane-I,2~iimine-~-diketone copper(U) derivative fCu(acac)(tmen)]’ [8], where the electron-donor properties of the solvent are paramount, and correlations are with solvent donor numbers, DN [l].
EXPERIMENTAL
Bi~clo~ntadienyl titanium(IV) thiocyanate ~~(Cs~s)*(NCS~*J was prepared and characterized as described previously [9], as were the tetraphenylphosphonium and tetraphenylarsonitim salts of the tungsten(IV) anions [W(CN),(bipy)]*- and [WO(CN)3(bipy)]- [lo, 111. Refluxing K~~~r(~N)s(NO~] with the Schiff base 1, itself prepared from Z,~ia~~ip~dine and methylamine, for 10h gave an impure sample of [Cr(CN),(LLL)],LLL = 1. it did not prove possible to get an analytically pure sample of this compound; the relatively low solvent sensitivity exhibited by * Author to whom correspondence should be addressed. WA) 47111-A
985
A. AL-ALOUSK et
986 Table 1. Solvent effects on charge-transfer
al.
bands of [Cr(CN,)(LLL)]-,
[Ti(cp),(NCS)r],
[W(CN),(bipy)]*-
and [WOWWbipy)l-
E$
Solvent Water 1,ZEthanediol 1,4-Butanediol Methanol 1,2_Pentanediol 2-Methoxyethanol Ethanol 2-Butoxyethanol I-Butanol 2-Propanol Propylene carbonate Nitromethane Acetonitrile Dimethyl sulphoxide Acetone Nitrobenzene Dichloromethane Dimethylformamide 1,l-Dichloroethane Chloroform Benzene Toluene Carbon tetrachloride *From t Value $ From !t From
[Ti(cph(NCSM
WOWWWy)l- FWW@-W
17 700$
15 OOO§
22 830
16 180 16 340$:
14 6006
22 730
I6 260$
I4 5006
22 620 23000
16260 15460 15800 15 150$ 14 930 14 750
14 270 I4 160 14200 14 1008 13890 13 6008 13 720
14 580
13 8008
63.1 56.3
(52.W 55.5 54.1 52.3 51.9 50.2 50.2 48.6 46.6 46.3 46.0 45.0 42.0 42.0 41.1 41.0 39.4 39.1 34.5 33.8 32.5
PWNMbW12-
23000 23090
20 770 20 390 20 370 20 310 20 260 20 290 20 280 20 280 20 240 20 040
20 410 20 620 20000
22 470 20 530
22 370 19490 22 170 22 120 21830
Ref. [12]. for 1,3_butanediol. Ref. [lo]. Ref. [Ill.
the impure
sample
(see
below) discouraged us from expending disproportionate effort on this
compound. *
All spectra were run on a Shimadzu UV-160 spectrophotometer, whose wavelength calibration was checked periodically against a didymium glass filter. This instrument reads in wavelengths, which were converted into wavenumbers for inclusion in the Table above. The uncertainties on measured wavelengths are f 0.5 nm.
RESULTS AND DISCUSSION
Wavenumbers
of maximum absorption for the lowest energy charge-transfer bands of PWAWW andWO%@ipy)12-are given in Table 1. This Table also includes data for the [WO(CN),(bipy)]anion, though in this case wavelengths are given not for the lowest energy charge-transfer band (which has considerable d-d character) but for the next band of slightly higher energy which shows greater solvatochromic shifts. Preliminary results for other chromium compounds can be obtained from the authors. * Further details of the preparhiion and solvatochromism the authors (J.B.).
of this, and related species, can be obtained from
New solvatochromic inorganic complexes
987
f I
c
1
40
20
E,I kcal mol -’-
Fig. 1. Correlation of frequencies of maximum absorption for the main charge-transfer band of Ti(cph(NC& with solvent ET values (0 hydraxylic solvents; 0 non-hydroxylic solvents).
Titanium (IV) complex
Wavenumbers of maximum absorption for the charge-transfer (LMCT) band of [Ti(cp)* (NCS)J are plotted against solvent Er values in Fig. 1. The I& scale is probably the most extensive and widely used of empirical measures of solvent polarity. It is based on the solvatochromic characteristics of Reichardt’s “I& (30)” betaine [12], whose charge-transfer band is remarkably sensitive to solvation and solvent nature. As so often for inorganic complexes, correlation of Y, with ET for this titanium complex shows two different correlation lines, for hydroxylic and non-hydroxylic solvents [6,13]. The novel feature is that the two lines are not only of markedly different slopes, but they actually cross. Different lines for hydroxylic and non-hydroxylic solvents merely emphasize the differences in hydrogen-bonding properties between this titanium(IV) complex and the organic betaine used as the reference for the ET scale [13]. Direct comparisons of the solvent sensitivity of [Ti(cp)z(NCS)z]and other solvatochromic inorganic species can be made simply by plotting v,,,, values for the titanium(IV) compound against the respective Y,, values for the other compound. This is shown, for comparison with [Mo(CO),(bipy)], in Fig. 2. Again there are two lines, here attributable in the main to differences in hydrogen bonding to thiocyanate and to carbonyl. The slope of the correlation line for non-hydroxylic solvents is a little over 0.4, for the three alcohols rather less than 0.3. Comparison with the much-studied iron(I1) compounds
21000~
(
)
20000
22000
Y WcGO)4~bipy)) Fig. 2. Interrelation between frequencies of maximum absorption for charge-transfer with Ti(cp)2(NCS)2 and Mo(CO),(bipy) (0 hydroxylic solvents; 0 non-hydroxylic solvents).
A. At_-A~ousv et al.
988
17000 -
t
V I.= W (CN),(bipyf 18000 -
v... Fe(CN),(bipy),
-
Fig. 3. Correlation of frequencies of maximum absorption for the principle charge-transfer band of the [W(CN),(bipy)]*- anion with respective values for Fe(CN)r(bipy),.
[Fe(CN),(bipy)z] and [Fe(CN)z(phen),] is difficult due to the low solubility of these complexes in many of the solvents in which the titanium(IV) compound is soluble. However the limited comparison possible for alcohol solvents indicates a relative solvent sensitivity of about 0.3 for [Ti(cp)l(NCS)J. Thus this titanium(IV) complex is a much less sensitive solvatochromic probe of its solvent environment than these molybdenum(0) and iron(U) complexes. It therefore seems unlikely that it will prove useful in this role, except perhaps in media with significant content of aromatic hydrocarbons, where the cyclopentadienyl groups may confer a useful degree of solubility. Tungsten(W)
complexes
Figure 3 includes published and additional (Table 1) data on solvatochromism of the WCW~(bW12-anion. Both hydroxylic and non-hydroxylic solvents lie on the correlation line, whose slope of 1.2 indicates modestly greater solvent sensitivity than that of [Fe(CN)2(bipy)2]. In fact the solvent sensitivity of [W(CN),(bipy)12- is approximately equal to that of the molybdenum(O) complex [Mo(CO),(LLL)], LLL = 1, which is 1.5 (relative to [Fe(CN),(bipy),]) [14,15]. In Fig. 4 wavenumbers of maximum absorption for the oxotungsten(IV) complex [WO(CN),(bipy)]are plotted against respective values for the [W(CN),(bipy)12- anion. It is apparent that there are two correlation lines,
l5ooo
-
t V
c”..
IWOVGN~3(bipy)lcm“
t4OQC
lScQc
V... [W(CN)l(bipyl
I’-/cd
-c
Fig. 4. Correlation of frequencies of maximum absorption for the principle charge-transfer band of the (WO(CN),(bipy)]- anion with respective values for the [W(CN),(bipy)]*- anion (0 hydroxylic solvents; 0 non-hydroxylic solvents).
New solvatochromic inorganic complexes
989
for hydroxylic and for non-hydroxylic solvents. What is more, the two lines intersect (cf. the titanium complex, above). The very different trends in Fig. 4 for the two types of solvents can be attributed with some confidence to the possibility of hydrogen bonding to the oxide ligand in [WO(CN)3(bipy)]‘. The slope of the correlation line in nonhydroxylic media is approximately 0.7. Thus here, as for ternary iron(I1) complexes, solvent sensitivities decrease as the number of cyanide ligands decreases. The decrease here on going from six to three cyanide ligands is comparable with that on going from tetracyanodiimineiron(I1) anions to their dicyano-bis-diimineiron(I1) analogues [15]. K,[W(CN),(bipy)] is freely soluble in water, while (Ph$), [W(CN),(bipy)] is soluble in alcohols and in many other organic solvents. Perhaps surprisingly it is extremely sparingly soluble in paraffins, carbon tetrachloride, and toluene (though it is soluble in polar nitrobenzene). With its fairly high solvent sensitivity, we expect this anion to prove a useful indicator of solvation and local environment in WCW~@im)1*water-rich media, including micellar systems and such “organized media”. A combination of this complex and the titanium(IV) complex discussed above, with their complementary solubility properties, may well prove invaluable in probing solvation in microemulsions of the common and important water-alkoxyethanol-hydrocarbon type. Chromium(IZI) complexes
In contrast to [W(CN)6(bipy)]2-, the tricyanochromium(III)-Schiff base complexes examined in a preliminary manner in the course of our search for new solvatochromic complexes showed a disappointingly low solvent sensitivity. The complex derived from methylamine has only half the solvent sensitivity of (Fe(CN),(bipy),], and offers no compensating advantages. Analogous complexes from hydrazine and from taurine had very broad charge-transfer bands with maxima too flat and broad for solvatochromic probing; the analogous complex from sulphanilic acid showed negligible solubility in the majority of solvents examined. Acknowledgememtv-We are grateful to ALISON WAITS for carrying out much of the preliminary investigation into the chromium complexes, and to the Royal Society for Grants-in-aid towards the purchase of one of the spectrophotometers used in the initial stages of this project.
REFERENCES R. W. Soukup and R. Schmid, .I. Chem. Educ. 62,459 (1985). J. G. Bos, I. Lifschitz and K. M. Dijkema, 2.. Anorg. Aflg. Chem. 242.97 (1939). J. Bjerrum, A. W. Adamson and 0. Bostrup, Acta Chem. Stand. 10,329 (1956). H. Bock and H. tom Dieck, Angew. Chem., fnt. Ed. Engl. 5, 520 (1966); C/rem. Ber. 100,228 (1%7). H. A. Sinn, PhD Thesis, Darmstadt, F. R. G. (1966); H. Saito, J. Fujita and K. Saito, Bull. Chem. Sot. Japan 41,863 (1968); H. tom Dieck and I. W. Renk, Angew. Chem., Int. Ed. Engl. 9,793 (1970). [6] J. Burgess, Spectrochim. Acta 26A, 1369, 1957 (1970); H. Kobayashi, B. V. Aganvala and Y. Kaizu, Bull. Chem. Sot. Japan 48,465 (1975). [7] U. Mayer, V. Gutmann and W. Gerger, Mona&h. Chem. 106, 1235 (1975); V. Gutmann, Monatsh. Chem. 119, 1251 (1988). [S] K. Sone and Y. Fukuda, Bull. Chem. Sot. Japan 45,465 (1972). [9] Razak bin Ah, J. Burgess and A. T. Casey, J. Organomet. Chem. 362, 305 (1989). [lo] J. Szklarzewicz and A. Samotus, TransitionMet. Chem. 13.69 (1988). [ll] A. Samotus, J. Szklarzewicz and N. W. Alcock, fnorg. Chim. Acta 172, 129 (1990); J. Szklarzewicz, A. Samotus, N. W. Alcock and M. Mall, J. Chem. Sot., Dalton Trans. 2959 (1990). [12] C. Reichardt, Liisungsmitteleffeekte in der Organischen Chemie. Verlag Chemie, Weinheim (1968); C. Reichardt and E. Harbusch-Gornert, Annalen 721 (1983). [13] J. Burgess, J. G. Chambers and R. I. Haines, TransitionMet. Chem. 6, 145 (1981). [14] Razak bin Ah, J. Burgess, M. Kotowski and R. van Eldik, TransitionMet. Chem. 12, 230 (1987). [15] M. Kotowski, R. van Eldik, Razak bin Ali, J. Burgess and S. Radulovic. Inorg. Chim. Acta 131, 225 (1987). [l] [2] [3] [4] [S]