- Email: [email protected]
Linkage isomers of alizarin-bis(bipyridine)ruthenium(II)
ELSEVIER
lnorganica Chimica Acta 281 (1998) 126-133
Linkage isomers of alizarin-bis (bipyridine) ruthenium (II) Antonietta DelMedico, William J. Pietro *, A.B.P. Lever * York Univerxity. Department of Chemistry, ~t700 Keele Street, North York, Toronu~, Ont., M3J IP3. Canada
Received 9 September 1997; accepted 23 February 1998
Abstract
Alizarin-bis(bipyridine) ruthenium( I1 ) complexes exhibit a unique interconversion and coordination not reported in other metal-alizarin complexes. Previously communicated linkage isomers of alizarin-bi:.:(bipyridine) ruthenium ( II ) ( ( 1,2 ) and ( 1,9 ) coordinated complexes ) are characterised here by FT-1R and NMR ( 1D and 2D) spectro~:copic techniques, giving definitive results on ".,e previously proposed mode of coordination. This work also includes the Fr-IR of the (i,2) coordinated one-electron oxidation product, as well as that of the similarly coordinated complex. I-hydroxyanthraquinone-bis( bip3 ridine) ruthenium( Ii ). © 1998 Elsevier Science S.A. All rights reserved. Keywordw Linkage isomerism; Ruthenium complexes; Alizarin complexes; Bipyridine complexes
1. I n t r o d u c t i o n The demand for smaller and faster electronic devices has resulted in extensive research in the area of molecular electronics. ~,4olecules which switch to a metastable state under an external influence [ 1], can be applied to molecular switches a n d / o r information storage systems. To date, the range of switching molecules available is dominated by organic systems. We report here alizarin-bis(bipyridine)ruthenium(II), one of the relatively few inorganic molecular systems reported in the literature cap,'~ble of acting as a switch [ 2 - 1 6 ] . Inorganic molecular switches are desirable in that these systems can be readily tuned by varying the substituents on the ligand. An example of this is the design of a potentially photodriven molecular switch, by the incorporation of a phenolic moiety into the alizarin-bis(bipyridine) ruthenium ( Ii ) molecule 1171. o
o
OH
Allulln
The switching behaviour of alizarin-bis(bipyridine)ruthenium( It ) is attributed to the ambidentate ligand, alizarin * Corresponding authors. A.B.P. Lever: tel.: + 1-416-736 5246; fax: + I-416-736 5936; e-mail: blever @yorku.ca
(I,2-dihydroxy-9,10-anthraquinone). Alizarin (di)anion may chelate to metal ions at the (1,2) catechol-like, or the (1,9) acetylacetonate-like fragment. The bis(bipyridine)ruthenium (II) moiety, I Ru (bpy) 2 ] -~~, can be coordinated by either the (1,2) or (1,9) site and the two complexes can be interconverted by a combination of proton-transfer and thermal methods [181. O f the many alizarin-metal systems reported in the literature [ 19-29], this work is unique in that it involves interconversion between isomers. In fact, only the (1,9) coordination is typically reported in the literature [ 1924 l. The (1,2) mode of coordination is seldom reported and/ or discussed [ 16,25-291. In 1994, Bergerhoff and WunderItch reported the crystal structure of calcium-aluminiumalizarinate which is (1,9) coordinated to aluminium and ( i , 2 ) coordinated to calcium, with bridging oxygens [ 16]. In the same year, we reported that bis(bipyridine)ruthenium(ll) can be coordinated by alizarin at either the ( ! ,2 ) or the ( 1,9) site, based largely on electrochemical data [ 181. It is possible that other metal-alizarin complexes may exhibit isomerisation and interconversion, under similar pH and temperature conditions to those used in our system. In the synthesis of alizarin-bis (bipyridine) ruthenium (II) complexes, when 1 equiv, of base is used, the (1,9) alizarin coordination is favored whereas when 2 equiv, of base are used, the (1,2) alizarin coordination is favored [ ! 81. Higher temperatures in a basic medium allows interconversion between alizarin-bis(bipyridine)ruthenium(rI) isomers [ 18]. We hope that this paper will stimulate others involved in synthesis and study of related alizarin complexes to inves-
0020-i693/98/$ - see front matter © 1998 Elsevier Science S.A. All rights reserved. PII S0020-1693(98)00153-4
A. DelMedico et aL / hTorganica Chimica Acta 281 ~19981126-133
tigate similar interconversion phenomena and contribute to the growing and exciting field of molecular electronics. In this paper is reported the complete characterisation of both the (1,2) and (1,9) coordinated complexes and the (1,2) coordinated oxidation product, as well as the similar (1,9) coordinated complex, l-hydroxyanthraquinonebis(bipyridine) ruthenium (II). Electronic spectroscopy and electrochemical data were reported previously in a preliminary communication of the mode of coordination of these bidentate complexes [181. Fourier transform infrared, 1D and 2D nuclear magnetic resonance data and AMI calculations, presented here, provide definitive characterisation to guide further research into isomeric complexes of alizarin and similar systems. The detailed electronic structure of the linkage isomzrs, and some of their corresponding redox species, will be presented in a subsequent paper discussing electron spin resonance, electronic spectroscopy and semiempirical molecular orbital calculations [ 301.
2. Experimental 2.1. Chemicals All solvents and reagents used were reagent grade or better and were used as purchased except where otherwise stated. For NMR data, dichloromethane-d_~ (DCM-d2) (Aldrich) and dimethyl-d¢,-sulfoxide (DMSO-d,) (CDN isotopes) were 99.6 atom % D. Purification of Ru( bpy ) ~( alizarin ) complexes was perlormed by column chromatography with Bio-Beads SXI. QCat -~- ( Ru u- 1,2) and QCat -~ ( Ru m- 1,2) were eluted with dichloromethane and QCatH ( R u " - ! , 9 ) was eluted with a 1: ! mixture of acetone and dichloromethane. Bio-Beads SX 1 (Bio-Rad Laboratories) contains redox inactive impurities which can be removed by Soxhlet extraction with dichloromethane for 4 days. QCat-'- (Run-l,2) was purified immediately prior to carrying out any spectroscopic techniques since like many quinones it undergoes a slow photochemically-induced decomposition I311. When exposed to UV light, solutions of QCat 2 - ( Ru n- 1,2) decompose more rapidly than in room light, to a pink species. In the dark, QCat'--(Run-l,2) decomposes at a slower rate. Due to the instability of QCat -~- ( Ru u- ! ,2), many attempts were necessary to obtain the reported COSY. All solid compounds were stored in a desiccator, in the dark and solutions were freshly prepared for all measurements.
2.2. Physical methods Physical data were recorded on instrumentation as follows: Fourier Transform Infrared (FT-IR) spectra, Nicolet SX-20; and Proton Nuclear Magnetic Resonance spectra ( ~H NMR), Bruker 400 MHz. One-dimensional ( I D ) and two-dimensional (2D) ~H NMR experiments were performed in the Fourier transform mode. The 2D experiments were per-
formed with the following parameters: ~H-~H COSY: 512 X 1024 data matrix, zero-filled to 1024 dam points in t~, spectral width of 2048 Hz, 16 scans per t~ value, 1.0 or 1.5 s for the recycie delay, and unshifted sine-bell filtering in t~ and t_,. The dichloromethane and dimethylsulfoxide proton resonances at 5.28 and 2.50 ppm, respectively, versus TMS were used as references. All AMI calculations were performed using Spartan 2.0 [ 321, on a Silicon Graphics 4D/35 Personal Iris computer. All calculations related to FT-IR were performed using the AMI method [33-351 and equilibrium geometries were determined by full Cartesian gradient optimisation. As AM! is not yet parametrised for transition metals, the [Rutbpy)_~] 2~ fragment was modelled by a difluoroboron (BF_~+ ) group to mimic the electron withdrawing properties [ 17.361.
2.3. Preparation of complexes QCat 2 (RulJ-l,2), QCatH- (RuU-l,9) and Q O - ( R u n1,9) were prepared according to the literature [ 18].
2.3.1. QCate (Rum-l.2) To QCat-" (Ru'LI,2) (0.023 g, 0.032 mmol) in CH3CN ( 25 mi ) was added AgPF~ ( 0.012 g, 0.047 mmol) in a minimum amount of double distilled water. Within 10 rain of stirring, there was a colonr change from blue to ~een. The mixture was filtered through Celite. NI--I4PF6 (0.5 g, 3.1 mmol) in a minimum amount of double distilled water was added to the filtrate and left stirring for 20 rain. The product was evaporated to a small volume and diethyl ether was added. 6 days later, small needles of the product were collected by filtration. The crystals were washed with double distilled water then oven dried in vacuo at 100~C for 24 h (0.014 g, 53% yield). Anal Calc. for C34H~,F~A~i~O~PRu-2H_~O: C, 49.04; H, 3.15, N, 6.73. Found: C, 49.38; H, 3.14; N, 6.76%. This species has also been prepared by controlled potential electrolysis.
3. Results and discussion Bis( bipyridine )ruthenium( II ) ( [ Ru(bpy) 21-"* ) can be coordinated to alizarin by either the (1,2) or (1,9) coordination site, and the two complexes can be interconverted by a combination of proton-transfer and thermal methods [ 18 ]. The mode of coordination of these isomers has been established previously by using electrochemistry and electronic spectroscopy, and by comparison with the l-hydroxyanthraquinone (QOH) bis(bipyridine)ruthenium complex, QO- (Run-l,9) [ 18]. Fourier transform infrared and nuclear magnetic resonance ( I D and 2D), reported here, provide definitive data on the mode of coordination of these isomers. Fourier transform infrared of the (1,2) oxidation product is also discussed here. Based on this technique, and other studies reported in a subsequent paper [30], this oxidation appears
A. DclMedico et al / lnorganica Chimica Acta 281 (1998) 126-133
128
els and comparison with similar systems in the literature. A computer generated structure ofQCatH - ( Ru 't- 1,9) indicates that H8 is directed into the bipyridine ring current, resulting in an upfield shift compared with H5, with chemical shifts of 7.72 and 8.23 ppm, respectively. In QCatH - (Rul'-l,9), H3 is expected to be shifted upfield compared with H4 as in the free ligand 137 ]. In QCatH- ( Ru"- 1,9 ), simple decoupling experiments established that the signal at (',.94 is strongly coupled to that at 7.62 ppm, corresponding to H3 and H4, respectively. In QCat-" (Ru"-l,2), H3 and H4 are expected to have different chemical shifts, due to the close proximity of [ Ru( bpy )_,1-" to H3. Based on a similar system [ 38 I, H3 is expected to be shifted downfield ( 7.23 ppm) compared to H4 (6.34 ppm). The J values of the alizarin protons are as expected [371. Due to the low symmetry of alizarin-bis(bipyridine)ruthenium complexes, the four pyridine segments per molecule have different environments, resulting in 16 distinguishable hydrogens for the bis(bipyridine) fragment. The assigned bipyridine peaks of these complexes (Table 1 ) are comparable io other cis-[ Ru"( bpy I_,XY ] complexes. For a given pyridine segment, bipyridine proton 3 is more deshielded than bipyridine proton 4, which is more deshielded than bipyridine proton 5 [38--47]. According to the literature, the chemical shift of bipyridine proton 6 varies with the ligand XY. Molecular models of QCat-" ( Ru n- 1,2) and QCatH (Rt, n-l.9) indicate that H6a and H6c are directed into the alizarin ring current whereas H6b and H6d are directed in the bipyridine ring current. The alizarin ring is believed to be more electron rich than the bipyridine ring,
to be largely metal based in character, contrary to our prior repoll [ I 8 i. 3 1 Nuclear maeneNc resonance
'H NMR data for QCat-" (Run-l,2) and QCatH (Ru n1,9) are given in Table 1. All signals present in the 'H NMR for QCat-" (R¢I-1,2) and QCatH ( Ru n- 1,9) ( including the exchangeable proton in QCatH (Ru n-l,gI) are in the aromatic region, and the majority overlap each o:her. The COSY spectra of QCat-" tRun-l,2) and QCatH-(Run-I,9) are shown in Figs. 1 and 2, respectively, and the numbering schemes adopted are shown in Figs. 3 and 4, respectively. For NMR experiments on QCat-" ( Ru"- 1.2), the best results were obtained with DMSO-d,, where the signals are most spread out and trace solvent impurities are reducing, favoring QCat-" (Ru"-l,2) rather than the paramagnetic oxidised species. NMR data (Table I ) are consistent with the previously assigned alizarin mode of coordination. In the (1,2) coordinated complex. H5 and H6 are effectively equivalent to H8 and H7, respectively, whereas in the ( 1,9 ) coordinated complex, H5 and H6 have different chemical shifts from H8 and H7. respectively, due to the closer proximity of the [Ru(bpy)_~] -'+ fragment. In QCa'I~ (Run-l,9), the broad signal at 7.17 ppm which varies in intensity from one 'H NMR to another and disappears upon addition of D_,O, is assigned to H2. Of the coupled protons (both alizarin and bipyridine l, we assigned the most deshielded proton based on molecular modTable I )H NMR data fnr QCat: (Ru"-l.2) and QCatH
(Ru n-l,9) "
Complex
Fragment
lt2
H3
QCatH I Ru *L1.9 ~
alizarin
7.17s "
6.94d 17.91 ' 8.39d (8.1) 8.46d t8.1) 8.35d t8.1) 8.46d i8.1)
bpy a bpy b bpy c bpy d QCat: I Ru"-1,2)
alizann bpy a bpy b bpy c bpy d
7.23m 8.65d 18.11 8.75d 18,11 8.59d ~ 8.()) 8.70d (8.1)
1-t4 7.b2m 7.94t (7.91 8.13t (7.7~ 7.87m 8. I It t7.7)
H5 8.23d 17.7) 7.28t (6.3) 7.62m 7.23t !6.8) 7.54m
H6 7.72m
H8
7.54m
7.72m
8.00m
7.66m
7.87711 8.78d 15.5) 7.80d (5.5) 8.65d (5.4)
6.34d (8.4~ 7.79m
7.66m
8.()Ore
7.23m
7.66m
8.()Ore
7.66m
7.79m
7.23m
8.0{)m
7.66m
8.92d (5.3) 7.55d t5.7) 8.85d 15.3)
"Obtained at 411t)MHz. The chemical shifts are reported in ppm (,-5) downfic!d from tetramethylsilane. :' s = single], d = doublet, t = triplet, m = multiple]. • J values are rel~med in brackets.
1t7
| 29
A. D¢'lMe'dico et al. / Inortlanica (~Tmnita Acta 281 t 19981 126-133
!t
¸
11+ ill
. . . .
]i
, ....
8. ,!.... ~ /
+
,
+i
'ii ++i111It
(
-
," ~'.............
i!
.... ~
ii! ."-:~
i
+
-
~
~ I7.0
+
i
ii~ i[i~ zs
+
i :Z5
!8+o
!
++:,.
~__!
+
i80
~
-
i
~
~ + ~
@
+
:8.5
pore
ppfn 85 80 75 70 65 Fig. I. ~H NMR anti ~H-~H COSY "~pcctra of QCat" ~Ru'LI,2) in DMSO-d,,.
ppm 85 80 75 70 Fig. 2. 'H NMR and H - H COSY ,pectra of QCatH (RuJLl.t~) in DCM-d:.
5
resulting in a larger ring current and therefore a greater upfield effect on H6a and H6c relative to H6d and H6b. The J values of the bipyridine protons are comparable to those in a similar bis(bipyridinelcatecholatoruthenium(ll) species reported by Masui [461. Due to the instability of QCat-" i R u " - l , 2 ) , NOSY was not performed. Such studies would be necessary, to confirm the proposed positions of pyridine segments a - d
4
6 ~'~""
"-
"
3
++
"
5a
"
::-~
~3b
6b 6d
5b
3G
3d The principal absorption bands for alizarin-bis( bipyridine)ruthenium and related species, in the 1700-500 cm +region, are shown in Table 2. The infrared spectra, particularly the carbonyl stretching frequencies obtained theoretically and experimentally, provide insight into the mode of coordination. AM! semi-empirical calculations performed on QCat:-(BF_,~-I,2), Q C a t H + ( B F , + - I , 9 ) and the free ligand ~ndicate that the para quinonoid carbonyl vibrations a~e uncoupled from each other, consistent with previous literature assignments [ 19-21 l. While AM 1 overestimates the actual frequencies quite significantly, useful information can
/4n
+
8
4(:
3.2. Fourier transform infrared ( FT-IR ) spectroscopy
!ias ! I
5d
4d Fig. 3. Numbering ~chemeused fi)r ~H NMR data of QCat: ! Ru"- 1.2).
be obtained about the coupling of the C = O vibrations and the differences between them t see Table 3 in Section 5 I. The FT-IR spectrum of Q O - I Ru"- 1,9) is consistent with other l-hydroxyanthraquinone divalent metal complexes reported in the literature [20,48-52]. The similarity of the FT-IR spectra of QCatH - (Rul:-l.9) ( C ~ = O : 1650 cm - i C , = O : 1594 cm ~) and QO~-(RuSLI,9) ( C . , = O : 1652 cm ~, C,,=O: 1586 cm " t ) suggests that these complexes
130
A. DelMedico et al. I bmrganica Chimica Acta 281 (19981 126-133
St
I
,=
ii
=1
5C
4c--y/~ 3C
QCat 2 - ( Ru u- 1,2) and QCatH - (Ru'- 1,9), experimentally, is 30 c m - i , which correlates well with 28 cm-~ obtained theoretically at the AMI level for the QCatH-(BF_.+-I,9) complex. QCatH-(Run-l,9) has a coordinated C,~=O stretching frequency which lies lower in energy than that of the non-coordinated C , = O stretching frequency in QCat-~-(Run-l,2), as expected and supported by the calculations. The stretching modes lying at 1512 and 1537 cm-~ for QCatH- ( Ru n- 1,9) and 1527 and 1539 cm i for QO ( Ru"1,9) are characteristic of a C - C - C segment in the acetylacetonate-tike chelate ring [ 50[, and are absent in the ( 1,2) coordinated complexes and the free ligand, as expected ( Table 21. For the (1,9) coordinated complexes, the degree of delocalisation found in the acetylacetonate-like chelate ring can be probed by FT-IR data. Good indicators of the extent of delocalisation in the chelate ring are the stretching frequencies of the coordinated CO groups. A low energy shift of the prominent C,,=O carbonyl band and a high energy shift of CI-O, compared to the free ligand (alizarin: C,,=O: 1634 cm i C~-O: 1350 c m - t. l-hydroxyanthraquinone: C,,=O: 1637 cm ~, C~-O: 1450 cm i ). reflects an increase in delo-
4,
....
\//
/%
6d
----
aa
6b . . . . .
3d" :: 5d 41:1
'=~ 5b
3b
4b
Fig. 4. Numbering scheme used for ~H NMR data o f QCatH ( Ru IL I,C)).
have similar modes of coordination, in contrast to QCat 2 ( Ru'- 1,21 ( see Table 2). The displacements of the experimental carbonyl stretching frequencies of QCatH (Ru"-l,9), compared with those of alizarin are consistent with previous literature for similar complexes [19-211. QCatH ( R u " - l , 9 ) has a C I . = O stretching frequency less affected by complexation ( - 19 cm i ) than the C,,=O stretching frequency ( - 40 cm i ). The difference in the C . , = O stretching frequency in
Table 2 FT-IR data and assignments fi~r alizarin-bisl bipyridiue)rutheninm and related species ( 1700-500 cm ~) ,,.h A: [QCatH ( Ru'-1,91 I PF,, '; B: [QO ( Ru tl1.9 ~l PE. ": C: QCat: ( Ru"- 1,2 ) ": D: I QCat: I Ru u=-1.21 ] P F , ' : E: I -hydroxy-9, I O-anthraquinone ,t; F: alizarin " A
B
C
D
E
F"
Assign
1650m 1594w 1604w 1586w
1652s 1586s obs obs 1559w 1539w
1620m 162()m obs 1588w
1651m 1642m 1603w, 1592w
1672m 1637s
1669s 1634s
1591m
1589s
AO ( 10-CO, str.) AQ ( 9-CO, sir. ) bpy ( CC sir., CN str. ) AQ (aromatic CC, str. ) bpy (CN str., CC sir. CCH str. ) AQ ( C~C-C segment in chelate ring )
1537w
153(h'w 1512
1532w 1527w 1502s
AQ ( C-C--C segment in the chelate ring ) 150Is
obs 1462s 1447s 1402m 1425m obs
obs 1462vs 1446 1410m 1428m, 1419m 1366s
ohs
obs
obs
obs
1461vs
1462vs 1450m 1450m
1455vs 1350s
1360s
1331s
AQ ( Cat ring str. mode ) bpy ( ring sir., CCH bend, CC str.. CN str.) AQ (CC aromatic) +bpy (C=tt. C=C, CHO AQ ( aromatic CC, str. 1 AQ ( I - C O ) hpy ( ring str., CCH bend, CC str.) AQ ( 2-CO str., possibly CC str.)
1327w 1292s
1296vs
AQ ( C=O + aromatic rings)
1270m
1270m
AQ ( CC str. chelate ring ) + bpy ( ring str., CCH
1419m 1337s 1322w
130gm 1265s
1244m. 1240m
13(16s
1308m 1282nt
1287s
1260s 1261m
1264s
1209vw 1182~
1205w
bend, CN str. ) AQ (C-O Cat ) bpy
obs 1230m
1192vw, l179vw 116(Ivw
118gw l167w.l161w
1180w l158w
AQ ( R2--CC-R,, sir., possibly R2-CO, str.) 1183s
AQ bpy (CCC bend, CCH bend, CNC bend, CC str.) (continued)
A. DelMedico et aL / Inorganica Chimica Acta 281 (I 998) 126--133
131
Table 2 I contbmed) A
B
C
D
E
F"
1144vw 112t vw
I 150w 1122vw 1105vw 1075vw
1142w
I 157w. 1144w
1074vw 1059vw
I 151m 1124vw 1102vw 1070w 104.4w
1038vw
1037w
1036vw
1037w
1022w 968vw
1025m 970w 957w, 923,.*,,905w 879m
1015m
1008m 973vw
1067w 1050w 1040w
1048w
1016w
1032 1013,.v
881w
895w
Assign AQ bpy {CC sir. CCH bend. CCC bend } bpy {C('H bend. CC str.. CN sir. I AQ bpy ~CH bend, CCH bend. CC slr., CCC bend) AQ bpy {CH bend ) AQI'OH ) AQ {ring interaction~ bpy I CH bend t bpy AQ I aromatic CH bend
895w 843vs obs 799vw 762m
843vs obs 801 w 782w 761s 749sh,w
835vw, 821vw obs 800vw
S35w 775m
764m
766m
PF,, 849w. g28w AQ {arom. CH bend * atom. CC bend) bpy ( ring bend. CH bend I AQ bpy 748w
729w 714w 670vw 660vw 648vw 637vw
obs 729m 706m 668w 659w
621w
AQ AQ + bpy bpy ( CH bend ) AQ {CH AQ AQ I arom. def. bpy {CCC bend, NCC bend bpy AQ
581w
AQ
733w 721 m
720s 708s
668vw 653w
656w
713s 675'.*,' 660w
640m
598vw 557m "vw = very week: w = weak: m = medium: s = strong: vs = vet)' strong: sh = shoulder: obs = obscured: AQ = ligand fragment {alizarin and l-hy'droxy-9.10anthtaquiaone ). "This is not an exhaustive listing. It contains the principal bands {some weak bands are omittedL • The samples were prepared as Nujol mulls. d The samples were prepared as KBr pellets.
calisation in the (1,9) coordinated species. It has been reported by Nakamoto et al., that for acetylacetonate divalent metal complexes (where metal = Co, Ni, Zn, Cu, Pd), the coordinated C = O stretching frequency varies from 1601 c m - t for little metal-ligand delocalisation (cobalt) to 1535 c m - t for a higher degree ofdelocalisation (palladium) [ 49 ]. Walker reported that for l-hydroxyanthraquinone divalent metal complexes (where metal = Be, Cu, VO, Ni, Mg, Cd, Fe, Co, Mn, Zn, Ca, Sr` Ba, Pb) little metal-ligand delocalisation exists, with coordinated C = O stretching frequencies which vary from 1634-1610 c m - ' 1481. The coordinated carbonyi groups o f Q O - ( R u U - I , 9 ) (1586 c m - 1 ) and Q C a t H - ( R u n- 1,9) (1594 c m - t ) are found at m u c h lower frequencies than those reported by Walker [48]. Rather, these coordinated carbonyl stretching frequencies resemble those found in related 5-hydroxy-1,4-naphthaquinone chelates (where metal = Z n , Cu, Ni, Pb, C o L which vary from 1550-1590 c m - t [53]. From carbonyi stretching frequency data, it appears that Q O - ( R u II-1,9) and Q C a t H - ( R u It-1,9) exhibit lower levels o f delocalisation than do acetylacetonate
divalent metal complexes [ 491 and higher levels o f delocalisation than other I-hydroxyanthraquinone complexes [ 48 ]. Coordinated C~-O stretching frequencies are not used here to discuss the degree of delocalisation since the assignment o f this band has been debated in the literature. In the free ligand l-hydroxyanthraquinone, the band at 1450 c m - ~ has been assigned as a C~-O stretching frequency by Urbansk, and co-workers [50] and assigned primarily as a C . - . C stretching frequency by Walker [48]. Bands at 1265 c m for Q C a t H - ( R u " - l , 9 ) and 1260 cm - ~ for Q O - (RuIl-l,9) are attributed to the C--C stretching frequency in the acetylacetonate-like chelate ring and this assignment is supported by several infrared analyses repc~rted for related systems [ 20,48-50]. Calculations on QCat-" ( BF2 ~- 1,2) indicate that the separation between the pare. quinonoid carbonyt stretching frequencies is small (15 c m - ~ ) . Hence, the experimentally observed broad band at 1620 c m ~ in QCat 2- ( R u n - l , 2 ) is assigned to the combined overlapping stretching frequencies of the p a r a quinonoid carbonyl groups.
132
A. l;,'lMedico er aL / blorganica Chimica Acta 281 (19981 126-133
QCat z (RuH-I,2).4H20 ha.~ a C~,=O stretching frequency lower in energy than the positively charged Q C a t H - ( R u U - l , 9 ) . H 2 0 This can be attributed to an increase in hydration and/or the effect of charge. An increase in hydration causes water molecules to be more likely to be hydrogen bonded to the non-coordinated carbonyl groups resulting in a lower carbonyl frequency [ 50]. Both ( 1,21 and (1,9) coordinated species exhibit a broad weak band at 36503100 cm ~, indicating water of crystallisation. The similarity o f the C , , = O stretching frequencies for QCat 2 - ( Ru m- 1,2 ) ( 1 6 5 1 c m ~)andQCatH ( R u n - l , 9 ) ( 1 6 5 0 c m ~),bothof which are positively charged, suggest that the neutral QC~t-" ( R u " - l , 2 ) species exhibits a lower carbonyl stretching frequency due to the decrease in charge. The FT-IR spectra of QCat 2 (Ru"-1,2) and QCat 2 (Rum-l,2) show bands at 1261 and 1264 cm ~, respectively, which are indicative of catecholate coordination CO stretching frequencies. The occurrence of a metal-based rather than ligand-based oxidation, suggested by FT-IR data, is contraD' to our earlier proposal [ 18 ]. Since our previous work, further studies have been performed, including electron spin resonance, electronic spectroscopy and semi-empirical calculations which confirm an oxidised species with the unpaired electron in an orbital which has significant metal character. A subsequent paper will describe the electronic structure of this species in detail [ 30]. The stretching vibrations of the aromatic ring, typically observed at 1480 c m - ~ for catecholate complexes, are masked by the Nujol bands. Data for QCat 2 (RuU-l,2) collected in a KBr pellet show intense bands at 1474. 1458, 1437 and 14 ! 8 cm t possibly attributed to aromatic stretching vibrations. Due to inductive effects and increased charge, the oxidised species QCat 2 - (Rum-l,2) has carbonyl stretching frequencies shifted to higher energies (Cm=O: 1651 cm ~, C~.=O: 1642 =m ~) compared with Q C a F (RuU-l,2) (C~,,=O: 1620cm ~ , C , , = 0 : 1 6 2 0 c m ~).
ence o f low lying transitions in the electronic spectrum and a highly n e g a t i v e p a r a - q u i n o n e / p a r a - s e m i q u i n o n e reduction potential in the cyclic voltammetry.
5. Supplementary material Table 3, A M I calculated infrared carbonyl stretching frequencies is available on our web page: http:// www.science.yorku.ca/chem/profs/lever/blever.htm
6. Abbreviations Alizarin will be abbreviated as QCatH< Q identifies the 9,10-dioxo unit and CatH_, identifies the doubly protonated 1,2-catechol unit. Similarily QCatH a,ld QCat 2 correspond to 1,2-catechol anion and dianion, respectively. Hydroxyanthraquinone anion will be abbreviated as QO . The abbreviations used for the complexes include the oxidation state of ruthenium and the site of bisIbipyridine)rttthenium coordination: for example, ( R u " - l , 9 ) indicates ruthenium(ll)bis(bipyridinel is coordinated in the (1.9) site.
Acknowledgements We are indebted to the Natural Sciences and Engineering Research Council (Ottawa), and the Office of Naval Research (Washington) for financial sttpport, to Drs E.S. Dodsworth, C. da Cunha, Y.H. Tse, and R. Metcalfe for their valuable discussions, Dr P.R. Auburn |br the initial synthesis of the ( 1,21 coordinated complex, Drs M. Monteiro and A. Mainkar for their aid in the COSY, and to the JohnsonMatthey Company for the loan of RuCI,.
4. Conclusions
References
Our studies have provided evidence concerning linkage isomers of alizarin-bis(bipyridine)ruthenium(II) complexes. Electrochemical and spectroscopic techniques exhibit important features distinguishing the ( 1,2 ) coordinated complex from the ( 1,91 coordinated complex [ 18]. In the FT-IR spectra, overlapping carbonyl stretching frequencies denote QCat-" ( Ru H- 1,21 whereas separated carbonyl stretching frequencies (approximately 56 cm ~ ,'~eparation) denote QCatH (Ru n- 1,91. In the NMR spectra, QCat: ( R u u- 1,21 exhibits resonances for alizarin protons 5 and 6 similar to those of alizarin protons 8 and 7 (Fig. 31, respectively. For QCatH (RuU-1,9), on the other hand, alizarin protons 5 and 6 have different chemical shifts to alizarin protons 8 and 7 (Fig. 4), respectively, due to the closer proximity o f the [ Ru(bpy) 2] 2 ~ fragment. Features characteristic of the (1,2) coordinated isomer, as reported previously [ 18 ], are the pres-
[ I I W. Gopel, C. Ziegler, NanostmcturesBased on MolecuhwMaterials. VCH, Weinheim,New York, 1992. 12 ] M. Haga,T. Ano, K. Kano,S. Yamabe,Inorg.Chem. 30 ( 1991 ) 3843. [31 M. Menon. A. Pramanik, N, Bag, A. Chakravorty. J. Chem. Sot., Dalton Trans. ( 19951 1543. 141 R. Wang, J.G. Vos, R.H. Schmehl. R. Hage, J. Am. Chem. Soc 114 ( 19921 1964. 151 M. Sano, H. Taube, J. Am. Chem. Soc. 113 ( 1991 ~ 2327. 161 E.C. Constable,S.J. Dunne, D.G.F. Rees, C.X. Schmitt.Chem.Commun, ( 19961 1169. 171 M. Jezowska-Bojczuk,H. Kozlowskt,A. Zubor. T. Kiss. M. Branca, G. Micera. A. Dessi. J. Chem. Sot., DaltonTrans. ( 19901 2903. [81 T. Roth, W. Kaim, Inorg. Chem. 31 ( 19921 1930. [91 G. Desantis. L. Fabbrizzi, M. Licchelli. P. Pallavicini, lnorg. Chim. Acta 225 ( 19941 239. [ 10] J. Fees.W. Kaim,M. Mos~:herosch,W. Matheis,J. Klima,M. Krejcik, S. Zalis, lnorg. Chem. 32 ( 19931 )66. I I ! 1 N.S. Hush, A.T. Wong, G.B. Bacskay, J,R. Reimers,J. Am, Chem. Soc. 112 ( 19901 4192.
A. DelMe,?:c':~et a'L /b~organica ChimicaActa 27tl ¢1998~ 126~133 [ 121 R.R. Ruminski. D. Freiheit, D. Serveiss. B, Snyder. J.E.B. Johnson. Inorg. Chim. Acta 224 ( 1994~ 27. [ 131 J,R. Schoonover, W.D. Bates, T.J. Meyer, Inorg. Chem. 34 ( 1995 ) 6421. [ 141 M.D. Ward. Chem. Soc. Rev. 24 ( 1995 ) 121. [ 15] B. Whittle. N.S, Everest, C. Ho;vard, M.D. Ward, lnorg. Chem. 34 (1995) 2025. [ 161 C.-H. Wunderlich, G. Bergerhoff. Chem. Ber. 127 (1994) 1185. [ 171 A. DelMedico, S.S. Fielder. A.B.P. Lever. W.J. Pietro. Inorg. Chem. 34 ( |995~ 1507. 1181 A. DelMedico, P.R. Auburn. E.S. Dodsworth, A.B.P. I,ever, W.J. Pietro, Inorg. Chem. 33 (1994) 1583. [ 191 M.N. Bakola-Christianopoulou, Polyhedron 3 ( 1984~ 729. [ 201 E.G. Kiel. P.M, Heertjes. J. Soc. Dyers Colour. 79 ( 19631 2 I. [211 M.S. Masoud. M.S. Ta,vfik. S.E. Zayan, Synth. React. lnorg. Met.Org. Chem. 14 (1984) I. [22] L.J. Larson, J.l. Zink, Inorg. Chim. Acta 169 ( 19901 17. [ 23 ] G. Parissakis. J. Kontoyannakos, Anal. Chim. Acta 29 ( 1963 ~ 220. [24} E.M. Larsen, S.T. Hirozawa, J. lnorg. NucL Chem. 3 11956~ 198. [251 J.F. Flagg, H.A. Liebhafsky, E.H. Winslov¢, J. Am. Chem. Soc. 71 ( 1949~ 3630. (261 H A . Liebhafsky, E.H. Winstow. J. Am. Chem. Soc. 69 11947 ~ 1130. (271 H E . Zittel, T.M. Florence, Anal. Chem. 39 ( 1967~ 320. [281 T.M. Florence. Y.J. Farrar. H.E. Zittel, Aust. J. Chem. 22 t 1960~ 2321. [291 J.B.B. Heyns. J.J. Cruvv.'agen, E.A. Rohv~er, Proc. 31st ICCC, Umversity of British Columbia, Vancouver. Canada, Aug. 18-23, 1996, poster 5P104. [30] A. DelMedieo. E.S. Dods',,.orth. W.J. Pietro, A.B,P, Lever, to be submitted. [ 31] J.M. Bruce, Chem. Rev. 21 11967) 405. [321 Spartan, Version3.1,2.,Wavefunctionlnc.. t8401VonKarman. Suite 370, Ir,'ine, CA 92715. [331 M.J.S. Dev,'ar, E.G. Zoebisch, E.F. Hotly, J.J.P. Stewart. J. Am. Chem. Soc. 107 i 1985) 3902,
133
[34] M.J.S. De,.var. E.G. Zoebisch. J. M(~I. St.2ct : THEOCHEM !80 ( 19881 I. [351 M.J.$. Dev at. Y. Yate-Ching. In~rg. Chem. 29 i 19(34jj 388. [ 36] R.A. Metcalfe, E.S. D~dsw~rth. A.B.P. Lever, W.J. Pietro. D.J. Stufkens. Inorg. Chem. 32 t 1993~ 3581. [ 37 ] S Patti ( ed. ), The Chemistry of the Quinonoid Compounds. VoL 1. Wiley, New York, 1974. p. 179. 1381 C.J, Da Cunha, S.S. Fielder. D.V, Stynes. H. MasuL P.R. Auburn. A.B.P. Lever, Inorg. Chim. Acta 242 ~ 1996~ 293. [ 39 ] F.E. Lytle, L.M. Petrosky. LR. Carl,,on. Anal. Chim. Acta 57 ( 1971 ) 239. {401 E.C. Corn, table. J. Lev.is. lnorg. Chim Acta 70 ( 19~;3 i 251. }41 t R. Hage, R. Prin',. J.G. Haasnoot, J. Reedijk. J,G, Vos. J. Chem, Soc.. Dalton Trans. t 1987~ 1389. 1421 R.P Thummel. F. Lefoulon. J,D. Kcrp. lnorg. Chem. 26 ~ 1987 ~2370. [431 R. Hage. A.HJ. Dijkhni~,. J.G Haasnoot. R. Prins. J. Reedjik. B.E. Buchanan. J.G. Vos. lnorg. Chem. 27 i 19881 2185. [ 441 P.B. Hitchcock. K.R. Seddon. J.E. Turp. Y.Z. Y¢~usiLJ.A. Zora. E.C. Constable. O. Wemberg. J. Chem. Soc.. Dalton Tran~;. ~ 1988 ~ 1837. [451 BD.JR. Fennema. R.A G de Graaf. R. Hage. J.G. Has.t',noor. J. Reedjik, J.G. Vcs. J. Chem. S~c., Dalton Tran,,. ~ 1991 ~ 1043, [46} H Masui. PhD. Thesis. York Uni,.ersity. Toronto. Canada, 1993. [47} J.D. Birchall. T D. O'Donoghue. JR. Wood. lnorg. Chim. Acta 37 (1979) L461, [481 R.A. Walker. Spectrt~him. Acta. Pan, A 27 ( 1971 ~ 1785. 1491 K. Nakamoto. P.J. McCarthy, A.E. ~,lartell. J. Am. Chem. Soc. 83 i 1961J 1272. [501 Z. Ja~orska. C.I Jose, T. Urban~ki. Spectrochim. Acta. Part A 30 (1974) 1161. [5! I R. West, R Riley, J. Inorg. Nucl. Chem. 5 i 1958) 295. 1521 V.M. Gooden. H Cai. T.P. Dasgupta. N R. Gordon. L.J. Hughes. G.G. Sadler, Inorg. Chim. Acta 225 11997 ~ 105. [ 531 R.S. Bouei. CP- McEachem. J. Inor.~. NucL Chem. 32 i 1970 ~ 2653.
lnorganica Chimica Acta 281 (1998) 126-133
Linkage isomers of alizarin-bis (bipyridine) ruthenium (II) Antonietta DelMedico, William J. Pietro *, A.B.P. Lever * York Univerxity. Department of Chemistry, ~t700 Keele Street, North York, Toronu~, Ont., M3J IP3. Canada
Received 9 September 1997; accepted 23 February 1998
Abstract
Alizarin-bis(bipyridine) ruthenium( I1 ) complexes exhibit a unique interconversion and coordination not reported in other metal-alizarin complexes. Previously communicated linkage isomers of alizarin-bi:.:(bipyridine) ruthenium ( II ) ( ( 1,2 ) and ( 1,9 ) coordinated complexes ) are characterised here by FT-1R and NMR ( 1D and 2D) spectro~:copic techniques, giving definitive results on ".,e previously proposed mode of coordination. This work also includes the Fr-IR of the (i,2) coordinated one-electron oxidation product, as well as that of the similarly coordinated complex. I-hydroxyanthraquinone-bis( bip3 ridine) ruthenium( Ii ). © 1998 Elsevier Science S.A. All rights reserved. Keywordw Linkage isomerism; Ruthenium complexes; Alizarin complexes; Bipyridine complexes
1. I n t r o d u c t i o n The demand for smaller and faster electronic devices has resulted in extensive research in the area of molecular electronics. ~,4olecules which switch to a metastable state under an external influence [ 1], can be applied to molecular switches a n d / o r information storage systems. To date, the range of switching molecules available is dominated by organic systems. We report here alizarin-bis(bipyridine)ruthenium(II), one of the relatively few inorganic molecular systems reported in the literature cap,'~ble of acting as a switch [ 2 - 1 6 ] . Inorganic molecular switches are desirable in that these systems can be readily tuned by varying the substituents on the ligand. An example of this is the design of a potentially photodriven molecular switch, by the incorporation of a phenolic moiety into the alizarin-bis(bipyridine) ruthenium ( Ii ) molecule 1171. o
o
OH
Allulln
The switching behaviour of alizarin-bis(bipyridine)ruthenium( It ) is attributed to the ambidentate ligand, alizarin * Corresponding authors. A.B.P. Lever: tel.: + 1-416-736 5246; fax: + I-416-736 5936; e-mail: blever @yorku.ca
(I,2-dihydroxy-9,10-anthraquinone). Alizarin (di)anion may chelate to metal ions at the (1,2) catechol-like, or the (1,9) acetylacetonate-like fragment. The bis(bipyridine)ruthenium (II) moiety, I Ru (bpy) 2 ] -~~, can be coordinated by either the (1,2) or (1,9) site and the two complexes can be interconverted by a combination of proton-transfer and thermal methods [181. O f the many alizarin-metal systems reported in the literature [ 19-29], this work is unique in that it involves interconversion between isomers. In fact, only the (1,9) coordination is typically reported in the literature [ 1924 l. The (1,2) mode of coordination is seldom reported and/ or discussed [ 16,25-291. In 1994, Bergerhoff and WunderItch reported the crystal structure of calcium-aluminiumalizarinate which is (1,9) coordinated to aluminium and ( i , 2 ) coordinated to calcium, with bridging oxygens [ 16]. In the same year, we reported that bis(bipyridine)ruthenium(ll) can be coordinated by alizarin at either the ( ! ,2 ) or the ( 1,9) site, based largely on electrochemical data [ 181. It is possible that other metal-alizarin complexes may exhibit isomerisation and interconversion, under similar pH and temperature conditions to those used in our system. In the synthesis of alizarin-bis (bipyridine) ruthenium (II) complexes, when 1 equiv, of base is used, the (1,9) alizarin coordination is favored whereas when 2 equiv, of base are used, the (1,2) alizarin coordination is favored [ ! 81. Higher temperatures in a basic medium allows interconversion between alizarin-bis(bipyridine)ruthenium(rI) isomers [ 18]. We hope that this paper will stimulate others involved in synthesis and study of related alizarin complexes to inves-
0020-i693/98/$ - see front matter © 1998 Elsevier Science S.A. All rights reserved. PII S0020-1693(98)00153-4
A. DelMedico et aL / hTorganica Chimica Acta 281 ~19981126-133
tigate similar interconversion phenomena and contribute to the growing and exciting field of molecular electronics. In this paper is reported the complete characterisation of both the (1,2) and (1,9) coordinated complexes and the (1,2) coordinated oxidation product, as well as the similar (1,9) coordinated complex, l-hydroxyanthraquinonebis(bipyridine) ruthenium (II). Electronic spectroscopy and electrochemical data were reported previously in a preliminary communication of the mode of coordination of these bidentate complexes [181. Fourier transform infrared, 1D and 2D nuclear magnetic resonance data and AMI calculations, presented here, provide definitive characterisation to guide further research into isomeric complexes of alizarin and similar systems. The detailed electronic structure of the linkage isomzrs, and some of their corresponding redox species, will be presented in a subsequent paper discussing electron spin resonance, electronic spectroscopy and semiempirical molecular orbital calculations [ 301.
2. Experimental 2.1. Chemicals All solvents and reagents used were reagent grade or better and were used as purchased except where otherwise stated. For NMR data, dichloromethane-d_~ (DCM-d2) (Aldrich) and dimethyl-d¢,-sulfoxide (DMSO-d,) (CDN isotopes) were 99.6 atom % D. Purification of Ru( bpy ) ~( alizarin ) complexes was perlormed by column chromatography with Bio-Beads SXI. QCat -~- ( Ru u- 1,2) and QCat -~ ( Ru m- 1,2) were eluted with dichloromethane and QCatH ( R u " - ! , 9 ) was eluted with a 1: ! mixture of acetone and dichloromethane. Bio-Beads SX 1 (Bio-Rad Laboratories) contains redox inactive impurities which can be removed by Soxhlet extraction with dichloromethane for 4 days. QCat-'- (Run-l,2) was purified immediately prior to carrying out any spectroscopic techniques since like many quinones it undergoes a slow photochemically-induced decomposition I311. When exposed to UV light, solutions of QCat 2 - ( Ru n- 1,2) decompose more rapidly than in room light, to a pink species. In the dark, QCat'--(Run-l,2) decomposes at a slower rate. Due to the instability of QCat -~- ( Ru u- ! ,2), many attempts were necessary to obtain the reported COSY. All solid compounds were stored in a desiccator, in the dark and solutions were freshly prepared for all measurements.
2.2. Physical methods Physical data were recorded on instrumentation as follows: Fourier Transform Infrared (FT-IR) spectra, Nicolet SX-20; and Proton Nuclear Magnetic Resonance spectra ( ~H NMR), Bruker 400 MHz. One-dimensional ( I D ) and two-dimensional (2D) ~H NMR experiments were performed in the Fourier transform mode. The 2D experiments were per-
formed with the following parameters: ~H-~H COSY: 512 X 1024 data matrix, zero-filled to 1024 dam points in t~, spectral width of 2048 Hz, 16 scans per t~ value, 1.0 or 1.5 s for the recycie delay, and unshifted sine-bell filtering in t~ and t_,. The dichloromethane and dimethylsulfoxide proton resonances at 5.28 and 2.50 ppm, respectively, versus TMS were used as references. All AMI calculations were performed using Spartan 2.0 [ 321, on a Silicon Graphics 4D/35 Personal Iris computer. All calculations related to FT-IR were performed using the AMI method [33-351 and equilibrium geometries were determined by full Cartesian gradient optimisation. As AM! is not yet parametrised for transition metals, the [Rutbpy)_~] 2~ fragment was modelled by a difluoroboron (BF_~+ ) group to mimic the electron withdrawing properties [ 17.361.
2.3. Preparation of complexes QCat 2 (RulJ-l,2), QCatH- (RuU-l,9) and Q O - ( R u n1,9) were prepared according to the literature [ 18].
2.3.1. QCate (Rum-l.2) To QCat-" (Ru'LI,2) (0.023 g, 0.032 mmol) in CH3CN ( 25 mi ) was added AgPF~ ( 0.012 g, 0.047 mmol) in a minimum amount of double distilled water. Within 10 rain of stirring, there was a colonr change from blue to ~een. The mixture was filtered through Celite. NI--I4PF6 (0.5 g, 3.1 mmol) in a minimum amount of double distilled water was added to the filtrate and left stirring for 20 rain. The product was evaporated to a small volume and diethyl ether was added. 6 days later, small needles of the product were collected by filtration. The crystals were washed with double distilled water then oven dried in vacuo at 100~C for 24 h (0.014 g, 53% yield). Anal Calc. for C34H~,F~A~i~O~PRu-2H_~O: C, 49.04; H, 3.15, N, 6.73. Found: C, 49.38; H, 3.14; N, 6.76%. This species has also been prepared by controlled potential electrolysis.
3. Results and discussion Bis( bipyridine )ruthenium( II ) ( [ Ru(bpy) 21-"* ) can be coordinated to alizarin by either the (1,2) or (1,9) coordination site, and the two complexes can be interconverted by a combination of proton-transfer and thermal methods [ 18 ]. The mode of coordination of these isomers has been established previously by using electrochemistry and electronic spectroscopy, and by comparison with the l-hydroxyanthraquinone (QOH) bis(bipyridine)ruthenium complex, QO- (Run-l,9) [ 18]. Fourier transform infrared and nuclear magnetic resonance ( I D and 2D), reported here, provide definitive data on the mode of coordination of these isomers. Fourier transform infrared of the (1,2) oxidation product is also discussed here. Based on this technique, and other studies reported in a subsequent paper [30], this oxidation appears
A. DclMedico et al / lnorganica Chimica Acta 281 (1998) 126-133
128
els and comparison with similar systems in the literature. A computer generated structure ofQCatH - ( Ru 't- 1,9) indicates that H8 is directed into the bipyridine ring current, resulting in an upfield shift compared with H5, with chemical shifts of 7.72 and 8.23 ppm, respectively. In QCatH - (Rul'-l,9), H3 is expected to be shifted upfield compared with H4 as in the free ligand 137 ]. In QCatH- ( Ru"- 1,9 ), simple decoupling experiments established that the signal at (',.94 is strongly coupled to that at 7.62 ppm, corresponding to H3 and H4, respectively. In QCat-" (Ru"-l,2), H3 and H4 are expected to have different chemical shifts, due to the close proximity of [ Ru( bpy )_,1-" to H3. Based on a similar system [ 38 I, H3 is expected to be shifted downfield ( 7.23 ppm) compared to H4 (6.34 ppm). The J values of the alizarin protons are as expected [371. Due to the low symmetry of alizarin-bis(bipyridine)ruthenium complexes, the four pyridine segments per molecule have different environments, resulting in 16 distinguishable hydrogens for the bis(bipyridine) fragment. The assigned bipyridine peaks of these complexes (Table 1 ) are comparable io other cis-[ Ru"( bpy I_,XY ] complexes. For a given pyridine segment, bipyridine proton 3 is more deshielded than bipyridine proton 4, which is more deshielded than bipyridine proton 5 [38--47]. According to the literature, the chemical shift of bipyridine proton 6 varies with the ligand XY. Molecular models of QCat-" ( Ru n- 1,2) and QCatH (Rt, n-l.9) indicate that H6a and H6c are directed into the alizarin ring current whereas H6b and H6d are directed in the bipyridine ring current. The alizarin ring is believed to be more electron rich than the bipyridine ring,
to be largely metal based in character, contrary to our prior repoll [ I 8 i. 3 1 Nuclear maeneNc resonance
'H NMR data for QCat-" (Run-l,2) and QCatH (Ru n1,9) are given in Table 1. All signals present in the 'H NMR for QCat-" (R¢I-1,2) and QCatH ( Ru n- 1,9) ( including the exchangeable proton in QCatH (Ru n-l,gI) are in the aromatic region, and the majority overlap each o:her. The COSY spectra of QCat-" tRun-l,2) and QCatH-(Run-I,9) are shown in Figs. 1 and 2, respectively, and the numbering schemes adopted are shown in Figs. 3 and 4, respectively. For NMR experiments on QCat-" ( Ru"- 1.2), the best results were obtained with DMSO-d,, where the signals are most spread out and trace solvent impurities are reducing, favoring QCat-" (Ru"-l,2) rather than the paramagnetic oxidised species. NMR data (Table I ) are consistent with the previously assigned alizarin mode of coordination. In the (1,2) coordinated complex. H5 and H6 are effectively equivalent to H8 and H7, respectively, whereas in the ( 1,9 ) coordinated complex, H5 and H6 have different chemical shifts from H8 and H7. respectively, due to the closer proximity of the [Ru(bpy)_~] -'+ fragment. In QCa'I~ (Run-l,9), the broad signal at 7.17 ppm which varies in intensity from one 'H NMR to another and disappears upon addition of D_,O, is assigned to H2. Of the coupled protons (both alizarin and bipyridine l, we assigned the most deshielded proton based on molecular modTable I )H NMR data fnr QCat: (Ru"-l.2) and QCatH
(Ru n-l,9) "
Complex
Fragment
lt2
H3
QCatH I Ru *L1.9 ~
alizarin
7.17s "
6.94d 17.91 ' 8.39d (8.1) 8.46d t8.1) 8.35d t8.1) 8.46d i8.1)
bpy a bpy b bpy c bpy d QCat: I Ru"-1,2)
alizann bpy a bpy b bpy c bpy d
7.23m 8.65d 18.11 8.75d 18,11 8.59d ~ 8.()) 8.70d (8.1)
1-t4 7.b2m 7.94t (7.91 8.13t (7.7~ 7.87m 8. I It t7.7)
H5 8.23d 17.7) 7.28t (6.3) 7.62m 7.23t !6.8) 7.54m
H6 7.72m
H8
7.54m
7.72m
8.00m
7.66m
7.87711 8.78d 15.5) 7.80d (5.5) 8.65d (5.4)
6.34d (8.4~ 7.79m
7.66m
8.()Ore
7.23m
7.66m
8.()Ore
7.66m
7.79m
7.23m
8.0{)m
7.66m
8.92d (5.3) 7.55d t5.7) 8.85d 15.3)
"Obtained at 411t)MHz. The chemical shifts are reported in ppm (,-5) downfic!d from tetramethylsilane. :' s = single], d = doublet, t = triplet, m = multiple]. • J values are rel~med in brackets.
1t7
| 29
A. D¢'lMe'dico et al. / Inortlanica (~Tmnita Acta 281 t 19981 126-133
!t
¸
11+ ill
. . . .
]i
, ....
8. ,!.... ~ /
+
,
+i
'ii ++i111It
(
-
," ~'.............
i!
.... ~
ii! ."-:~
i
+
-
~
~ I7.0
+
i
ii~ i[i~ zs
+
i :Z5
!8+o
!
++:,.
~__!
+
i80
~
-
i
~
~ + ~
@
+
:8.5
pore
ppfn 85 80 75 70 65 Fig. I. ~H NMR anti ~H-~H COSY "~pcctra of QCat" ~Ru'LI,2) in DMSO-d,,.
ppm 85 80 75 70 Fig. 2. 'H NMR and H - H COSY ,pectra of QCatH (RuJLl.t~) in DCM-d:.
5
resulting in a larger ring current and therefore a greater upfield effect on H6a and H6c relative to H6d and H6b. The J values of the bipyridine protons are comparable to those in a similar bis(bipyridinelcatecholatoruthenium(ll) species reported by Masui [461. Due to the instability of QCat-" i R u " - l , 2 ) , NOSY was not performed. Such studies would be necessary, to confirm the proposed positions of pyridine segments a - d
4
6 ~'~""
"-
"
3
++
"
5a
"
::-~
~3b
6b 6d
5b
3G
3d The principal absorption bands for alizarin-bis( bipyridine)ruthenium and related species, in the 1700-500 cm +region, are shown in Table 2. The infrared spectra, particularly the carbonyl stretching frequencies obtained theoretically and experimentally, provide insight into the mode of coordination. AM! semi-empirical calculations performed on QCat:-(BF_,~-I,2), Q C a t H + ( B F , + - I , 9 ) and the free ligand ~ndicate that the para quinonoid carbonyl vibrations a~e uncoupled from each other, consistent with previous literature assignments [ 19-21 l. While AM 1 overestimates the actual frequencies quite significantly, useful information can
/4n
+
8
4(:
3.2. Fourier transform infrared ( FT-IR ) spectroscopy
!ias ! I
5d
4d Fig. 3. Numbering ~chemeused fi)r ~H NMR data of QCat: ! Ru"- 1.2).
be obtained about the coupling of the C = O vibrations and the differences between them t see Table 3 in Section 5 I. The FT-IR spectrum of Q O - I Ru"- 1,9) is consistent with other l-hydroxyanthraquinone divalent metal complexes reported in the literature [20,48-52]. The similarity of the FT-IR spectra of QCatH - (Rul:-l.9) ( C ~ = O : 1650 cm - i C , = O : 1594 cm ~) and QO~-(RuSLI,9) ( C . , = O : 1652 cm ~, C,,=O: 1586 cm " t ) suggests that these complexes
130
A. DelMedico et al. I bmrganica Chimica Acta 281 (19981 126-133
St
I
,=
ii
=1
5C
4c--y/~ 3C
QCat 2 - ( Ru u- 1,2) and QCatH - (Ru'- 1,9), experimentally, is 30 c m - i , which correlates well with 28 cm-~ obtained theoretically at the AMI level for the QCatH-(BF_.+-I,9) complex. QCatH-(Run-l,9) has a coordinated C,~=O stretching frequency which lies lower in energy than that of the non-coordinated C , = O stretching frequency in QCat-~-(Run-l,2), as expected and supported by the calculations. The stretching modes lying at 1512 and 1537 cm-~ for QCatH- ( Ru n- 1,9) and 1527 and 1539 cm i for QO ( Ru"1,9) are characteristic of a C - C - C segment in the acetylacetonate-tike chelate ring [ 50[, and are absent in the ( 1,2) coordinated complexes and the free ligand, as expected ( Table 21. For the (1,9) coordinated complexes, the degree of delocalisation found in the acetylacetonate-like chelate ring can be probed by FT-IR data. Good indicators of the extent of delocalisation in the chelate ring are the stretching frequencies of the coordinated CO groups. A low energy shift of the prominent C,,=O carbonyl band and a high energy shift of CI-O, compared to the free ligand (alizarin: C,,=O: 1634 cm i C~-O: 1350 c m - t. l-hydroxyanthraquinone: C,,=O: 1637 cm ~, C~-O: 1450 cm i ). reflects an increase in delo-
4,
....
\//
/%
6d
----
aa
6b . . . . .
3d" :: 5d 41:1
'=~ 5b
3b
4b
Fig. 4. Numbering scheme used for ~H NMR data o f QCatH ( Ru IL I,C)).
have similar modes of coordination, in contrast to QCat 2 ( Ru'- 1,21 ( see Table 2). The displacements of the experimental carbonyl stretching frequencies of QCatH (Ru"-l,9), compared with those of alizarin are consistent with previous literature for similar complexes [19-211. QCatH ( R u " - l , 9 ) has a C I . = O stretching frequency less affected by complexation ( - 19 cm i ) than the C,,=O stretching frequency ( - 40 cm i ). The difference in the C . , = O stretching frequency in
Table 2 FT-IR data and assignments fi~r alizarin-bisl bipyridiue)rutheninm and related species ( 1700-500 cm ~) ,,.h A: [QCatH ( Ru'-1,91 I PF,, '; B: [QO ( Ru tl1.9 ~l PE. ": C: QCat: ( Ru"- 1,2 ) ": D: I QCat: I Ru u=-1.21 ] P F , ' : E: I -hydroxy-9, I O-anthraquinone ,t; F: alizarin " A
B
C
D
E
F"
Assign
1650m 1594w 1604w 1586w
1652s 1586s obs obs 1559w 1539w
1620m 162()m obs 1588w
1651m 1642m 1603w, 1592w
1672m 1637s
1669s 1634s
1591m
1589s
AO ( 10-CO, str.) AQ ( 9-CO, sir. ) bpy ( CC sir., CN str. ) AQ (aromatic CC, str. ) bpy (CN str., CC sir. CCH str. ) AQ ( C~C-C segment in chelate ring )
1537w
153(h'w 1512
1532w 1527w 1502s
AQ ( C-C--C segment in the chelate ring ) 150Is
obs 1462s 1447s 1402m 1425m obs
obs 1462vs 1446 1410m 1428m, 1419m 1366s
ohs
obs
obs
obs
1461vs
1462vs 1450m 1450m
1455vs 1350s
1360s
1331s
AQ ( Cat ring str. mode ) bpy ( ring sir., CCH bend, CC str.. CN str.) AQ (CC aromatic) +bpy (C=tt. C=C, CHO AQ ( aromatic CC, str. 1 AQ ( I - C O ) hpy ( ring str., CCH bend, CC str.) AQ ( 2-CO str., possibly CC str.)
1327w 1292s
1296vs
AQ ( C=O + aromatic rings)
1270m
1270m
AQ ( CC str. chelate ring ) + bpy ( ring str., CCH
1419m 1337s 1322w
130gm 1265s
1244m. 1240m
13(16s
1308m 1282nt
1287s
1260s 1261m
1264s
1209vw 1182~
1205w
bend, CN str. ) AQ (C-O Cat ) bpy
obs 1230m
1192vw, l179vw 116(Ivw
118gw l167w.l161w
1180w l158w
AQ ( R2--CC-R,, sir., possibly R2-CO, str.) 1183s
AQ bpy (CCC bend, CCH bend, CNC bend, CC str.) (continued)
A. DelMedico et aL / Inorganica Chimica Acta 281 (I 998) 126--133
131
Table 2 I contbmed) A
B
C
D
E
F"
1144vw 112t vw
I 150w 1122vw 1105vw 1075vw
1142w
I 157w. 1144w
1074vw 1059vw
I 151m 1124vw 1102vw 1070w 104.4w
1038vw
1037w
1036vw
1037w
1022w 968vw
1025m 970w 957w, 923,.*,,905w 879m
1015m
1008m 973vw
1067w 1050w 1040w
1048w
1016w
1032 1013,.v
881w
895w
Assign AQ bpy {CC sir. CCH bend. CCC bend } bpy {C('H bend. CC str.. CN sir. I AQ bpy ~CH bend, CCH bend. CC slr., CCC bend) AQ bpy {CH bend ) AQI'OH ) AQ {ring interaction~ bpy I CH bend t bpy AQ I aromatic CH bend
895w 843vs obs 799vw 762m
843vs obs 801 w 782w 761s 749sh,w
835vw, 821vw obs 800vw
S35w 775m
764m
766m
PF,, 849w. g28w AQ {arom. CH bend * atom. CC bend) bpy ( ring bend. CH bend I AQ bpy 748w
729w 714w 670vw 660vw 648vw 637vw
obs 729m 706m 668w 659w
621w
AQ AQ + bpy bpy ( CH bend ) AQ {CH AQ AQ I arom. def. bpy {CCC bend, NCC bend bpy AQ
581w
AQ
733w 721 m
720s 708s
668vw 653w
656w
713s 675'.*,' 660w
640m
598vw 557m "vw = very week: w = weak: m = medium: s = strong: vs = vet)' strong: sh = shoulder: obs = obscured: AQ = ligand fragment {alizarin and l-hy'droxy-9.10anthtaquiaone ). "This is not an exhaustive listing. It contains the principal bands {some weak bands are omittedL • The samples were prepared as Nujol mulls. d The samples were prepared as KBr pellets.
calisation in the (1,9) coordinated species. It has been reported by Nakamoto et al., that for acetylacetonate divalent metal complexes (where metal = Co, Ni, Zn, Cu, Pd), the coordinated C = O stretching frequency varies from 1601 c m - t for little metal-ligand delocalisation (cobalt) to 1535 c m - t for a higher degree ofdelocalisation (palladium) [ 49 ]. Walker reported that for l-hydroxyanthraquinone divalent metal complexes (where metal = Be, Cu, VO, Ni, Mg, Cd, Fe, Co, Mn, Zn, Ca, Sr` Ba, Pb) little metal-ligand delocalisation exists, with coordinated C = O stretching frequencies which vary from 1634-1610 c m - ' 1481. The coordinated carbonyi groups o f Q O - ( R u U - I , 9 ) (1586 c m - 1 ) and Q C a t H - ( R u n- 1,9) (1594 c m - t ) are found at m u c h lower frequencies than those reported by Walker [48]. Rather, these coordinated carbonyl stretching frequencies resemble those found in related 5-hydroxy-1,4-naphthaquinone chelates (where metal = Z n , Cu, Ni, Pb, C o L which vary from 1550-1590 c m - t [53]. From carbonyi stretching frequency data, it appears that Q O - ( R u II-1,9) and Q C a t H - ( R u It-1,9) exhibit lower levels o f delocalisation than do acetylacetonate
divalent metal complexes [ 491 and higher levels o f delocalisation than other I-hydroxyanthraquinone complexes [ 48 ]. Coordinated C~-O stretching frequencies are not used here to discuss the degree of delocalisation since the assignment o f this band has been debated in the literature. In the free ligand l-hydroxyanthraquinone, the band at 1450 c m - ~ has been assigned as a C~-O stretching frequency by Urbansk, and co-workers [50] and assigned primarily as a C . - . C stretching frequency by Walker [48]. Bands at 1265 c m for Q C a t H - ( R u " - l , 9 ) and 1260 cm - ~ for Q O - (RuIl-l,9) are attributed to the C--C stretching frequency in the acetylacetonate-like chelate ring and this assignment is supported by several infrared analyses repc~rted for related systems [ 20,48-50]. Calculations on QCat-" ( BF2 ~- 1,2) indicate that the separation between the pare. quinonoid carbonyt stretching frequencies is small (15 c m - ~ ) . Hence, the experimentally observed broad band at 1620 c m ~ in QCat 2- ( R u n - l , 2 ) is assigned to the combined overlapping stretching frequencies of the p a r a quinonoid carbonyl groups.
132
A. l;,'lMedico er aL / blorganica Chimica Acta 281 (19981 126-133
QCat z (RuH-I,2).4H20 ha.~ a C~,=O stretching frequency lower in energy than the positively charged Q C a t H - ( R u U - l , 9 ) . H 2 0 This can be attributed to an increase in hydration and/or the effect of charge. An increase in hydration causes water molecules to be more likely to be hydrogen bonded to the non-coordinated carbonyl groups resulting in a lower carbonyl frequency [ 50]. Both ( 1,21 and (1,9) coordinated species exhibit a broad weak band at 36503100 cm ~, indicating water of crystallisation. The similarity o f the C , , = O stretching frequencies for QCat 2 - ( Ru m- 1,2 ) ( 1 6 5 1 c m ~)andQCatH ( R u n - l , 9 ) ( 1 6 5 0 c m ~),bothof which are positively charged, suggest that the neutral QC~t-" ( R u " - l , 2 ) species exhibits a lower carbonyl stretching frequency due to the decrease in charge. The FT-IR spectra of QCat 2 (Ru"-1,2) and QCat 2 (Rum-l,2) show bands at 1261 and 1264 cm ~, respectively, which are indicative of catecholate coordination CO stretching frequencies. The occurrence of a metal-based rather than ligand-based oxidation, suggested by FT-IR data, is contraD' to our earlier proposal [ 18 ]. Since our previous work, further studies have been performed, including electron spin resonance, electronic spectroscopy and semi-empirical calculations which confirm an oxidised species with the unpaired electron in an orbital which has significant metal character. A subsequent paper will describe the electronic structure of this species in detail [ 30]. The stretching vibrations of the aromatic ring, typically observed at 1480 c m - ~ for catecholate complexes, are masked by the Nujol bands. Data for QCat 2 (RuU-l,2) collected in a KBr pellet show intense bands at 1474. 1458, 1437 and 14 ! 8 cm t possibly attributed to aromatic stretching vibrations. Due to inductive effects and increased charge, the oxidised species QCat 2 - (Rum-l,2) has carbonyl stretching frequencies shifted to higher energies (Cm=O: 1651 cm ~, C~.=O: 1642 =m ~) compared with Q C a F (RuU-l,2) (C~,,=O: 1620cm ~ , C , , = 0 : 1 6 2 0 c m ~).
ence o f low lying transitions in the electronic spectrum and a highly n e g a t i v e p a r a - q u i n o n e / p a r a - s e m i q u i n o n e reduction potential in the cyclic voltammetry.
5. Supplementary material Table 3, A M I calculated infrared carbonyl stretching frequencies is available on our web page: http:// www.science.yorku.ca/chem/profs/lever/blever.htm
6. Abbreviations Alizarin will be abbreviated as QCatH< Q identifies the 9,10-dioxo unit and CatH_, identifies the doubly protonated 1,2-catechol unit. Similarily QCatH a,ld QCat 2 correspond to 1,2-catechol anion and dianion, respectively. Hydroxyanthraquinone anion will be abbreviated as QO . The abbreviations used for the complexes include the oxidation state of ruthenium and the site of bisIbipyridine)rttthenium coordination: for example, ( R u " - l , 9 ) indicates ruthenium(ll)bis(bipyridinel is coordinated in the (1.9) site.
Acknowledgements We are indebted to the Natural Sciences and Engineering Research Council (Ottawa), and the Office of Naval Research (Washington) for financial sttpport, to Drs E.S. Dodsworth, C. da Cunha, Y.H. Tse, and R. Metcalfe for their valuable discussions, Dr P.R. Auburn |br the initial synthesis of the ( 1,21 coordinated complex, Drs M. Monteiro and A. Mainkar for their aid in the COSY, and to the JohnsonMatthey Company for the loan of RuCI,.
4. Conclusions
References
Our studies have provided evidence concerning linkage isomers of alizarin-bis(bipyridine)ruthenium(II) complexes. Electrochemical and spectroscopic techniques exhibit important features distinguishing the ( 1,2 ) coordinated complex from the ( 1,91 coordinated complex [ 18]. In the FT-IR spectra, overlapping carbonyl stretching frequencies denote QCat-" ( Ru H- 1,21 whereas separated carbonyl stretching frequencies (approximately 56 cm ~ ,'~eparation) denote QCatH (Ru n- 1,91. In the NMR spectra, QCat: ( R u u- 1,21 exhibits resonances for alizarin protons 5 and 6 similar to those of alizarin protons 8 and 7 (Fig. 31, respectively. For QCatH (RuU-1,9), on the other hand, alizarin protons 5 and 6 have different chemical shifts to alizarin protons 8 and 7 (Fig. 4), respectively, due to the closer proximity o f the [ Ru(bpy) 2] 2 ~ fragment. Features characteristic of the (1,2) coordinated isomer, as reported previously [ 18 ], are the pres-
[ I I W. Gopel, C. Ziegler, NanostmcturesBased on MolecuhwMaterials. VCH, Weinheim,New York, 1992. 12 ] M. Haga,T. Ano, K. Kano,S. Yamabe,Inorg.Chem. 30 ( 1991 ) 3843. [31 M. Menon. A. Pramanik, N, Bag, A. Chakravorty. J. Chem. Sot., Dalton Trans. ( 19951 1543. 141 R. Wang, J.G. Vos, R.H. Schmehl. R. Hage, J. Am. Chem. Soc 114 ( 19921 1964. 151 M. Sano, H. Taube, J. Am. Chem. Soc. 113 ( 1991 ~ 2327. 161 E.C. Constable,S.J. Dunne, D.G.F. Rees, C.X. Schmitt.Chem.Commun, ( 19961 1169. 171 M. Jezowska-Bojczuk,H. Kozlowskt,A. Zubor. T. Kiss. M. Branca, G. Micera. A. Dessi. J. Chem. Sot., DaltonTrans. ( 19901 2903. [81 T. Roth, W. Kaim, Inorg. Chem. 31 ( 19921 1930. [91 G. Desantis. L. Fabbrizzi, M. Licchelli. P. Pallavicini, lnorg. Chim. Acta 225 ( 19941 239. [ 10] J. Fees.W. Kaim,M. Mos~:herosch,W. Matheis,J. Klima,M. Krejcik, S. Zalis, lnorg. Chem. 32 ( 19931 )66. I I ! 1 N.S. Hush, A.T. Wong, G.B. Bacskay, J,R. Reimers,J. Am, Chem. Soc. 112 ( 19901 4192.
A. DelMe,?:c':~et a'L /b~organica ChimicaActa 27tl ¢1998~ 126~133 [ 121 R.R. Ruminski. D. Freiheit, D. Serveiss. B, Snyder. J.E.B. Johnson. Inorg. Chim. Acta 224 ( 1994~ 27. [ 131 J,R. Schoonover, W.D. Bates, T.J. Meyer, Inorg. Chem. 34 ( 1995 ) 6421. [ 141 M.D. Ward. Chem. Soc. Rev. 24 ( 1995 ) 121. [ 15] B. Whittle. N.S, Everest, C. Ho;vard, M.D. Ward, lnorg. Chem. 34 (1995) 2025. [ 161 C.-H. Wunderlich, G. Bergerhoff. Chem. Ber. 127 (1994) 1185. [ 171 A. DelMedico, S.S. Fielder. A.B.P. Lever. W.J. Pietro. Inorg. Chem. 34 ( |995~ 1507. 1181 A. DelMedico, P.R. Auburn. E.S. Dodsworth, A.B.P. I,ever, W.J. Pietro, Inorg. Chem. 33 (1994) 1583. [ 191 M.N. Bakola-Christianopoulou, Polyhedron 3 ( 1984~ 729. [ 201 E.G. Kiel. P.M, Heertjes. J. Soc. Dyers Colour. 79 ( 19631 2 I. [211 M.S. Masoud. M.S. Ta,vfik. S.E. Zayan, Synth. React. lnorg. Met.Org. Chem. 14 (1984) I. [22] L.J. Larson, J.l. Zink, Inorg. Chim. Acta 169 ( 19901 17. [ 23 ] G. Parissakis. J. Kontoyannakos, Anal. Chim. Acta 29 ( 1963 ~ 220. [24} E.M. Larsen, S.T. Hirozawa, J. lnorg. NucL Chem. 3 11956~ 198. [251 J.F. Flagg, H.A. Liebhafsky, E.H. Winslov¢, J. Am. Chem. Soc. 71 ( 1949~ 3630. (261 H A . Liebhafsky, E.H. Winstow. J. Am. Chem. Soc. 69 11947 ~ 1130. (271 H E . Zittel, T.M. Florence, Anal. Chem. 39 ( 1967~ 320. [281 T.M. Florence. Y.J. Farrar. H.E. Zittel, Aust. J. Chem. 22 t 1960~ 2321. [291 J.B.B. Heyns. J.J. Cruvv.'agen, E.A. Rohv~er, Proc. 31st ICCC, Umversity of British Columbia, Vancouver. Canada, Aug. 18-23, 1996, poster 5P104. [30] A. DelMedieo. E.S. Dods',,.orth. W.J. Pietro, A.B,P, Lever, to be submitted. [ 31] J.M. Bruce, Chem. Rev. 21 11967) 405. [321 Spartan, Version3.1,2.,Wavefunctionlnc.. t8401VonKarman. Suite 370, Ir,'ine, CA 92715. [331 M.J.S. Dev,'ar, E.G. Zoebisch, E.F. Hotly, J.J.P. Stewart. J. Am. Chem. Soc. 107 i 1985) 3902,
133
[34] M.J.S. De,.var. E.G. Zoebisch. J. M(~I. St.2ct : THEOCHEM !80 ( 19881 I. [351 M.J.$. Dev at. Y. Yate-Ching. In~rg. Chem. 29 i 19(34jj 388. [ 36] R.A. Metcalfe, E.S. D~dsw~rth. A.B.P. Lever, W.J. Pietro. D.J. Stufkens. Inorg. Chem. 32 t 1993~ 3581. [ 37 ] S Patti ( ed. ), The Chemistry of the Quinonoid Compounds. VoL 1. Wiley, New York, 1974. p. 179. 1381 C.J, Da Cunha, S.S. Fielder. D.V, Stynes. H. MasuL P.R. Auburn. A.B.P. Lever, Inorg. Chim. Acta 242 ~ 1996~ 293. [ 39 ] F.E. Lytle, L.M. Petrosky. LR. Carl,,on. Anal. Chim. Acta 57 ( 1971 ) 239. {401 E.C. Corn, table. J. Lev.is. lnorg. Chim Acta 70 ( 19~;3 i 251. }41 t R. Hage, R. Prin',. J.G. Haasnoot, J. Reedijk. J,G, Vos. J. Chem, Soc.. Dalton Trans. t 1987~ 1389. 1421 R.P Thummel. F. Lefoulon. J,D. Kcrp. lnorg. Chem. 26 ~ 1987 ~2370. [431 R. Hage. A.HJ. Dijkhni~,. J.G Haasnoot. R. Prins. J. Reedjik. B.E. Buchanan. J.G. Vos. lnorg. Chem. 27 i 19881 2185. [ 441 P.B. Hitchcock. K.R. Seddon. J.E. Turp. Y.Z. Y¢~usiLJ.A. Zora. E.C. Constable. O. Wemberg. J. Chem. Soc.. Dalton Tran~;. ~ 1988 ~ 1837. [451 BD.JR. Fennema. R.A G de Graaf. R. Hage. J.G. Has.t',noor. J. Reedjik, J.G. Vcs. J. Chem. S~c., Dalton Tran,,. ~ 1991 ~ 1043, [46} H Masui. PhD. Thesis. York Uni,.ersity. Toronto. Canada, 1993. [47} J.D. Birchall. T D. O'Donoghue. JR. Wood. lnorg. Chim. Acta 37 (1979) L461, [481 R.A. Walker. Spectrt~him. Acta. Pan, A 27 ( 1971 ~ 1785. 1491 K. Nakamoto. P.J. McCarthy, A.E. ~,lartell. J. Am. Chem. Soc. 83 i 1961J 1272. [501 Z. Ja~orska. C.I Jose, T. Urban~ki. Spectrochim. Acta. Part A 30 (1974) 1161. [5! I R. West, R Riley, J. Inorg. Nucl. Chem. 5 i 1958) 295. 1521 V.M. Gooden. H Cai. T.P. Dasgupta. N R. Gordon. L.J. Hughes. G.G. Sadler, Inorg. Chim. Acta 225 11997 ~ 105. [ 531 R.S. Bouei. CP- McEachem. J. Inor.~. NucL Chem. 32 i 1970 ~ 2653.