Halide anion recognition by new acyclic ruthenium(II) bipyridyl-polypyridinium receptors

ELSEVIER

lnorganicaChimicaActa251 (1996) 335-340

Halide anion recognition by new acyclic ruthenium(II) bipyridyl-polypyridinium receptors Paul D. Beer ~'*, Nicholas 12. Fletcher a, Trevor Wear b ~'Inorganic Chemistry Laboratory, Universityof Oxford, South Park~ Road, Oxford OXI 3QR. UK b Kodak Limited, Head~toneDrive, Harrow. Middlesex HAl 4TY, UK

Received12 March 1996;revised 16 May 1996

Abstract New acyclic ruthenium(I1) bipyridyt-pyridinium receptor molecules have been synthesised. ~H NMR spectroscopy, and cyclic and square wave voltammetry have established these receptors complex and electrochemicallysense the chloride anion. Disappointinglyspectraldetection of halide anions by electronic absorption and fluorescence-emissionspectroscopic measurements was unsuccessful. Keywords: Halideanionrecognition;Bipyridylreceptorcomplexes,Rutheniumcomplexes:Polypyfidiniumreceptorcomplexes

1. I n t r o d u c t i o n

Inspired by how anions play essential roles in biological and chemical processes, the molecular recognition of negatively charged species by positively charged or electron deficient neutral synthetic receptor molecules is an area of intense current research activity [ 1]. Examples of anion receptors reported to date include protonated polyammonium [2] and expanded porphyrin macrocycles [3], macropolycyclic ammonium quaternary salts [4], guanidinium derivatives [5 ], and Lewis acid tin [6], mercury [ 7], silicon [ 8 ], uranylcontaining ligands [9]. The design and syntheses of specific ligands that have the capability of electrochemically [ 10] and/or optically detecting anions is surprisingly rare however [ 11 ]. We have recently shown that acyclie polybipyridinium receptors can electrochemically detect halide anions [ 12], whilst ruthenium(ll) bipyridyl amide containing iigands spectroelectrochemically sense a wide variety of anionic guest species [ 13]. In an effort to combine recognition features of these two classes of anion receptor, we report here the syntheses and halide anion coordination studies of new acyclic ruthenium(lI) bipyridyl-polypyridiniura receptor molecules.

tonitrile, followed by conversion of the resultant precipitate into the hexafluorophosphate salt, gave the dicationic compound 3 in 65% yield (Scheme 1). Analogous reactions of 1 with pyridine and nicotinamide produced the pyridinium derivatives 4 and 5 in good yields (Scheme 2). Treatment of two equivalents of 5-bromomethyl-2,2'-bipyridine (6) [ 14] with 2 gave initially a cream coloured precipitate which on dissolution in water and addition of excess NI-I4PF6produced 7 in 63% yield (Scheme 3). The ruthenium(H) complexes 8-11 were prepared by refluxing the appropriate pyridinium derivative with [(hipy)2RuCl2]-2H20 in either ethylene glycol or 50% aqueous ethanol, followed by precipitation of the hexafluorophosphate salts by addition ofexcess NH~F6 and purification using Sephadex LH20 column chromatography. The reaction of 8 with excess methyl iodide in nitro-

i..) O'110¢ Retl~

2, Results and discussion 241. Syntheses

The reaction of 5,5'-bis(bromomethyt)-2,2'-bipyridine (1) [ 14] with a large excess of 4,4'-bipyridine (2) in ace* Correspondingauthor. 0020-1693/96/$15.00 © 1996ElsevierScienceS.A.All fightsreserved PII S0020-1693 (96) 0528 7-5

SchemeI.

336

P.D. Beeret al. I lnorganica Chi:ni,'aActa 251 (1996)335-340

s~

i) R~ux

~

,N__k ii)Nti,pFdH2O/ . = N ,, (I)

~.~

/~,

2~

~,.u

B

r (6)

÷ N ~ b r (2)

(4)

tar~ excess 0

i) CI-I~CNReflux ii)NH4PF6/ H20

H2N~

/=x/=x

tar~*ac~s ~ r , ~

0'~'1~

Scheme3.

0 Scheme2. methane and conversion to the hexafluorophosphate salt gave 12 as an orange-red powder.

4~d

19) ~

4~d (10)

,,

ride to (CD3)2SO IH NMR solutions of 8-12 resulted in ~ignificant shifts of the respective protons of all five receptors, ,~vith the largest perturbations of the ortho-pyridinium- and ruthenium(II)-4,4'-bipyridyl protons being observed. For example the ortho-pyridinium protons of 9 are perturbed by A ~ = 0.12 ppm after the addition of one equivalent of chloride anion. Smaller but significant proton perturbations were also observed with the receptors on addition of bromide anion. The computer program EQNMR [ 15 ] was used to estimate the stability constants from the IH NMR titration data assuming 1:1 receptor:anion stoichiometry and the results are summarised in Table 1. Generally all the receptors complex chloride anion with similar thermodynamic stability of the order of 30 dm 3 mol- I. Comparing the chloride and bromide stability constant values of receptors 9 and 10 there is, within experimental error, no selectivity preference exhibited by the former receptor and a marginal selectivity preference for Brexhibited by 10. 2.3. Electrochemical anion recognition studies

The electrochemical properties of all new acyclic ruthenium(II) bipyridyl-polypyridinium receptors were investigated in acetonitrile using cyclic and square wave voltammetry with NBu4PF6 as the supporting electrolyte. Each compound exhibits the combined electrochemical properties of ruthenium(II) bipyridyl [ 16] and pyridinium [ 17] moieties (Table 2). For example receptor 12 displays a (8)

~

(l 2)

J

All the new acyclic ruthenium(II) bipyridyl-polypyridinium receptors were characterised by IH NMR, elemental analyses and FAB mass spectrometry (see Section 4). 2.2. Halide anion coordination studies 2.2.1. Stability constant determinations from ~H NMR titrations Solubility problems necessitated the use of deuteriated dimethyl sulfoxide as solvent for the ~H NMR halide anion binding studies. The addition of tetrabutylammonium ohio-

Table 1 Stabilityconstantdatafor 9-12 withhalideanionsin (CD3)2SO Receptor

Anion

K ~(din3 mol- ' )

8 9 9

CICI-

30 30

BrCIBrCiCI-

25 25 45 20 35

10 tO II 12

aErrorsestimatedto be ~ 10%.

P.D. Beer et al. / inorganica Chimica Acta 25. (1996) 335-340

2.4. UV-Vis investigations

Table 2 Electrochemical data ~ Receptor

Ruli/lll

Ligand reduction couples

El/2

El

0.99 1.03 1.00 1.00 1.04

- 1.30 b -I.30b -0.60 -0,67

(V)

8 9 10 II 12

337

(V)

E2

E3

E4

Es

-0.96 - 1.07

-131 - 1.69 -1.69 - !.69 - 1.71

-I,92 - 1.91 -i,98 -1.90 -t.90

-2.25 -2.25 b -2,23 -2.15 ~' -2,12

(V) (V) (V) (V)

-I.14h

Obtained in acetonitrile solution using Bu4NPF6 as supporting electrolyte, Ag/AgCI reference electrode. h Irreversible process.

The UV-Vis electronic absorption spectra of the receptors were acquired in acetonitrile. As with [Ru(bipy)3] 2+, the respective spectrum is dominated by the ligand-centred (LC) and metal-to-ligand charge transfer (MLCT) bands (Table 3). Compared to [ Ru (hipy)3 ] 2+ all the lowe: #avelength MLCT bands are bathochromically (red) shifted by approximately 10 nm and the lower wavelength MLCT bands generally slightly blue shifted. The addition of chloride or bromide anions to acetonitrile solutions of 8-12 disappointingly led to insignificant perturbations of the electronic spectra.

2.5. Fluorescence-emission studies

~ D°~A....~(a.)~

(b) 1.5 I 0.5 0 -0.5 -! +1.5 -2 -2.5 Potential/ V vsAg/AgCI Fig. I, (a) Cyclic and (b) square wave voltammograms of 12 in acetonitrile.

reversible ruthenium ll/IIl oxidation, two 4,4'-bipyridinium reduction and three bipyridyl reduction waves (Fig. 1). Cyclic and square wave voltammograms were also recorded after progressively adding stoichiometric equivalents of chloride anion to the electrochemical solutions. Significant cathodic perturbations of 40 mV of the respective 4,4'-bipyridinium redox couples of 11 and 12 were noteworthy. Smaller shifts of typically 20 mV of the first two (least cathodic) 2,2'-bipyridyl reduction waves were observed with 8, 9, 10 and 11. Similar chloride anion induced magnitudes of cathodic shifts were noted with mono-substituted cobaltoeenium amide derivatives [ 18].

Table 4 shows the fluorescence emission data of 8-12 obtained in acetonitrile solution. The emission bands are assigned as a triplet metal to ligand charge transfer (3MLCT) level and are red shifted when compared to [Ru(bipy)3] 2+. The relative quantity of light emitted by the receptors is considerably less than [ Ru(bipy) 3] 2+; a similar observation has been noted with related compounds prepared by Grigg et al. [ 19] and with amide functionalised ruthenium(H) bipyridyl derivatives [20]. It is noteworthy that 11 and 12 display the greatest magnitude of quenching (loss of emission) as a consequence of the receptor*s appended 4,4'-bipyridinimn moieties' well known ability to accept electrons via photochemical stimulation [17]. Generally the lifetimes of the excited states are of similar magnitudes to [Ru(bipy)3] 2+ with 12 being the noteable exception exhibiting a remarkably short lived excited state due to photo-electron transfer to the appended viologen moiety. The emission and liietimes of the receptors were examined upon the addition of chloride and bromide anions in acetonitrile solution. Unfortunately only minor insignificant perturbations were observed even after large excess amounts of halide anion had been added.

Table 3 Electron!c absorFhon data in acetonitrile Receptor

[ Ru(bipy ) 3] 2+ 8 9 10 11 12

MLCr

LC

(nm)

c (M - I cm - I )

Wavelength {rim)

287 288 288 288 287 287

79800 90600 78100 836~) 1888200 93800

452 448 445 444 452 438

Wavelength

Wavelength (nm)

(M -I

244 256 254 248 255 256

27200 49700 32800 35400 70400 57700

cm-I)

MLCT

M -tcm-') 14300 I ! 300 ! 1400 14300 24400 13700

338

P.D.Beeret al. / lnorganica ChbnicaActa251 (I 996)335-340

Table4 Luminescencedatain acetonitrile

4.3. Syntheses

Receptor

Emission (nm)

Intensity (art). units)

Lifetime,¢ ~/zs)

[Ru(bipy)~]-'÷ 8 9 10 11 12

609 672 668 649 629 659

55 5 17.9 23.4 i 8.9 12.1 0.4

0.19 0.18 0. !8 0.20 0.10 0.01

Recordedin acetonitrileat 298 K. 3. Conclusions

New acyclic ruthenium(II) bipyridyl-polypyridinium receptor molecules have been prepmed and shown to coordinate chloride and bromide anions by ~H NMR spectroscopy. Stability constant evaluations for 1:1 stoichiometric receptor:halide anion complexes in deuteriated DMSO gave magnitudes of up to 45 dm 3 mol - i. Cyclic and square wave voltammetry revealed these receptors can electrochemically recognise the chloride anion by significant cathodic perturbations of pyridinium and 2,2'bipyridyl reduction couples of the respective ligand. Disappointingly spectral detection of halide anions via electronic absorption and fluorescence-emission spectroscopy was unseccessful.

4.3.1. 5,5'-Bis( 4, 4'-bipyridyl-N-metb~,lene )-2,2'-bipyridine b is( hexafluorophosphate ) (3) 4,4'-Bipyridine (2) (4.20 g, 26.1 mmol) was dissolved in dry acetonitrile (400 ml) and heated to reflux. A solution of 5,5'-bis(bromomethyl)-2,2-bipyridine (1) ( 1.00 g, 2.92 mmol) in acetonitrile (200 ml) was added dropwise over 1 h and the resultant solution refluxed for 20 h giving a brown precipitate. The mixture was cooled to room temperature and the volume of the solvent reduced to approx. 400 mi. The brown solid was collected by filtration, washed with acetonitrile (3 ×50 ml) and dried in vacuo. The solid was dissolved in water (200 ml) at 50°C and filtered through Celite®. A saturated aqueous solution of ammonium hexafluorophosphate was added until no further precipitation occurred. The mixture was cooled to 0°C ensuring complete precipitation of the product. The pale cream precipitate was collected by filtration, washed with water ( 3 x 2 0 ml) and dried in vacuo. Yield 1.49 g, 65,0%. M.p. > 300°C. 1H NMR (CD3)2SO: 8 6.00 (4H, s, CH2), 8.02 (4H, d, J=6.1 Hz, 4,4'//3'), 8.15 (2H, d/d, J=8.3 and 2.0 Hz, bipy/-P), 8.45 (2H, d, J=8.3 Hz, bipyH3), 8.67 (4H, d, J=6.7 Hz, 4,4'H3), 8.87 (4H, d, J=6.1 Hz, 4,4'HZ'), 8.95 (2H, d, J=2.0 Hz, bipyH6), 9.40 (4H, d, J=6.7 Hz, 4,4'/-/2). 13C NMR (CD3):SO: 860,3 (CH2), 120.8, 125.9, 130.7, 138.0, 140.8, 145.5, 149.6, 151.0, 153.0, 155.3 (bipy C). Anal. Calc. for C32H26Ft2NrP2: C, 49.0; H, 3.3; N, 10.7. Found: C, 48.8; H, 3.4; N, 10.6%. FAB-MS: [ M - P F r ] ÷ 639.

4. Experimental

4.1. Instrumentation NMR spectra were obtained on a Bruker AM300 instrument using the solvent deuterium signal as internal reference. Fast atom bombardment (FAB) mass spectrometry was performed by the SERC mass spectrometry service at University College, Swansea. Electrochemical measurements were carded out using an E.G.&G. Princeton Applied Research 362 scanning potentiostat. Elemental analyses were performed at the Inorganic Chemist~ Laboratory, University of Oxford. 4.2. Solvent and reagent pretreatment Where necessary, solvents were purified prior to use and stored under nitrogen. Aeetonitrile was predried over class 4 ,~, molecular sieves (4-8 mesh) and then distilled from calcium hydride. Unless stated to the contrary commercial grade chemicals were used without further purification. 5,5'Bis(bromomethyl )-2,2'-bipyridine ( 1 ) and 5-bromomethyl2,2'-bipyridine (6) were prepared according to literature procedures l ! 4 ].

4.3.2. 5,5'-Bis(pyridyl-N-methylene )-2,2'-bipyridine bis( hexafluor ophosphate ) (4) A solution of 5,5'-bis ( bromomethyl )-2,2'-bipyridine (1) (0.10 g, 0.29 mmoi) in acetonitrile (50 ml) was added dropwise over 1 h to pyridine (75 ml) and the resultant solution refluxed for 18 h giving a brown precipitate. The mixture was cooled to 0°C and the brown solid was collected by filtration, washed with acetonitrile (2 × 10 ml) and dried in vacuo. The solid was dissolved in water (50 ml) at 50°C and filtered to remove dark coloured impurities. A saturated aqueous solution of ammonium hexafluorophospha~e was added until no further precipitza,on occurred. The mixture was stored overnight at 4°C to ensure complete precipitation of the product. The pale cream precipitate was collected by filtration, washed with water (3× 10 ml) and dried in vacuo. Yield 0.t4 g, 76.0%. M.p. > 300°C. tH NMR (CD3)2SO: 8 5.97 (4H, s, CH2), 8.09 (2H, d/ d, J=8.2 and 2.0 Hz, bipyH'*), 8.21 (4H, t/m, J=7.0 Hz, PyH3), 8.43 (2H, d, J = 8.2 Hz, bipyH3), 8.65 (2H, t, J = 7.8 Hz, PyH4), 8.90 (2H, d, J=2.0 Hz, bipyHr), 9.25 (4H, d, J=6.7 Hz, PyH2). a3C NMR (CD3)2SO: 8 60.6 (CH2), 120.9, 128.6, 130.6, 138.0, 138.2, 145.5, 146.2, 149.8 (bipy C). Anal. Calc. for C22H2oFt2NaP2: C, 41.9; H, 3.2; N, 8.9. Found: C, 41.5; H, 3.2; N, 8.5%. FAB-MS: [ M - PF~] + 485.

P.D. Beeret aL / lnorganica Ch#nicaActa251 (1996)335-340 4.3.3. 5,5'-Bis(nicotinamide-N-methylene)-2,2'-bipyridine bis( hexafluorophosphate ) (5) A solution of 5,5'-bis(bromomethyl)-2,2-bipyridyl (1) (0.15 g, 0.44 mmoi) and nicotinamide ( 1.40 g, 11.5 mmoi) was refluxed for 20 h in aeetonitrile (250 mi) giving a brown precipitate. The mixture was stored overnight at 4°C and subsequently the brown solid was collected by filtration, washed with acetonitrile (2 X 20 ml) and dried in vacuo. The solid was dissolved in water ( 100 ml) to which ammonium hexafluorophosphate (1.00 g) was added in water (3 ml) giving a white precipitate. The mixture was stored overnight at 4°C to ensure complete precipitation of the product. The white solid was collected by filtration, washed with water (3× 10 ml) and dried in an oven (60°C). Yield 0.29 g, 92.3%. M.p. > 300°C. IH NMR (CD3)2SO: 8 6.03 (4H, s, CH2), 8.14 (2H, d, J=8.4 Hz, bipyH4), 8.19 (2H, s, NH.~), 8.31 (2H, t/m, J=7.0 Hz, Nic/-/5), 8.44 (2H, d, J=8.4 Hz, bipyH3), 8.57 (2H, s, NHz), 8.93 (2H, s, bipy/~), 8.97 (2H, d, J = 8.5H, NicH4), 9.34 (2H, d, J=6.2 Hz, Nic/-P), 9.65 (2H, s, NicH:). 13C NMR (CDa)zSO: 8 61.0 (CH2), 120.8, 128.2, 128.4, 134.3, 138.2, 143.9, 145.2, 146.5, 150.0, 155.3, 162.7 (bipy C). Anal. Calc. for C24H.~zF~2N602P2"2H20: C, 38.3; H, 3.5; N, 11.2. Found: C, 38.0; H, 3.4; N, 11.0%. FAB-MS: [ M - PF6] + 571. 4.3.4. N,N '-Bis( 2,2'-bipyridine-5-methylene )-4, 4"-bipyridinium bis(hexafluorophosphate) (7) 5-Bromomethyl-2,2'-bipyridine (6) (0.80 g, 3.21 mmol) and 4,4'-bipyridyl (2) (0.20 g, t.28 mmol) were dissolved in acetonitrile (80 ml). The solution was then heated to reflux for 24 h giving a yellow precipitate. After cooling to 0°C, the solid was collected by filtration, washed with acetonitrile (2 × 10 ml) and dried under vacuum. It was then dissolved in water (75 ml) and ammonium hexafluorophosphate ( 1.0 g) in water (2 ml) added furnishing a cream precipitate. The solid was collected by filtration, washed with water (2 X 10 ml) and dried in an oven (60°C). Yield 0.63 g, 62.7%. d.p. > 300°C. IH NMR (CD3)2SO: 86.05 (4H, s, bipyCH2), 7.48 (2H, d/d, J=4.9 and 7.1 Hz, bipyHS'), 7.97 (2H, t/m, J=7.65 Hz, bipy/P'), 8.15 (2H, d, J=8.2 Hz, bipy/-/4), 8.38 (2H, d, J=7.9 Hz, bipyH3'), 8.45 (2H, d, J=8.2 Hz, bipyH3), 8.69 (2H, d, J=4.1 Hz, bipy/-/6'), 8.74 (4H, d, J=6.7 Hz, 4,4'H3), 8.94 (2H, s, bipy/-/6), 9.52 (4H, d, J=6.7 Hz, 4,4"/-/2). 13C NMR (CD3)2SO: ~$61.0 (bipyCHa), 120.7, 120.8, 124.7, 127.2, 2× (129.9), 137.6, 138.0, 145.9, 149.4, 149.8, 154.4, 156.I (bipyC). Anal. Calc. for C32H26Ft2N6P,.: C, 48.9; H, 3.3; N, 10.7. Found: C, 48.1; H, 3.2; N, 10.4%. FAB-MS: [M-PF6] + 639. 4.3.5. lRu(bipy)z(3)ff+ 4PF6 - (8) Ligand 3 (0.12 g, 0.15 mmol) and [Run(bipy)2Cl~] • 2H20 (89 mg, 0.17 mmol) were heated at approx. 10&C for 5 days in ethylene glycol (20 ml) during which time the solution went from purple to dark red. The clear solution was

339

cooled to room temperature and ammonium hexafiuorophosphate ( 1.0 g) was added in water (20 ml) giving an immediate brown precipitate. This was collected by vacuum filtration, washed with water (2× 10 ml) and dried in an oven. The dark powder was then repeatedly columned on Sephadex® LH20, e!uted with 1:! acetonitrile/methanot, collecting the middle brown fraction. The solvent was evaporated to give the product as a dark red-brown glass. Yield 0.17 g, 77.9%. IH NMR (CD3)2SO: 85.81 (4H, s, CH2), 7.47-7.52 (4H, m, bipyHS), 7.61 (2H, d, J=5.3 Hz, bipyH3), 7.77 (2H, s, bipyh¢'), 7.80 (2H, d, J=5.5 Hz, bipy/-P), 8.07 (4H, d, J=6.1 Hz, 4,4'H3'), 8.06-8.25 (8H, m, bipyH3~ 4 ) , 8.65 (4H, d, J=6.8 Hz, 4A'H3), 8.76-8.90 (4I-t, m, bipyL/6), 8.93 (4H, d, J=6.0 Hz, 4,4'/-/e'), 9.13 (4H, d, J=6.9 Hz, 4,4'H2). Anal. Calc. for Cs,.H42F,_4N,oP4Ru-2H20:C, 41.0; H, 3.0; N, 9.2. Found: C, 40.1; H, 2.8; N, 9.1%. FAB-MS: [ M - PF6] + 1344, [ M - CH~-4,4'-bipy-PF6] + ! 174, [ ! 174H-PF6] * 1028. 4.3.6. Receptor l2 Complex 8 (78 mg, 52.4 #mol) was dissolved in acetonitrile (5 ml) to which was added methyl iodide (0.5 ml) and refluxed for 93 h. The solvent was removed and the resulting orange solid was dissolve,.lin 50% aqueous methanol (100 ml), to which was added ammonium hexafluorophosphate (1.0 g), resulting in a brown precipitate. The solution was stored for 48 h at 4°C, then filtered under vacuum. The dark powder was dried in vacuo and repeatedly columned on Sephadex® LH20 eluting with a 1:1 acetonitrile/methanol mixture. Following the removal of the solvent, the product was obtained as a dark brown glass. Yield 70rag, 73.9%. IH NMR (CD3)zSO: 8 4.46 (6H, s, 4A'N+-CH3), 5.84 (4H, s, bipyCH2), 7.46-7.52 (4H, m, bipy/-/s), 7.62 (2H, d, J=5.3 Hz, bipyH3), 7.78 (2H, d, J=5.3 Hz, bipy/'/4), 7.85 (2H, s, bipy/'/6), 8.09-8.22 (SH, m, bipyH3~ 4 ) , 8.74 (4H, d, J=6.6 Hz, 4,4'H3'), 8.78 (4H, d, J=6.6 Hz, 4.4'H3), 8.78-8.91 (4H, m, bipy/-/6), 9.27 (4H, d, J=6.6 Hz, 4,4'HZ'), 9.31 (4H, d, J=6.6 Hz, 4A'H2). Anal. Calc. for Cs4H4sF36NtoP6Ru: C, 35.9; H, 2.7; N, 7.7. Found: C, 35.6;

H, 2.5; N, 7.6%. 4.3.Z [Rutl(bipy)2(4)ff +4PF6- (9) Ligand 4 (96 mg, 0.15 mmol) and [Ru~(bipy).,Cle] 2H20 (0.100 g, 0.17 mmol) were heated at approx. 10f¢C for 20 h in ethylene glycol (20 ml) during which time the solution went from purple to dark red. The clear solution was cooled to toom temperature and ammoniumhexafluorophosphate ( 1.0 g) ,vas added in water (50 ml) giving an immediate orange preclp~:ate. This was collected by vacuum filtration, washed with water [2× i0 ml) and dried in an oven. The red powder was then repeatedly columned on Sephadex® LH20, eluted with 1:I acetonitrile/methanol, collecting the middle red fraction. The solvent was evapo-

340

P.D. Beer et at./lnorganica ChhnicaActa 251 (1996) 335-340

rated to give the product as a red-brown glass. Yield 0.196 g, 96.3%. ~H NMR (CDa)2SO: 85.79 (4H, s, CH2), 7.46--7.51 (4H, m, bipyHS), 7.58 (2H, s, bipy/-/6), 7.59 (2H, d, J = 5 . 5 Hz, bipyH3), 7.75 (2H, d, J = 5 , 5 Hz, bipy/-P), 8.t3-8.19 (8H, m, bipyH3 ~d4), 8.67 (2H, t, J = 7 . 6 Hz, py/_/4), 8.76 (4H, d/d, J = 7.6 and 6.0 Hz, pyH3), 8.76--8.90 (4H, m, bipy/-P), 8.93 (4H, d, J = 6 . l Hz, pyHZ). Anal. Calc. for C42H36F24NsP4Ru"H,O: C, 37.3; H, 2.8; N, 8.3. Found: C, 37.3; H, 2.8; N, 8.3%. FAB-MS: [M-PF6] + 1189, [MH-2PH~] + [ 1043-py] ÷ 956. 4.3.8. [Ru(bipy)z(5)]4+ 4PF6 - (10)

Ligand 5 (83 mg, 0.12 mmol) and [RuU(bipy)zCI2] • 2H20 (96 mg, 0.18 retool) were heated at approx. 100°C for 14 h in ethylene glycol (20 ml) during which time the solation went from purple to dark red. The resulting clear solution was cooled to room temperature and ammonium hexafluorophosphate (1.0 g) was added in water (30 ml) giving an immediate orange precipitate. This was collected by vacuum filtration, washed with water (2 × 20 ml) and dried in an oven. The red powder was then repeatedly columned on Sephadex® LH20, eluted with 1:1 acetonitrile/methanol, collecting the middle red fraction. The solvent was evaporated to give the product as a red-brown glass. Yield 82 rag, 49.4%. IH NMR (CD3)2SO: 85.84 (4H, s, CH2), 7.45-7.50 (4H, m, bipy/-P), 7.70 (2H, d, J = 4 . 8 Hz, bipyH3), 7.58 (2H, s, bipy/-/6), 7.74 (2H, d, J--4.8 Hz, bipy/-P), 8.13-8.20 (8H, m, bipy3 ~da), 8.22 (2H, S, nicNHz), 8.27 (2H, d/d, J = 6 . 3 and 8.3 Hz, nic/-/~), 8.58 (2H, 2s, nicnH:), 8.72-8.88 (4H, m, bipy/--/6), 8.99 (2H, d, J---8.2 Hz, nic/'P), 9.03 (2H, d, J = 6 . 2 Hz, nicH6), 9.37 (2H, s, nicH2), Anal. Calc. for C~H38Fz4NIoO2P4Ru: C, 37.2; H, 2.7; N, 9.9. Found: C, 37.6; H, 2.9; N, 10.0%. FAB-MS: [ M - P F 6 + 1275, [MH-2PF6] + 1129, [ 1129-nic] ÷ 1008. 4.3,9. [RuU(bipy)2(7)] 4+ 4 P F 6 - (11)

Ligand 7 (0.136 g, 0.173 mmol) and [Run(bipy)2Cl2] • 2H20 (0.213 g, 0.41 mmol) were heated at approx. IO0°C for 20 h in 1:1 ethanol/water mixtures (50 ml) during which time the solution went from purple to dark red. The clear solution was cooled to room temperature and the ethanol removed by rotary evaporation. Ammonium hexafluorophosphate (2.0 g) was added in water (20 ml) giving an immediate orange precipitate. This was collected by vacuum filtration, washed with water ( 2 × 10 ml) and dried in an oven. The red powder was then repeatedly columned on Sephadex® LH20, eluted with 1:1 acetonitrile/methanoi, collecting the first red fraction. The solvent was evaporated to give the product as a red-brown glass. Yield 0.306 g, 80.8%. IH N-MR (CD3) 2SO: 8 5.86 (4H, s, CH2). 7.47-7.53 ( 10H, m, bipy/-/s), 7.64-7.73 (1014, m, bipyH3), 7.85 (2H, d,

I--6.7 Hz, bipyH3), 7.99 (2H, s, bipy/-~'), 8.09 (2H, d, J = 6.7 Hz, bipyH4'), 8.13-8.20 ( I 0H, m, bipy/-/4), 8.78 (4H, d, J = 6.5 Hz, 4,4'H3), 8.81-8,87 (4H, m, bipyHr), 9.33 (2H, el, J = 6 . 2 Hz, 4,4'/-/2). Anal. Calc. for CT:HssF36N14PrRu2-2H20: C, 38.8; H, 2.8; N, 8.8. Found: C, 38.8; H, 2.8; N, 8.8%.

Acknowledgements We thank the EPSRC for a CASE studentship (N.C.F.) and for use of the Mass Spectrometry Service of University College Swansea. We also thank Dr lain Morrison and Dr Robert Denning at the ICL, University of Oxford forcarrying out the luminescence decay measurements.

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