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Cite this: Dalton Trans., 2014, 43,3939

Received 30th October 2013,Accepted 20th December 2013

DOI: 10.1039/c3dt53069h

www.rsc.org/dalton

Bidirectional non-innocence of the β-diketonatoligand 9-oxidophenalenone (L−) in [Ru([9]aneS3)-(L)(dmso)]n, [9]aneS3 = 1,4,7-trithiacyclononane†

Hemlata Agarwala,a Thomas Michael Scherer,b Shaikh M. Mobin,c Wolfgang Kaim*b

and Goutam Kumar Lahiri*a

The new compound [RuII([9]aneS3)(L)(dmso)]ClO4 ([1]ClO4) ([9]aneS3 = 1,4,7-trithiacyclononane, HL =

9-hydroxyphenalenone, dmso = dimethylsulfoxide) has been structurally characterised to reveal almost

equal C–O bond distances of coordinated L−, suggesting a delocalised bonding situation of the β-diketo-nato ligand. The dmso ligand is coordinated via the sulfur atom in the native (1+) and reduced states

(1 and 1−) as has been revealed by X-ray crystallography and by DFT calculations. Cyclic voltammetry of

1+ exhibits two close-lying one-electron oxidation waves at 0.77 V and 0.94 V, and two similarly close

one-electron reduction processes at −1.43 V and −1.56 V versus SCE in CH2Cl2. The electronic structures

of 1n in the accessible redox states have been analysed via experiments (EPR and UV-vis-NIR spectroelec-

trochemistry) and by DFT/TD-DFT calculations, revealing the potential for bidirectional non-innocent be-

haviour of coordinated L•/−/•2−. Specifically, the studies establish significant involvement of L based

frontier orbitals in both the oxidation and reduction processes: [([9]aneS3)(dmso)RuIII–L•]3+ (13+) ⇌ [([9]-

aneS3)(dmso)RuIII–L−]2+/[([9]aneS3)(dmso)RuII–L•]2+ (12+) ⇌ [([9]aneS3)(dmso)RuII–L−]+ (1+) ⇌ [([9]aneS3)-

(dmso)RuII–L•2−] (1) ⇌ [([9]aneS3)(dmso)RuII–L3−]−/[([9]aneS3)(dmso)RuI–L•2−]− (1−).

Introduction

β-Diketonato ligands such as 2,4-pentanedionato (acetylaceto-nato, acac−) and its derivatives have long been considered aspassive, redox-inactive witnesses to the electron transfer pro-cesses of coordinating transition metal ions or of redox-activeco-ligands,1 although DFT calculations of ruthenium–acetyl-acetonato complexes have sometimes suggested the partialinvolvement of acac− in metal-based electron-transfer.2 Therecent observation of “hidden non-innocence” of a β-diketimi-nato ligand in Ni(NacNac)2

3 has revealed the potential of suchkinds of β-diketonato derived ligands for non-innocent behav-iour.4 The charge sequences in typical non-innocent ligands

(NIL) with two-step electron transfer potential generally followone of the three alternatives (1)–(3):4b,c

ðNIL0Þ=ðNIL•�Þ=ðNIL2�Þ ð1Þ

(e.g. O2, quinones, α-dithiolenes, α-diimines, s-tetrazines,TCNX),

ðNILþÞ=ðNIL•Þ=ðNIL�Þ ð2Þ

(e.g. NO, N-methylpyrazinium), or

ðNIL•�Þ=ðNIL2�Þ=ðNIL•3�Þ ð3Þ

(e.g. porphinato).In this study we explore the possibility to have the anionic

β-diketonato ligand 9-oxidophenalenone (L−) as a non-inno-cent ligand in both directions, i.e. according to (4):

ðL•Þ=ðL�Þ=ðL•2�Þ ð4Þ

L− is known to accommodate electrons on complexation withpositively charged Lewis acid centres such as BIII, AlIII, SiIV,and GeIV.5 Its potential as a redox non-innocent ligand in tran-sition metal complexes has been reported for certain ruthe-nium frameworks using co-ligands with different electronicproperties, viz., σ-donating acetylacetonate, π-accepting 2,2′-bipyridine (bpy) and 2,2′:6′,2″-terpyridine (trpy) and stronger

†Electronic supplementary information (ESI) available: X-ray crystallographicfile in CIF format for [1]ClO4, DFT data set for 1n (Tables S1–S8, Fig. S3), massspectrum of 1+ (Fig. S1), 1H/1H–1H COSY/13C/1H–13C HSQC NMR spectra of 1+

(Fig. S2). CCDC 965324. For ESI and crystallographic data in CIF or other elec-tronic format see DOI: 10.1039/c3dt53069h

aDepartment of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai-

400076, India. E-mail: lahiri@chem.iitb.ac.inbInstitut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55,

D-70550 Stuttgart, Germany. E-mail: kaim@iac.uni-stuttgart.decDiscipline of Chemistry, School of Basic Sciences, Indian Institute of Technology

Indore, Indore-452017, India

This journal is © The Royal Society of Chemistry 2014 Dalton Trans., 2014, 43, 3939–3948 | 3939

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π-accepting 2-phenylazopyridine (pap),6 demonstrating theone-electron oxidation of ruthenium coordinated 9-oxido-phenalenone to its radical state (L− → L•).

The present report deals with [Ru([9]aneS3)(L)(dmso)]ClO4,[1]ClO4 ([9]aneS3 = 1,4,7-trithiacyclononane, dmso = dimethyl-sulfoxide, Scheme 1), its synthesis, structural characterisationand electron transfer properties including spectroelectrochem-istry (UV-vis-NIR, EPR) and DFT/TD-DFT calculations, estab-lishing the significant involvement of 9-oxidophenalenone inboth oxidation and reduction processes of 1n.

Results and discussionSynthesis, 1H/13C NMR spectroscopy and structure

The complex [1]ClO4 has been prepared from the precursorRu([9]aneS3)(dmso)(Cl)2

7 in the presence of 9-hydroxyphenale-none (HL) and the base NEt3 under aerobic conditions. Theidentity of the complex was confirmed by microanalysis andelectrospray ionisation mass spectrometry (Experimental andFig. S1†). The 1 : 1 stoichiometry of [1]ClO4 was affirmed byconductivity measurements (Experimental) and by singlecrystal X-ray structure determination (Fig. 1). The bands at1100 and 632 cm−1 in the IR spectrum (Experimental) confirmthe presence of ClO4

−.The 1H NMR spectrum of diamagnetic [1]ClO4 in CDCl3

(Fig. S2a†) exhibits narrow signals corresponding to theexpected number of 25 protons (Experimental). The proton res-onances in the “aromatic region”, three doublets and onetriplet for L−, have been assigned by 1H–1H COSY experiments(Scheme 1, Experimental, Fig. S2b†). The observed four protonresonances for L− imply the presence of only one confor-mation of the macrocyclic [9]aneS3 in solution.8

The compound was crystallised for single crystal X-ray struc-ture determination as a monohydrate, [1]ClO4·H2O (Fig. 1).Selected crystallographic and bond parameters are listed inTables 1 and 2. The DFT calculated bond distances and bondangles of optimised 1+ reproduce the experimental values

(Tables 2, Sl and Fig. S3†). The [9]aneS3 ligand binds to themetal through the S donors in a tris-endodentate fashion,forming three five-membered chelate rings while the ligand L−

binds to ruthenium through its oxygen donors to form a six-membered chelate ring. The monodentate dmso ligand isbonded to the “soft” ruthenium(II) ion through the sulfuratom. The trans and cis angles formed by the coordinatingatoms of the ligands with the pivotal ruthenium centre deviateslightly from the ideal values of 180° and 90°, respectively,implying the inherent distortion in the octahedral geometry ofthe complex. The average RuII–O(L−) distance of 2.062 Å (DFT:2.071 Å) is appreciably longer than that reported for the analo-gous ruthenium(II) complexes of L− encompassing 2,2′-bipyri-dine (bpy, 2.035(16) Å),6a 2-phenylazopyridine (pap, 2.026(3)Å),6b and 2,2′:6′,2″-terpyridine (trpy, 2.0465(4) Å)6c as co-ligands. An important factor is the relatively strong π-acceptingcharacter of [9]aneS3.8c The almost equal bond distances of

Fig. 1 Molecular structure of [1]ClO4. Thermal ellipsoids are drawn atthe 50% probability level. The counter anion (ClO4

−) and hydrogenatoms are omitted for clarity.

Table 1 Selected crystallographic data for [1]ClO4

[1]ClO4·H2O

Formula C21H27ClO8S4RuMr 672.19Crystal system OrthorhombicSpace group Pbcaa/Å 15.5811(2)b/Å 14.2098(2)c/Å 22.6877(3)α (°) 90β (°) 90γ (°) 90V/ Å3 5023.15(12)Z 8µ/mm−1 1.109T/K 150(2)ρcalcd (g cm−3) 1.778F (000) 27362θ range (°) 6.00 to 50.00Data/restraints/parameters 4415/2/326R1, wR2 [I > 2σ(I)] 0.0418, 0.1062R1, wR2(all data) 0.0445, 0.1093GOF on F2 1.033Largest difference in peak and hole/e Å−3 0.965 and −0.910

Scheme 1 Representation of 1+ with atom labeling for L−.

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C7–O1 (1.288(4) Å (exp.), 1.294 Å (DFT)) and C17–O2 (1.286(4)Å (exp.), 1.294 Å (DFT)) involving L− in 1+ suggest a delocalisedsituation, similar to that in analogous ruthenium coordinatedacac− ligands2 and in other ruthenium(II) complexes of L−:6

C–O(L): 1.285(3)/1.289(3) Å in [RuII(bpy)2(L)]ClO4, 1.302(6)/1.300(5) Å in [RuII(pap)2(L)]ClO4 and 1.248(7)/1.268(7) Å in[RuII(trpy)(L)(Cl)]. The average RuII–S([9]aneS3) distance in 1+

(2.309(10) Å) is comparable to that reported for [Ru(bpy)([9]-aneS3)Cl]+ (2.308 Å),8b [Ru(phen)([9]aneS3)Cl]+ (2.282 Å)8b

(phen = 1,10-phenanthroline), and [Ru(pap)([9]aneS3)Cl]+

(2.323 Å).8c The S–C–C–S, C–S–C–C and C–C–S–C endocyclictorsion angles of coordinated [9]aneS3 in 1+ (Table S2†)confirm its [333] conformation in the Dale nomenclature.8–11

Electrochemistry, spectroelectrochemistry (EPR, UV-vis-NIR)and DFT calculations. Compound [1]ClO4 exhibits two close-lying one-electron oxidations and two one-electron reductionsin CH2Cl2, a solvent which was chosen because of its non-co-ordinating feature, hence not competing with dmso as aligand (Fig. 2 and Table 3). The comproportionation constants(Kc) (RT 1n Kc = nF(ΔEp)) for the odd-electron intermediates are102.9 for 1•2+ and 102.2 for 1•. The comparison of the first oxi-dation processes (Table 3) reveals systematic changes depend-ing on the π-acceptor properties of the co-ligands as well as onthe overall charge of the complexes. The oxidation potentialthus decreases along the series (pap)2 ([9]aneS3/dmso), (bpy)2,(trpy/Cl−) with decreasing π-accepting strength of the co-ligands. A similar sequence is observed for the first reduction(Table 3) which, however, involves mostly the co-ligands,except for the case 1/1+ presented here (see below).

In 1+, both ruthenium and the potentially redox non-inno-cent L− are susceptible to participate in electron-transfer pro-cesses. Therefore, the electrogenerated intermediateshave been investigated via EPR and UV-vis-NIR

spectroelectrochemistry and by DFT calculations whichprovide the composition of molecular orbitals as well as spindensity distributions for the paramagnetic states.

The MO study of 1+ in its S = 0 ground state predicts thatHOMO is primarily composed of Ru (30%) and L (56%) basedorbitals (Table S3†). The one-electron oxidised species 12+ dis-plays an anisotropic EPR spectrum at 110 K with partiallymetal based spin, caused by the large spin–orbit coupling con-tribution12 provided by the heavy metal (Fig. 3a). However, therelatively small g1 − g3 = Δg value of 0.32 for 12+ in comparisonwith the mostly RuIII based situations in analogous[RuIII(bpy)2(L)]

2+ (Δg = 0.860)6a and [RuIII(acac)2(L)] (Δg =0.753)6b (Table 4) and typical ruthenium(III) complexes2,13 sig-nifies appreciable contributions from oxidised L• to the singlyoccupied MO (Table S4†), as has been outlined previously for[RuIII(pap)2(L)]

2+ (Δg = 0.374)6b (Table 4). This result isreflected in the DFT calculated spin density distributions of12+: Ru, 0.624; L, 0.352 (Tables 5, 6 and Fig. 4a), obtained forthe isomer with O coordinated dmso as the lowest energyspecies. The S → O coordination change of the dmso ligand iswell established for oxidisable ruthenium complexes.14 Thus,the one-electron oxidised species 12+ can be described as an

Table 2 Selected experimental and DFT calculated bond distances (Å)and bond angles (°) of [1]ClO4

[1]ClO4

X-ray DFT

Ru(1)−O(1) 2.063(2) 2.071Ru(1)−O(2) 2.061(3) 2.071Ru(1)−S(1) 2.297(10) 2.375Ru(1)−S(2) 2.294(10) 2.367Ru(1)−S(3) 2.335(10) 2.391Ru(1)−S(4) 2.277(9) 2.328O(1)−Ru(1)−O(2) 89.54(10) 89.145O(1)−Ru(1)−S(1) 176.73(8) 176.983O(1)−Ru(1)−S(2) 90.88(7) 90.827O(1)−Ru(1)−S(3) 88.24(8) 88.871O(1)−Ru(1)−S(4) 90.33(8) 91.648O(2)−Ru(1)−S(1) 91.00(7) 91.830O(2)−Ru(1)−S(2) 174.66(8) 176.559O(2)−Ru(1)−S(3) 85.71(8) 88.110O(2)−Ru(1)−S(4) 92.68(8) 91.742S(1)−Ru(1)−S(2) 88.28(4) 88.029S(1)−Ru(1)−S(3) 88.59(4) 88.308S(1)−Ru(1)−S(4) 92.87(3) 91.176S(2)−Ru(1)−S(3) 88.98(4) 88.449S(2)−Ru(1)−S(4) 92.63(4) 91.698S(3)−Ru(1)−S(4) 177.86(4) 179.458

Table 3 Electrochemical dataa for [1]ClO4 and reported analogouscomplexes of L

E0298/Vb (ΔEp/mV)

Compound Ox 2 Ox 1 Red 1 Red 2 Reference

[RuII([9]aneS3)-(L)(dmso)]+ (1+)c

0.94(60) 0.77(60) −1.43(60)d −1.56(61)d This work

[RuII(bpy)2(L)]+ 1.78(ir) 0.50(70) −1.48(70)e −1.74(80)e 6a

[RuII(pap)2(L)]+ — 1.22(70) −0.50(60) f −1.00(70) f 6b

RuII(trpy)(L)(Cl) 1.32(100) 0.12(80) −1.58(70)g — 6c

a From cyclic voltammetry in CH3CN/0.1 mol dm−3 Et4NClO4 at100 mV s−1. b Potential in V versus SCE; peak potential differences ΔEp/mV (in parentheses). c In CH2Cl2.

d L based reductions. e bpy basedreductions. f pap based reduction. g trpy based reduction.

Fig. 2 Cyclic voltammogram of [1]ClO4 in CH2Cl2/0.1 mol dm−3 [Et4N]-[ClO4] at 298 K versus SCE. Scan rate: 100 mV s−1.

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O-dmso containing complex (Table S8b†) with the resonanceforms {RuIII–L−} ↔ {RuII–L•} (Scheme 2).

On the other hand, the 79% and 66% contributions of L tothe SOMO(α) and the HOMO(β) of 12+ (S = 1/2), respectively,(Table S4†) as well as the 80%, 87% and 52% contributions ofL to the SOMO1(α), the SOMO2(α) and the LUMO(β), respect-ively, of 13+ (S = 1, ΔE(S=0–S=1) = 1866 cm−1, Tables S8, S5†)suggest that the second oxidation occurs at the ligand L,leading to a {RuIII–L•} formulation (Scheme 2). This is sup-ported by the calculated spin density distribution for 13+ in itslow energy triplet state: L, 0.926; Ru, 0.986; [9]aneS3, 0.018;dmso, 0.084 (Table 6 and Fig. 4b). The almost equal spin den-sities on L and Ru in 13+ (with O-dmso coordination) favourthe triplet over the singlet state by 1866 cm−1 (Table S8†). AnEPR signal at half field, expected for a triplet species, was notobserved even after exhaustive oxidation both at 110 K and4 K. Such forbidden ΔMS = ±2 transitions can be very low inintensity and are thus not always observed under standardconditions.12

The 94% and 91% contributions of L to the LUMO of 1+

(Table S3†) and to the SOMO(α) of 1 (with S-coordinated dmsoin the ground state; Table S6†), respectively, justify an L basedfirst reduction, leading to the valence formulation of {RuII–L•2−}for 1. The free radical-type, unresolved EPR signal15,2e,g of 1 at110 K (Fig. 3b) with g = 1.887 affirms the {RuII–L•2−} configur-ation (Scheme 2). While relatively low in comparison with g(free electron) = 2.0023, the isotropic g factor of 1.887 for 1 istypical of radical complexes of ruthenium(II), the deviation tosmaller values being attributed to low-lying unoccupied MOsnext to the SOMO and to the significant spin–orbit couplingparameter of the associated heavy metal.12 The increase in theDFT calculated C–O(L) bond distance from 1.294 Å to 1.334 Åon moving from 1+ to 1 (Table S1†) and the L centred spindensity of 0.989 (Table 6 and Fig. 4c) in 1 further confirm the{RuII–L•2−} valence configuration of 1.

The 12% and 73% contributions of Ru and L, respectively,to the LUMO(β) of 1 (Table S6†) and the 89% contribution of Lto the SOMO1(α) of 1− (Table S7†) suggest an L based secondreduction to yield {RuII–L3−}. However, the compositions ofSOMO2(α) (Ru: 0.50, L: 0.05, [9]aneS3: 0.15, dmso: 0.31) andHOMO(β) (Ru: 0.50, L: 0.26, [9]aneS3: 0.15, dmso: 0.09) of 1−

(Table S7†) suggest an intermediate situation between {RuII–L3−}and {RuI–L•2−} (Scheme 2). The stabilisation of the triplet state(S = 1) over the singlet state (S = 0) by calculated ΔE(S=0–S=1) =2135 cm−1 (Table S8†) implies that the unpaired spins onRu/L are uncoupled in 1−. Like the doubly oxidised form 13+

(see above), the doubly reduced form 1− did not exhibit a clearhalf field EPR signal both at 110 K and 4 K even after pro-longed electrolysis of 1. The resonance description of 1− as{RuII–L3−} and {RuI–L•2−} forms is further supported by thespin density calculations which yield almost equal spin den-sities on L and Ru as 1.004 and 0.868, respectively (Table 6and Fig. 4d).

The UV-vis-NIR spectroelectrochemical response of 1n (n =+3, +2, +1, 0, −1) has been studied in non-coordinating CH2Cl2(Fig. 5 and Table 7) to prevent exchange of the dmso ligand.

Fig. 3 EPR spectra of (a) 12+ and (b) 1 at 110 K in CH2Cl2/0.1 mol dm−3

[Bu4N][PF6].

Table 4 EPR parameters for 12+ and analogous complexes

Compound g1 g2 g3 <g>a Δgb Reference

[Ru([9]aneS3)(L)-(dmso)]2+ (12+)c

2.207 2.172 1.887 2.094 0.320 This work

[Ru(bpy)2(L)]2+ 2.539 2.204 1.680 2.170 0.860 6a

[Ru(pap)2(L)]2+ 2.243 2.003 1.869 2.044 0.374 6b

[Ru(acac)2(L)] 2.303 2.170 1.550 2.034 0.753 6b[Ru(trpy)(L)(Cl)]+ 2.379 2.118 1.989 2.418 0.390 6c

a <g> = {(1/3)(g12 + g2

2 + g32)}1/2. bΔg = g1 − g3.

cO-coordinated dmsoassumed.

Table 5 Spin densities for 12+ and analogous complexes

Compound Ru L Reference

[Ru([9]aneS3)(L)(dmso)]2+ (12+)a 0.624 0.352 This work[Ru(bpy)2(L)]

2+ 0.703 0.253 6a[Ru(pap)2(L)]

2+ 0.559 0.492 6b[Ru(acac)2(L)] 0.824 0.077 6b[Ru(trpy)(L)(Cl)]+ 0.727 0.050 6c

aO-coordinated dmso ligand.

Table 6 Spin density values for the paramagnetic complexes 1n (n =3+, 2+, 0, 1−) as calculated from DFT (UB3LYP)

Compounda Ru L [9]aneS3 dmso

13+ (κ-O) (S = 1) 0.986 0.926 0.018 0.08412+ (κ-O) (S = 1/2) 0.624 0.352 0.025 −0.0011 (κ-S) (S = 1/2) −0.001 0.989 0.004 0.0071− (κ-S) (S = 1) 0.868 1.004 0.024 0.102

aO-coordinated dmso ligand for the cationic forms (3+, 2+),S-coordination for 1, 1−.

Paper Dalton Transactions

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The origins of the transitions have been assigned by TD-DFTcalculations using the DFT optimised structures of the com-plexes in each redox state including dmso O/S coordinationchange (Table 8). The experimental transitions are generallyreproduced by the TD-DFT calculations.

Besides multiple intraligand and interligand transitions inthe higher energy UV region, 1+ exhibits an intense (dπ)Ru →(π*)L MLCT (metal-to-ligand charge transfer) transition at392 nm, associated with shoulders at the lower (499 nm, (π)L→ (π*)L, LLCT, ligand-to-ligand charge transfer) and higher(338 nm, (dπ)Ru → (π*)L, MLCT) energy regions. On one-elec-tron oxidation to 12+, one broad, weak LMCT (ligand-to-metalcharge transfer) transition corresponding to (π)L → (dπ)Ru

emerges at the lower energy region at 875 nm, followed by oneshoulder corresponding to a (π)L → (π*)L (LLCT) transition at500 nm. The further oxidised 13+ exhibits one moderatelyintense (π)L/(dπ)Ru → (dπ)Ru/(π*)L based LMMLCT transitionat 894 nm as well as one very weak near-IR band at 1953 nminvolving a (dπ)Ru → (dπ)Ru (MMCT, metal-to-metal chargetransfer) transition.

The one-electron reduced species 1 shows one weak (π)L →(dπ)Ru LMCT transition at 670 nm. The second reduced state1− displays weak LMCT ((π)L → (dπ)Ru), mixed MLLCT ((dπ)-Ru/(π)L → (π*)L) and LL/MCT ((π)L → (π*)[9]aneS3/(dπ)Ru)transitions in the form of shoulders between 614 nm and497 nm.

In addition to the reasonable assignment of electronic tran-sitions, the TD-DFT reproduction of experimental absorptions(Table 8) confirms the identity of the redox forms and supportsthe spin and dmso ligand coordination states.

Conclusions

The replacement of N-donor co-ligands (bpy, trpy, and pap) incomplexes with {Ru(L)} by the S-donor ligands [9]aneS3 anddmso leads to a system 1n which can be investigated in five oxi-dation states (n = +3, +2, +, 0, −). DFT calculations suggest theexpected S → O coordination change of bonded dmso after oxi-dation of the structurally characterised RuII precursor 1+. TheEPR and UV-vis-NIR spectroelectrochemical results in conjunc-tion with DFT and TD-DFT calculations reveal mixed oxidationof the non-innocent β-diketonate ligand, L− → L• and of themetal (RuII → RuIII) on stepwise oxidation, whereas thereduction occurs largely on the ligand (L− → L•2−). The provenusefulness of the tricyclic π system of Ln for metal binding6,16

and materials construction17 is thus employed here to demon-strate its capacity for both electron loss and uptake in thesame molecular framework, thus revealing unprecedentedbidirectional non-innocence. Further planned studies will

Fig. 4 DFT calculated Mulliken spin density plots of (a) 12+, (b) 13+, each with κ-O-dmso, and of (c) 1 and (d) 1−, each with κ-S-dmso.

Scheme 2 Electronic structural forms of 1n in different redox states.

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clarify whether the remarkable stabilities of several oxidationstates observed here can be attributed to the electronic πacceptor capacity of thioether donors or to the macrocycliceffect of [9]ane ligands.

Experimental sectionMaterials

The precursors Ru(dmso)4(Cl)2,18 Ru([9]aneS3)(dmso)(Cl)2

7

and 9-hydroxyphenalenone (HL)19 were prepared according toprocedures reported in the literature. The ligand 1,4,7-trithia-cyclononane ([9]aneS3) was purchased from Aldrich. Otherchemicals and solvents were of reagent grade and used asreceived. For spectroscopic and electrochemical studies HPLCgrade solvents were used.

Physical measurements

Solution electrical conductivity was checked using a Systronicconductivity bridge 305. The EPR measurements were made ina two electrode capillary tube20 with an X-band (9.5 GHz)Bruker system ESP300 spectrometer. Cyclic voltammetricmeasurements were done using a PAR model 273A electro-chemistry system. Platinum wire as working and auxiliary elec-trodes and saturated calomel as the reference electrode (SCE)were used in a standard three-electrode configuration withtetraethylammonium perchlorate (TEAP) as the supportingelectrolyte (substrate concentration ca. 10−3 mol dm−3; scanrate 100 mV s−1). All electrochemical experiments were carriedout under a dinitrogen atmosphere. UV-vis-NIR spectroelectro-chemical studies were performed in CH2Cl2/0.1 mol dm−3

Bu4NPF6 at 298 K using an optically transparent thin-layer elec-trode (OTTLE) cell21 mounted in the sample compartment of aJ&M TIDAS spectrophotometer. The elemental analyses weredone on a Perkin-Elmer 240C elemental analyser. Electrospraymass spectral measurements were carried out using a BrukerMaxis Impact mass spectrometer.

Crystal structure determination

Single crystals of [1]ClO4 were obtained by slow evaporation ofCDCl3 solution of [1]ClO4 at 298 K. X-ray diffraction data werecollected using a CCD Agilent Technologies (Oxford Diffrac-tion) SUPER NOVA diffractometer. The data were collected bythe standard phi-omega scan techniques, and were scaled andreduced using CrysAlisPro RED software. The structure wassolved by direct methods using SHELXS-97 and refined by fullmatrix least-squares with SHELXL-97, refining on F2.22 All non-hydrogen atoms were refined anisotropically. The remaininghydrogen atoms were placed in geometrically constrained

Fig. 5 UV-vis-NIR spectroelectrochemistry of 1n (n = +3, +2, +1, 0, −1) in CH2Cl2/0.1 mol dm−3 [Bu4N][PF6].

Table 7 UV-vis-NIR spectroelectrochemical data for 1n (n = +3, +2, +1,0, −1) in CH2Cl2/0.1 mol dm−3 [Bu4N][PF6]

Compound λ/nm (ε/dm3 mol−1 cm−1)

13+ 1953(270), 1574(240), 894(3540), 538(1380), 410(16 560),356(7800), 318(5560), 238(15 450), 215(10 890, sh)

12+ 875(970), 500(1840), 405(10 160), 394(9970, sh),358(7200, sh), 339(5810), 323(4180, sh), 258(11 990),238(13 970), 215(10 750)

1+ 499(1940), 392(8510), 338(5900), 321(3800, sh),290(5900, sh), 262(12 730), 237(13 350), 220(10 780)

1 1058(150), 670(1980), 626(1790, sh), 584(1660),427(12 690), 345(4570), 283(8840, sh), 265(12 020),239(14 150), 218(10 780)

1− 614(890, sh), 578(1285, sh), 472(3210, sh), 394(6490),347(5860, sh), 344(5950), 337(6240), 293(7990, sh),262(12 930), 239(14 050), 216(10 400)

Paper Dalton Transactions

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positions and refined with isotropic temperature factors,generally 1.2Ueq of their parent atoms. Hydrogen atoms wereincluded in the refinement process as per the riding model.

Computational details

Full geometry optimisations were carried out using the densityfunctional theory method at the (U)B3LYP level for 13+, 12+, 1,1− and (R)B3LYP for 1+.23 All elements except ruthenium wereassigned the 6-31G(d) basis set. The SDD basis set witheffective core potential was employed for the rutheniumatom.24 Vibrational frequency calculations were performed toensure that the optimised geometries represent the localminima and there are only positive eigenvalues. All calcu-lations were performed with the Gaussian09 program

package.25 Vertical electronic excitations based on B3LYP opti-mised geometries were computed for 13+, 12+, 1+, 1, 1− usingthe time-dependent density functional theory (TD-DFT) form-alism26 in dichloromethane using the conductor-like polarisa-ble continuum model (CPCM).27 Chemissian 1.728 was used tocalculate the fractional contributions of various groups to eachmolecular orbital. All the calculated structures were visualisedusing ChemCraft.29

Preparation of [1]ClO4

The starting complex [Ru([9]aneS3)(dmso)(Cl)2] (50 mg,0.09 mmol) was taken in EtOH (25 cm3) and the ligand9-hydroxyphenalenone (HL) (18 mg, 0.09 mmol) was addedto it followed by the addition of NEt3 (0.09 mmol) to it.

Table 8 TD-DFT ((U)B3LYP/CPCM/CH2Cl2) calculated electronic transitions for 1n (n = +3, +2, +1, 0, −1)

E/eVλ/nm (expt.) (ε/dm3

mol−1 cm−1) λ/nm (DFT) ( f ) Transition Character

13+ (κ-O) (S = 1)0.5785 1953(270) 2143(0.0029) HOMO−1(β) → LUMO+1(β)(0.73) Ru(dπ) → Ru(dπ)1.4991 894(3540) 827(0.3592) HOMO(β) → LUMO+1(β)(0.62) L(π) → Ru(dπ)

HOMO−1(β) → LUMO(β)(0.55) Ru(dπ) → L(π*)2.4689 538(1380) 502(0.0426) SOMO2(α) → LUMO(α)(0.68) L(π) → L(π*)3.0254 410(16 560) 409(0.0215) HOMO−10(β) → LUMO(β)(0.59) [9]aneS3(π) → L(π*)3.0965 400(0.0255) HOMO−9(β) → LUMO+1(β)(0.73) L(π) → Ru(dπ)3.4912 356(7800) 355(0.2152) HOMO(β) → LUMO+2(β)(0.42) L(π) → L(π*)

12+ (κ-O) (S = 1/2)1.4694 875(970) 844(0.1132) HOMO−1(β) → LUMO(β)(0.82) L(π) → Ru(dπ)

HOMO−2(β) → LUMO(β)(0.50) Ru(dπ) → Ru(dπ)2.2088 500(1840) 561(0.0076) HOMO(β) → LUMO+1(β)(0.68) L(π) → L(π*)3.1038 405(10 160) 399(0.3546) HOMO(β) → LUMO+1(β)(0.58) L(π) → L(π*)

HOMO−1(α) → LUMO(α)(0.55) L(π) → L(π*)3.6923 339(5810) 336(0.1043) HOMO−1(α) → LUMO+2(α)(0.35) L(π) → Ru(dπ)/[9]aneS3(π*)

HOMO(β) → LUMO+3(β)(0.30) L(π) → [9]aneS3(π*)/Ru(dπ)

1+ (κ-S) (S = 0)2.6438 499(1940) 468(0.0204) HOMO → LUMO(0.66) L(π)/Ru(dπ) → L(π*)

HOMO−1 → LUMO(0.21) L(π) → L(π*)3.2034 392(8510) 387(0.3612) HOMO−2 → LUMO(0.59) Ru(dπ) → L(π*)

HOMO−4 → LUMO(0.12) Ru(dπ) → L(π*)3.6205 338(5900) 342(0.0414) HOMO−3 → LUMO(0.67) Ru(dπ) → L(π*)3.8716 321(sh) 320(0.0672) HOMO−4 → LUMO(0.65) Ru(dπ) → L(π*)4.0373 290(sh) 307(0.0460) HOMO−5 → LUMO(0.67) L(π) → L(π*)4.5553 262(12 730) 272(0.0635) HOMO → LUMO+3(0.60) L(π)/Ru(dπ) → Ru(dπ)5.1514 237(13 350) 240(0.4520) HOMO → LUMO+8(0.46) L(π) → Ru(dπ)/[9]aneS3(π*)

HOMO → LUMO+6(0.34) L(π) → [9]aneS3(π*)5.5906 220(10 780) 221(0.1152) HOMO−3 → LUMO+3(0.61) Ru(dπ) → Ru(dπ)

1 (κ-S) (S = 1/2)2.0059 670(1980) 618(0.0062) SOMO(α) → LUMO+1(α)(0.95) L(π) → Ru(dπ)2.1569 584(1660) 574(0.0195) SOMO(α) → LUMO+3(α)(0.90) L(π) → [9]aneS3(π*)3.0810 427(12 690) 402(0.4285) HOMO−1(β) → LUMO(β)(0.80) L(π) → L(π*)3.9494 345(4570) 313(0.0321) HOMO−3(β) → LUMO(β)(0.80) L(π) → L(π*)4.5007 265(12 020) 275(0.0265) HOMO−1(α) → LUMO+3(α)(0.55) L(π) → [9]aneS3(π*)

1 (κ-S) (S = 1)2.0124 614(sh) 616(0.0142) SOMO1(α) → LUMO+2(α)(0.67) L(π) → Ru(dπ)

HOMO(β) → LUMO(β)(0.47) Ru(dπ)/L(π) → L(π*)2.1466 578(sh) 577(0.0256) HOMO−1(β) → LUMO(β)(0.62) Ru(dπ)/L(π) → L(π*)2.4944 472(sh) 497(0.1884) SOMO1(α) → LUMO+7(α)(0.47) L(π) → [9]aneS3(π*)/Ru(dπ)

HOMO−1(β) → LUMO(β)(0.39) Ru(dπ)/L(π) → L(π*)3.3534 394(6490) 369(0.0961) HOMO−4(β) → LUMO(β)(0.69) L(π) → L(π*)

SOMO1(α) → LUMO+10(α)(0.43) L(π) → L(π*)3.5726 347(sh) 347(0.0090) SOMO1(α) → LUMO+11(α)(0.65) L(π) → [9]aneS3(π*)/Ru(dπ)3.6117 344(5950) 343(0.0043) HOMO−2(α) → LUMO(α)(0.93) Ru(dπ)/L(π) → Ru(dπ)3.6609 337(6240) 338(0.0341) HOMO(β) → LUMO+3(β)(0.57) Ru(dπ)/L(π) → Ru(dπ)

HOMO(β) → LUMO+5(β)(0.34) Ru(dπ)/L(π) → Ru(dπ)/[9]aneS3(π*)

Dalton Transactions Paper

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The mixture was refluxed under aerobic conditions for 6 h.The initial yellow solution changed to dark brown. The reac-tion mixture was then evaporated to dryness under reducedpressure. The dry mass was then moistened with a few dropsof CH3OH followed by the addition of saturated aqueous solu-tion of NaClO4 to it. The mixture was chilled overnight andthen filtered and dried. The solid mass was purified bycolumn chromatography using a neutral Al2O3 column. Thedesired brown band was eluted by CH2Cl2–CH3OH (20 : 1). Onremoval of the solvent under reduced pressure the purecomplex [1]ClO4 was obtained as a dark brown solid which wasfurther dried under vacuum. Yield: [1]ClO4 (38 mg, 60%). Anal.Calcd for C21H25S4O7ClRu: C, 38.50; H, 3.80. Found: C, 38.19;H, 3.56. Molar conductivity (ΛM (Ω−1 cm2 dm3 mol−1), CH3CN):110. IR (KBr pellet): νmax/cm

−1 1100 and 632 (ClO4−). NMR

(400 MHz; CDCl3; Me4Si):1H: δH 7.96 (2H, d, J 7.6 Hz, Hc(L)),

7.91 (2H, d, J 9.28 Hz, Hb(L)), 7.49 (1H, t, J 7.56 Hz, Hd(L)),7.08 (2H, d, J 9.28 Hz, Ha(L)), 3.10 (4H, m, [9]aneS3), 2.91(11H, m, dmso, [9]aneS3), 2.76 (3H, m, [9]aneS3). δC 177.87(Ce(L)), 138.73 (Cb(L)), 132.50 (Cc(L)), 128.91 (Cg(L)), 128.10(Ca(L)), 125.99 (Cf(L)), 123.71 (Cd(L)), 114.04 (Ch(L)), 43.55(C(dmso)), 35.40 (C([9]aneS3)), 33.36 (C([9]aneS3)), 30.72(C([9]aneS3)). ESI-MS(+) (m/z, CH2Cl2): 554.9673 (Calc.554.9727 for {C21H25S4O3Ru}

+).(CAUTION! Perchlorate salts are explosive and should be

handled with appropriate care).

Acknowledgements

Financial support received from the Department of Scienceand Technology and the Council of Scientific and IndustrialResearch (fellowship to H.A.), New Delhi (India), and theDAAD, FCI and DFG (Germany) is gratefully acknowledged.

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