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Inorganic Chemistry Communications 11 (2008) 526–530

Novel Rh(III) pentamethylcyclopentadienyl and Ru(II)cyclopentadienyl complexes containing 1,3,5-triazine-2,4,6-trithiol in

trinucleating mode

Manoj Trivedi a, Daya Shankar Pandey a,*, Ru-Qiang Zou b, Qiang Xu b,*

a Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi 221 005, Uttar Pradesh, Indiab National Institute of Advanced Industrial Science and Technology (AIST), 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577, Japan

Received 19 November 2007; accepted 26 December 2007Available online 8 January 2008

Abstract

Two homo-trinuclear complexes [{(g5-C5Me5)RhCl}3(l3-L)] (1) and [{(g5-C5H5)Ru(PPh3)}3(l3-L)] (2) (H3L = 2,4,6-trimercapto-1,3,5-triazine) are reported. Both the complexes have been fully characterized by elemental analyses, FAB-MS, IR, NMR, electronicand emission spectral techniques. Molecular structure of 1 has been authenticated by single crystal X-ray diffraction analyses. Complex1 revealed the strong intra- and inter-molecular C–H� � �X (X = Cl, p) and p–p stacking interactions, which play important roles to sta-bilize crystal space packing. Furthermore, the p–p interactions in 1 lead to a double-helical motif.� 2008 Elsevier B.V. All rights reserved.

Keywords: Rhodium–Cp*; Ruthenium–Cp; Trithiocyanuric acid; X-ray; Emission; Weak interactions

Enormous current attention has been paid towards syn-thesis and characterisation of bi- and polynuclear transitionmetal complexes. In this regard polyazine ligands viz., tri-azine, tetraazine and their derivatives have drawn specialattention [1]. 1,3,5-Triazine-2,4,6-trithiol (H3L or TMT) isan effective analytical reagent and find potential applicationsin the removal of univalent and divalent heavy metal ionsfrom waste water [2]. As far as coordination of TMT withmetal ions is concerned, it has been established that TMTacts as a versatile ambidentate ligand in a variety of coordi-nation modes viz., monodentate N� or S� donor [3], biden-tate chelating [N,S]� [4] or bridging two metal ions throughtwo of the bis-chelating [N,S]� donor sets [5]. The trinucleat-ing coordination mode of 2,4,6-trimercapto-1,3,5-triazinideðC3N3S3�

3 Þ derived from TMT using all the three available[N,S]� donor sites is limited to only a few complexes

1387-7003/$ - see front matter � 2008 Elsevier B.V. All rights reserved.

doi:10.1016/j.inoche.2007.12.039

* Corresponding authors. Tel.: +91 (0) 9450960400 (D.S. Pandey), +8172 751 9652 (Q. Xu).

E-mail addresses: dsprewa@yahoo.com (D.S. Pandey), q.xu@aist.go.jp (Q. Xu).

[{(g5-CH3C5H4)2TiIII}3(l3-L)] [6], [Os3H(CO)10]3 (TMT) [7],[{(bpy)2/(phen)2RuII}3(l3-L)](ClO4)3 (bpy = 2,20-bipyridine,phen = 1,10-phenanthroline) [8] and [{(L0)2RuII}3(l3-L)]-(ClO4)3, [L = 1,3,5-triazine-2,4,6-trithiolato, L0 = arylazo-pyridine] [9], [Cu3(C9H23N3)3(C3N3S3)] (ClO4)3 [10a],[Zn3(C9H23N3)3(C3N3S3)](ClO4)3 [10b]. Furthermore, struc-turally characterized complexes involving trinucleatingmode of TMT are rare [9].

On the other hand, the chemistry and photo-physicalproperties of Rh(III) and Ru(II) derived from [{(g5-C5Me5)Rh(l-Cl)Cl}2] and [(g5-C5H5)Ru(PPh3)2Cl] are welldocumented [11]. The complexes undergo rich variety ofchemistry resulting in the formation of interesting neutraland cationic complexes [12]. Despite extensive studies onthe complexes derived from [{(g5-C5Me5)Rh(l-Cl)Cl}2]and [(g5-C5H5)Ru(PPh3)2Cl], its reactivity with TMT hasyet to be explored. In this regard, we have examined thereactivity of the chloro-bridged rhodium complex[{(g5-C5Me5)Rh(l-Cl)Cl}2] and ruthenium complex [(g5-C5H5)Ru(PPh3)2Cl] with TMT in presence of a base,and successfully isolated two novel trinuclear complexes

Fig. 1. ORTEP diagram of 1 (ellipsoids with 50% probability; hydrogenatoms are omitted for clarity). Selected bond lengths (A) and bond angles(�) for 1; Rh(1)–N(3) 2.117(5), Rh(1)–Cl(1) 2.4030(17), Rh(1)–S(1)2.4388(17), Rh(2)–N(1) 2.125(5), Rh(2)–S(2) 2.4581(17), Rh(2)–Cl(2)2.3915(16), Rh(3)–N(2) 2.123(6), Rh(3)–S(3) 2.4417(18), Rh(3)–Cl(3)2.391(2), S(1)–C(1) 1.719(6), S(2)–C(2) 1.710(6), S(3)–C(3) 1.695(7),Rh(1)–Cct 1.764, Rh(1)–Cav 2.145, Rh(2)–Cct 1.773, Rh(2)–Cav 2.146,Rh(3)–Cct 1.769, Rh(3)–Cav 2.146, N(3)–Rh(1)–S(1) 67.29(15), N(1)–Rh(2)–S(2) 67.02(14), N(3)–Rh(3)–S(3) 67.28(14), N(3)–Rh(1)–Cl(1)82.30(15), N(1)–Rh(2)–Cl(2) 86.91(14), N(2)–Rh(3)–Cl(3) 91.39(15),Cl(1)–Rh(1)–S(1) 90.31(6), Cl(2)–Rh(2)–S(2) 90.47(6), Cl(3)–Rh(3)–S(3)92.98(7).

M. Trivedi et al. / Inorganic Chemistry Communications 11 (2008) 526–530 527

[{(g5-C5Me5)RhCl}3(l3-L)] (1) and [{(g5-C5H5)Ru-(PPh3)}3(l3-L)] (2) containing TMT in its relatively rarecoordination mode. In this paper, we describe reproduciblesynthesis and spectral properties of both of the homo-tri-nuclear complexes as well as the crystal structure and theinter-molecular weak interactions in 1.

Reaction of the chloro-bridged dimeric rhodium com-plex [{(g5-C5Me5)Rh(l-Cl)Cl}2] [13] with 1,3,5-triazine-2,4,6-trithiol in 1.5:1 stoichiometric ratio in a mixture ofdichloromethane and methanol (1:1 v/v) in presence oftriethylamine under stirring conditions at RT affordedhomo-trinuclear complex [{(g5-C5Me5)RhCl}3(l3-L)] (1).The ruthenium complex [{(g5-C5H5)Ru (PPh3)}3(l3-L)] (2)was synthesized from reaction of [(g5-C5H5)Ru(PPh3)2Cl][14] with TMT in 3:1 stoichiometric ratio in absolute etha-nol under refluxing conditions in reasonably good yield.The Rh and Ru centre in these complexes is a stereogeniccentre, it may lead to several stereoisomers, but we haveisolated the major product and our studies mainly dealwith the major product. A scheme showing the synthesesof 1 and 2 is shown in Scheme 1 [15].

The complexes were isolated as air-stable, non-hygro-scopic solids. Complex 1 is soluble in common organicsolvents viz., methanol, dichloromethane, chloroform,dimethylformamide and dimethylsulphoxide but insolublein petroleum ether and diethyl ether. Complex 2 is solublein dimethylformamide and dimethylsuphoxide, partiallysoluble in halogenated solvents like dichloromethane,chloroform but insoluble in petroleum ether and diethylether. Both the complexes were fully characterised by IR,1H NMR, UV–Vis, FAB-MS, electronic and emission spec-tral studies. Analytical data of the complexes corroboratedwell to their respective formulations [15]. FAB-MS spectraof both the complexes corresponded well to their formula-tions (see F-1 and F-2, supporting material).

It has been shown that TMT moiety present in aromaticform with covalent metal–sulphur bond displays bands at�1490, 1232 and 879 cm�1 [16]. Infrared spectrum of 1 innujol displayed bands at 1443, 1244 and 888 cm�1 whereascorresponding bands in 2 were observed at 1460, 1232,

N

N

SH

HS

N

N

N

S

SS

Rh

Rh

Cl

Cl

RhCl

(i) [{( η5-C5M

CH2Cl2+C

(ii) [( η5-C5H5

Absolute E[1]

(i)

Scheme

879 cm�1. It suggested that TMT moiety in both the com-plexes 1 and 2 exists in aromatic form with covalent metal–sulphur bonds. Bands associated with m(C@N) vibration in1 and 2 appeared at�1631–1637 cm�1 [4,16]. 1H NMR spec-tral data in d6-DMSO exhibits a distinct singlet associatedwith g5-Cp* protons at d 1.56 ppm in 1 and g5-Cp protonsat 4.70 ppm in 2. The aromatic protons in 2 associated withPPh3, resonated as a broad multiplet in the expected region(7.32–7.82 ppm). The position and integrated intensity ofthe various resonances corroborated well to the formulationof 1 and 2. Absorption spectra of 1 and 2 in dimethylsulph-oxide (see F-3 supporting material) displayed transitions in

Ru

N

SH

e5)Rh(μ-Cl)Cl}2] /Et3N

H3OH(1:1)

N

N

N

S

SS

Ru

Ru

Ph3P

Ph3P

)Ru(PPh3)2Cl] /KOHthanol

[2]

(ii)

PPh3

1.

Table 1Hydrogen bond parameters for 1

D–H� � �A–X d(H� � �A) (A) D(D� � �A) (A) h(D–H� � �A) (�)

C(13)–H(13A)� � �Cl(2)a 2.78 3.692(8) 159C(19)–H(19C)� � �Cl(1)b 2.81 3.718(9) 157C(21)–H(21B)� � �Cl(3)c 2.81 3.725(9) 161C(29)–H(29C)� � �Cl(2)d 2.73 3.680(14) 171C(31)–H(31C)� � �Cl(1)e 2.82 3.651(8) 146C(11)–H(11c)� � �C(3) 2.75 3.368 122C(11)–H(11A)� � �C(21) 2.85 3.555 130C(21)–H(21C)� � �C(7) 2.68 3.000 158C(21)–H(21C)� � �C(6) 2.65 3.423 137

a 1 � x, �y, �z.b �x, �y, �z, 1 � x.c �1/2 + y, 1/2 � z.d �1 + x, y, z.e x, 1/2 � y, �1/2 + z.

528 M. Trivedi et al. / Inorganic Chemistry Communications 11 (2008) 526–530

the low energy side at 428 nm and 398 nm, respectively. Ithave been assigned to Mdp!Lp� metal to ligand charge trans-fer transitions (MLCT), while the transitions in the higherenergy side at ca. 302–313 nm have been assigned to theintra-ligand p–p* transitions [4,8]. Complexes 1 and 2 werefound to be luminescent at ambient temperature in DMSO(see F-4, supporting material). Upon excitation at 313 nm,complex 1 shows weak emission at 380 nm, however excita-tion at 428 nm (lowest energy MLCT band), emits stronglyat 600 nm, this may be attributed to metal to ligand(Rh–L) charge transfer. Similarly, complex 2 upon excitationat 302 nm exhibits broad emission band at 414 nm, butexcitation at 398 nm (lowest energy MLCT band), resultsin emission at 530 nm, which may be attributed to tripletmetal-to-ligand charge transfer state (3MLCT) [8,17]. Since,

Fig. 2. Double-helical structure in 1 resulting from p–p inter

H3L exhibits emission around 439 nm at room temperature,the observed emissions at 380–414 nm may probably origi-nate from TMT moiety.

Crystals of the [{(g5-C5Me5)RhCl}3(l3-L)] (1) suitablefor single crystal X-ray diffraction were obtained fromCHCl3/diethyl ether by slow diffusion techniques at roomtemperature [18]. ORTEP depiction of 1 with atom-labelsis shown in Fig. 1 and hydrogen bond parameters are listedin Table 1. The TMT ligand in triazenide form is bondedto three rhodium centres using all the three available bis-che-lating [N,S]�donor sites. Each of the rhodium is coordinatedthrough nitrogen and sulphur atoms of TMT, chloride andCp* in g5-coordination mode. Considering Cp* as a singlecoordination site, overall coordination geometry about eachrhodium centre is pseudo-tetrahedral or typical piano stoolgeometry. Average Rh1–Ccp� , Rh2–Ccp� , Rh3–Ccp� distancesare 2.145 (range 2.133(6)–2.154(7) A; Rh1–Cct 1.764 A),2.146 (range 2.125(6)–2.165(7) A; Rh2–Cct 1.773 A) and2.146 A (range 2.134(8)–2.157(8) A; Rh3–Cct 1.769 A),respectively [19]. The C–C bond lengths within the Cp* ringand C–CH3 bond lengths are normal and comparable withthose in other Rh–Cp* complexes [20]. The Rh–Cl distancein 1 is normal [Rh(1)–Cl(1) = 2.403(17), Rh(2)–Cl(2) =2.391(16), Rh(3)–Cl(3) = 2.391(2)] [19]. as the Rh–N bonddistances [Rh(1)–N(3) = 2.117(5), Rh(2)–N(1) = 2.125(5),Rh(3)–N(2) = 2.123(6)], which are comparable to Rh–Cland Rh–N bond distances reported in the literature [19,20].The angles N–Rh–Cl [N(3)–Rh(1)–Cl(1) = 82.30(15),N(1)–Rh(2)–Cl(2) = 86.91, N(2)–Rh(3)–Cl(3) = 91.39(15)]are normal. The N–Rh–S bite angles are in the range of67.02(14)–67.29(15)�, which indicates that the bridging

action: (a) wire-frame model and (b) space-filled model.

M. Trivedi et al. / Inorganic Chemistry Communications 11 (2008) 526–530 529

TMT ligand suffer from a considerable strain [9]. TheRh(III)–S distances are 2.438(17) A [Rh(1)–S(1)], 2.458 A[Rh(2)–S(2)] and 2.441(18) A [Rh(3)–S(3)]. These bond dis-tances are comparable to the one reported in other Rh(III)complexes [21].

Crystal packing in 1 is stabilised by inter- and intra-molecular C–H� � �X (X = Cl, p) and p–p interactions. Aninteresting feature of the crystal packing in 1 is a double-helical motif (Fig. 2) resulting from p–p interactions. Con-tact distances for p–p interactions are 3.36–3.39 A[22a,22b]. C–H� � �Cl type inter- and intra-molecular hydro-gen bonds are also present. The C–H� � �Cl contact dis-tances are in the range of 2.73–2.82 A and associatedangles are in the range 146–159� (see F-5, supporting mate-rial). These distances are within the range reported in theliterature [22b]. The inter-molecular C–H� � �p weak interac-tions in 1 results in parallel chain-like structure, in whichpentamethylcyclopentadienyl rings are arranged in alter-nate manner as shown in Fig. 2. Contact distances forC–H� � �p interactions are in the range of 2.66–2.82 A (seeF-6, supporting material).

In conclusion, in this work we have presented novel neu-tral homo-trinuclear rhodium complex [{(g5-C5Me5)RhCl}3(l3-L)] (1) and ruthenium complex [{(g5-C5H5)Ru(PPh3)}3(l3-L)] (2). Coordination of the bridging ligand2,4,6-trimercapto-1,3,5-triazine in rather rare coordinationmode have been established by analytical, spectral andstructural studies. To our knowledge complex 1 representsthe first example of a structurally characterized trinuclearrhodium complex incorporating 2,4,6-trimercapto-1,3,5-triazine as a bridging ligand.

Acknowledgements

We gratefully acknowledge financial support from coun-cil of Scientific and Industrial Research, New Delhi (SeniorResearch Fellowship to M.T.). We also thank the Head,SAIF, Central Drug Research Institute, Lucknow for ana-lytical and spectral facilities, the Head, Department ofChemistry, Faculty of Science, Banaras Hindu University,Varanasi and National Institute of Advanced IndustrialScience and Technology (AIST), Ikeda, Osaka, Japan forextending facilities.

Appendix A. Supplementary material

CCDC 662727 contains the supplementary crystallo-graphic data for this paper. These data can be obtained freeof charge from The Cambridge Crystallographic Data Cen-tre via www.ccdc.cam.ac.uk/data_request/cif. Supplemen-tary data associated with this article can be found, in theonline version, at doi:10.1016/j.inoche.2007.12.039.

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[15] [{(g5-C5Me5)RhCl}3(l3-L)] (1): To a suspension of 2,4,6-trimercapto-1,3,5-triazine (0.045 g, 0.25 mmol) in dichloromethane and methanol

530 M. Trivedi et al. / Inorganic Chemistry Communications 11 (2008) 526–530

(1:1 v/v) (50 ml), chloro-bridged dimeric rhodium complex [{(g5-C5Me5) Rh(l-Cl)Cl}2] (0.231 g, 0.37 mmol) and 0.5 ml triethylaminewere added. The suspension was stirred at room temperatureovernight. Slowly, it gave a clear red solution and finally a dark redcoloured compound separated. The red compound thus obtained wasfiltered, washed with H2O, ethanol, diethyl ether and dried undervacuo. Dark red; Yield: (0.257 g, 70%). Anal. Calc. forC33H45N3S3Cl3Rh3: C, 39.83; H, 4.53; N, 4.23. Found: C, 39.86; H,4.56; N, 4.03%. IR (cm�1, nujol): m = 3450, 2920, 1702, 1637, 1443,1244, 1154, 1025, 888, 536, 432. 1H NMR (d ppm, 300 MHz, d6-DMSO, 298 K): 1.56 (Cp*, s, 45H). FAB-MS: m/z obs. (calcd.), rel.int., assignments: 988 (993), 5 [M+], 958 (957), 60 [M�Cl]+�, 650(651), 50 [M�2Cp*�2Cl]+�. UV/Vis (nm): kmax (e (dm3 mol�1

cm�1)) = 428 (36,680), 313 (32,150), 289 (33,110). [{(g5-C5H5)Ru(PPh3)}3(l3-L)] (2):To a suspension of 2,4,6-trimercapto-1,3,5-triazine (0.044 g, 0.25 mmol) in absolute ethanol (30 ml), KOH(0.042 g, 0.75 mmol) was added and stirred at room temperature for�30.0 min. Slowly it dissolved and gave a clear solution. This solutionwas treated with [(g5-C5H5)Ru(PPh3)2Cl] (0.546 g, 0.75 mmol) andrefluxed overnight under nitrogen atmosphere. The resulting orangered compound was filtered, washed with H2O, ethanol and diethylether. Orange red; Yield: (0.765 g, 70%). Anal. Calc. forC72H60N3S3P3Ru3: C, 59.26; H, 4.11; N, 2.88. Found: C, 59.32; H,4.18; N, 2.86. IR (cm�1, nujol): m = 3076, 2950, 1631, 1460, 1232,1150, 1010, 879, 416. FAB-MS: m/z: obs. (calcd.), rel. int., assign-ments: 1460 (1458), 40 [M+]; 1195 (1196), 40 [M�PPh3]+�, 934 (934),30 [M�(PPh3)2]+�.1H NMR (d ppm, 300 MHz, CDCl3, 298 K): 7.56(multiplet, 45H, due to PPh3), 4.70 (s, 15H). UV/Vis (nm): kmax (e(dm3 mol�1 cm�1)) = 398 (33,570), 302 (34,890).

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[18] X-ray data for 1 was collected on Bruker SMART APEX CCDdiffractometer using graphite-monochromated Mo Ka radiation(k = 0.71073 A) at 293(2) K. The structure was solved by directmethods and refined by using MAXUS-99 and SHELX-97. Non-hydrogen atoms were refined anisotropically. All the hydrogen atomswere geometrically fixed and allowed to refine using a riding model.Non-hydrogen atoms were refined with anisotropic displacementparameters. [{(g5-C5Me5)RhCl}3(l3-L)], C33H45Cl3N3Rh3S3, M =994.98, Monoclinic, P21/c, a = 12.4740(8) A, b = 24.2357(15) A,c = 13.5389(9) A, b = 106.2500(10)�, V = 3929.5(4) A3, Z = 4, Dc =1.682 g cm�3, F(000) = 1992, T = 293(2) K, R1 = 0.0755, wR2 =0.2173, GOF = 1.552. A total of 25,070 reflections were collected,9630 unique (Rint = 0.0280).

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