Incorporation of non-planar chelating ligands in the coordination sphere of ruthenium(II) complexes

www.elsevier.nl/locate/ica Inorganica Chimica Acta 313 (2001) 43 – 55

Incorporation of non-planar chelating ligands in the coordination sphere of ruthenium(II) complexes Unusual S-thioether N-pyridyl chelation mode of di-2-pyridyl sulfide (dps) to Ru(N,N-dps)2 core: NMR studies of sterically induced internal dynamics Rosario Scopelliti, Giuseppe Bruno, Caterina Donato, Giuseppe Tresoldi * Dipartimento di Chimica Inorganica, Chimica Analitica e Chimica Fisica, Uni6ersita` di Messina, 98166 Messina, Italy Received 19 November 1999; accepted 29 September 2000

Abstract The unexpected products of the reaction of Ru(N,N-dps)2Cl2 with L [L = di-2-pyridyl sulfide (dps) and 2-(6-methylpyridyl) 2-pyridyl sulfide (mdps) are [Ru(dps)2(N,S-L)][PF6]2, where L is acting in an N,S-bidentate chelate mode as shown in the crystal structure of [Ru(N,N-dps)2(N,S-dps)][PF6]2·H2O (1). The Ru atom exhibits a distorted octahedral geometry involving five N atoms and an S atom. The four-membered chelate ring and the coordinated pyridine ring of the NS-ligand are coplanar, whereas the pendant pyridine is rotated by 113.9(2)°. In addition to the pendant ring, the N,S-coordination produces a sulfur chiral centre. The variable-temperature 1H and 13C NMR spectra show the fluxionality of the complexes. In acetone at all temperatures the spectra are consistent with the presence of intramolecular processes, whereas in acetonitrile above 300 K dissociation occurs and [Ru(N,N-dps)2(solvent)2]2 + and free ligand are present. In order to understand this dynamic behaviour, a synthetic methodology to obtain other octahedral [Ru(N,N-diimmine)2(N,S-L%)][PF6]2 and [Ru(dps)2(N,S-T)][PF6] complexes has been developed (N,N-diimmine= dps, dipyrimidin-2-yl sulfide (dprs), 2,2%-bipyridine (bipy); N,S-L%=phenyl pyridyl sulfide (phpys); N,S-T=2mercaptopyridinate and 2-mercaptopyrimidinate). [Ru(dps)2(phpys)][PF6]2 and [Ru(dprs)2(phpys)][PF6]2 are fluxional species suitable for DNMR studies because of the presence of the anisochronous ortho (and meta) protons on the phenyl group. In acetone, restricted rotation of the uncoordinated ring is observed below 240 K and DH ‡, DS ‡ and DG ‡ calculated. Above this latter temperature a more extensive internal rearrangement occurs, and the latter process may involve inversion at the sulfur chiral centre. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Ruthenium(II) complexes; NMR studies; Crystal structures; Energetics; Pendant phenyl ring

1. Introduction The chemistry of the ruthenium compounds containing bipyridine, polypyridine and similar ligands has been thoroughly explored over many years. This interest is mainly due to the relevance of this chemistry to photophysical, photochemical and redox phenomena. In a series of previous papers we have reported extensive studies on the ligating properties of di-2* Corresponding author. Tel.: + 39-090-676 5710; fax: + 39-090393 756. E-mail address: [email protected] (G. Tresoldi).

pyridyl sulfide (dps) and pyrazin-2-yl 2-pyridyl sulfide (pzpys) ligands [1–5]. The normal bonding mode to metals of these non-planar ligands is the N,N bidentate chelate. Recently, we have focused attention on the bipy or bipy-like ruthenium(II) complexes in which one or more ligands are replaced by non-planar ligands with the aim to modify the chemical and physical properties of the complexes [2,3]. Although the reaction of Ru(bipy)2Cl2 (bipy= 2,2%-bipyridine) with dps easily gives [Ru(bipy)2(N,N-dps)][PF6]2, our attempts to prepare tris-chelate complexes by reaction of bipy or 1,10phenanthroline and Ru(dps)2Cl2, failed [2]. Furthermore, pzpys reacts easily with Ru(bipy)2Cl2 to

0020-1693/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 0 - 1 6 9 3 ( 0 0 ) 0 0 3 4 3 - 1

R. Scopelliti et al. / Inorganica Chimica Acta 313 (2001) 43–55

44

sulfide (dprs), phpys= phenyl pyridyl sulfide] and [Ru(dps)2(N,S-T)][PF6] (T= 2-mercaptopyridinate and 2-mercaptopyrimidinate) are also reported.

give mono- and bi-nuclear compounds containing the ligand coordinated to the ruthenium centre in a monodentate or chelate fashion, whereas the same reaction with Ru(dps)2Cl2 allows only the mono-coordination of the ligand [3]. Similar unusual coordination is shown by dps [4,5] and related ligands [6]. These results were explained taking into account the sterically hindering nature of the dps ligand, which may be assimilated to that of other non-planar diimmines [7]. This paper extends ruthenium non-planar ligands ligation chemistry. Taking advantage of the steric hindrance of the cis-Ru(N,N-dps)2 core and the sterically demanding nature of dps, we were able to introduce into the aforementioned centre an N,S-coordinated dps ligand and to provide the possibility for pairs of chemically distinct coordination mode being present. It is worth noting that although the N,S-coordination of pyridine-2-thiolate and similar ligands is well known [8–10], [Ru(dps)2(N,S-L)][PF6]2 [L =dps (1) and 2-(6-methylpyridyl) 2-pyridyl sulfide (mdps) (2)] are the first examples of compounds in which dps or related ligands are N,S-coordinated with a pendant ring containing an uncoordinated N atom. The presence of the N,S-chelation mode produces a chiral sulfur centre with a pendant pyridine ring. The consequent internal dynamics have been studied by variable-temperature NMR spectra. The crystal structure of [Ru(dps)2(N,S-L)][PF6]2·H2O (1) and the synthesis of the complexes [RuL2(phpys)][PF6]2 [L= bipyridine (bipy), dps and dipyrimidin-2-yl

2. Results and discussion

2.1. Synthesis and characterisation of mdps, phpys and dprs The novel ligands were prepared by refluxing, in DMF under N2, equimolar amounts of the appropriate bromide and the mercapto-derivative [2-bromo,6methylpyridine and 2-mercaptopyridine (mdps), 2-bromopyridine and thiophenol (phpys), 2-bromopyrimidine and 2-mercaptopyrimidine (dprs)] in the presence of K2CO3. DMF was removed by distillation at 100 mmHg. Mdps and phpys were obtained as pale yellow oils by distillation at 7 mmHg, whereas dprs was obtained as a pale yellow powder by recrystallisation from CH2Cl2 –heptane. Their structures were determined by a combination of elemental analysis and the usual spectroscopic techniques. The 1H and 13C NMR data of the ligands in (CD3)2CO are collected in Table 1. The proton signals due to the pyridyl ring of the mdps and phpys (four multiplets in the range l 6.9 –8.5) are consistent with ABMX systems. The signals due to the 6-methyl-pyridine group of mdps consist of three multiplets in the range l 7.6 –7.1 and a singlet at l 2.44. The signals of

Table 1 1 H and 13C NMR dataa for the new ligands

Ligand

Pyridyl ring position 6

Mdps

Phpys

Dprs

5

Other ring position 4

3

8.48 7.23 7.71 J65 =4.5, J64 = 1.5, J63 = 0.6 J54 =7.6, J53 = 1.0, J43 = 7.8 148.95 120.65 136.40 8.37 7.09 7.57 J65 =4.5, J64 = 1.6, J63 = 0.5 J54 =7.2, J53 = 1.2, J43 = 8.0 149.95 120.55 137.35 c

c

7.36 8.69 J65 =J54 =4.9 158.65c 119.75c

2

4%

158.00

154.80

161.40

7.58 7.46 7.48 J5%4% =J4%3% =7.0, J6%4% =J4%2% =2.5 J6%5% =J3%2% =6.0 135.40 130.15 129.60

6.91

121.40

5%

7.60 7.25 J5%4% =7.4, J5%3% =0.9, J4%3% =7.6

7.47

124.25

6%

120.00

136.10

3%

2%

1% 2.44b

7.10

121.60

156.30

7.46

7.58

130.15

135.40

c

7.36

158.65c

–d

Recorded at 295 K in (CD3)2CO at 300.15 and 75.56 MHz; l (ppm) with respect to internal SiMe4; coupling constant J in hertz. Methyl signals. c Pyrimidinyl ring. d Not observed. a

b

22.45b

131.40

R. Scopelliti et al. / Inorganica Chimica Acta 313 (2001) 43–55

Fig. 1. Molecular structure of the cation of 1 including the atom numbering scheme.

the phenyl group are observed at l 7.58 (H2% and H6%), 7.48 (H4%) and 7.46 (H3% and H5%). The first of these signals, assigned to the protons near the sulfur atom, is partially overlapped with the H4 pyridine signal. The proton signals of dprs consist of a triplet at l 7.36 (H5) and a doublet at l 8.69 (H4 and H6). All the systems are fully resolved by a second-order computer-assisted analysis. The 13C signals are easily assigned. The methyl signal of mdps is observed at l 22.45 and the phenyl signals of phpys are at l 135.40 (C6% and C2%), 130.15 (C3% and C5%) and 129.60 (C4%); the pyridyl signals of the novel ligands are in the ranges l 149 – 150 (C6), 120 – 121 (C5) 136 – 138 (C4), 121 –125 (C3) and 158 – 162 (C2). The 13C signals of dprs are observed at l 158.65 (C4 and C6) and 119.75 (C5).

2.2. Synthesis of the compounds containing an N,S-chelate ligand The air-stable [Ru(dps)2(N,S-L)][PF6]2 and [Ru(dps)2(N,S-T)][PF6] compounds [L=dps, mdps and phpys; T= 2-mercaptopyridinate (pyt) and 2-mercaptopyrimidinate (prt)] were obtained by the reaction of [Ru(dps)2Cl2] with an excess of dps (1), mdps (2), phpys (3), 2-mercaptopyridine (6) and 2-mercaptopyrimidine (7) in boiling ethanol/water (1:1) followed by addition of aqueous NH4PF6. [Ru(bipy)2(phpys)][PF6]2 (4) (bipy = 2,2%-bipyridine) and [Ru(dprs)2(phpys)][PF6]2 (5) were prepared similarly from phpys and [Ru(bipy)2Cl2] and [Ru(dprs)2Cl2], respectively. All the compounds are soluble in acetone or acetonitrile and slightly soluble in methanol, ethanol and water.

45

Conductivity measurements in acetone or acetonitrile solution indicate that 1–5 and 6, 7 are 1–2 and 1–1 electrolytes, respectively. In comparing the IR spectrum of 1 with those of the known [1–5] dps complexes and free dps we observe in the spectrum of 1 the presence of four bands around 1590 cm − 1, assigned to w(CN), and four around 750 cm − 1, characteristic of the out-of-plane CH deformations. (In these regions of the free dps spectrum six bands are observed at 1605w, 1571vs, 1558s, 756vs, 740ms and 721s cm − 1.) These results are indicative of two different structural arrangements of the dps molecules in the solid state. In fact, the bands at 1624w, 1590s, 1561s, 773vs, 763vs and 725s cm − 1 are compatible with the N,N-coordination [1–5], which shifts the w(CN) and the CH deformations to higher wavenumbers with respect the free dps, whereas the bands at 1573s and 740ms cm − 1 suggest the presence of uncoordinated pyridine residues on the dps ligand [5]. We apply similar considerations to the IR spectrum of [Ru(dps)2(N,S-mdps)][PF6]2, where seven bands at 1640br, 1589vs, 1556s, 776vs, 761vs, 741ms and 725s cm − 1 are observed (in the free mdps there are six bands at 1667vs, 1576vs, 1559vs, 763vs, 739s and 723vs cm − 1).

3. Crystal structure of 1 The cation [Ru(dps)3]2 + , two PF6− anions (one of which is disordered) for charge balance and a disordered water molecule are present in the asymmetric unit. The crystal packing is determined by several hydrogen-bond interactions involving the fluorine atoms of the PF6− anions and the hydrogen atoms of the dps ligands [F···H contacts ranging from 2.38(3) to 2.54(1) A, ]. The geometry about the ruthenium(II) ion is distorted octahedral (Fig. 1), with the coordination polyhedron defined by five nitrogen atoms and a sulfur atom: two N,N-chelate dps ligands are cis to each other and a molecule of dps behaves as bidentate through S(3) and N(5). N,S-coordination of dps, or similar ligands, has not been found before. The distortion of the geometry is mainly due to the coordination of the S(3), as testified by the geometrical parameters [N(5)RuS(3) =67.8(2)° and N(2)RuS(3) = 165.8(2)°]. Moreover, the lengths of the RuN(2), RuN(5) and RuN(4) bonds differ significantly [2.061(5) A, , 2.080(5) A, and 2.095(4) A, , respectively], whereas those of the RuN(1) and RuN(3) bonds [2.074(5) A, and 2.082(5) A, , respectively] are quite similar (Table 2). On comparing the RuN bond lengths of 1 [mean value 2.078(5) A, ] with those of Ru(dps)2Cl2 [mean 2.072(3) A, ] [2], [Ru(bipy)3][PF6]2 [2.056(2) A, ] [11] and Ru(bipy)2Cl2 [mean 2.033(2) A, ] [12], we observe that the RuN bond lengths of the dps complexes are

R. Scopelliti et al. / Inorganica Chimica Acta 313 (2001) 43–55

46

larger than those of the bipy complexes. It is likely that these data reflect the reduction in back bonding between the filled dp orbitals of the metal and the delocalised p* orbitals of the polypyridine ligands when dps replaces bipy. In the N,S-coordinated dps ligand the RuS(3) bond distance [2.424(2) A, ] is in the range of values reported for the ruthenium polypyridine derivatives (Cambridge Structural Database) and, for example, compares with that in [Ru(bipy)2(pyt)][ClO4] (pyt =pyridine-2-thiolate) [2.434(3) A, ] [10]. The SC bond distances [S(3)C(25) = 1.777(6) A, , S(3)C(26) = 1.790(7) A, ] are larger than the other four that are present in the same compound and the C(25)N(5)Ru and N(5)C(25)S(3) angles [104.4(4° and 107.9(4)°, respectively] are considerably distorted from the 120° expected for sp2-hybridised atoms. The last data and the above-cited N(5)RuS(3) angle point to the strain of the four-membered ring [RuN(5)C(25)S(3)]. A remarkable feature of this structure is the almost coplanar disposition [dihedral angle 3.3(1)°] of the pyridine plane N(5)C(25)C(24)C(23)C(22)C(21) and the four-membered ring (likely an effect of the steric hindrance that mainly interest this part of the ruthenium cation) and the rotated disposition [113.9(2)°] of the pendant pyridine ring with respect to this pyridine plane.

4. 1H NMR studies The temperature-dependent 1H NMR spectra of the compounds were obtained in (CD3)2CO and CD3CN in the range 180 –350 K. Selected data are listed in Tables Table 2 Selected bond lengths (A, ) and angles (°) in complex 1 RuN(2) RuN(3) RuN(5) RuN(l) RuN(4) RuS(3)

2.061(5) 2.074(5) 2.080(5) 2.082(5) 2.095(5) 2.424(2)

C(5)S(1) S(1)C(6) C(15)S(2) S(2)C(16) C(25)S(3) S(3)C(26)

1.749(6) 1.768(8) 1.743(7) 1.744(7) 1.777(6) 1.790(7)

N(2)RuN(3) N(2)RuN(5) N(3)RuN(5) N(2)RuN(l) N(3)RuN(l) N(5)RuN(l) N(2)RuN(4) N(3)RuN(4) N(5)RuN(4) N(1)RuN(4) N(2)RuS(3) N(3)RuS(3) N(5)RuS(3) N(1)RuS(3) N(4)RuS(3)

91.9(2) 98.8(2) 89.5(2) 89.5(2) 177.8(2) 91.9(2) 86.9(2) 90.1(2) 174.3(2) 88.4(2) 165.8(2) 92.8(1) 67.8(2) 86.1(2) 106.5(2)

N(5)C(25)S(3) C(5)S(1)C(6) C(15)S(2)C(16) C(25)N(5)C(21) C(25)N(5)Ru C(21)N(5)Ru C(25)S(3)C(26) C(25)S(3)Ru C(26)S(3)Ru

107.9(4) 104.3(3) 102.4(3) 116.4(6) 104.4(4) 139.2(5) 98.7(3) 79.7(2) 120.4(3)

3 and 4, respectively. Fig. 2 shows the numbering scheme for proton assignments of the pyridyl rings and, on the righ, for the phenyl ring.

4.1. Solution beha6iour of 1 Owing to the low symmetry of 1, each pyridyl ring is different from the others (the pyridyl rings of 1 are labelled A–F in Fig. 2) and six ABMX systems are expected in the NMR spectra [2–4,13,14] when the dynamic processes are slow on the NMR chemical-shift time scale. In acetone at 200 K, signals due to six rings were detected and assigned using a two-dimensional COSY spectrum, by analogy with the spectra of other dps compounds [2–4] and by comparison with the spectra of the compounds 2–7. The signals (Table 3) at l 9.42 (H6A) and 7.82 (H6B), both assigned to the ortho protons (6-position), were correlated to those at l 7.74 (H5A), 8.04 (H4A) and 7.27 (H3A) and 7.46 (H5B), 7.98 (H4B) and 7.88 (H3B). We assign these signals to the protons of the coordinated and uncoordinated ring, respectively, of the N,S-chelate ligand. Furthermore, the signals at l 9.50 (H6C) and 8.98 (H6D) are assigned to the ortho protons that lie next to the four-membered ring (Fig. 2). The signals of the pyridine ring (F), which is trans to the sulfur atom, are expected to be different from the other resonances, since they experience the trans effect of S. On the basis of the above argument, the signal that appeared at the highest field for the individual H6, H5 and H4 (l 7.59, 7.16 and 7.98, respectively) was assigned to the corresponding F ring. The H3F signal (l 7.95) is deshielded with respect to the H3A signal (l 7.21), which appears at the highest field likely due to the shielding effect of the uncoordinated ring. This result is consistent with the rotated position (113.9°) of the pendant pyridine with respect to the N,S-coordinated ring. The spectra in the range 210 –240 K in (CD3)2CO or CD3CN exhibit a slight broadening in certain of the proton signals. For example, slight broadening is observed in the signal at l 7.82 assigned to the ortho proton (H6B) of the pendant pyridine ring (Fig. 3(a)). Although signal overlap problems in acetone or acetonitrile and the sparing solubility in the other solvents prevent detailed NMR studies in this range of temperatures, we attribute these changes to a slowing down of the rotation of the uncoordinated pyridine ring. Justification of this assumption is borne out by the full interpretation of the low-temperature spectra of complexes 3 and 5 (see infra). Warming the acetone solution of 1 above 240 K caused further extensive changes (Fig. 3(b) –(e)). All spectral lines broaden, eventually vanish and reappear at different positions with the notable exception of the H6A signal of the N,S-coordinated ligand and the H3E signal of the pyridine ring trans to the ring A, which

Table 3 Selected 1H NMR dataa Complex

N,S-ligand signals

Other signals Uncoordinated pyridyl ring

Uncoordinated phenyl ring

H6A

H5A

H4A

H3A

H6B

H5B

H4B

H3B

1b 1c

9.42 9.31

7.74 7.74

8.04 8.03

7.27 7.21

7.82 7.98

7.46 7.41

7.98 7.86

2b 2c

9.40 9.28

7.73 7.70

8.04 8.03

7.31 7.27

3.55d 2.50d

7.53 7.49

7.79 7.71

3b 3c

9.47 9.33

7.82 7.75

8.07 8.05

7.27 8.02

8.01 6.89

7.60 7.23

7.53 7.48

6.91 7.23

4e

7.98

7.67

8.30

8.00

6.94

7.13

7.27

5 5c,g

9.52 9.45

7.87 7.85

8.15 8.15

7.40 7.34

8.00 6.94

7.62 7.30

7.55 7.52

6e

8.67

6.69

7.17

6.35

e

9.09

6.80

8.10

b,f

7

H6%B

H6C

H5C

H6D

H5D

H6E

H5E

H6F

H5F

7.88 7.76

9.50 8.92

7.69 7.39

8.98 8.82

7.51 7.50

7.74 7.59

7.24 7.26

7.59 7.41

7.15 7.16

7.68 7.60

9.46 8.92

7.68 7.37

8.98 8.81

7.53 7.49

7.68 7.52

7.24 7.22

7.54 7.38

7.15 7.12

5.56 6.89

9.52 8.87

7.68 7.37

9.10 8.87

7.61 7.54

7.79 7.58

7.25 7.24

7.59 7.36

7.14 7.12

7.13

6.94

9.77

7.99

8.52

7.54

8.00

7.46

7.98

7.67

7.00 7.30

5.87 6.94

9.89 9.27

7.85 7.53

9.37 9.05

7.67 7.55

8.84 8.66

7.57 7.44

8.74 8.58

7.41 7.30

8.81

7.28

8.60

7.24

7.55

7.17

7.38

7.04

8.76

7.33

8.60

7.25

7.57

7.19

7.42

7.08

Recorded in (CD3)2CO at 300.15 MHz, l (ppm) with respect to internal SiMe4. At 200 K. c At 330 K. d Me signals. e At 296 K. f H4C, H4D, H4E and H4F signals are observed at l 8.95, 8.87, 9.04 and 8.87, respectively. g H4C, H4D, H4E and H4Fsignals are observed at l 8.85, 8.85, 8.95 and 8.85, respectively. a

b

H5%B

H4%B

H3%B

H2%B

R. Scopelliti et al. / Inorganica Chimica Acta 313 (2001) 43–55

Coordinated ring

47

R. Scopelliti et al. / Inorganica Chimica Acta 313 (2001) 43–55

48 Table 4 13 C NMR dataa Complex

Temp. (K)

C5

C4

C3

C2

C6

C5

C4

C3

C2

155.85b

125.50b

138.55b

127.85b

157.05b

150.05c

124.30c

137.95c

127.70c

151.85c

157.70b

127.45b

140.55b

129.95b

159.15b

152.05c

125.90c

139.70c

129.80c

152.80c

160.45 156.65 158.05 156.90 161.70 158.35 159.60 158.30

125.40 125.25 126.15 125.25 126.85 127.10 127.95 127.10

139.15 138.55 138.80 138.55 140.85 140.50 140.40 140.15

129.25 128.35 128.55 128.55 129.75 129.90 130.35 129.30

162.75 157.70 157.75 157.20 163.70 159.75 159.20

220

155.65b

125.35b

138.70b

127.80b

157.10b

123.90c

137.75c

127.05c

150.10c

330

159.15c 22.80d 157.55b

127.25b

140.55b

129.95b

156.80b

159.70c 24.20d

125.45c

139.50c

129.80c

150.50c

160.45 156.65 157.90 156.85 161.70 158.40 159.40 158.10

125.35 125.10 126.05 125.00 126.95 127.05 127.85 126.80

138.70 138.50 138.85 138.20 140.50 140.50 140.35 140.10

128.30 127.80 128.50 127.80 129.80 129.60 130.30 129.30

163.00 157.65 157.70 156.95 161.55 159.60 159.10 159.05

156.40b

125.55b

138.40b

129.65b

157.30b

127.30c

129.65c

129.15c

157.90b

127.30b

140.40b

130.15b

158.80b

129.10c

131.25c

131.15c

160.70 156.95 158.10 156.75 161.55 159.20 158.05 157.90

125.90 125.95 126.30 125.30 126.85 127.45 127.75 126.75

139.90 138.95 138.90 138.80 141.15 140.35 140.20 139.90

128.70 129.70 129.95 128.50 129.60 130.15 130.55 128.85

164.25 157.90 157.90 157.75 164.75 159.50 157.30 157.20

153.55b

129.50b

140.45b

130.55c

129.50c

127.80 128.75 128.95 127.20

139.30 138.80 138.80 138.40

125.10 124.90 124.30 124.15

157.90

127.00c

154.35 153.70 152.90 154.00

155.30b

140.10b

127.75c

126.40b 126.70b 130.15c

157.75b

128.70b

142.32b

130.15c

131.85c

131.65c

167.30f 165.10f 164.55f 164.30f 168.95f 167.10f 166.35f 165.95f

121.95f 121.56f 121.25f 120.85f 123.90f 123.35f 123.05f 122.90f

158.25f 158.00f 157.80f 157.55f 160.40f 160.05f 159.85f 159.85f

158.60b

163.60 157.80 157.90 157.65

124.85 125.05 126.70 125.60

137.70 137.40 137.95 137.85

127.70 128.10 128.40 127.10

163.80 159.80 159.50 158.80

158.55b

163.10 157.75 157.70 157.60

125.15 125.15 126.80 125.80

137.95 137.65 138.20 138.15

128.00 128.30 128.55 127.35

159.45 159.65 158.30

330

2

220

3

330

295

4

210

5

dps

C6 220

1

N,S-coordinated ligand

330

132.30b 130.40c,e 133.05b

129.80c

6

295

154.45b

115.60b

134.55b

7

295

162.45b

113.26b

155.60b

128.15c,e 132.15b 129.20c,e 124.10b

170.83f 169.85f 169.85f 169.75f 172.10f 170.80f 166.80f 165.20f

a

Recorded at 75.56 MHz in (CD3)2CO. Some quaternary carbon signals are not observed. Coordinated ring. c Uncoordinated ring. d Methyl signal. e C1% signal. f Dprs signals. b

remain sharp throughout the entire temperature range. The COSY spectrum at 330 K seems consistent with a species containing two N,N-chelated dps ligands and the N,S-chelated in which a rapid rotation of the pendant

ring and an almost rapid inversion at the sulfur chiral centre occur. In particular, at the highest temperature achievable in acetone, the H6D signal reappears at l 8.82 and that of H6C at l 8.92 with some residual broadening.

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4.2. Solution beha6iour of 3 and 5 The COSY experiment for 3 at 190 K in acetone allowed us to assign the proton signals (Table 3). In particular, the signals at l 5.56 (H2%B) and 8.01 (H6%B) were assigned to the protons of the pendant phenyl ring in ortho position with respect to the sulfur atom. The signal of the para proton was observed at l 7.53 and those of the meta protons at l 6.91 (H3%B) and 7.60 (H5%B) (Fig. 4(a)). These data showed clearly that the N,S-coordination produces a sulfur chiral centre that differentiates the two ortho positions (and the two meta) of the phenyl ring. Thus separate signals are observed when the rotation of the pendant ring and inversion at the chiral sulfur are arrested. The ortho proton H2%B adjacent to the ring C appears at an abnormally low frequency due to the strong shielding effect of this aromatic ring. This implies that the plane of the pendant ring is rotated considerably relative to the plane of the coordinated pyridine ring of phpys, as well as in 1 (Fig. 2). Similar considerations apply to the COSY spectrum (Fig. 5) of [Ru(dprs)2(phpys)][PF6]2 (5) (dprs = dipyrimidin-2-yl sulfide). On warming the acetone solutions of both the complexes the signals of H2%B and H6%B, as well as those of H3%B and H5%B, exhibit gross broadening; this leads to coalescence at approximately 240 K followed by a sharpening to an exchange-averaged signal at approximately 330 K (Fig. 4(b)). The proton signal of the para

49

phenyl proton and the signals of the N,N-chelate ligands are essentially unaffected in the range 180 –240 K, suggesting that the changes are associated with the arresting of the rotation of the phenyl ring. On further elevation of temperature there is a noticeable exchange between the proton signals of the the N,N-chelate ligands, which is in agreement with a more extensive internal rearrangement. In order to follow the process occurring at low temperature, the signals of the protons of the phenyl group for compounds 3 and 5 were monitored carefully. Total band-shape analysis was carried out on the phenyl region of the variable-temperature spectra. The case of 5 is shown in Fig. 6. Not all the experimental and computer-simulated spectra are shown. In the experimental spectra the dprs signals, which have almost identical chemical shifts, indicate that only the phenyl rotation seems affect the spectra in the range 180 – 240 K. Because of the occurrence of a more extensive internal rearrangement at higher temperatures, the calculated activation energies were based on fittings of seven experimental spectra in the temperature range 180 –240 K (where the accuracy was greatest). DH ‡, DS ‡ and DG ‡298 values are 47.39 1.5 kJ mol − 1, − 4.69 2.0 J K − 1 mol − 1 and 48.69 1.0 kJ mol − 1, respectively, for 3, and 47.691.3 kJ mol − 1, −1.99 1.0 J K − 1 mol − 1 and 48.291.0 kJ mol − 1, respectively, for 5. At low temperatures, whereas the slow 180° rotation of the phenyl ring (which is required to exchange the

Fig. 2. Numbering scheme for the proton assignments of the pyridyl rings (on the left), and the phenyl ring (on the right). The rings are labelled A –F.

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7.34) and the phenyl ring [l 6.94 (H2%B and H6%B), 7.30 (H3%B and H5%B) and 7.52 (H4%B)] of the N,S-chelate ligand. The above signals were assigned with the help of COSY experiments. These spectra, as with those of 1 at the same temperature, seem to be consistent with a process involving the rapid rotation of the pendant ring and the almost

Fig. 4. The 1H NMR spectrum of 3 at (a) 190 K, (b) 330 K. The phenyl proton signals are labelled.

Fig. 3. Variable-temperature spectra of 1 in acetone at (a) 215, (b) 260, (c) 275, (d) 298 and (e) 320 K.

ortho and the meta protons) produces equivalent configurations, the slow inversion at the sulfur chiral atom, coordinated to the ruthenium chiral centre, should produce two invertomers. However, the attempts carried out at the lowest temperature achievable in acetone (180 K) failed to find proton signals due to the presence of a minor isomer. Similar results were also obtained in CD3CN at low temperatures, whereas solubility problems prevent detailed NMR studies in other solvents. It is likely that in acetone and acetonitrile at low temperatures a species structurally similar to 1 largely predominates. The 1H NMR spectrum of 3 in acetone at 330 K consists of five ABMX systems and three phenyl signals at l 6.89, 7.23 and 7.48, relatively intensities 2, 2, and 1. The H6D and H6C signals are overlapped at l 8.87 with residual exchange broadening (Table 3 and Fig. 4(b)). The spectrum of the complex [Ru(dprs)2(phpys)][PF6]2 (5) (dprs = dipyrimidin-2-yl sulfide) at 330 K in acetone shows the signals of the four pyrimidine rings (Table 3), the pyridyl (l 9.45, 7.85, 8.15 and

Fig. 5. The 1H – 1H COSY spectrum of 5 in acetone at 190 K.

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51

Fig. 6. Selected variable-temperature 1H NMR spectra of 5 in acetone. Computer-synthesised spectra of the last protons are shown on the left.

rapid inversion at the sulfur chiral centre. On cooling, the spectra show extensive and complex changes. These may be interpreted as being due to the slowing down of both the sulfur inversion and the rotation of the pendant ring, such that at 240 K the signals may be attributed to a species similar to 1 in which only the rotation of the pendant ring is operative. According to this suggestion, we can speculate that the combination of the pyramidal inversion and rotation process precludes an estimation of the pyramidal inversion barrier. It is worth noting the following. (1) The spectra of 1, 3 and 5 in acetone were found to be perfectly temperature reversible and concentration independent, in keeping with an intramolecular change. Furthermore, when free ligand was added separate signals were observed, even at the highest temperatures achievable in acetone. (2) The similar behaviour of 1, 3 and 5 at various temperatures indicates that the presence of an uncoordinated N atom does not affect the dynamic behaviour of the complexes. This last result rules out a metallotropic shift in which the sulfur and the two nitrogen atoms of dps are involved [15]. (3) The H6A and the H3E signals of the pyridyl rings trans to each other in 1 and 3 remain sharp throughout the entire temperature range. A similarl behaviour also occurs for the H6A proton signal of the only pyridyl ring present in 5. Moreover, at higher temperatures the H6D and H6C proton signals of 3 are overlapped at l 8.87. All these results seem to be consistent with a process involving

the rotation of the pendant ring, and above 240 K the inversion at the sulfur chiral centre.

4.3. Effects of the temperature in CD3CN and in better-coordinating sol6ents At low temperatures in CD3CN the dynamic behaviour of the above complexes parallels that observed in acetone. However, above 310 K, free ligand (dps, mdps, phpys) and the known [Ru(dps)2(CD3CN)2]+ species [2] are present, in agreement with the dissociation of the N,S-coordinated ligand in coordinating solvents. In pyridine, this last dissociation occurs slowly at room temperature.

5.

13

C NMR studies

The 13C NMR spectra, with the help of CH correlate experiments, allow us to assign the 13C signals at low temperatures (Table 4). Although significant changes occurred when the temperature was increased, the spectra are consistent with the N,S-coordination at all the temperatures. Moreover, the 13C NMR studies in acetone (or in CD3CN at low temperatures) and the 1H NMR studies indicate the occurrence of the intramolecular processes. Fig. 7 shows the 13C NMR spectra (range l 165 –150) of 1 in (CD3)2CO in the range 240 –320 K. Although the simultaneous slow rotation

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of the pendant ring and inversion at the sulfur chiral centre bring about complex changes, it is worth nothing that, (in the range 250 – 265 K, the broad signals of the C6B and C2B carbon atoms of the uncoordinated ring and the C6C and C2C carbon atoms of the ring next to the sulfur atom are likely due to the combination of the rotation and inversion processes, whereas in the range 270 – 290 K the inversion process seems to affect only the signals of C6C, C2C and C2B.

6. NMR data of [Ru(bipy)2(N,S-phpys)][PF6]2 and the complexes containing thiolate ligands In order to obtain more information on the NS coordination we synthesised the complex [Ru(bipy)2(phpys)][PF6]2 (4) and other complexes containing the Ru(dps)2 moiety and the N,S-coordinated pyridine-2thiolate (pyt) (6) and pyrimidine-2-thiolate (prt) (7). The NMR spectra of these compounds are temperature independent. For complex 4 this result is likely due to the presence on the Ru(bipy)2 core of two planar bipy ligands, which reduces the steric hindrance at the ruthenium centre (in agreement with this suggestion we prepared [2] [Ru(bipy)2(dps)][PF6]2 complex containing the N,N-chelate dps ligand) and favours a rapid rotation of the phenyl ring as well as a rapid inversion at the sulfur chiral centre. The assignment of 1H NMR signals (Table 3) was made with the help of COSY experiments and those of 13C NMR signals (Table 4) with the help of CH correlate experiments. On comparing the 1H and 13C NMR spectra of 6 and 1 we observe that almost all the proton and carbon signals of the complex containing the thiolate ligand are shielded with respect to those of 1 due to the charge of the compounds. However, the H6B and C6B signals of the uncoordinated ring of 1 (l 7.82 and 150.05, respectively at 220 K) are shielded with respect to the H6 and C6 signals of 6, in agreement with the downfield shift of the C6 and H6 resonances due to the transfer of electron density from the ligand to the metal. All other data are in acceptable agreement with those reported in the literature [2,3,8 –10].

7. Conclusion

Fig. 7. 13C NMR spectra in the range l 150–165 of 1 in (CD3)2CO at (a) 240, (b) 255, (c) 265, (d) 285 and (e) 320 K showing the broadening of the C6 and C2 carbon atoms due to the rotation and inversion processes.

These studies have extended the chemistry of ruthenium polypyridine compounds containing N,S-chelate ligands. The treatment of Ru(dps)2Cl2 with an excess of dps provides a convenient route to [Ru(dps)2(N,Sdps)][PF6]2 (1). The same procedure was successful for the compounds [Ru(dps)2(N,S-ligand)][PF6]n (n=1 and 2). The single-crystal X-ray diffraction study of 1 has provided conclusive evidence of the first N,S-coordination of a dps ligand, and a dynamic behaviour in solution was inferred by the 1H and 13C NMR studies. The process at low temperatures is clearly due to the rotation of the uncoordinated ligand; a more extensive rearrangement occurs at higher temperatures, which may involve the inversion at the sulfur chiral centre. On the other hand, the metallotropic shift [15] involving the S and the two N atoms can be excluded by comparison of the dynamic behaviour of complexes containing N,S-chelate dps (or mdps) and complexes containing N,S-chelate phpys. It is consistent with the

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congestion of the transition state of the metallotropic shift, which should produce a quasi-seven pentagonal bipyramid [16] containing the N,S,N-coordinated ligand. On the contrary, the crystal structure of 1 indicates that the N,S-coordination, the almost coplanar disposition of the N,S-chelate ring and the four-membered ring and the rotated disposition of the uncoordinated ring are due to the steric hindrance of the Ru(dps)2 core and the steric demand of dps. Moreover, the N,S-coordination is in agreement with the thioether nature of the dps ligand. The Ru(bipy)2 core favours the N,N-coordination of dps [2], and when the N,S-coordinating phpys ligand is used no dynamic process is observed. The different chemistry of dps and phpys with regard to the Ru(bipy)2 and the Ru(dps)2 substrates is consistent with the planar disposition of the bipy ligands which reduces the steric hindrance of the Ru(N,N-chelate diimmine)2 core. In accordance with the suggestion that the sulfur inversion plays a role for the fluxion at the higher temperatures we not observe any dynamic process also when the N,S-thiolate ligands are coordinated to the Ru(dps)2 core. Thus, a probable conclusion is that a delicate balance of the steric hindrance of the ruthenium substrates and the steric demand of the ligand associated with the ligating properties and the conformational flexibility of the non-planar ligands can produce unusual coordinating properties and dynamic processes. Several attempts are under way to produce and study the solution behaviour of mono- and bi-nuclear compounds containing other N,S-chelate diimmines.

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(15 g, 0.1 mol) were stirred vigorously in DMF (40 cm3) under N2 and refluxed for 5 h. The solvent was then distilled under reduced pressure (100 mmHg) and the residue distilled at 7 mmHg (b.p.120°C). The yellow oil obtained was kept at − 15°C to give a solid. Yield 8.90 g (44%). Anal. Found: C, 65.20; H, 5.00; N, 13.80; S, 16.00. Calc. for C11H10N2S: C, 65.30; H, 5.00; N, 13.85; S, 15.85%. Selected IR data (cm − 1): 1667vs, 1576vs, 1559vs, 1440vs, 1418vs, 1281s, 1251s, 1237s, 1168vs, 1148vs, 1121vs, 1097vs, 1046vs, 987vs, 864vs, 842ms, 763vs, 739 s, 723vs, 678s, 619s, 548s.

8.1.2. Phenyl 2 -pyridyl sulfide (phpys) This pale yellow oil was prepared in the same way (Section 8.1.1) starting from thiophenol (11.0 g, 0.1 mol) and 2-bromopyridine 15.70 g, 0.1 mol. Yield 11.98 g (64%). Anal. Found: C, 70.40; H, 5.00; N, 7.40; S, 17.00. Calc. for C11H9NS: C, 70.55; H, 4.85; N, 7.50; S, 17.10%. Selected IR data (cm − 1): 1677s, 1575vs, 1561vs, 1475 vs, 1451vs, 1418vs, 1280vs, 1143vs, 1122vs, 1085vs, 1068vs, 1045vs, 1024vs, 986vs, 842s, 758vs, 723vs, 704vs, 692vs, 618s, 516vs. 8.1.3. Di-pyrimidin-2 -yl sulfide (dprs) This pale yellow solid was prepared in the same way (Section 8.1.1) starting from 2-bromopyrimidine (15.9 g, 0.1 mol) and 2-sulfanylpyrimidine 11.20 g, 0.1 mol. After the removal of DMF the pure compound was obtained by recrystallisation from CH2Cl2 – heptane. Yield 7.04 g (37%). Anal. Found: C, 50.40; H, 3.30; N, 29.40; S, 16.80. Calc. for C8H6N4S: C, 50.50; H, 3.20; N, 29.45; S, 16.85%. Selected IR data (cm − 1): 1615ms, 1563br, 1554br, 1263s, 1155vs, 987ms, 824vs, 806vs, 784s, 770vs, 746vs, 630vs, 521s.

8. Experimental Di-2-pyridyl sulfide [13] and [Ru(dps)2Cl2] [2], were prepared by published methods. Other reagents and solvents were used as received. Elemental analyses were carried by Redox Microanalytical Laboratory of Cologno Monzese (Milano). Conductivity measurements were done on a Radiometer CDM 3 conductivity meter. Infrared spectra were recorded on an FT-IR 1720X spectrophotometer with samples as Nujol mulls placed between CsI plates, electronic absorption spectra on a Perkin –Elmer Lambda 5 spectrophotometer and the 1H and 13C NMR spectra on a Bruker AMX 300 spectrometer. The following Bruker programs are used: zg, homodecnew, cosy, zgpg, jmod, hxco, invb.

8.1. Preparations 8.1.1. 2 -(6 -Methyl)pyridyl 2 -pyridyl sulfide (mdps) 2-Bromo,6-methylpyridine (17.2 g, 0.1 mol), 2-sulfanylpyridine (11.3 g, 0.1 mol) and potassium carbonate

8.1.4. [Ru(dprs)2Cl2] ·2H2O RuCl3·3H2O (1 g, 3,8 mmol), LiCl (1 g, 23,6 mmol) and dprs (1.53 g, 8 mmol) were refluxed in DMF (25 cm3) under N2 for 4 h. After cooling at room temperature and addition of acetone (50 cm3) the mixture was allowed to stand at −15°C overnight, giving a red solid which was filtered off, washed with acetone and water, then dried and washed again with acetone and diethyl ether. The compound was dried over P4O10 in vacuo. Yield 0.89 g (40%). Anal. Found: C, 32.60; H, 2.80; N, 19.10; S, 10.80. Calc. for C16H16Cl2N8O2RuS2: C, 32.65; H, 2.75; N, 19.05; S, 10.90%. Selected IR data (cm − 1): 1565vs, 1539vs, 1159vs, 1094s, 1074s, 1006vs, 770vs, 763s, 744vs, 724vs, 653s, 518s. 8.1.5. [Ru(dps)2(N,S-dps)][PF6]2 ·H2O (1) [Ru(dps)2Cl2]·2H2O (0.585 g, 1 mmol) and dps (0.565 g, 3.0 mmol) were refluxed in 60 cm3 of ethanol/ water (1:1). After 1 h the red complex was dissolved and the yellow solution was filtered hot. By addition of

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30 cm3 of water containing 1.304 g (8 mmol) of NH4PF6 a yellow precipitate was obtained. It was filtered, washed with 50 cm3 of cold water and dried overnight. The solid was washed copiously with diethyl ether and dried again; then it was dissolved in acetone (20 cm3) and diethyl ether (approximately 40 cm3) was added slowly until a yellow solid was obtained. The compound was washed with diethyl ether and dried over P4O10 in vacuo. Yield 0.68 g (70%). Anal. Found: C, 36.90; H, 2.70; N, 8.55; S, 9.95. Calc. for C30H26F12N6OP2RuS3: C, 37.00; H, 2.70; N, 8.65; S, 9.90%. Selected IR data (cm − 1): 1624w, 1590s, 1573s, 1561s, 1281s, 1135s, 1116s, 886s, 841br, 773vs, 763vs, 740ms, 725s, 646ms, 616m, 558vs, 292ms. \M(MeCN, 2× 10 − 4 mol dm − 3, 20°C) = 280 V − 1 cm2 mol − 1.

8.1.6. [Ru(dps)2(N,S-mdps)][PF6]2 ·H2O (2) This yellow compound was prepared in similar fashion to that for 1 (Section 8.1.5) by using mdps (0.607 g, 3.0 mmol) in place of dps. Yield 0.49 g (50%). Anal. Found: C, 37.60; H, 2.90; N, 8.55; S, 9.75. Calc. for C31H28F12N6OP2RuS3: C, 37.70; H, 2.85; N, 8.50; S, 9.75%. Selected IR data (cm − 1): 1640br, 1589vs, 1556s, 1164s, 776vs, 761vs, 741ms, 725s, 559vs. \M(MeCN, 2× 10 − 4 mol dm − 3, 20°C) = 287 V − 1 cm2 mol − 1. 8.1.7. [Ru(dps)2(N,S-phpys)][PF6]2 ·H2O (3) This yellow compound was prepared in similar fashion to that for 1 (Section 8.1.5) by using phpys (0.652 g, 3.0 mmol) in place of dps. Yield 0.58 g (60%). Anal. Found: C, 38.20; H, 2.90; N, 7.15; S, 9.90. Calc. for C31H27F12N5OP2RuS3: C, 38.30; H, 2.80; N, 7.20; S, 9.90%. Selected IR data (cm − 1): 1625br, 1589s, 1556s, 1286s, 1164s, 844br, 769vs, 742s, 727ms, 559vs. \M(MeCN, 2 × 10−4 mol dm − 3, 20°C) = 285 V − 1 cm2 mol − 1. 8.1.8. [Ru(bipy)2(N,S-phpys)][PF6]2 ·H2O (4) [Ru(bipy)2Cl2]·2H2O (0.520 g, 1 mmol) and phpys (0.652 g, 3.0 mmol) were refluxed in 60 cm3 of ethanol/ water (1:1). After 1 h the red complex was dissolved and the yellow solution was filtered hot. By addition of 30 cm3 of water containing 1.304 g (8 mmol) of NH4PF6 an orange precipitate was obtained. It was filtered, washed with 50 cm3 of cold water and dried overnight. The solid was dissolved in acetone (15 cm3) and added to the top of a chromatography column (diameter 2 cm) packed with aluminium oxide (80 g; Aldrich, neutral, STD grade, 150 mesh) deactivated with water (3 g). Elution with acetone/toluene (3:2) gave an orange band, which was collected. The solvent was removed in vacuo and the remaining residue was dissolved in acetone (10 cm3) and treated with diethyl ether (90 cm3). The orange solid obtained was washed copiously with diethyl ether and dried over P4O10 in vacuo. Yield 0.45 g (50%). Anal. Found: C, 40.90; H,

2.95; N, 7.65; S, 3.55. Calc. for C31H27F12N5OP2RuS: C, 41.00; H, 3.00; N, 7.70; S, 3.55%. Selected IR data (cm − 1): 1606w, 1581s, 1562ms, 1244s, 1163s, 884s, 764vs, 742ms, 731s, 690ms, 559vs. \M(MeCN, 2 × 10 − 4 mol dm − 3, 20°C)=280 V − 1 cm2 mol − 1.

8.1.9. [Ru(dprs)2(N,S-phpys)][PF6]2 ·H2O (5) This yellow –orange compound was prepared as described for 4 (Section 8.1.8) starting from [Ru(dprs)2Cl2]·2H2O (0.588 g, 1 mmol) and phpys (0.652 g, 3.0 mmol). Yield 0.39 g (40%). Anal. Found: C, 33.10; H, 2.40; N, 12.80; S, 9.90. Calc. for C27H23F12N9OP2RuS3: C, 33.20; H, 2.35; N, 12.90; S, 9.85%. Selected IR data (cm − 1): 1634br, 1577vs, 1550vs, 1168vs, 1086s, 845br, 769s, 754vs, 741s, 723s, 690, 651ms, 559vs, 518ms. \M(MeCN, 2 × 10−4 mol dm − 3, 20°C)=280 V − 1 cm2 mol − 1. 8.1.10. [Ru(dps)2(pyt)][PF6] ·H2O (6) This yellow –orange compound was prepared as described for 1 (Section 8.1.5) by using pyridine-2-thiol (0.278 g, 2.5 mmol) in place of dps. Yield  80%. Anal. Found: C, 40.10; H, 2.90; N, 9.30; S, 12.80. Calc. for C25H22F6N5OPRuS3: C, 40.00; H, 2.95; N, 9.35; S, 12.80%. Selected IR data (cm − 1): 1580vs, 1550s, 1278s, 1087s, 877s, 843br, 766vs, 725s, 644ms, 558vs. \M(MeCN, 2x10 − 4 mol dm − 3, 20°C)=140 V − 1 cm2 mol − 1. 8.1.11. [Ru(dps)2(prt)][PF6] ·H2O (7) This yellow compound was obtained in the same way (Section 8.1.10) starting from [Ru(dps)2Cl2]·2H2O (0.585 g, 1 mmol) and pyrimidine-2-thiol (0.280 g, 2.5 mmol). Yield 90%. Anal. Found: C, 38.40; H, 2.75; N, 11.15; S, 12.80. Calc. for C24H21F6N6OPRuS3: C, 38.35; H, 2.80; N, 11.20; S, 12.80%. Selected IR data (cm − 1): 1585ms, 1560s, 1540s, 1280s, 1163s, 1087ms, 1006ms, 844br, 762vs, 725s, 559vs. \M(MeCN, 2 × 10 − 4 mol dm − 3, 20°C)=135 V − 1 cm2 mol − 1. 8.2. Crystal structure determination of [Ru(dps)2(N,S-dps)][PF6]2 ·H2O (1) Suitable crystals of 1 were obtained by diffusion of diethyl ether vapour into an acetone solution of the compound. Single-crystal X-ray diffraction measurements were performed at room temperature on a Siemens R3m/v automatic four-circle diffractometer using graphite-monochromatised Mo Ka radiation. Crystal data: [Ru(dps)3][PF6]2·H2O, monoclinic, space group P21/c, a=20.848(3), b= 11.060(2), c= 17.452(3) A, , i= 97.46(1)°, U= 3990(1) A, 3, Z=4, Dc= 1.621 Mg m − 3, crystal dimensions 0.46×0.16× 0.12 mm3, R= 0.050 for 3235 observed reflections with I] 2s(I). Lattice parameters were obtained from leastsquares refinement of the setting angles of 30 reflections

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within 1552q 5 28° range. No crystal deterioration was evidenced by the measurement of three standard reflections, monitored every 197 measurements. The intensities of the 7883 reflections collected were evaluated by a learnt-profile-fitting procedure [17] among 2q shells and then corrected for Lorentz-polarisation and absorption (semi-empirical method by azimuthal scan data: min. and max. transmission factors were 0.719 and 1.000) effects. No account was taken for extinction effects. All calculations were performed using the SHELXTL 5.05 system (Siemens Analytical X-Ray Instruments Inc., Madison, WI, 1996). The structure was solved by standard methods and subsequently completed by a combination of least-squares technique and Fourier syntheses. All non-hydrogen atoms were refined anisotropically, except the two co-crystallised water oxygen atoms. Whereas the final difference Fourier maps showed several hydrogen positions, the H atoms were placed in calculated positions (the idealised geometry depending on the parent atom type) and included in the refinement (except the water hydrogen atoms) among the ‘riding model’ method with a unique common fixed thermal isotropic displacement parameter (Uiso = 0.070 A, 2). One PF6− anion appeared to be affected by rotational disorder and it was split into two orientations. The refinement was carried out by the full-matrix least-squares technique, minimising the function Sw(F o2 − F c2)2 by using all the 7092 independent reflections. In the last difference Fourier map the minimum and maximum density residuals were −0.44 e− A, − 3 and 0.79 e− A, − 3, respectively. Neutralatom scattering factors and anomalous dispersion corrections are those included in the program [18].

9. Supplementary material Final atomic coordinates, thermal parameters, bond lengths and angles have been deposited at the Cambridge Crystallographic Data Centre under the depository number CCDC 139635. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: + 44-1223-336033; e-mail: [email protected]. ac.uk or www: http://www.ccdc.cam.ac.uk).

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Acknowledgements This work was supported by the Consiglio Nazionale delle ricerche (CNR) and Ministero dell’Universita` e della Ricerca Scientifica e Tecnologica (MURST) of Italy.

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