Synthesis, structure and redox properties of some thiosemicarbazone
complexes of rhodium
Swati Dutta,aFalguni Basuli,aShie-Ming Peng,bGene-Hsiang Leeband Samaresh Bhattacharya*a
a
Department of Chemistry, Inorganic Chemistry Section, Jadavpur University, Kolkata 700032, India. E-mail: [email protected]
b
Department of Chemistry, National Taiwan University, Taipei, Taiwan, ROC
Received (in Montpellier, France) 31st May 2002, Accepted 19th July 2002 First published as an Advance Article on the web 25th September 2002
Reaction of salicylaldehyde thiosemicarbazone (H2L 1
), 2-hydroxyacetophenone thiosemicarbazone (H2L 2
) and 2-hydroxynaphthaldehyde thiosemicarbazone (H2L3) (general abbreviation H2L, where H2stands for the two dissociable protons, one phenolic proton and one hydrazinic proton) with [Rh(PPh3)3Cl] afforded a family of rhodium(III) complexes of the type [Rh(PPh3)2(L)Cl]. The crystal structure of [Rh(PPh3)2(L2)Cl] has been determined by X-ray diffraction. The thiosemicarbazone ligands are coordinated, via dissociation of the two protons, as dianionic tridentate O,N,S-donor ligands forming one six-membered and one five-membered chelate rings. The complexes are diamagnetic (low-spin d6, S¼ 0) and their1
H NMR spectra are in excellent agreement with their compositions. All three [Rh(PPh3)2(L)Cl] complexes display intense absorptions in the visible and ultraviolet regions. They also show strong emission in the visible region at ambient temperature. Cyclic voltammetry on all the complexes shows two irreversible oxidations, the first one is observed within 0.77 to 0.85 V vs. SCE and the second one within 1.13 to 1.23 V vs. SCE, and one irreversible reduction within1.05 to1.14 V vs. SCE.
There has been considerable interest in the chemistry of transition metal complexes of thiosemicarbazone ligands, primarily because of their bioinorganic relevance.1This class of complexes is of particular importance because of the potentially beneficial biological (viz. antibacterial, antimalar-ial, antiviral and antitumor) activities of these compounds.2 Thiosemicarbazones usually bind to a metal ion as bidentate N,S-donor ligands via dissociation of the hydrazinic proton, forming five-membered chelate rings (1).3 When a third donor site (D) is incorporated into the ligands, linked to the carbonylic carbon via one or two intervening atoms, normally D,N,S-tricoordination (2) takes place.4 Examples are also known where such ligands, in addition to displaying D,N,S-tricoordination, bridge a second metal ion through the sulfur.5 However, we have observed that in its reaction with [M(PPh3)3X2] (M¼ Ru, Os; X ¼ Cl, Br) salicylalde-hyde thiosemicarbazone, in spite of having the phenolic oxy-gen as a potential third donor site, coordinates as a bidentate N,S-donor forming a rather unusual four-mem-bered chelate ring (3).6 Some other thiosemicarbazone ligands are also known to display a similar coordination mode.7 Though formation of such a chelate ring (3) by sal-icylaldehyde thiosemicarbazone, leaving some potential donor sites unused, has been successfully utilized in the con-struction of polynuclear complexes,8 this unusual coordina-tion mode has encouraged us to search for suitable synthetic conditions so that the expected normal O,N,S-tri-coordination (4) from the same salicylaldehyde thiosemicar-bazone ligand may take place.
In the present work, which has originated from our interest in the different coordination modes of the thiosemicarbazone ligands in general,3–9 and to induce coordination mode 4 in particular, we have chosen the thiosemicarbazones of salicyl-aldehyde, 2-hydroxyacetophenone and 2-hydroxynaphth-aldehyde as the ligands and rhodium as the metal. The thiosemicarbazone ligands are abbreviated in general as H2L, where H2stands for the two dissociable protons, the phenolic proton and the hydrazinic proton. Individual ligand abbrevia-tions are shown in 5. It may be mentioned here that chemistry of the thiosemicarbazone complexes of rhodium appears to remain unexplored. As the rhodium starting material, we have chosen Wilkinson’s catalyst, viz. [Rh(PPh3)3Cl], because it is known to undergo dissociation in solution, producing free PPh3 and a formally tricoordinated Rh(PPh3)2Cl species,
10
which has been observed by us to serve as an useful synthon for the preparation of interesting complexes,11 furthermore, this tricoordinated species appears suitable for the desired O,N,S-tricoordination of the thiosemicarbazone ligands. This strategy has indeed worked nicely, affording a group of rho-dium complexes of type [Rh(PPh3)2(L)Cl] containing the thio-semicarbazone ligands coordinated in the tridentate fashion (4). The chemistry of these complexes is reported in this paper with special reference to synthesis, structure and electrochemi-cal properties.
Experimental
Materials and physical measurements
Rhodium trichloride was obtained from Arora Matthey, Kolkata, India and triphenylphosphine was purchased from Loba Chemie, Mumbai, India. [Rh(PPh3)3Cl] was synthesized following a reported procedure.12 The thiosemicarbazone ligands were prepared by condensing the respective aldehyde or ketone with thiosemicarbazide. Purification of dichloro-methane and preparation of tetrabutylammonium perchlorate (TBAP) for electrochemical work were performed as before.13 Microanalyses (C,H,N) were performed using a Heraeus Carlo Erba 1108 elemental analyzer. IR spectra were obtained on a Shimadzu FTIR-8300 spectrometer with samples pre-pared as KBr pellets. Electronic spectra were recorded on a JASCO V-570 spectrophotometer. Emission spectra were recorded on a Spex Fluorolog spectrometer. Magnetic suscept-ibilities were measured using a PAR 155 vibrating sample mag-netometer fitted with a Walker Scientific L75FBAL magnet. 1
H NMR spectra were recorded in CDCl3 solution with a Brucker drx500 NMR spectrometer using TMS as the internal standard. Electrochemical measurements were done in 1 : 9 dichloromethane–acetonitrile solution (0.1 M TBAP), using a CH Instruments model 600A electrochemical analyzer. The addition of 10% dichloromethane was necessary to dissolve the complexes while the acetonitrile was necessary for the detection of the rhodium(III)–rhodium(II) reductive response.
A platinum disc working electrode, a platinum wire auxiliary electrode and an aqueous saturated calomel reference electrode (SCE) were used in a three-electrode configuration. Electroche-mical measurements were made under a dinitrogen atmo-sphere. All electrochemical data were collected at 298 K and are uncorrected for junction potentials.
Synthetic procedures
[Rh(PPh3)2(L1)Cl]. H2L1(21 mg, 0.11 mmol) was dissolved in benzene and to it were added triethylamine (22 mg, 0.22 mmol) and [Rh(PPh3)3Cl] (100 mg, 0.11 mmol). The mix-ture was then heated at reflux under a dinitrogen atmosphere for 12 h to afford an orange solution. Evaporation of this solu-tion gave an orangish-yellow solid, which was subjected to purification by thin layer chromatography on a silica plate. With benzene–acetonitrile (3 : 1) as the eluant, an orange band separated, which was extracted with acetonitrile. Upon evaporation of the acetonitrile extract [Rh(PPh3)2(L
1 )Cl] was
obtained as a crystalline orange solid. Yield: 75%. Calcd: C, 61.72; H, 4.33; N, 4.91. Found: C, 61.05; H, 4.37; N, 4.97%.
[Rh(PPh3)2(L2)Cl]. This complex was prepared by following the same procedure as above, using H2L2 instead of H2L1. Yield: 70%. Calcd: C, 62.11; H, 4.49; N, 4.83. Found: C, 61.65; H 4.42; N, 4.88%.
[Rh(PPh3)2(L3)Cl]. This complex was prepared by following the same procedure as for [Rh(PPh3)2(L1)Cl], using H2L3 instead of H2L1. Yield: 72%. Calcd: C, 63.62; H, 4.31; N, 4.64. Found: C, 63.27; H, 4.52; N, 4.70%.
X-Ray crystallography Single crystals of [Rh(PPh3)2(L
2
)Cl] were grown by slow diffu-sion of hexane into a dichloromethane solution of the complex. Selected crystal data and data collection parameters are given in Table 1. Data were collected on an Enraf–Nonius CAD4 diffractometer using graphite monochromated MoKa radia-tion (l¼ 0.71073 A˚ ) by o 2y scans. The data were corrected for empirical absorption on the basis of psi scans. X-Ray struc-ture solution and refinement were done using the SHELXS-97 and SHELXL-97 programs.14Hydrogen atoms were fixed at calculated positions and were refined using a riding mode. The structure was solved by direct methods.
CCDC reference number 192601. See http://www.rsc.org/ suppdata/nj/b2/b205338c/ for crystallographic files in CIF or other electronic format.
Results and discussion
Reaction of the thiosemicarbazone ligands H2L with [Rh(PPh3)3Cl] proceeds smoothly in refluxing benzene in the presence of triethylamine to afford the [Rh(PPh3)2(L)Cl] com-plexes in decent yields. Elemental (C, H, N) analytical data of the complexes are consistent with their compositions. It is interesting to note that rhodium has undergone a two-electron oxidation during the course of the synthetic reaction and the trace of oxygen, present in the reaction vessel, might have served as the oxidizing agent. It appears from the formulation of these complexes that the thiosemicarbazone ligands are ser-ving as tridentate ligands. To find out the coordination mode of the thiosemicarbazone ligands and the stereochemistry of the complexes, the structure of one member of this family, viz. [Rh(PPh3)2(L
2
)Cl], has been determined by X-ray crystal-lography. A view of the complex molecule is shown in Fig. 1 and selected bond parameters are listed in Table 2. The thio-semicarbazone ligand (L2) is coordinated to rhodium in the
Table 1 Crystallographic data of [Rh(PPh3)2(L2)Cl]
Formula C45H39ClN3OP2SRh
Formula weight 870.15 Crystal system Monoclinic
Space group P21/c a/A˚ 23.236(3) b/A˚ 17.497(4) c/A˚ 19.446(3) b/deg 90.055(13) U/A˚3 7906(3) Z 8 T/K 295 m/mm1 0.763 Reflections collected 13917 Independent reflections 13917 Rint 0.00 R1 0.0429 wR2 0.0902
tridentate fashion (4), forming five- and six-membered chelate rings with bite angles of85(N–Rh–S) and93(O–Rh–N),
respectively. The thiosemicarbazone ligand, the coordinated chloride ion and rhodium constitute the pseudo-equatorial plane and the two triphenylphosphine ligands are mutually trans. The ONSP2ClRh core is a distorted octahedron, as reflected in all the bond parameters around rhodium. The Rh–Cl and Rh–P lengths are quite normal and so are the Rh–N, Rh–O and Rh–S distances.11,15 Comparison of the bond lengths in the coordinated thiosemicarbazone (L2) ligand with those in the free thiosemicarbazone (H2L2) ligand16 shows that, upon coordination, the C–S bond has elongated while the adjacent C–N bond has contracted. These changes in bond lengths are attributable to stabilization of the
iminothiolate form of the thiosemicarbazone ligand upon com-plexation via loss of the hydrazinic proton. The phenolic C–O length has also decreased upon coordination. Similar struc-tural features are known for other metal complexes of such ligands that have O,N,S coordination.4d–g,17As all three com-plexes display similar spectral and electrochemical properties (vide infra), the other two complexes are assumed to have the same structure as [Rh(PPh3)2(L2)Cl].
The difference in coordination mode displayed by the salicyl-aldehyde thiosemicarbazone ligand (and similar ligands) in their reaction with [Ru(PPh3)3Cl2] (mode 3) and [Rh(PPh3)3Cl] (mode 4) is really interesting and hence deserves careful scru-tiny. The reason is probably kinetic in nature, which has been illustrated in Scheme 1. [Ru(PPh3)3Cl2] is known to undergo dissociation upon dissolution, affording free PPh3and a for-mally tetracoordinated [Ru(PPh3)2Cl2] species.18 Formation of the bis thiosemicarbazone complex (6) from this reactive [Ru(PPh3)2Cl2] species therefore involves chelation of the two thiosemicarbazone ligands via breaking of two Ru–Cl bonds (reaction 1). [Rh(PPh3)3Cl] also dissociates in solution into PPh3 and a formally tricoordinated [Rh(PPh3)2Cl] spe-cies.10However, formation of the [Rh(PPh3)2(L1)Cl] complex (7) from the tricoordinated [Rh(PPh3)2Cl] species involves only chelation by the thiosemicarbazone ligand without breaking any pre-existing Rh–ligand bond (reaction 2). Hence coordina-tion of salicyladehyde thiosemicarbazone in the tridentate fashion appears to have taken place without any difficulty in the case of rhodium (reaction 2). Formation of such an O,N,S-chelate (as in 7) has not been possible in the ruthenium case (reaction 1) probably because three coordination posi-tions were not available on ruthenium in the reactive [Ru(PPh3)2Cl2] intermediate. In reaction 1, formation of four-membered chelate rings and cleavage of Ru–Cl bonds probably take place synergistically.
Magnetic susceptibility measurements show that the [Rh(PPh3)2(L)Cl] complexes are diamagnetic, which is in accordance with the trivalent state of rhodium (low-spin d6,
Fig. 1 View of the [Rh(PPh3)2(L 2
)Cl] molecule.
Table 2 Selected bond parameters (distances in A˚, angles in) for
[Rh(PPh3)2(L2)Cl] Molecule 1 Molecule 2 Rh(1)–N(1) 2.012(3) Rh(2)–N(4) 2.013(3) Rh(1)–O(1) 2.035(3) Rh(2)–O(2) 2.026(3) Rh(1)–P(1) 2.3920(12) Rh(2)–P(3) 2.3889(12) Rh(1)–P(2) 2.3929(12) Rh(2)–P(4) 2.4003(12) Rh(1)–S(1) 2.2935(12) Rh(2)–S(2) 2.3030(13) Rh(1)–Cl(1) 2.3634(10) Rh(2)–Cl(2) 2.3561(11) C(9)–O(1) 1.312(4) C(54)–O(2) 1.313(5) C(2)–N(1) 1.299(4) C(47)– N(4) 1.307(5) N(1)–N(2) 1.415(4) N(4)–N(5) 1.402(5) N(2)–C(1) 1.298(5) N(5)–C(46) 1.294(5) C(1)–S(1) 1.724(4) C(46)–S(2) 1.710(5) C(1)–N(3) 1.369(5) C(46)–N(6) 1.381(6) O(1)–Rh(1)–S(1) 176.00(8) O(2)–Rh(2)–S(2) 177.15(8) P(1)–Rh(1)–P(2) 174.83(4) P(3)–Rh(2)–P(4) 172.56(4) N(1)–Rh(1)–Cl(1) 177.27(9) N(4)–Rh(2)–Cl(2) 178.27(10) N(1)–Rh(1)–O(1) 92.63(11) N(4)–Rh(2)–O(2) 92.34(12) S(1)–Rh(1)–P(1) 92.99(4) S(2)–Rh(2)–P(3) 92.87(4) S(1)–Rh(1)–P(2) 90.35(4) S(2)–Rh(2)–P(4) 90.78(4) S(1)–Rh(1)–Cl(1) 92.79(4) S(2)–Rh(2)–Cl(2) 93.50(4) N(1)–Rh(1)–P(1) 89.62(10) N(4)–Rh(2)–P(3) 92.85(10) Cl(1)–Rh(1)–P(1) 90.73(4) Cl(2)–Rh(2)–P(3) 86.86(4) O(1)–Rh(1)–Cl(1) 90.09(8) O(2)–Rh(2)–Cl(2) 89.35(8) N(1)–Rh(1)–P(2) 94.63(10) N(4)–Rh(2)–P(4) 93.94(10) N(1)–Rh(1)–S(1) 84.49(9) N(4)–Rh(2)–S(2) 84.81(10) O(1)–Rh(1)–P(1) 84.21(8) O(2)–Rh(2)–P(3) 87.23(9) O(1)–Rh(1)–P(2) 92.65(8) O(2)–Rh(2)–P(4) 89.45(9) Cl(1)–Rh(1)–P(2) 85.16(4) Cl(2)–Rh(2)–P(4) 86.45(4) Rh(1)–S(1)–C(1) 94.37(14) Rh(2)–S(2)–C(46) 94.43(16) Scheme 1
S¼ 0) in these complexes. In the1H NMR spectra of all the complexes the PPh3protons show broad signals within 7.1 to 7.8 ppm. In the [Rh(PPh3)2(L1)Cl] complex, six signals were expected from the coordinated thiosemicarbazone ligand (L1) and all of them have been distinctly observed [at 4.20 (singlet, NH2), 6.55 (singlet, azomethine proton), 6.16 (triplet), 6.28 (doublet), 6.68 (doublet) and 6.90 (triplet) ppm]. Similarly, in the [Rh(PPh3)2(L
2
)Cl] complex, all the six expected signals from the coordinated thiosemicarbazone ligand (L2) have been clearly observed [at 4.50 (singlet, NH2), 2.10 (singlet, CH3), 6.30 (quartet), 6.66 (doublet), 6.80 (triplet) and 6.85 (doublet) ppm]. In the [Rh(PPh3)2(L3)Cl] complex, eight signals were expected from the coordinated thiosemicarbazone ligand (L3), of which seven have been observed [at 4.58 (singlet, NH2), 8.76 (singlet, azomethine proton), 7.00 (doublet), 7.03 (doublet), 7.12 (triplet), 7.74 (doublet) and 8.34 (singlet) ppm]. The last signal could not be detected because of overlap with the PPh3signals. The
1
H NMR spectral data are therefore consistent with the compositions of the complexes.
Infrared spectra of the [Rh(PPh3)2(L)Cl] complexes show three strong bands near 520, 695 and 745 cm1, which are attributable to the Rh(PPh3)2 fragment.11 Comparison with the spectrum of [Rh(PPh3)3Cl] shows the presence of some additional bands in the [Rh(PPh3)2(L)Cl] complexes (e.g., near 1620, 1530, 1435 and 1100 cm1), which must be due to the coordinated thiosemicarbazone ligand. The [Rh(PPh3)2(L)Cl] complexes are readily soluble in dichloromethane, chloroform, acetone, etc., producing intense yellow solutions. Electronic spectra of all the complexes have been recorded in dichloro-methane solution. Spectral data are presented in Table 3 and a selected spectrum is shown in Fig. 2. Each complex shows
several intense absorptions in the visible and ultraviolet regions. The absorptions in the ultraviolet region are assign-able to transitions within the ligand orbitals and those in the visible region are probably due to charge-transfer transitions involving both metal and ligand orbitals. For a better under-standing of the nature of the transitions in the visible region, qualitative EHMO calculations have been performed19 on computer generated models of all three complex molecules in which the phenyl rings of the PPh3ligands have been replaced by hydrogens. A partial MO diagram is displayed in Fig. 3 and the composition of some selected molecular orbitals is given in Table 4. The highest occupied molecular orbital (HOMO) and the next two filled orbitals (HOMO-1 and HOMO-2) have a major contribution from the dxy, dyz and dzx orbitals of rhodium20 and hence these three filled orbitals may be regarded as components of the metal t2 orbitals. The lowest unoccupied molecular orbital (LUMO) and the next couple of vacant orbitals (e.g., LUMO + 1 and LUMO + 2) are loca-lized almost entirely on different parts of the thiosemicarba-zone ligands. Hence the absorptions in the visible region may be assigned to charge-transfer transitions occurring from the filled t2 orbitals of rhodium to the vacant p* orbitals of the thiosemicarbazone ligands. As metal-to-ligand charge-transfer transitions are relatively less common in complexes of rhodiu-m(III), the observed charge-transfer transitions displayed by
the [Rh(PPh3)2(L)Cl] complexes in the visible region have tempted us to explore the luminescence properties of these complexes. This has been carried out in 1 : 9 dichloro-methane–ethanol solution at ambient temperature (298 K). All three complexes show strong emission in the visible region
Fig. 2 (a) Absorption spectrum of [Rh(PPh3)2(L2)Cl] in
dichloro-methane solution and (b) emission spectrum of [Rh(PPh3)2(L 2
)Cl] in
1 : 9 dichloromethane–ethanol solution at 298 K (lex¼ 316 nm). Fig. 3 Partial molecular orbital diagram of [Rh(PPh3)2(L1)Cl].
Table 3 Electronic absorption and emission spectral data
Emission datab
lmax/nm
Compound Absorption dataal
max/nm (e/M1cm1) Excitation Emission Quantum yield(f)
[Rh(PPh3)2(L1)Cl] 428(8400), 340(16400), 300(30000), 260c(42000) 332 417 0.85 103
[Rh(PPh3)2(L2)Cl] 406c(8200), 332(21200), 278c(39500) 316 421 2.01 103
[Rh(PPh3)2(L3)Cl] 464(4500), 442(4500), 346c(8600), 304c(16200), 272(23400) 324 425 1.63 103 a In dichloromethane.b In 1 : 9 dichloromethane–ethanol at 298 K.c Shoulder.
using an excitation wavelength of320 nm (Fig. 2, Table 3). Quantum yields (f) of these emissions, evaluated with refer-ence to [Ru(bpy)3](ClO4)2,21indicate that the emission inten-sity increases appreciably when the azomethine proton in [Rh(PPh3)2(L1)Cl] is replaced by an electron-donating methyl group (as in [Rh(PPh3)2(L2)Cl]). Compared to [Rh(PPh3)2(L1)Cl] the emission intensity is also higher in the [Rh(PPh3)2(L
3
)Cl] complex, which is attributable to the higher degree of charge delocalization possible over the naphthyl ring in this complex.
Electrochemical properties of the [Rh(PPh3)2(L)Cl] com-plexes have been studied by cyclic voltammetry. Voltammetric data are presented in Table 5 and a selected voltammogram is displayed in Fig. 4. Each complex shows two oxidative responses on the positive side of the SCE and one reductive response on the negative side. All three responses are irreversi-ble in nature. The first oxidative response is assigned to rho-dium(III) to rhodium(IV) oxidation. The one-electron nature
of this oxidation has been established by comparing its current height (ipa) with that of the ferrocene/ferrocenium couple under identical experimental conditions. The second oxidative response is believed to be centered on the thiosemicarbazone
ligand. The reductive response is assigned to the rhodium(III)
to rhodium(II) reduction. The irreversible nature of the redox
responses indicates that while the trivalent state of rhodium is quite comfortable in these complexes, the higher and lower oxidation states are not.
Conclusion
The present study shows that salicylaldehyde thiosemicarba-zone and similar ligands can smoothly bind to a metal ion as tridentate O,N,S-donors, provided an adequate number of coordination sites are readily available on the target metal ion. With the knowledge gained from the present study, attempts are now underway to bind these ligands in the O,N,S-tridentate fashion to ruthenium and osmium, for which only four-membered N, S-chelates were obtained before.
Acknowledgements
Financial assistance received from the Council of Scientific and Industrial Research, New Delhi [Grant No. 01(1675)/00/ EMR-II] is gratefully acknowledged. The authors thank Pro-fessor S. Lahiri of Department of Organic Chemistry, Indian Association for the Cultivation of Science, Kolkata, for her help and the Bose Institute, Calcutta 700054, for NMR spec-tral measurements. SD thanks CSIR for her fellowship.
References
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Compound Contributing fragment HOMO HOMO-1 HOMO-2 LUMO LUMO + 1 LUMO + 2 [Rh(PPh3)2(L1)Cl] Rhodium ligand (L1) 52% 38% 81% 12% 50% 41% 4% 90% 0% 98% 0% 97%
[Rh(PPh3)2(L2)Cl] Rhodium ligand (L2) 52% 38% 81% 12% 52% 35% 3% 90% 0% 97% 0% 92%
[Rh(PPh3)2(L3)Cl] Rhodium ligand (L3) 79% 15% 32% 61% 59% 31% 6% 90% 10% 88% 0% 98%
Fig. 4 Cyclic voltammogram of [Rh(PPh3)2(L2)Cl] in 1 : 9
dichloro-methane–acetonitrile solution (0.1 M TBAP) at a scan rate of 50 mV s1. Table 5 Cyclic voltammetric data
Compound E/V vs. SCE
a
Epa Epc
[Rh(PPh3)2(L1)Cl] 0.85, 1.13 1.05
[Rh(PPh3)2(L2)Cl] 0.83, 1.40 1.14
[Rh(PPh3)2(L3)Cl] 0.77, 1.23 1.13 a In 1 : 9 dichloromethane–acetonitrile; supporting electrolyte, TBAP;
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20 The HOMO-1 in [Rh(PPh3)2(L3)Cl] has slightly less metal
character.
![Table 1 Crystallographic data of [Rh(PPh 3 ) 2 (L 2 )Cl]](https://thumb-ap.123doks.com/thumbv2/9libinfo/8874743.249737/2.897.103.389.242.419/table-crystallographic-data-rh-pph-l-cl.webp)
![Table 2 Selected bond parameters (distances in A˚, angles in ) for [Rh(PPh 3 ) 2 (L 2 )Cl] Molecule 1 Molecule 2 Rh(1)–N(1) 2.012(3) Rh(2)–N(4) 2.013(3) Rh(1)–O(1) 2.035(3) Rh(2)–O(2) 2.026(3) Rh(1)–P(1) 2.3920(12) Rh(2)–P(3) 2.3889(12) Rh(1)–P(2) 2.3929](https://thumb-ap.123doks.com/thumbv2/9libinfo/8874743.249737/3.897.122.399.76.357/table-selected-parameters-distances-angles-pph-molecule-molecule.webp)
![Fig. 2 (a) Absorption spectrum of [Rh(PPh 3 ) 2 (L 2 )Cl] in dichloro- dichloro-methane solution and (b) emission spectrum of [Rh(PPh 3 ) 2 (L 2 )Cl] in](https://thumb-ap.123doks.com/thumbv2/9libinfo/8874743.249737/4.897.69.828.99.251/absorption-spectrum-dichloro-dichloro-methane-solution-emission-spectrum.webp)
![Fig. 4 Cyclic voltammogram of [Rh(PPh 3 ) 2 (L 2 )Cl] in 1 : 9 dichloro- dichloro-methane–acetonitrile solution (0.1 M TBAP) at a scan rate of 50 mV s 1 .Table 5Cyclic voltammetric data](https://thumb-ap.123doks.com/thumbv2/9libinfo/8874743.249737/5.897.84.823.97.181/voltammogram-dichloro-dichloro-methane-acetonitrile-solution-cyclic-voltammetric.webp)
