Photophysical properties, X-ray structures, electrochemistry, and DFT computational chemistry of osmium complexes

We report the synthesis of phosphorescent divalent osmium complexes of the form [Os(N-N)₂(L-L) or Os(L-L)₂(N-N)]²⁺ (PF₆)₂ where N-N is a derivative of 1,10-phenanthroline, and L-L is a diarsine or diphosphine ligand: 1,2-bis(dimethylphosphino)ethane, 1,2-bis(dicyclohexylphosphino)ethane, or 1,2-bis(dimethylarseno)benzene. X-ray structures have been determined, luminescent and electrochemical properties have been measured and DFT calculations have been performed on the complexes. The emission lifetime of complexes of structure Os(II)(L-L)₂(N-N) are longer than the those of Os(II)(N-N)₂(L-L). The DFT calculations show that there is significant mixing of the π−π^∗ into the dπ−π^∗ charge-transfer state for the complexes of the form Os(II)(L-L)₂(N-N) resulting in a longer lived excited state. Through DFT calculations we were able to conclude that the HOMO of the complexes is a d orbital on the osmium while the LUMO is the b₁(ψ) π^∗ system of the phenanthroline. However, we found that the HOMO did not have the correct symmetry to enable strong charge transfer to the phenanthroline to be observed, and the strong MLCT transition observed in the spectra is the metal d HOMO(−1) to the b1 π^∗ LUMO of the phenanthroline.     

DNA interaction and cytotoxicity studies of new ruthenium(II) cyclopentadienyl derivative complexes containing heteroaromatic ligands

Four ruthenium(II) complexes with the formula [Ru(η⁵-C₅H₅)(PP)L][CF₃SO₃], being (PP = two triphenylphosphine molecules), L = 1-benzylimidazole, ; (PP = two triphenylphosphine molecules), L = 2,2′bipyridine, ; (PP = two triphenylphosphine molecules), L = 4-Methylpyridine, ; (PP = 1,2-bis(diphenylphosphine)ethane), L = 4-Methylpyridine, , were prepared, in view to evaluate their potentialities as antitumor agents. The compounds were completely characterized by NMR spectroscopy and their crystal and molecular structures were determined by X-ray diffraction. Electrochemical studies were carried out giving for all the compounds quasi-reversible processes. The images obtained by atomic force microscopy (AFM) suggest interaction with pBR322 plasmid DNA. Measurements of the viscosity of solutions of free DNA and DNA incubated with different concentrations of the compounds confirmed this interaction. The cytotoxicity of compounds 1234 was much higher than that of cisplatin against human leukemia cancer cells (HL-60 cells). IC₅₀ values for all the compounds are in the range of submicromolar amounts. Apoptotic death percentage was also studied resulting similar than that of cisplatin.     

Synthesis and structural studies of heteroleptic complexes of ytterbium(III) involving aryloxy- or alkoxy- and cyclopentadienyl ligands

Treatment of tris-cyclopentadienyl-ytterbium in thf with one equivalent of 2,6-di(tert-butyl)phenol, N,N-dimethyl-2-aminoethanol or N,N-diethyl-2-aminoethanol resulted in substitution of one cyclopentadienyl ligand and formation of [YbCp₂(O-C₆H₃^tBu-2,6)(thf)] (1), [{YbCp₂(μ-OCH₂CH₂NMe₂)}₂] (2) or [{YbCp₂(μ-OCH₂CH₂NEt₂)}₂] · (thf)₂ (3), respectively. All compounds were characterised by spectroscopic and X-ray crystallographic techniques, the latter two also being studied by variable temperature ¹H NMR spectroscopy. Compound (1) is mononuclear with the Yb centre bound by two η⁵-cyclopentadienyl ligands one O-bound thf and an O-bound phenoxy ligand. Compounds (2) and (3) are centrosymmetric dimers with the Yb centre bound by two η⁵-cyclopentadienyl ligands, while the bidentate ligands chelate the metal centre and also bridge to the adjacent Yb through the alkoxy oxygen atom. Variable temperature ¹H NMR studies on compounds (2) and (3) show a solution-state equilibrium between the dimeric solid-state structure and one with the nitrogen atoms non-bound to Yb.     

Reactivity study of cyclopentadienyl osmium(II) bisphosphine azido complexes with activated alkynes and nitriles: Isolation of osmium triazolato and tetrazolato complexes by 1,3-dipolar addition

The cyclopentadienyl osmium(II) complexes [(η⁵-C₅H₅)Os(PPh₃)₂X] [X = Br (1), CH₃CN (2)] reacts with sodium azide (NaN₃) to yield the corresponding azido complex [(η⁵-C₅H₅)Os(PPh₃)₂N₃] (3). This undergoes [3+2] dipolar cycloaddition reaction with activated alkynes like dimethyl and diethyl acetylenedicarboxylate to yield triazolato complexes [(η⁵-C₅H₅)Os(PPh₃)₂{N₃C₂(CO₂R)₂}] [R = –CH₂CH₃ (4) and –CH₃ (5)]. The complex 3 also reacts with nitriles such as tetracyanoethylene (TCE), fumaronitrile and p-nitrobenzonitrile to yield complexes of the type [(η⁵-C₅H₅)Os(PPh₃)₂{N₄C₂(CN)C(CN)₂}] (6), [(η⁵-C₅H₅)Os(PPh₃)₂{N₃C₂HCN}] (7) and [(η⁵-C₅H₅)Os(PPh₃)₂{N₄C(C₆H₄–p-NO₂)}] (8). These complexes were fully characterized on the basis of microanalyses, FT-IR and NMR spectroscopic data. The molecular structure of the representative complex [(η⁵-C₅H₅)Os(PPh₃)₂{N₃C₂(CO₂CH₂CH₃)₂}] (4) was determined by single crystal X-ray analysis.     

Cyclopentadienyl ruthenium(II) dithiocarbamate complexes: Crystal structures of [CpRu(PPh3)(S2CNPr2)] and [CpRu(PPh3)(S2CNMeBu)]

Thermolysis of [CpRuCl(PPh₃)₂] and NaS₂CNPr₂ or NaS₂CNMeBu in methanol affords the ruthenium(II) dithiocarbamate complexes, [CpRu(PPh₃)(S₂CNPr₂)] and [CpRu(PPh₃)(S₂CNMeBu)], which have been crystallographically characterized. A similar treatment of two equivalents of [CpRuCl(PPh₃)₂] with the bis(dithiocarbamate) ligand derived from 1,3-homopiperazine affords [{CpRu(PPh₃)}₂(μ-S₂CNC₅H₁₀NCS₂)].     

Synthesis, properties and solution speciation of lanthanide chloride complexes of triphenylphosphine oxide

The reaction of Ph₃PO with LnCl₃ · nH₂O (Ln=La-Lu ≠ Pm) in a 3.5:1 ratio in acetone produces [LnCl₃(Ph₃PO)₃], whilst from a 6:1 ratio in ethanol the products are [LnCl₂(Ph₃PO)₄]Cl · n(solvate). In the presence of [NH₄][PF₆] in ethanol solution, [LnCl₂(Ph₃PO)₄]PF₆ can be isolated. The last complexes are stable in solution but the [LnCl₃(Ph₃PO)₃] and [LnCl₂(Ph₃PO)₄]Cl partially interconvert in non-coordinating solvents, the neutral species being preferred by the lighter lanthanides, the cationic tetrakis complexes becoming more favoured towards the end of the series. The complexes have been characterised in the solid state by analysis and IR spectroscopy and in solution by ³¹P{¹H} NMR spectroscopy and conductance measurements. The crystal structures of trans-[LnCl₂(Ph₃PO)₄]Cl · nEtOH (Ln=Tb or Yb) and mer-[LnCl₃(Ph₃PO)₃] · 0.5Me₂CO (Ln=La or Ce) are reported and discussed.     

Inhibition of cancer cell growth by ruthenium(II) cyclopentadienyl derivative complexes with heteroaromatic ligands

Inhibition of the growth of LoVo human colon adenocarcinoma and MiaPaCa pancreatic cancer cell lines by two new organometallic ruthenium(II) complexes of general formula [Ru(η⁵-C₅H₅)(PP) L][CF₃SO₃], where PP is 1,2-bis(diphenylphosphino)ethane and L is 1,3,5-triazine (Tzn) 1 or PP is 2x triphenylphosphine and L is pyridazine (Pyd) 2 has been investigated. Crystal structures of compounds 1 and 2 were determined by X-ray diffraction studies. Atomic force microscopy (AFM) images suggest different mechanisms of interaction with the plasmid pBR322 DNA; while the mode of binding of compound 1 could be intercalation between base pairs of DNA, compound 2 might be involved in a covalent bond formation with N from the purine base.     

Optically active iridium complexes with cyclopentadienyl-phosphine ligands: synthesis and oxidative addition of methyl iodide

The dimer [Ir(μ-Cl)(C₈H₁₄)₂]₂ reacts with the ligands (S)-(C₅H₄CH₂CH(Ph)PPh₂)Li and (R)-(C₅H₄CH(Cy)CH₂PPh₂)Li to give (S)-[Ir(η⁵-C₅H₄CH₂CH(Ph)PPh₂-κP)(C₈H₁₄)] and (R)-[Ir(η⁵-C₅H₄CH(Cy)CH₂PPh₂-κP)(C₈H₁₄)], which upon treatment with CH₃I at room temperature afford the cationic iridium(III) compounds (S,S_Ir)-[Ir(η⁵-C₅H₄CH₂CH(Ph)PPh₂-κP)(CH₃)(C₈H₁₄)][I] as a single diastereomer, and (R)-[Ir(η⁵-C₅H₄CH(Cy)CH₂PPh₂-κP)(CH₃)(C₈H₁₄)][I] as a 9:1 mixture of two diastereomers. If the oxidative addition reaction is performed at reflux in methylene chloride, the starting complexes convert to the neutral compounds (S)-[Ir(η⁵-C₅H₄CH₂CH(Ph)PPh₂-κP)(CH₃)(I)] and (R)-[Ir(η⁵-C₅H₄CH(Cy)CH₂PPh₂-κP)(CH₃)(I)] as 1.6:1 and 3.3:1 mixtures of diastereoisomers, respectively. Carbonyl iridium complexes are synthesized by reacting [IrCl(CO)(PPh₃)₂] with the ligands to afford (S)-[Ir(η⁵-C₅H₄CH₂CH(Ph)PPh₂-κP)(CO)] and (R)-[Ir(η⁵-C₅H₄CH(Cy)CH₂PPh₂-κP)(CO)]. They give upon treatment with CH₃I the cationic species (S)-[Ir(η⁵-C₅H₄CH₂CH(Ph)PPh₂-κP)(CH₃)(CO)][I] and (R)-[Ir(η⁵-C₅H₄CH(Cy)CH₂PPh₂-κP)(CH₃)(CO)][I] as 1.6:1 and 3:1 mixture of diastereomers, respectively. No migratory-insertion of the methyl group into the carbonyl-metal bond has been observed even after prolonged heating.     

Synthesis of a series of first-row tris-imidazolylphosphine sandwich complexes and their potential for formation of polymetallic species

A series of tris-[2-(1-methylimidazolyl)phosphine] sandwich complexes with Co²⁺ (1), Ni²⁺ (2), Cu²⁺ (3) and Zn²⁺ (4) have been synthesized and characterized with the intent of using these complexes as templates for building polymetallic species. X-ray analysis reveals that each metal is six-coordinate with octahedral geometry. Compound 3 exhibits a tetragonal distortion resulting from a Jahn-Teller distortion of a Cu²⁺ (d⁹) complex. Electrochemistry of 1-4 displayed peaks assigned to both ligand-based oxidation at 1.45-1.56 V and a perchlorate-based reduction at −2.36 to −2.78 V versus FcH⁺/FcH. Metal-based reduction was also observed for 2, with a reversible Ni^2+/3+ oxidation at 0.89 V, consistent with the relatively poor donor ability of the imidazolyl nitrogen bases; and 3, with a irreversible Cu^2+/1+ reduction at −1.29 V versus FcH⁺/FcH, consistent with the decomposition of the complex upon reduction. X-ray structures indicate large steric crowding around the phosphorus atom resulting from the orientation of the methyl substituent on the imidazoles. This crowding may prohibit the formation of polymetallic species through phosphorus-metal bonding.     

Reactions of [Os3(CO)10(MeCN)2] with ethynyl thiophenes: The formation of linked clusters

The reaction of 2 equiv. of [Os₃(CO)₁₀(MeCN)₂] with R-CC-L-CC-R (R = H, L = (C₄H₂S); R = SiMe₃, L = (C₄H₂S-C₄H₂S), (C₄H₂S-C₄H₂S-C₄H₂S), (C₄H₂S)-(C₁₄H₈)-(C₄H₂S)) affords the series of linked clusters [{Os₃(CO)₁₀}(HCC(C₄H₂S)CCH){Os₃(CO)₁₀}] (1), [{Os₃(CO)₁₀}(Me₃SiCC(C₄H₂S-C₄H₂S)CCSiMe₃){Os₃(CO)₁₀}] (2), [{Os₃(CO)₁₀}(Me₃SiCC(C₄H₂S-C₄H₂S-C₄H₂S)CCSiMe₃){Os₃(CO)₁₀}] (4) and [{Os₃(CO)₁₀}(Me₃SiCC(C₄H₂S)-(C₁₄H₈)-(C₄H₂S)CCSiMe₃){Os₃(CO)₁₀}] (6) as the major products. The complexes have been characterised by a range of spectroscopic methods and, in the case of 1 and 2 by single crystal X-ray crystallography. The alkyne groups cap the osmium triangles in the expected μ₃-η²-||-bonding mode and each triangle is coordinated by nine terminal and one μ₂-carbonyl group. Solution UV-Vis spectra of the complexes were similar to those observed for the free ligands consistent with there being little delocalisation between the cluster units and the thiophene groups.     

Synthesis, spectroscopy and structural characterization of silver(I) complexes containing unidentate N-donor azole-type ligands

From the interaction between azole-type ligands L and AgX (X = NO₃ or ClO₄) or [AgX(PPh₃)_n] (X = Cl, n = 3; X = MeSO₃, n = 2), new ionic mononuclear [Ag(L)₂]X and [Ag(PPh₃)₃L][X] or neutral mono-([Ag(PPh₃)_nL(X)]) or di-nuclear ([{Ag(PPh₃)(L)(μ-X)}₂]) complexes have been obtained which have been characterized through elemental analysis, conductivity measurements, IR, ¹H NMR and, in some cases, also by ³¹P{¹H} NMR spectroscopy, and single-crystal X-ray studies. Stoichiometries and molecular structures are dependent on the nature of the azole (steric hindrance and basicity), of the counter ion, and on the number of the P-donor ligands in the starting reactants. Solution data are consistent with partial dissociation of the complexes, occurring through breaking of both Ag-N and Ag-P bonds.     

Synthesis, structure and electronic spectra of new three-coordinated copper(I) complexes with tricyclohexylphosphine and diimine ligands

Three new copper(I) complexes with tricyclohexylphosphine (PCy₃) and different diimine ligands, [Cu(phen)(PCy₃)]BF₄ (1) (phen = 1,10′-phennanthroline), [Cu(bpy)(PCy₃)₂]BF₄ (2) (bpy = 2,2′-bipyridine) and [Cu(MeO-CNN)(PCy₃)]BF₄ (3) (MeO-CNN = 6-(4-methoxyl)phenyl-2,2′-bipyridine), have been synthesized and characterized. X-ray structure reveals that complexes 1 and 3 are three-coordinated with trigonal geometry, while complex 2 adopts distorted tetrahedron geometry. Complexes 1 and 3 exhibit ligand redistribution reactions in chloromethane solution by addition of excess amount of PCy₃, in which three-coordinated 1 changes into four-coordinated [Cu(phen)(PCy₃)₂]⁺, and 3 leads to form [Cu(PCy₃)₂]BF₄ and CNN-OMe. All the three complexes display yellow ³MLCT emissions in solid state at room temperature with λ_max at 558, 564 and 582 nm for 1, 2 and 3, respectively, and red-shift to 605, 628 and 643 nm at 77 K in dichloromethane solution.     

The reaction of [Os6(CO)18] with [(SPPh2)2NH]: Facile rearrangement of the metal framework

The reaction of [Os₆(CO)₁₈] 1 with [(SPPh₂)₂NH] in the presence of Me₃NO produces a purple compound characterized spectroscopically and by X-ray crystallography, as [HOs₆(CO)₁₇(SPPh₂)₂N] 2. The structure shows the hexanuclear fragment to have suffered a geometrical rearrangement to give a metal framework that can be described as an edge-bridged tetrahedron with an additional terminal osmium atom bonded to one of the bridged metal atoms. The ligand acts as a bimetallic tetraconnective unit through both sulphur atoms between two non-bonded osmium atoms.     

Osmadisiloxane and osmastannasiloxane complexes derived from silanolate complexes of osmium(II)

Treatment of the five-coordinate chlorodimethylsilyl complex, Os(SiMe₂Cl)Cl(CO)(PPh₃)₂ with hydroxide readily produces Os(SiMe₂OH)Cl(CO)(PPh₃)₂ (1). Complex 1 is deprotonated by ^tBuLi giving the silanolate complex, Os(SiMe₂OLi)Cl(CO)(PPh₃)₂ (2), which reacts further with Me₃SiCl or Me₃SnCl to give Os(SiMe₂OSiMe₃)Cl(CO)(PPh₃)₂ (3) or Os(SiMe₂OSnMe₃)Cl(CO)(PPh₃)₂ (4), respectively. The structures of 3 and 4 have been determined by X-ray crystallography. Reaction between OsH(κ²-S₂CNMe₂)(CO)(PPh₃)₂ and HSiMe₂Cl gives Os(SiMe₂Cl)(κ²-S₂CNMe₂)(CO)(PPh₃)₂ (5). This six-coordinate chlorodimethylsilyl complex, is unreactive towards hydroxide at room temperature and at 60 °C forms Os[Si(OH)₃](κ²-S₂CNMe₂)(CO)(PPh₃)₂ (7). Complex 5 is, however, smoothly converted to the hydroxy derivative, Os(SiMe₂OH)(κ²-S₂CNMe₂)(CO)(PPh₃)₂ (6) upon chromatography on silica gel. Complex 6 is deprotonated by ^tBuLi giving the intermediate silanolate complex, Os(SiMe₂OLi)(κ²-S₂CNMe₂)(CO)(PPh₃)₂, which reacts further with Me₃SiCl to give Os(SiMe₂OSiMe₃)(κ²-S₂CNMe₂) (CO)(PPh₃)₂ (8). Crystal structure determinations for 5, 6, 7, and 8 have been obtained and structural comparisons of these related compounds are made.     

Crystallography and luminescence of divalent osmium complexes green osmium emitters and possible evidence for d-orbital backbonding

The preparation, photophysics, and solid-state structures of three osmium cored complexes are reported. The osmium complexes take the general form of [OsCl(N-N)(L-L)(CO)]⁺ hexafluorophosphate where N stands for a derivative of 1,10-phenanthroline and L stands for a phosphine type ligand. The emission of the complexes is shown to be blue shifted to the osmium emission of Os(bpy)₃ ²⁺. The emissions of the various complexes range from yellow (560 nm) to yellow-green (550 nm) to green (520 nm). The quantum yields vary between 60% and 75%. The complexes show lifetimes that are much longer than expected with ranges of 6.5-38 μs. Crystallographic results show that the carbonyl is trans to a phenanthroline nitrogen and the chloro ligand is trans to phosphorus. A discussion will be presented as to the nature of the bonding in these complexes based upon the data from the crystallography.     

Coordination chemistry of 1,2-bis{di-(4-methoxyphenyl)phosphino}ethane (L-L) to nickel, palladium and platinum: Single crystal structures of [MCl2(L-L)] (M = Ni, Pd)

Square planar Ni(II), Pd(II) and Pt(II) complexes of the para-methoxy derivatised analogue of dppe, 1,2-bis{di-(4-methoxyphenyl)phosphino}ethane (L-L), [MCl₂(L-L)] and [M(L-L)₂]Cl₂ (M = Ni, Pd, Pt) are readily prepared, and have been characterised by elemental analysis, IR and NMR spectroscopies. The structures of [NiCl₂(L-L)] and [PdCl₂(L-L)] have been determined by single-crystal X-ray diffraction.     

Syntheses, structures and magnetic properties of heterobimetallic complexes based on a new tetracyanometalate precursor

A new mononuclear tetracyanometallic complex, (n-Bu₄N)[(dbphen)Fe(CN)₄] (1, dbphen = 5,6-dibromo-1,10-phenanthroline), has been prepared by reacting [(dbphen)Fe^II(py)₂(SCN)₂] and KCN in water and further oxidized with chlorine. With the use of 1 as building block, two trinuclear Fe₂M complexes, [(dbphen)₂Fe₂(CN)₈Cu(Me₃tacn)]·3H₂O (2), [(dbphen)₂Fe₂(CN)₈Ni(dabhctd)]·2H₂O (3) and a chain complex of squares [(dbphen)₂Fe₂(CN)₈Co(MeOH)₂]_n (4), have been synthesized and structurally characterized. Magnetic studies show ferromagnetic coupling between Fe^III and M^II (M = Cu, 2; Ni, 3) ions bridged by cyanides in complexes 2 and 3, while complex 4 exhibits meta-magnetic behavior.     

Synthesis of rhodium and iridium boryl complexes via oxidative addition of haloboranes

B-Chlorocatecholborane undergoes oxidative addition to M(PR₃)₃Cl (M = Rh, R = Me; M = Ir, R = Me, Et) yielding six-coordinate complexes of general formula mer,cis-(PR₃)₃Cl₂M(BO₂C₆H₄). The same M(PR₃)₃Cl complexes also react with B-bromocatecholborane to give a mixture of metal boryl homo- and heterodihalides (PR₃)₃X¹X²M(BO₂C₆H₄) (X¹, X² = Cl, Br), and the observed disproportionation is believed to involve the formation of a heteronuclear halide-bridged intermediate. The alkene 4-vinylanisole failed to react with the six-coordinate, 18-electron (PR₃)₃Cl₂M(BO₂C₆H₄) complexes at ambient temperatures.     

Structure diversity of silver(I) [1,1′-bis(diphenylphosphino)cobaltocenium] complexes: Effect of counteranions

Single crystal X-ray structural characterizations are recorded for an array of adducts of the form {AgX:[dppc][PF₆]}_n (n = 1 or 2), [dppc][PF₆] = 1,1′-bis(diphenylphosphino)cobaltocenium hexafluorophosphate, X = Cl, Br, NO₃, NO₂, C₆H₅CO₂, CF₃CO₂. Synthetic procedures for all adducts are reported. All compounds have been fully characterised by elemental analysis and spectroscopic techniques. The structures in the solid state were found to depend on the nature of the counterion, for X = NO₃, NO₂, the complex being monomeric {[dppc-P,P′]Ag(NO₃)₂} or {[dppc-P,P′]Ag(NO₂)}, for X = Cl, Br, C₆H₅CO₂, CF₃CO₂, the complex is a dimer.     

Vibrational and structural mapping of [Os(bpy)3] and [Os(phen)3]

Structural changes between [Os^IIL₃]²⁺ and [Os^IIIL₃]³⁺ (L: 2,2′-bipyridine; 1,10-phenanthroline) and molecular and electronic structures of the Os^III complexes [Os^III(bpy)₃]³⁺ and [Os^III(phen)₃]³⁺ are discussed in this paper. Mid-infrared spectra in the ν(bpy) and ν(phen) ring stretching region for [Os^II(bpy)₃](PF₆)₂, [Os^III(bpy)₃](PF₆)₃, [Os^II(phen)₃](PF₆)₂, and [Os^III(phen)₃](PF₆)₃ are compared, as are X-ray crystal structures. Absorption spectra in the UV region for [Os^III(bpy)₃](PF₆)₃ and [Os^III(phen)₃](PF₆)₃ are dominated by very intense absorptions (ε = 40 000-50 000 M⁻¹ cm⁻¹) due to bpy and phen intra-ligand π → π^∗ transitions. In the visible region, relatively narrow bands with vibronic progressions of ∼1500 cm⁻¹ appear, and have been assigned to bpy or phen-based, spin-orbit coupling enhanced, ¹π → ³π^∗ electronic transitions. Also present in the visible region are ligand-to-metal charge transfer bands (LMCT) arising from π(bpy) → t_2g(Os^III) or π(phen) → t_2g(Os^III) transitions. In the near infrared, two broad absorption features appear for oxidized forms [Os^III(bpy)₃](PF₆)₃ and [Os^III(phen)₃](PF₆)₃ arising from dπ-dπ interconfigurational bands characteristic of dπ⁵Os^III. They are observed at 4580 and 5090 cm⁻¹ for [Os^III(bpy)₃](PF₆)₃ and at 4400 and 4990 cm⁻¹ for [Os^III(phen)₃](PF₆)₃. The bpy and phen infrared vibrational bands shift to higher energy upon oxidation of Os(II) to Os(III). In the cation structure in [Os^III(bpy)₃](PF₆)₃, the Os^III atom resides at a distorted octahedral site, as judged by ∠N-Os-N, which varies from 78.78(22)° to 96.61(22)°. Os-N bond lengths are also in general longer for [Os^III(bpy)₃](PF₆)₃ compared to [Os^II(bpy)₃](PF₆)₂ (0.010 Å), and for [Os^III(phen)₃](PF₆)₃ compared to [Os^II(phen)₃](PF₆)₂ (0.014 Å). Structural changes in the ligands between oxidation states are discussed as originating from a combination of dπ(Os^II) → π^∗ (bpy or phen) backbonding and charge redistribution on the ligands as calculated by natural population analysis.