BIS-μ-[BIS(Diphenylphosphino)Methane]Dihalodiplatinum-(Pt-Pt) and its hydrido ‘A’-frame derivatives revisited

Definitive ¹H, ³¹P and ¹⁹⁵Pt NMR data are reported for the complexes [PtX₂(dppm)] (X = Cl, Br or I; dppm = Ph₂PCH₂PPh₂), [Pt₂X₂(μ-dppm)₂], [Pt₂X₂(μ-H)(μ-dppm)₂]⁺, [Pt₂H₂(μ-H)(μ-dppm)₂]⁺, [Pt₂Cl₂(μ-Y)(μ-dppm)₂] (Y = CH₂. S or SO₂), [Pt₂Me₂(μ-Cl)(μ-dppm)₂]⁺ and [Pt₂Me₃(μ-dppm)₂]⁺. The complexes [Pt₂X₂(μ-H)(μ-dppm)₂]⁺ (X = Br or I) are reported for the first time, and the evidence is presented that [Pt₂H₂Cl(μ-ddpm)₂]⁺ has a ‘T’-frame structure (involving a donor-acceptor metal-metal bond) rather than an ‘A’-frame structure. Early preparative routes to [Pt₂X₂)μ-dppm)₂] (X = Cl, Br or I) were shown to give complexes contaminated with small amounts of [Pt₂X₂(μ-H)(μ-dppm)₂]X, and rapid intermolecular proton transfer between [Pt₂X₂(μ-dppm)₂] and [Pt₂X₂(μ-H)(μ-dppm)₂]⁺ was observed: for X = Cl, ΔG^≠ is 44.1 kJ mol⁻¹. The merits of ¹⁹⁵Pt NMR spectroscopy for studying platinum dimers are discussed, and a correlation between ¹J(PtPt) and r(PtPt) was observed.     

Di‐μ‐pivalamidato‐κ4N:O;O:N‐bis­[(2,2′‐bi­pyridine‐κ2N,N′)(sulfato‐κO)­platinum(III)] tetrahydrate in a head‐to‐tail isomerism

The title compound, [Pt₂^III(C₅H₁₀NO)₂(SO₄)₂(C₁₀H₈N₂)₂]·4H₂O, is the first reported example of a complex in which an amidate‐bridged Pt(bpy) dimer is stabilized in the oxidation level of Pt^III (bpy is 2,2′‐bi­pyridine). The asymmetric unit consists of one half of the formula unit with a twofold axis passing through the center of the dimer. The intradimer Pt^III—Pt^III bond distance [2.5664 (6) Å] is comparable to those reported for α‐pyridonate‐bridged cis‐diammineplatinum(III) dimers [2.5401 (5)–2.5468 (8) Å; Hollis & Lippard (1983). Inorg. Chem. 22 , 2605–2614], in spite of the close contact between the bpy planes within the dimeric unit. The axial Pt—O_sulfate distance is 2.144 (7) Å.     

Influence of the chloride counterion on the redox reactivity of tetraammineplatinum(II) cation with octacyanotungstate(V) anion: Crystal structure of [Pt(NH3)4]2[W(CN)8]

The redox reaction between [Pt(NH₃)₄]²⁺ and [W(CN)₈]³⁻ in the presence of Cl⁻ anions in aqueous solution affords single crystals of [Pt^II(NH₃)₄]₂[W^IV(CN)₈] and [Pt^IV(NH₃)₄Cl₂]Cl₂. Trapped cyano ligands of [W(CN)₈]⁴⁻ rectangular antiprisms of D₂ point symmetry between parallel Pt(II) square planes show that the inner-sphere redox pathway is prohibited. The presence of Cl⁻ counterions enables the formation of [Pt(NH₃)₄Cl₂]Cl₂ as the product of the rare outer-sphere pathway of the oxidation of Pt(II) by [W(CN)₈]³⁻.     

Binuclear platinum(I) complexes with bis(dimethylphosphino)methane ligands: evidence for both short- and long-range NMR trans-influences

The diplatinum(I) complexes or complex ions [Pt₂X₂(μ-dmpm)₂] (X = Cl or I), [Pt₂X(PPh₃)(μ-dmpm)₂]⁺] (X = I, Br or Me), and [Pt₂(PPh₃)₂(μ-dmpm)₂]²⁺, where dmpm = Me₂PCH₂PMe₂, have been prepared and characterized by ¹H and ³¹P NMR spectroscopy. In the linear X-Pt-Pt-Y unit the trans-influence of X is felt primarily at the PtPt bond, but groups X having a very high trans-influence (X = H or Me) can also exert a weaker long-range trans-influence on the PtY bond.     

Darstellung von Nonahalogenodiplatinaten(IV), [Pt2X9]−, X  Cl,Br Spektroskopische Charakterisierung,Normalkoordinatenanalyse und Kristallstruktur von (PPN)[Pt2Br9]

Preparation of the Nonahalogenodiplatinates(IV), [Pt₂X₉]^?, X ? Cl, Br Spectroscopic Characterization, Normal Coordinate Analysis, and Crystal Structure of (PPN)[Pt₂Br₉] On heating the tetrabutylammonium salts (TBA)₂[PtX₆], with trifluoroacetic acid the nonahalogenodiplatinates(IV) (TBA)[Pt₂X₉], with X ? Cl, Br are formed. The X-ray structure determination on (PPN)[Pt₂Br₉] (orthorhombic, space group Pca2, Z = 4) shows for the anions pairs of face-sharing octahedra with nearly D_3h symmetry. The mean terminal and bridging Pt? Br bond lengths are determined to be 2.42 and 2.52 Å, respectively. The electrostatic interaction of the Pt atoms results in the Pt? Pt distance of 3.23 Å and an elongation as it has been forecasted by the MO scheme for d⁶ systems. Using the structural data a normal coordinate analysis based on a general valence force field for [Pt₂Br₉]^? has been performed, revealing a good agreement of the calculated frequencies with the bands observed in the IR and Raman spectra. The stronger bonding of the terminal as compared to the bridging ligands is shown by the valence force constants, f_a(Br₁) = 1,55 > f_d(Br_b) = 0,93 mdyn/ Å.     

Pt2II and Pt2III dimers containing a Pt2(2,2′‐bipyridine)2(μ‐N,N‐dimethyl­guanidinato)2 unit

The syntheses and crystal structures of the title Pt₂^II and Pt₂^III dimers doubly bridged with N,N‐dimethyl­guanidinate ligands, namely bis­(μ‐N,N‐dimethyl­guanidinato)bis­[(2,2′‐bipyridine)platinum(II)](Pt—Pt) bis­(hexa­fluoro­phosphate) acetonitrile disolvate, [Pt₂^II(C₃H₈N₃)₂(C₁₀H₈N₂)₂](PF₆)₂·2CH₃CN, (I), and guanidinium bis­(μ‐N,N‐dimethyl­guanidinato)bis­[(2,2′‐bipyridine)sulfatoplatinum(III)](Pt—Pt) bis­(hexa­fluoro­phosphate) nitrate hexa­hydrate, (C₃H₁₀N₃)[Pt^III₂(C₃H₈N₃)₂(SO₄)₂(C₁₀H₈N₂)₂]NO₃·6H₂O, (II), are reported. The oxidation of the Pt₂^II dimer into the Pt₂^III dimer results in a marked shortening of the Pt—Pt distance from 2.8512 (6) to 2.5656 (4) Å. The change is mainly compensated for by the change in the dihedral angle between the two Pt coordination planes upon oxidation, from 21.9 (2) to 16.9 (3)°. We attribute the relatively strong one‐dimensional stack of dimers achieved in the Pt₂^II compound in part to the strong Pt^II⋯C(bpy) associations (bpy is 2,2′‐bipyridine) in the crystal structure [Pt⋯C = 3.416 (10) and 3.361 (12) Å].     

Observation of the Properties of a Single Unit of a Limited CDW Structure in a PtII/PtIV Host–Guest Binary System Based on a Square‐Shaped Complex

A macrocyclic tetranuclear platinum(II) complex [Pt(en)(4,4′‐bpy)]₄(NO₃)₈ ( 1 ?(NO₃)₈; en=ethylenediamine, 4,4′‐bpy=4,4′‐bipyridine) and a mononuclear platinum(IV) complex [Pt(en)₂Br₂]Br₂ ( 2 ?Br₂) formed two kinds of Pt^II/Pt^IV mixed valence assemblies when reacted: a discrete host–guest complex 1 ? 2 ?Br₁₀ ( 3 ) and an extended 1‐D zigzag sheet 1 ?( 2 )₃?Br₈(NO₃)₆ ( 4 ). Single crystal X‐ray analysis showed that the dimensions of the assemblies could be stoichiometrically controlled. Resonance Raman spectra suggested the presence of an intervalence interaction, which is typically observed for quasi‐1‐D halogen‐bridged M^II/M^IV complexes. The intervalence interaction indicates the presence of an isolated {Pt^II???X? Pt^IV? X???Pt^II} moiety in the structure of 4 . On the basis of electronic spectra and polarized reflectance measurements, we conclude that 4 exhibits intervalence charge transfer (IVCT) bands. A Kramers–Kronig transformation was carried out to obtain an optical conductivity spectrum, and two sub‐bands corresponding to slightly different Pt^II–Pt^IV distances were observed.     

Structure and Bonding of the Mixed‐Valent Platinum Trihalides,PtCl3 and PtBr3

The isotypical crystal structures of the mixed valent trihalides PtCl₃ and PtBr₃ were redetermined by single crystal methods (space group R3¯; trigonal setting; PtCl₃: a = 21.213Å, c = 8.600Å, c/a = 0.4054; Z = 36; 1719 hkl; R = 0.035; PtBr₃: a = 22.318Å, c = 9.034Å; c/a = 0.4048; Z = 36; 1606 hkl; R = 0.027). A cubic closest packing of X^— anions forms the basis of an optimized arrangement of cuboctahedrally [Pt₆X₁₂] cluster molecules with Pt^II and enantiomers of helical chains of edge‐condensed [PtX₂X_4/2] octahedra with Pt^IV in cis‐Δ‐ and cis‐Λ‐configuration, respectively. The bond lengths vary with the function of the X^— ligands (d¯(Pt^II—X) = 2.315 and 2.445Å; d¯(Pt^II—Pt^II) = 3.336 and 3.492Å; d(Pt^IV—X) = 2.286 — 2.417Å and 2.437 — 2.563Å). The Pt^II atoms are shifted outwards the X₁₂ cuboctahedra by 0.045Å and 0.024Å, respectively. The symmetry governed Periodic Nodal Surface, PNS, perfectly separates the regions of different valencies. Quantum chemical calculations exclude the possible additional interactions between Pt^II and one of the exo‐ligands of Pt^IV.     

Structural and Oxidation State Alternatives in Platinum and Palladium Complexes of a Redox-Active Amidinato Ligand

Reaction of [Pt(DMSO)₂Cl₂] or [Pd(MeCN)₂Cl₂] with the electron-rich LH=N,N’-bis(4-dimethylaminophenyl)ethanimidamide yielded mononuclear [PtL₂] ( 1 ) but dinuclear [Pd₂L₄] ( 2 ), a paddle-wheel complex. The neutral compounds were characterized through experiments (crystal structures, electrochemistry, UV-vis-NIR spectroscopy, magnetic resonance) and TD-DFT calculations as metal(II) species with noninnocent ligands L⁻. The reversibly accessible cations [PtL₂]⁺ and [Pd₂L₄]⁺ were also studied, the latter as [Pd₂L₄][B{3,5-(CF₃)₂C₆H₃}₄] single crystals. Experimental and computational investigations were directed at the elucidation of the electronic structures, establishing the correct oxidation states within the alternatives [Pt^II(L⁻)₂] or [Pt^.(L )₂], [Pt^II(L^0.5−)₂]⁺ or [Pt^III(L⁻)₂]⁺, [(Pd^II)₂(μ-L⁻)₄] or [(Pd^1.5)₂(μ-L^0.75−)₄], and [(Pd^2.5)₂(μ-L⁻)₄]⁺ or [(Pd^II)₂(μ-L^0.75−)₄]⁺. In each case, the first alternative was shown to be most appropriate. Remarkable results include the preference of platinum for mononuclear planar [PtL₂] with an N-Pt-N bite angle of 62.8(2)° in contrast to [Pd₂L₄], and the dimetal (Pd₂⁴⁺→Pd₂⁵⁺) instead of ligand (L⁻→L ) oxidation of the dinuclear palladium compound.     

Platinum‐Containing Polyoxometalates: syn‐ and anti‐[PtII2(α‐PW11O39)2]10− and Formation of the Metal–Metal‐Bonded di‐PtIII Derivatives

The first examples of dimeric, di‐Pt^II‐containing heteropolytungstates are reported. The two isomeric di‐platinum(II)‐containing 22‐tungsto‐2‐phosphates [anti‐Pt^II₂(α‐PW₁₁O₃₉)₂]^10? ( 1 a ) and [syn‐Pt^II₂(α‐PW₁₁O₃₉)₂]^10? ( 2 a ) were synthesized in aqueous pH 3.5 medium using one‐pot procedures. Polyanions 1 a and 2 a contain a core comprising two face‐on PtO₄ units, with a Pt???Pt distance of 2.9–3 Å. Both polyanions were investigated by single‐crystal XRD, IR, TGA, UV/Vis, ³¹P NMR, ESI‐MS, CID‐MS/MS, electrochemistry, and DFT. On the basis of DFT and electrochemistry, we demonstrated that the {Pt₂^II} moiety in 1 a and 2 a can undergo fully reversible two‐electron oxidation to {Pt₂^III}, accompanied by formation of a single Pt?Pt bond. Hence we have discovered the novel subclass of Pt^III‐containing heteropolytungstates.     

Unusual Metal–Metal Bonding in a Dinuclear Pt–Au Complex: Snapshot of a Transmetalation Process

The dinuclear Pt–Au complex [(CNC)(PPh₃)Pt Au(PPh₃)](ClO₄) ( 2 ) (CNC=2,6‐diphenylpyridinate) was prepared. Its crystal structure shows a rare metal–metal bonding situation, with very short Pt–Au and Au–C_ipso(CNC) distances and dissimilar Pt–C_ipso(CNC) bonds. Multinuclear NMR spectra of 2 show the persistence of the Pt–Au bond in solution and the occurrence of unusual fluxional behavior involving the [Pt^II] and [Au^I] metal fragments. The [Pt^II]??? [Au^I] interaction has been thoroughly studied by means of DFT calculations. The observed bonding situation in 2 can be regarded as a model for an intermediate in a transmetalation process.     

The synthesis,characterisation and crystal structure of [Pt3(PPh3)2(CNC6H3Me2)6](PF6)2; a linear trinuclear cluster of platinum

[Pt₂(PPh₃)₂(CN-xylyl)₄]²⁺ (CN-xylyl = 2,6-dimethylphenyl isocyanide) and [Pt₃(PPh₃)₂(CN-xylyl)₆]²⁺ have been synthesized by reaction of [Pt(PPh₃)₂(C₂H₄)] with either [Pt(PPh₃)₂Cl₂] and CN-xylyl or [Pt(CN-xylyl)₄]²⁺. The products have been characterised by ³¹P{¹H} and ¹⁹⁵Pt{¹H} NMR spectroscopy, and a single crystal X-ray diffraction study of the trinuclear compound has demonstrated that the skeletal atoms are linear.     

Darstellung von trans-[Pt(ox)2X2]2− (X = Cl,Br, I,SCN, OH) durch oxydative Addition an [Pt(ox)2]2− in organischen Solventien

Preparation of trans-[Pt(ox)₂X₂]^2? (X = Cl, Br, I, SCN, OH) by Oxidative Addition to [Pt(ox)₂]^2? in Organic Solvents After extraction of [Pt(ox)₂]^2? with long-chain alkyl-ammonium ions into organic solvents the new Pt^IV complexes trans-[Pt(ox)₂X₂]^2?, X = Cl, Br, I, SCN, OH, are formed directly by oxidative addition. In nonpolar solvents the bulky organic cations prevent the formation of compounds with columnar structure which by partial oxidation in aqueous solution are formed immediately. The IR and Ra spectra of the stable anhydrous (TBA) salts are assigned according to point group D_2h. A characteristical dependence of the C?O, C? O, and Pt? O stretching modes in response to the oxidation state of the central ion is observed. There is vibrational fine structure in the absorption spectrum of [Pt(ox)₂]^2? measured at 10 K with long progressions by coupling of d—d transitions with v_s(Pt? O) and v_s(C?O). The characteristical feature in the UV/VIS spectra of the Pt^IV complexes is caused by intensive π(O, X) ← e_g(Pt) CT transitions.     

Moderating the nucleophilicity of the sulfide ligands in the dinuclear {Pt2S2} metalloligand system using triphenylarsine

Reaction of cis-[PtCl₂(AsPh₃)₂] with excess sodium sulfide in benzene gave the triphenylarsine analogue of the well-known metalloligand [Pt₂(μ-S)₂(PPh₃)₄] as an orange solid.The compound was characterised by detailed mass spectrometry studies, and by conversion to various alkylated and metallated derivatives.The sulfide ligands in [Pt₂(μ-S)₂(AsPh₃)₄] are less basic than the triphenylphosphine analogue, and the complex gives a relatively weak [M+H]⁺ ion in the positive-ion electrospray (ESI) mass spectrum, compared with the phosphine analogue.Methylation of an equimolar mixture of [Pt₂(μ-S)₂(PPh₃)₄] and [Pt₂(μ-S)₂(AsPh₃)₄] with MeI gave the species [Pt₂(μ-S)(μ-SMe)(AsPh₃)₄]⁺ and [Pt₂(μ-SMe)₂(PPh₃)₃I]⁺, indicating a reduced tendency for the sulfide of [Pt₂(μ-S)(μ-SMe)(AsPh₃)₄]⁺ to undergo alkylation.The lability of the arsine ligands is confirmed by the reaction of an equimolar mixture of [Pt₂(μ-S)₂(PPh₃)₄] and [Pt₂(μ-S)₂(AsPh₃)₄] with n-butyl chloride, giving [Pt₂(μ-S)(μ-SBu)(EPh₃)₄]⁺ (E = P, As), which with Me₂SO₄ gave a mixture of [Pt₂(μ-SMe)(μ-SBu)(PPh₃)₄]²⁺ and [Pt₂(μ-SMe)(μ-SBu)(AsPh₃)₃Cl]⁺.Reactivity towards 1,2-dichloroethane follows a similar pattern.The formation and ESI MS detection of mixed phosphine-arsine {Pt₂S₂} species of the type[Pt₂(μ-S)₂(AsPh₃)_n(PPh₃)_4−n] is also discussed. Coordination chemistry of [Pt₂(μ-S)₂(AsPh₃)₄] towards a range of metal-chloride substrates, forming sulfide-bridged trinuclear aggregates, has also been probed using ESI MS, and found to be similar to the phosphine analogue. The X-ray crystal structure of [Pt₂(μ-S)₂(AsPh₃)₄Pt(cod)](PF₆)₂ (cod = 1,5-cyclo-octadiene) has been determined for comparison with the (previously reported) triphenylphosphine analogue. ESI MS is a powerful tool in exploring the chemistry of this system; in some cases the derivatising agent p-bromobenzyl bromide is used to convert sparingly soluble and/or poorly ionising {Pt₂S₂} species into soluble, charged derivatives for MS analysis.     

Selective Detection of Methomyl Pesticide by a Catalytic Chemosensing Assay

The catalytic chemosensing assay (CCA), a new indicator displacement assay, was developed for selective detection of methomyl, a highly toxic pesticide. Trimetallic complex {[Fe^II(dmbpy)(CN)₄]-[Pt^II(DMSO)Cl]₂-[Ru^II(bpy)₂(CN)₂]} ( 1 ; dmbpy=4,4′-dimethyl-2,2′-bipyridine, bpy=2,2′-bipyridine) was synthesized as a task-specific catalyst to initially reduce and degrade methomyl to CH₃SH/CH₃NH₂/CH₃CN/CO₂. The thus-produced CH₃SH interacts with the trimetallic complex to displace the cis-[Ru^II(bpy)₂(CN)₂] luminophore for monitoring. Other pesticides, including organophosphates and similar carbamate pesticides, remained intact under the same catalytic conditions; a selective sensing signal is only activated when 1 recognizes methomyl. Furthermore, 1 can be applied to detect methomyl in real water samples. In the luminescent mode of the assay, the method detection limit (MDL) of 1 for methomyl (LD₅₀=17 mg kg⁻¹) was 1.12 mg L⁻¹.     

Kinetics and catalysis by NaY entrapped Pt carbonyl clusters in the CO+NO reaction

[Pt₁₂(CO)₂₄]^2–/NaY and [Pt₉(CO)₁₈]^2–/NaY exhibited much higher activities in the CO+NO reaction at 473 K compared with Pt/Al₂O₃. Kinetic study andin-situ FTIR results suggest that NO adsorption is the rate-limiting step in the CO+NO reaction on intrazeolite Pt carbonyl clusters.     

"Directed" assembly of metallacalix[n]arenes with pyrimidine nucleobase ligands of low symmetry: interchanging metals in mixed-metal metallacalix[4]arenes and incorporating additional metals at the exocyclic groups

The pyrimidine (pym) nucleobase cytosine (H₂C) forms cyclic ring structures (“metallacalix[n]arenes”) when treated with square‐planar cis‐a₂M^II entities (M=Pt, Pd; a=NH₃ or a₂=diamine). The number of possible linkage isomers for a given n and the number of possible rotamers can be substantially reduced if a “directed” approach is pursued. Hence, two cytosine ligands are bonded in a defined way to a kinetically robust platinum corner stone. In the accompanying paper (Part I: A. Khutia, P. J. Sanz Miguel, B. Lippert, Chem. Eur. J. 2010 , 17, DOI: 10.1002/chem.2010002722) we have demonstrated this principle by allowing cis‐[Pta₂(H₂C‐N3)₂]²⁺ to react with (en)Pd^II to give cycles of (N1,N3 ? N3,N1?)_x (with x=2 or 3; ? represents Pt^II and ? represents Pd^II). In an extension of this work we have now prepared cis‐[Pta₂(HC‐N1)₂] ( 1 ; HC=monoanion of cytosine) and treated it with (bpy)Pd^II (bpy=2,2′‐bipyridine) to give the Pt₂Pd₂ cycle cis‐[{Pt(NH₃)₂(N1‐HC‐N3)₂Pd(bpy)}₂](NO₃)₄ ? 13H₂O ( 5 ) with the coordination sites of the metals inverted; hence, platinum is bonded to N1 and palladium is bonded to N3 sites. Again, not only the expected single linkage isomer is formed, but at the same time the solid‐state structure and ¹H NMR spectroscopy reveal the preferential occurrence of a single rotamer (1,3‐alternate). The addition of (bpy)Pd^II to 5 led to the formation of Pd₆Pt₂ complex 6 in which the exocyclic N4H₂ groups of the cytosine ligands have undergone deprotonation and chelate four more (bpy)Pd^II entities through the O2 and N4H sites. With a large excess of (bpy)Pd^II over 5 (4:1), cis‐(NH₃)₂Pt^II is eventually substituted by (bpy)Pd^II to give the Pd₈ complex 7 . In both 6 and 7 stacks of three (bpy)Pd^II entities occur. The linkage isomer of 5 , cis‐[{Pt(NH₃)₂(N3‐HC‐N1)₂Pd(bpy)}₂](NO₃)₄ ? 9H₂O ( 8 ), has been structurally characterized and the two complexes compared. The acid/base properties of cis‐[Pt(NH₃)₂(H₂C‐N1)₂] ( 1 ) have been determined and compared with those of the corresponding N3 isomer. The complexation of AgCl by 1 is reported.     

Electrochemistry of the two-dimensional heteronuclear [Fe3Pt3(CO)15] n clusters (n=2-, 1-, 0): MO treatment of the skeletal adjustments in 86-84e − congeners

Electrochemical studies show that it is possible to move step-wise and reversibly between the redox congeners of the series [Fe₃Pt₃(CO)₁₅] ⁿ ,n=2-/1-/0. By contrast, a multielectron reduction of the dianion leads to an irreversible demolition of the species. When [Fe₃Pt₃(CO)₁₅]^2– is treated with one or two equimolar amounts of the oxidant [Fe(C₅H₅)₂]⁺, the oxidized species (n=1- andn=0) can be also obtained. It can be established or extrapolated from the already known structures of the dianion and the monoanion that the successive oxidations strengthen the inner Pt-Pt linkages of the overall quasiplanar Fe₃Pt₃ skeleton. MO analysis, by establishing the antibonding nature of the frontier level from which the electrons are added or subtracted, allows the correlation of the bonding features of the inner Pt₃ skeleton with the redox propensities of the system.     

High nuclearity PtRh carbonyl clusters. Synthesis and X-ray characterization of the [Pt2Rh9(CO)22]3− trianion

The new mixed PtRh cluster trianion [Pt₂Rh₉(CO)₂₂]^3? has been isolated as a minor product of the pyrolysis of [PtRh₅(CO)₁₅]^?, and has been characterized by X-ray diffraction. The metal skeleton, which has ideal D_3h symmetry, consists of three face-to-face condensed octahedra, as previously found in the isoelectronic species [Rh₁₁CO)₂₃]^3?, with the Pt atoms on the three-fold axis, in the positions of maximum MM connectivity.