Analogous Platinum Research Articles

Hemilability and structural considerations in complexes of platinum(II) comprising bis(diphenylphosphanyl)methane monoxide, monosulfide, and monoselenide.

The structure of a platinum(II) complex containing (R)-(dimethylamino)ethylnapthyl and bis(diphenylphosphanyl)methane monosulfide ligands, namely, {(R)-1-[1-(dimethylamino)ethyl]napthyl-κ2N,C2}[(diphenylphosphanylmethyl)diphenylphosphine sulfide-κ2P,S]platinum(II) hexafluoridoantimonate dichloromethane monosolvate, [Pt(C14H16N)(C25H22P2S)][SbF6]·CH2Cl2, was determined. The structural features are compared with analogous platinum bis(diphenylphosphanyl)methane monoxide [dppm(O)] and bis(diphenylphosphanyl)methane monoselenide [dppm(Se)] complexes in relation to their potential hemilability and stereochemical nonrigidity.

Carbazolyl-bis(triazole) and Carbazolyl-bis(tetrazole) Complexes of Palladium(II) and Platinum(II)

The synthesis of several carbazole-bis(triazole) (CzTrR ) and carbazole-bis(tetrazole) (CzTR ) ligands (5a–d and 6a–d, respectively, where R=Me (a), i –Pr (b), Bz (c) and CH2-2,4,6-C6H2Me3 (d)) is reported. Reaction of these ligands with PdCl2 in refluxing acetonitrile affords the complete series of square planar complexes, Pd(CzTrR)Cl (7a–d) and Pd(CzTR)Cl (8a–d). The analogous platinum complexes are prepared by deprotonation of ligand carbazole nitrogen under nitrogen followed by reaction with Pt(COD)Cl2 to give Pt(CzTrR)Cl (9b, 9d) and Pt(CzTR)Cl (10b, 10d). The X-ray structure of several ligands (5b, 5c, 6c) and their metal complexes (8b, 8d, 9b) are reported. Complexes 7–10d were examined by cyclic voltammetry and DFT calculations to shed light on their electronic structures. The Pd and Pt complexes of the same ligand (CzTr: 7d, 9d; CzT: 8d, 10d) showed very similar oxidation potentials suggesting the lowest oxidation is ligand based. In contrast, oxidations of the tetrazole complexes 7d and 9d were notably more difficult than the triazole complexes 8d and 10d. Both of these observations are supported by DFT calculations that indicate the HOMO is essentially carbazole π-bonding in character.

Inhibition of Type IV Secretion Activity and Growth of Helicobacter pylori by Cisplatin and Other Platinum Complexes.

Type IV secretion systems are protein secretion machineries that are frequently used by pathogenic bacteria to inject their virulence factors into target cells of their respective hosts. In the case of the human gastric pathogen Helicobacter pylori, the cytotoxin-associated gene (Cag) type IV secretion system is considered a major cause for severe disease, such as gastric cancer, and thus constitutes an attractive target for specific treatment options against H. pylori infections. Here, we have used a Cag type IV secretion reporter assay for screening a repurposing compound library for inhibitors targeting this system. We found that the antitumor agent cisplatin, a platinum coordination complex that kills target cells by formation of DNA crosslinks, is a potent inhibitor of the Cag type IV secretion system. Strikingly, we found that this inhibitory activity of cisplatin depends on a ligand exchange reaction which incorporates a solvent molecule (dimethylsulfoxide) into the complex, a modification which is known to be deleterious for DNA crosslinking, and for its anticancer activity. We extended our analysis to several analogous platinum complexes containing N-heterocyclic carbene, as well as DMSO or other ligands, and found varying inhibitory activities toward the Cag system which were not congruent with their DNA-binding properties, suggesting that protein interactions may cause the inhibitory effect. Inhibition experiments under varying conditions revealed effects on adherence and bacterial viability as well, and showed that the type IV secretion-inhibitory capacity of platinum complexes can be inactivated by sulfur-containing reagents and in complex bacterial growth media. Taken together, our results demonstrate DNA binding-independent inhibitory effects of cisplatin and other platinum complexes against different H. pylori processes including type IV secretion.

From a Diphosphanegermylene to Nickel, Palladium, and Platinum Complexes Containing Germyl PGeP Pincer Ligands.

The PGeP pincer-type germylene Ge(NCH2 PtBu2 )C6 H4 (1) has been used to prepare a family of group 10 metal complexes, namely, [MCl{κ3 P,Ge,P-GeCl(NCH2 PtBu2 )2 C6 H4 }] (M=Ni (2Ni ), Pd (2Pd ), Pt (2Pt )), featuring a chloridogermyl PGeP pincer ligand and a Cl-Ge-M-Cl bond sequence. Their reactivity is not initially centered on the metal atom but on their Ge atom. Complexes 2Ni and 2Pd easily led to the hydrolyzed products [Ni2 Cl2 {μ-(κ3 P,Ge,P-Ge(NCH2 PtBu2 )2 C6 H4 )2 O}], which features a Cl-Ni-Ge-O-Ge-Ni-Cl bond sequence, and [PdCl{κ3 P,Ge,P-Ge(OH)(NCH2 PtBu2 )2 C6 H4 }], which contains a hydroxidogermyl PGeP pincer ligand (2Pt is reluctant to undergo hydrolysis). Simple chloride exchange reactions led to the methoxidogermyl, methylgermyl, and phenylgermyl derivatives [MCl{κ3 P,Ge,P-GeR(NCH2 PtBu2 )2 C6 H4 }] (M=Pd, Pt; R=OMe, Me, Ph). Whereas the palladium complexes [PdCl{κ3 P,Ge,P-GeR(NCH2 PtBu2 )2 C6 H4 }] (R=Me, Ph) reacted with more MeLi or PhLi to give palladium black and GeR2 (NCH2 PtBu2 )2 C6 H4 (R=Me, Ph), similar reactions with the analogous platinum complexes afforded the transmetalation derivatives [PtR{κ3 P,Ge,P-GeR(NCH2 PtBu2 )2 C6 H4 }] (R=Me, Ph). The short length of the CH2 PtBu2 arms of the PGeP pincer ligands forces the metal atoms of all these complexes to be in a very distorted square-planar ligand environment. The reactivity results have been rationalized with theoretical calculations.

Group 10 Metal Benzene-1,2-dithiolate Derivatives in the Synthesis of Coordination Polymers Containing Potassium Countercations.

The use of theoretical calculations has allowed us to predict the coordination behavior of dithiolene [M(SC6H4S)2]2- (M = Ni, Pd, Pt) entities, giving rise to the first organometallic polymers {[K2(μ-H2O)2][Ni(SC6H4S)2]}n and {[K2(μ-H2O)2(thf)]2[K2(μ-H2O)2(thf)2][Pd3(SC6H4S)6]}n by one-pot reactions of the corresponding d10 metal salts, 1,2-benzenedithiolene, and KOH. The polymers are based on σ,π interactions between potassium atoms and [M(SC6H4S)2]2- (M = Ni, Pd) entities. In contrast, only σ interactions are observed when the analogous platinum derivative is used instead, yielding the coordination polymer {[K2(μ-thf)2][Pt(SC6H4S)2]}n.

Divergent reactivity of platinum(ii) and palladium(ii) methylperoxo complexes and the formation of an unusual hemi-aminal complex.

The 6,6''-diaminoterpyridine palladium(ii) methylperoxo complex eliminates methyl hydroperoxide and reacts with acetone to form a novel hemi-aminal palladium complex, whereas the analogous platinum(ii) complex generates formaldehyde and a platinum(ii) hydroxo complex.

Palladium(II) benzisothiazolinate (bit) complexes with amino-, acetylamino-, heterocyclic and phosphine co-ligands. Crystal structure of [Pd(bit)2(κ2-dppe)]·2EtOH

A series of square-planar palladium(II) benzisothiazolinate (bit) of the general type [Pd(bit)2L2] have been prepared and characterized by analytical and spectroscopic methods. Two synthetic routes have been employed, namely reactions of [Pd(bit)2]·H2O with two equivalents of ligands (L=amine, amide, phosphine) or nucleophile displacement of chloride by benzisothiazolinate starting from trans-[PdCl2L2]. Both routes afford the new complexes in good yields as easily isolated, air and moisture stable, colored solids. The precursor, [Pd(bit)2]·H2O, is itself prepared in high yields upon reaction of Na[bit] with Na2[PdCl4] in methanol and the analogous platinum complex, [Pt(bit)2]·H2O, is similarly prepared from K2[PtCl4]. It is not clear if these species are mono- or dimeric, and formulation as [M2(μ-bit)4(H2O)2] with the four benzisothiazolinate spanning the metal–metal vector and possibly binding through coordination of nitrogen and oxygen is suggested. Diphosphine adducts, cis-[Pd(bit)2{κ2-Ph2P(CH2)nPPh2}] (n=1–4) can be prepared both upon addition of the diphosphine to [Pd(bit)2]·H2O and from reactions of cis-[PdCl2{κ2-Ph2P(CH2)nPPh2}] with two equivalents of Na[bit]. A crystal structure of cis-[Pd(bit)2(κ2-dppe)] reveals that the benzisothiazolinate ligands are bonded in a monodentate fashion through nitrogen and this binding mode is proposed for all [Pd(bit)2L2] and [Pd(bit)2L] complexes. With dppb (n=4) a second product is seen by NMR spectroscopy being proposed to be the part-substituted complex cis-[PdCl(bit)(κ2-dppb)], while with dppm (n=1) two further products are seen spectroscopically, proposed as trans-[Pd(bit)2(κ1-dppm)2] and (more tenuously) [Pd2(bit)4(dppm)2]. The former is also prepared in good yields from reaction of [Pd(κ2-dppm)2]Cl2 with Na[bit]. These studies show that palladium benzisothiazolinate are easily accessed and show good air and moisture stability.

Luminescent metallomesogens based on platinum complex containing triphenylene unit

To explore the influence of mesogenic unit on the liquid crystals and luminescence properties of metal complex, two novel triphenylene-based platinum complexes of TppyPtacac and TppyPtPhacac featuring donor–acceptor framework have been designed and synthesized, in which Tppy is triphenylene–phenylpyridine skeleton and acac/Phacac is pentane-2,4-dione derivative. Differential scanning calorimetry (DSC), polarized optical microscopy (POM) and X-ray diffraction (XRD) techniques demonstrate the complex TppyPtPhacac shows a column mesophase in the region of 55–110 °C. Both platinum complexes exhibit intense emission at about 550 nm in CH2Cl2 solution. Compared to the analogous platinum complexes without triphenylene unit, TppyPtacac and TppyPtPhacac display a remarkable red-shifted emission profiles (ca. 50 nm) due to strong intramolecular charge transfer. Furthermore, the hole mobilities up to 2.5×10−4 cm2 V−1 s−1 and 2.99×10−5 cm2 V−1 s−1 are achieved for the annealed film of TppyPtacac and TppyPtPhacac, respectively, which is one of the highest hole mobility with respect to cyclometalated platinum complexes.

Indole-7-carbaldehyde thiosemicarbazone as a flexidentate ligand toward ZnII, CdII, PdII and PtII ions: cytotoxic and apoptosis-inducing properties of the PtII complex

A new thiosemicarbazone (LH2) derived from indole-7-carbaldehyde was synthesized and reacted with Zn(II), Cd(II), Pd(II) and Pt(II) salts. The reactions with zinc and cadmium salts in 2 : 1 (ligand-metal) molar ratio afforded complexes of the type MX2(LH2)2, (X = Cl, Br or OAc), in which the thiosemicarbazone acts as a neutral S-monodentate ligand. In the presence of potassium hydroxide, the reaction of LH2 with ZnBr2 resulted in deprotonation of the thiosemicarbazone at the hydrazine and indole nitrogens to form Zn(L)(CH3OH). The reaction of LH2 with K2PdCl4 in the presence of triethylamine, afforded Pd(L)(LH2) which contains two thiosemicarbazone ligands: one being dianionic N,N,S-tridentate while the other one is neutral S-monodentate. When PdCl2(PPh3)2 was used as the Pd(II) ion source, Pd(L)(PPh3) was obtained. In a similar manner, the analogous platinum complex, Pt(L)(PPh3), was synthesized. The thiosemicarbazone in the latter two complexes behaves in a dianionic N,N,S-tridentate fashion. The platinum complex was found to have significant cytotoxicity toward four cancer cells lines, namely MDA-MB-231, MCF-7, HT-29, and HCT-116 but not toward the normal liver WRL-68 cell line. The apoptosis-inducing properties of the Pt complex was explored through fluorescence microscopy visualization, DNA fragmentation analysis and propidium iodide flow cytometry.

Influence of Equatorial and Axial Carboxylato Ligands on the Kinetic Inertness of Platinum(IV) Complexes in the Presence of Ascorbate and Cysteine and within DLD-1 Cancer Cells

The rapid and premature reduction of platinum(IV) complexes in vivo is a significant impediment to these complexes being successfully employed as anticancer prodrugs. This study investigates the influence of the platinum(IV) coordination sphere on the ease of reduction of the platinum center in various biological contexts. In the presence of the biological reductants, ascorbate and cysteine, platinum(IV) complexes with dicarboxylato equatorial ligands were observed to exhibit lower reduction potentials and slower reduction rates than analogous platinum(IV) complexes with dichlorido equatorial ligands. Diaminetetracarboxylatoplatinum(IV) complexes exhibited unusually long half-lives in the presence of excess reductants; however, the complexes exhibited moderate potency in vitro, indicative of rapid reduction within the intracellular environment. By use of XANES spectroscopy, trans-[Pt(OAc)2(ox)(en)] and trans-[PtCl2(OAc)2(en)] were observed to be reduced at a similar rate within DLD-1 cancer cells. This large variability in kinetic inertness of diaminetetracarboxylatoplatinum(IV) complexes in different biological contexts has significant implications for the design of platinum(IV) prodrugs.

Palladium(II) and Platinum(II) Compounds of 1,1′-Bis(phosphino)metallocene (M = Fe, Ru) Ligands with Metal–Metal Interactions

The reaction of [Pd(dtbpf)Cl2] (dtbpf = 1,1′-bis(di-tert-butylphosphino)ferrocene) with a chemical oxidant led unexpectedly to the formation of [Pd(dtbpf)Cl]+. Further study found that a variety of reagents could be used to abstract a chloride ligand from [Pd(dtbpf)Cl2] to yield [Pd(dtbpf)Cl]+. The solid-state structure suggests the formation of an Fe–Pd interaction. The presence of the bulky tert-butyl groups is essential, as similar reactions with [Pd(PP)Cl2] (PP = other 1,1′-bis(phosphino)ferrocene ligands) results in the formation of [Pd(PP)(μ-Cl)]22+. The analogous platinum compounds have also been investigated and appear to behave in a similar manner. Similar compounds of the type [M′(PP)(PR3)]2+ (M′ = Pd, Pt, R = Ph, Me) have been prepared, and a metal–metal interaction has also been observed. Steric and electronic effects dictate the formation of these compounds. X-ray crystal structures were obtained for eight of these compounds and were used as the basis for a computational analysis of the metal...

Novel clioquinol and its analogous platinum complexes: importance, role of the halogen substitution and the hydroxyl group of the ligand

In this communication, we present the synthesis of new platinum complexes based on hydroxyquinoline ligands. We demonstrate the importance and the role of the halogen substitution as well as the chelation, which are essential structural characteristics for finding good cytotoxicities.

Platinum(ii) and platinum(iv) complexes stabilized by abnormal/mesoionic C4-bound dicarbenes

Platinum(II) complexes comprising abnormal diimidazolylidene ligands were synthesized from cis-PtMe(2)(DMSO)(2) using microwave-assisted double C-H bond activation. NMR analysis revealed an unusual solvolysis process, induced by coordinating solvents such as DMSO and MeCN, which has not been observed in related normal dicarbene complexes. NMR and IR spectroscopy and crystallographic analysis of the mono-substituted DMSO complex indicate a sulfur-bonding of the DMSO ligand to the platinum(II) center. Analysis of the DMSO exchange kinetics provided for the first time a quantitative measure of the trans effect of abnormal carbene ligands. The kinetic exchange rate in these bidentate abnormal dicarbene complexes is 0.050(±2) s(-1) and thus similar to analogous platinum(II) complexes containing phenylpyridine, yet significantly slower than that induced by pyridylidene pyridine. Reaction of the dicarbene platinum(II) complexes with PhICl(2), Br(2) and I(2) afforded the corresponding platinum(IV) complexes. Linkage isomerism of the Pt(IV)-bound DMSO was observed when the bromination reaction was performed in DMSO solution. Moreover, solvolysis was less pronounced in the platinum(IV) complexes than in the corresponding platinum(II) analogues.

Gold(I) Analogues of a Platinum−Acridine Antitumor Agent Are Only Moderately Cytotoxic but Show Potent Activity against Mycobacterium tuberculosis

Cationic gold(I) complexes containing 1-[2-(acridin-9-ylamino)ethyl]-1,3-dimethylthiourea (1), [AuL(1)](n+) (where L is Cl(-), Br(-), SCN(-), PEt(3), PPh(3), or 1), derived from a class of analogous platinum(II) antitumor agents, have been synthesized. Unlike platinum, gold does not form permanent adducts with DNA, and its complexes are 2 orders of magnitude less cytotoxic in non-small-cell lung cancer cells than the most active platinum-based agent. Instead, several gold analogues show submicromolar and selective antimicrobial activity against Mycobacterium tuberculosis.

Metal Effects on the Asymmetric Cycloaddition Reaction between 3,4-Dimethyl-1-phenylarsole and Diphenylvinylphosphine Oxide

The organopalladium complex containing ortho-metalated (S)-[1-(dimethylamino)ethyl]naphthalene as the chiral auxiliary has been used successfully to promote the asymmetric cycloaddition reaction between 3,4-dimethyl-1-phenylarsole and diphenylvinylphosphine oxide in high stereoselectivity (only one isomer). However, the neutral dichloro palladium complex obtained upon removal of the auxiliary is very unstable and instantly decomposed to produce the arsenic elimination reaction product (3,4-dimethyl-2,4-cyclohexadienyl)diphenylphosphine oxide. However when the same reaction was promoted by the analogous platinum complex, only one stereoisomer was again obtained, but the resulting dichloro platinum complex is very stable in the solid state as well as in solution and coordinates to the platinum center as a As−O bidentate ligand, as confirmed by 1H NMR and single-crystal X-ray analysis. The enantiomerically pure As P═O hetero-bidentate ligand could be readily liberated from the dichloro platinum complex as a...

Long-Range Through-Bond Heteronuclear Communication in Platinum Complexes

Four analogous platinum stilbene- and stilbazole-based complexes exhibit unusual long-range heteronuclear spin-spin coupling in solution. Single crystal analysis and NMR experiments show that the (19)F, (31)P, and (195)Pt nuclei communicate over large distances (0.9-1.3 nm) through bond rather than through space. Spin-spin couplings between (195)Pt and (19)F over seven bonds and between (31)P and (19)F over eight bonds are observed with (7)J(PtF) = 2.9 Hz and (8)J(PF) = 11.8 Hz. Remarkably, a very large spin coupling between (195)Pt and (19)F over six bonds ((6)J(PtF) = 40.1 Hz) is also observed in a structurally related pyridinium complex. Experimental and gNMR (version 5.0) simulated (19)F{(1)H}, (31)P{(1)H}, and (195)Pt{(1)H} spectra of the complexes reveal a three-spin AMY system (A = (31)P, M = (31)P, Y = (19)F) or a five-spin AMY(3) flanked by a four-spin AMXY or a six-spin AMXY(3) system (X = (195)Pt), respectively. Density functional theory calculations at the PBE0/SDD level of theory show a pi-conjugated metal-ligand network, which may contribute to the experimentally observed spin-spin interactions.

Platinum-based complexes of bioactive 3-(5-nitrofuryl)acroleine thiosemicarbazones showing anti-Trypanosoma cruzi activity

Eight new platinum(II) complexes with 3-(5-nitrofuryl)acroleine thiosemicarbazones showing anti-trypanosomal activity were synthesized, characterized and in vitro evaluated. Most of the complexes showed IC(50) values in the micromolar range against two different strains of Trypanosoma cruzi, causative agent of Chagas disease (American Trypanosomiasis). In addition, most of the newly developed complexes, together with the analogous platinum 5-nitrofuraldehyde containing thiosemicarbazones previously reported, resulted more active than the reference trypanocidal drug nifurtimox on the infective trypomastigote form of the parasite. Their capacity to produce free radicals that could lead to parasite death was evaluated by ESR experiments in the parasite and by respiration measurements. Compounds were tested for their DNA interaction ability. Results showed that some of the compounds could act as dual inhibitors in the parasite, through production of toxic free radicals and interaction with DNA. All the results were compared with those previously reported for the free ligands, the analogous palladium(II) compounds and the previously reported series of platinum(II) compounds.

Electrospray mass spectrometric studies of a potential antitumor drug and its analogous platinum(II) and platinum(IV) complexes with the ethylenediamine-N,N′-di-3-propanoato ligand and its dibutyl ester

The electrospray mass spectrometric (ESI–MS) behavior of the complexes trans-dichloro(ethylenediamine-N,N′-di-3-propionato)platinum(IV), trans-dibromo(ethylenediamine-N,N′-di-3-propionato)platinum(IV), dichloro(ethylenediamine-N,N′-di-3-propionic acid)platinum(II), tetrachloro(O,O′-di-n-butyl-ethylenediamine-N,N′-di-3-propanoate)platinum(IV), chlorotribromo(O,O′-di-n-butyl-ethylenediamine-N,N′-di-3-propanoate)platinum(IV), and dichloro(O,O′-di-n-butyl-ethylenediamine-N,N′-di-3-propanoate)platinum(II), with the formulae trans-[PtCl2(eddp)] (1), trans-[PtBr2(eddp)] (2), [PtCl2(H2eddp)] (3), [PtCl4(Bu2eddp)] (4), [PtBr3Cl(Bu2eddp)] (5), and [PtCl2(Bu2eddp)]·H2O (6), is reported. The deprotonated molecular ions or halide adducts are usually observed. ESI–MS data demonstrate the usefulness of the method for efficient characterization of metal complexes in solution.

Fluxional Behavior of Platinum(0) Complexes: Intra vs Intermolecular Reaction Pathways

The fluxional behavior of two analogous platinum complexes has been studied in solution by NMR spectroscopy to elucidate the reaction mechanism and to determine the activation parameters. This includes variable temperature NMR spectroscopy, 2D (1)H- (1)H exchange spectroscopy, and spin saturation transfer measurements. A platinum moiety, Pt(PEt 3) 2, translocates between two carbon-carbon double bonds of two vinylpyridine moieties bridged by an arene (i.e., phenyl, anthracene) at elevated temperatures. Magnetization transfer NMR experiments in the presence of free ligands unambiguously revealed an intramolecular pathway for the "phenyl" system. An intermolecular pathway is proposed for the "anthracene" complex.

Alternativ-Liganden XXXVIII. [1] Neue Versuche zur Synthese von Pd(0)- und Pt(0)-Komplexen des Tripod-Phosphanliganden FSi(CH2CH2PMe2)3 / Alternative Ligands XXXVIII. [1] Further Attempts to Synthesize Pd(0) and Pt(0) Complexes with the Tripod Phosphane Ligand FSi(CH2CH2PMe2)3

The tripod phosphane ligand FSi(CH2CH2PMe2)3 (1) has been prepared again and attempts to generate F3CSi(CH2CH2PMe2)3 (2) were undertaken for the preparation of transition metal cage compounds of the type A(CCP)3M or A(CCP)3M-L (A = FSi, F3CSi). The photochemical addition of dimethylphosphane to trifluoromethyl-trivinylsilane, however, gave 1 instead of the expected CF3Sitripod ligand 2, obviously due to difluorocarbene elimination. 1 was used to prepare the chromium carbonyl derivative (CO)3Cr[(Me2PCH2CH2)3SiF] (3) from Cr(CO)3CHT, and 3 was characterized by NMR and IR spectroscopy. The novel complex FSi(CH2CH2PMe2)3Pd (4) and its PPh3 derivative [FSi(CH2CH2PMe2)3Pd]PPh3 (5) have been obtained by reacting 1 with Pd(PPh3)4 and were characterized by NMR (4) and X-ray diffraction (5). The data prove the expected Pd→Si interaction by characteristic coordination shifts and a Pd-Si distance of 3.875 Å which is smaller than the Ni-Si distance in the corresponding nickel compound (3.92 Å ). The preparation of the analogous platinum complex from the precursors Pt(PPh3)4, Pt(C7H10)3, or (Ph3P)2Pt(η2-C2H4) failed, whereas the reaction of 1 with Pt(PEt3)4 was successful, but surprisingly led to the trinuclear complex [FSi(CH2CH2PMe2)3Pt]3(PMe2CH2CH2)3SiF (6) with three cages of type 4 and an additional ligand 1 as a bridging unit. Complex 6 was isolated and characterized spectroscopically. Quantum chemical calculations have been used to elucidate the coordination geometry expected for 4, 5 and the corresponding platinum cage 4′ in 6. The calculations support the structure of 5 within the expected limitations of the experimental and theoretical methods and - in spite of the extremely soft coordination sphere of the studied cages - are in accord with the spectroscopic results.