Platinum(II) complexes with aryl tellurols and diaryl ditellurides: Syntheses and spectral investigations

Arytellurol complexes [PtCl(TeAr)(PPh₃)₂] (I) and [Pt(TeAr)₂(PPh₃)₂] (II) are readily obtained from cis-[PtCl₂(PPh)₃)₂] and NaTeAr (Ar = C₆H₅, 4-CH₃OC₆H₄ and 4-CH₃CH₂OC₆H₄) in ethanolbenzene at room temperature. ³¹P NMR spectra of (I) and (II) indicate their trans configuration in solution. Metathetical reactions between I (Ar = 4-CH₃OC₆H₄) and NaX (X = I, Br, SCN) occur in methanol to give [Pt(X)(TeC₆H₄OCH₃-4)(PPh₃)₂]. ¹H NMR shows that equimolar proportions of NaTeC₆H₅, NaTeC₆H₄OCH₂CH₃-4 and cis-[PtCl₂(PPh₃)₂] give a mixture of three complexes: II, Ar = C₆H₅; II, Ar = 4-CH₃CH₂OC₆H₄; and [Pt(TeC₆H₅)(TeC₆H₄OCH₂CH₃-4)(PPh₃)₂]. Polymeric complexes [PtCl(TeAr)]_n (III) and [Pt(TeAr)₂]_n (IV) result from reaction between K₂[PtCl₄] and NaTeAr in aqueaous ethanol. They react with excess of PPh₃ in CDCl₃ to yield monomeric complexes I and II respectively which were characterized in situ by ¹H and ³¹P NMR of the reaction mixtures. IR spectra indicate the presence of bridging chloride ligands in III. An alternating chloride and tellurol bridged chain structure for III and a tellurol bridged for IV have been proposed. Reaction between equimolar amounts of III and PPh₃ in dichloromethane yielded a tellurol bridged dimeric complex [PtCl(μ-TeAr)(PPh₃)]₂ (V) with terminal chloride ligand as suggested by IR study. Ethanolic solutions of diarylditellurides also react readily with an aqueous solution of K₂[PtCl₄] at 10 °C to give complexes for which the structure trans-[PtCl₂(ArTeTeAr)₂] (VI) is suggested from their elemental analyses, IR, Raman (in one case only), ¹H, ¹²⁵Te (in one case only), and ¹⁹⁵Pt NMR spectra and reactions with triphenylphosphine which liberated free ditellurides. At 40 °C or above the same ditellurides form polymeric complexes III with K₂[PtCl₄] in aquaeous ethanol.     

Bioreduction of platinum salts into nanoparticles: a mechanistic perspective

A mechanism for the bioreduction of H₂PtCl₆ and PtCl₂ into platinum nanoparticles by a hydrogenase enzyme from Fusarium oxysporum is proposed. Octahedral H₂PtCl₆ is too large to fit into the active region of the enzyme and, under conditions optimum for nanoparticle formation (pH 9, 65°C), undergoes a two-electron reduction to PtCl₂ on the molecular surface of the enzyme. This smaller molecule is transported through hydrophobic channels within the enzyme to the active region where, under conditions optimal for hydrogenase activity (pH 7.5, 38°C) it undergoes a second two-electron reduction to Pt(0). H₂PtCl₆ was unreactive at pH 7.5, 38°C; PtCl₂ was unreactive at pH 9, 65°C.     

Novel trans-platinum complexes of the histone deacetylase inhibitor valproic acid; synthesis, in vitro cytotoxicity and mutagenicity

The first examples of Pt complexes of the well known anti-epilepsy drug and histone deacetylase inhibitor, valproic acid (VPA), are reported. Reaction of the Pt(II) am(m)ine precursors trans-[PtCl₂(NH₃)(py)] and trans-[PtCl₂(py)₂] with silver nitrate and subsequently sodium valproate gave trans-[Pt(VPA_−1H)₂(NH₃)(py)] and trans-[Pt(VPA_−1H)₂(py)₂], respectively. The valproato ligands in both complexes are bound to the Pt(II) centres via the carboxylato functionality and in a monodentate manner. The X-ray crystal structure of trans-[Pt(VPA_−1H)₂(NH₃)(py)] is described. Replacement of the dichlorido ligands in trans-[PtCl₂(py)₂] and trans-[PtCl₂(NH₃)(py)] by valproato ligands (VPA_−1H) to yield trans-[Pt(VPA_−1H)₂(py)₂] and trans-[Pt(VPA_−1H)₂(NH₃)(py)] respectively, significantly enhanced cytotoxicity against A2780 (parental) and A2780 cisR (cisplatin resistant) ovarian cancer cells. The mutagenicity of trans-[Pt(VPA_−1H)₂(NH₃)(py)] and trans-[Pt(VPA_−1H)₂(py)₂] was determined using the Ames test and is also reported.     

Kinetics and mechanism for reduction of halo- and haloam(m)ine platinum(IV) complexes by l-ascorbate

Reduction of the model platinum(IV) complexes cis-[PtCl₄(NH₃)₂] (1), trans-[PtCl₄(NH₃)₂] (2), trans-[PtCl₂(en)₂]²⁺ (3), trans-[PtBr₂(NH₃)₄]²⁺ (4), [PtCl₆]²⁻ (5), and [PtBr₆]²⁻ (6) with l-ascorbic acid (H₂Asc) in 1.0 M aqueous medium at 25 °C in the region 1.75≤pH≤7.20 has been investigated using stopped-flow spectrophotometry. The redox reactions follow the rate law: −d[Pt(IV]/dt=k[H₂Asc]_tot[Pt(IV)] where k is a pH-dependent second-order rate constant and [H₂Asc]_tot, the total concentration of ascorbic acid. The pH-dependence of k is attributed to parallel reduction of Pt(IV) by the protolytic species HAsc⁻ and Asc²⁻. Analysis of the kinetics data reveals that the ascorbate anion Asc²⁻ is up to seven orders of magnitude more reactive than HAsc⁻ while H₂Asc is unreactive. Electron transfer from HAsc⁻/Asc²⁻ to the Pt(IV) compounds is suggested to take place by a mechanism involving a reductive attack on any one of the mutually trans-halide ligands by Asc²⁻ and/or HAsc⁻ forming a halide-bridged activated complex. The rapid reduction of these complexes supports the assumption that ascorbate Asc²⁻ might be an important reductant at physiological conditions for anticancer active Pt(IV) pro-drugs capable of undergoing reductive trans elimination. The parameters ΔH^≠ and ΔS^≠ for reduction of Pt(IV) with Asc²⁻ have been determined from the study of the temperature dependence of k.     

Mechanisms for acceleration of halide anation reactions of platinum(IV) complexes. REOA versus ligand assistance and platinum(II) catalysis Without central ion exchange

Chloride anation of trans-Pt(CN)₄ClOH₂⁻ has been studied with and without Pt(CN)₄²⁻ present at 25.0°C by use of stopped-flow and conventional spectrophotometry and a 1.00 M perchlorate medium. The rate law in the absence of Pt(CN)₄²⁻ is Rate=(p₁ + p₂ [H⁺] ) [Cl⁻]² [complex]/(1 + q [Cl₋]) with p₁=(3.0 ± 0.1) × 10⁻⁵ M⁻²s⁻¹, p₂=(3.6 ± 0.1) × 10⁻⁵ M⁻³ s⁻¹ and q=(0.62 ± 0.02) M⁻¹. It is compatible with a chloride assistance via an intermediate of the type Cl-Cl-Pt(CN)₄···OH₂²⁻, in which the reactivity of the aqua ligand is enhanced due to a partial reduction of the platinum. This mechanism of halide assistance is in principle the same as the modified reductive elimination oxidative addition (REOA) mechanism proposed by Poë, in which the intermediate is not split into free halogen, platinum(II) and water, and in which electron transfer not necessarily involves complete reduction to platinum(II). To avoid confusion with complete reductive eliminations, reactions without split of the intermediates are here termed halide-assisted reactions. The pH-dependence indicates acid catalysis via a protonated intermediate ClClPt(CN)₄···OH₃⁻.The Pt(CN)₄²⁻accelerated path has the rate law Rate=

[Cl-] [Pt(CN)₄²⁻] [complex] where k=(39.9±0.5) M⁻² s⁻¹ and K_a=(4.0±0.2)10⁻² M is the protolysis constant of trans-Pt(CN)₄ClOH²⁻.Reaction between PtCl₅OH₂⁻ and chloride is accelerated by Pt(CN)₄²⁻ and gives PtCl₆²⁻ as the reaction product. The rate law is Rate=k [Cl⁻] [Pt(CN)₄²⁻] [PtCl₅OH₂⁻] with k=(5.6 ± 0.2)10⁻³ M⁻² s⁻¹ at 35.0°C and for a 1.50 M perchlorate acid medium. The reaction takes place without central ion exchange. Alternative mechanisms with two consecutive central ion exchanges can be excluded. The role of Pt(CN)₄²⁻ in this reaction is very similar to that of the assisting halide in the halide assisted anations. [p ]Reaction between trans-Pt(CN)₄ClOH₂⁻ and PtCl₄²⁻ gives Pt(CN)₄²⁻ and PtCl₅OH₂⁻ as products and has the rate law Rate=k[PtCl₄²⁻] [trans-Pt(CN)₄ClOH₂⁻] with k=(3.32 ± 0.02) M⁻¹ s⁻¹ at 25 °C for a 1.00 M perchloric acid medium. The formation of an aqua complex as the primary reaction product and the rate independent of [Cl⁻] shows that formation of a bridged intermediate of the type Pt(II)Cl₄ClPt(IV)(CN)₄OH₂³⁻ is formed in the initial reaction step, not five-coordinated PtCl₅³⁻.     

Platinum(II) complexes of methyl-substituted xanthines: crystal structures of K[Pt(theobromine)Cl3]·H2O,trans-[ Pt(isocaffeine)2Cl2]·H2O and K(isocaffeinium)[PtCl4]·H2O

The preparations of Pt(theophylline)₂Cl₂, K[Pt- (theophylline)Cl₃], K[Pt(theobromine)Cl₃]·H₂O (1), trans-[Pt(isocaffeine)₂Cl₂]·H₂O (2), and K(isocaffeinium)[PtCl₄]·H₂O (3) are reported.Crystals of 1 are monoclinic P2₁/n with a=7.641- (2), b=11.873(3), c=15.868(4) Å, β=90.80(2)°, Z=4. The structure was refined on 1443 reflections to R=0.028. In the planar [Pt(theobromine)Cl₃]⁻ anion Pt-N(9)=2.016(6) Å, Pt-Cl=2.299(2), 2.289(2), and 2.303(2) Å. The imidazole ring is rotated away from the coordination plane by 79.8°. Symmetry related theobromine units pack parallel to each other with a mean inter-ring separation of 3.27 Å.Crystals of 2 are monoclinic P2₁/a with a=7.345- (2), b=20.021(5), c=8.031(2) Å, β=104.18(2)°, Z=2. The structure was refined on 1132 reflections to R=0.029. The Pt-N(7) distance is 2.003(3) Å and Pt-Cl=2.298(1) Å. The imidazole ring is rotated away from the PtCl₂N₂ plane by 76.8°. In this compound, the isocaffeine units do not stack, but form a staggered arrangement within the unit cell.Crystals of 3 are monoclinic P₁/c with a= 7.382- (1), b=14.014(4), c=15.757(4) », β=92.30(2)°, Z=4. The structure was refined on 2057 reflections to R=0.032. The isocaffeine is protonated at N(7). The Pt-Cl distances in the PtCl₄²⁻ anion range between 2.29–2.31 Å. The protonated isocaffeine cations and the PtCl₄²⁻ anions form a very nearly parallel infinitely stacked arrangement with minimum interlayer atomic separations of 3.37 and 3.44 Å.     

The interaction of methylcobalamin with tetracyanoplatinate(II), tetrathiocyanoplatinate(II) and tetrachloroplatinate(II)

The interactions of methylcobalamin (CH₃-B₁₂) with Pt(CN)₄^2?, PtCl₄^2?, and Pt(SCN)₄^2? in aqueous solution were studied by UV-visible and ¹H NMR spectroscopy. Together with earlier results on the mechanism of the Pt(IV)-dependent methyl-transfer reaction from CH₃-B₁₂ to Pt(II), these studies suggest at least three Pt binding sites on CH₃-B₁₂. One site, which is occupied by all three complexes (K₁ = 4 X 10³ M^?1 for Pt(CN)₄^2? and 3 X 10³ M^?1 for PtCl₄^2?), is located on the CoCH₃ side of the corrin macrocycle, and is involved in the methyl-transfer process in the presence of a Pt(IV) complex. An additional site for Pt(SCN)₄^2? is the N-3 of the benzimidazole group, resulting in dissociation of this group from the cobalt. An additional site for Pt(CN)₄^2? has a binding constant of 16 M^1? and ¹H NMR changes indicate perturbation but not dissociation of the benzimidazole group. Only the first interaction is discerned for PtCl₄^2?.     

Synthesis, characterization and cytotoxicity of a series of tetrachloridoplatinum(IV) complexes

Two platinum(IV) complexes, [Pt(4bt)Cl₄] (4) and [Pt(dpyam)Cl₄]·DMF (5) (where 4bt is 4,4′-bithiazole and dpyam is 2,2′-dipyridylamine) were prepared from the reaction of H₂PtCl₆·6H₂O with 4,4′-bithiazole and 2,2′-dipyridylamine, respectively, in methanol. Both complexes were fully characterized and their structures were determined by the X-ray diffraction method. These complexes have a bidentate nitrogenous ligand with four chloride anions attached to a Pt(IV) metal in a distorted octahedral environment. These complexes along with three previously reported analogous complexes were used for in vitro cytotoxicity evaluation against four cultures, NIH-3T3, Caco-2, HT-29 and T47D by MTT assay. The methyl group position in the ligand plays an important role in the cytotoxicity of relevant compounds in different cultures. Interestingly, in some cases, the IC₅₀ values of the new complexes were higher for normal cells but lower against cancer cells in comparison with cisplatin, especially in T47D (breast ductal carcinoma).     

Synthesis and kinetic studies of new bipyridyl platinum(II) phenoxide complexes by phase transfer catalysis: Crystal structure of [(bipy)Pt(OC6H4-4-OMe)2]

The synthesis of new platinum bipy (bipy = 2,2′-bipyridyl) complexes containing phenoxide ligands is reported, together with kinetic studies of their oxidative addition reactions with MeI to produce phenoxo platinum(IV) complexes. Complexes of the form [(bipy)Pt(OC₆H₄-4-X)₂] (X = OCH₃, CH₃, H, Br, Cl) are prepared by the reaction of the chloro complex [(bipy)PtCl₂] with substituted phenols and KOH in a two phase system of water and chloroform in the presence of benzyl triphenylphosphonium chloride. Platinum(IV) complexes are formed by oxidative addition of MeI to the platinum(II) complexes obtained. The complexes are characterized by elemental analysis, UV-Vis, IR, mass spectrometry and ¹H and ¹³C NMR spectroscopy.The reaction of methyl iodide with [(bipy)Pt(OC₆H₄-4-OMe)₂] to give [(bipy)PtMe(I)(OC₆H₄-4-OMe)₂] follows the rate law rate = k₂[(bipy)Pt(OC₆H₄-4-OMe)₂][MeI]. The values of k₂ increase with increasing polarity of the solvent, suggesting a polar transition state for the reaction.     

A new route to N(1)-5R-tetrazole complexes via azidation to nitriles coordinated to Pt(II) and Pt(IV)

New tetrazolate complexes trans-[PtCl₂(RCN₄)₂]²⁻, trans-[PtCl₄(RCN₄)₂]²⁻ with Ph₃PCH₂Ph⁺ and (CH₃)₂NH₂⁺ counterions have been obtained by azidation of nitriles coordinated to Pt(II) and Pt(IV) {trans-[PtCl₂(RCN)₂] and trans-[PtCl₄(RCN)₂] (R = Et, Ph)} and characterized. The composition and the molecular structure of the complexes obtained were established by the СHN elemental analyses, ¹Н and ¹³С NMR spectroscopy, IR spectroscopy, mass spectrometry, and X-ray diffraction. The coordination of nitriles to Pt(II) and Pt(IV) is shown significantly activate the azidation: the reaction proceeds with a higher rate and at relatively low temperature compared with the classical 1,3-dipolar addition of azides to nitriles.     

Effects of diethyldithiocarbamate (ddtc) on the plasma biotransformations of tetrachloro(d,i-trans)-1,2-diaminocyclohexaneplatinum(iv) (tetraplatin) in fischer 344 rats

We have studied the effects of diethyldithiocarbamate (DDTC) on the biotransformations of toxic doses of tetrachloro (d,l-trans)1,2-diaminocyclohexaneplatinum(IV) (tetraplatin) in Fischer 344 rats. In animals not treated with DDTC, tetraplatin was rapidly converted to dichloro(d,I-trans)1,2-diaminocyclohexaneplatinum(II) [PtCl₂(dach]. Subsequent biotransformations included the transient formation of the (d,I-trans)1,2-diaminocyclohexane-aquachloroplatinum(II) [Pt(H₂O)(Cl)(dach)]+ complex, followed by formation of the platinum (Pt)-methionine and either Pt-cysteine or Pt-ornithine complexes. Significant amounts of free (d,I-trans) 1,2-diaminocyclohexane (dach) were observed in plasma as a result of intracellular trans-labilization reactions. DDTC caused a marked decrease in both total and protein-bound platinum in the circulation. A significant increase in the plasma concentration of free dach was also observed as a result of formation of the Pt(DDTC)₂ complex. Some of the free dach could have arisen from intracellular reactions with DDTC, but the displacement of platinum from plasma proteins was more than sufficient to account for the increase in free dach in the circulation. DDTC treatment also decreased plasma concentrations of tetraplatin, PtCl₂(dach), [Pt(H₂O)(Cl)(dach)]⁺, the Pt-methionine complex, and one unidentified biotransformation product, but had no effect on the Pt-cysteine (or Pt-ornithine) complex. These effects of DDTC on protein-bound platinum and low-molecular-weight biotransformation products in plasma may contribute to the decrease in tetraplatin toxicity seen in DDTC-treated rats.     

Visible light-induced H2 production from cellulose using photosensitization of Mg chlorophyll a

A photoinduced-H₂ production system, coupling cellulose degradation by cellulase and glucose dehydrogenase (GDH) and H₂ production with colloidal Pt as a catalyst using the visible light-induced photosensitization of Mg chlorophyll a, has been developed. When the sample solution containing methylcellulose, cellulase, GDH, NAD⁺, Mg chlorophyll a, Methyl viologen and colloidal Pt was irradiated, continuous H₂ production was observed. The amount of H₂ production was about 12 mol after 4 h irradiation.     

Methimazole complexes of platinum(II): Synthesis, characterization and redox behavior

A variety of platinum(II) complexes of methimazole (2-mercapto-1-methylimidazole; HImS = neutral form and ImS = thiolate form), coordinated in both thione and thiolate forms, have been isolated by reacting methimazole with [PtCl(terpy)]Cl (terpy = 2,2′:6′,2″ terpyridine), [PtCl₂(bipy)] (bipy = bipyridine), [PtCl₂(o-phen)] (o-phen = o-phenanthroline), [PtCl₂(CH₃CN)₂] and [PtCl₂(COD)] (COD = 1,5-cyclooctadiene). These complexes were characterized by electronic absorption, IR and NMR (¹H, ¹³C, ¹⁹⁵Pt) spectroscopies. Molecular structure of [Pt(bipy)(HImS)₂]Cl₂·3H₂O (3a·3H₂O) has been established by single crystal X-ray crystallography. Platinum thiolate complex, [Pt(ImS)₂(HImS)₂] (5), could be obtained by treatment of [Pt(HImS)₄]Cl₂ with sodium methoxide in methanol. The solution of 5 in organic solvents yielded bi- and tri-nuclear platinum complexes. The effect of diimine ligands on oxidation of methimazole moiety in the complexes has been studied by electrochemical oxidation and pulse radiolytic oxidation employing specific one-electron oxidant, radical.     

Synthesis of 5,6-dihydro-4H-1,3-oxazines from neutral and cationic platinum(II) nitrile complexes. X-ray structure of trans-[Pt(CF3){ H2CH2}(PPh3)2]BF4

The 1,3-oxazine complexes cis- and trans-[PtCl₂{ C(R)OCH₂CH₂C}H₂₂] (cis: R=CH₃ (1a), CH₂CH₃ (2a), (CH3)₃C (3a), C₆H₅ (4a); trans:R =CH₃ (1b), C₆H₅ (4b)) were obtained in 51-71% yield by reaction in THF at 0 °C of the corresponding nitrile complexes cis- and trans-[PtCl2(NCR)₂] with 2 equiv. of ⁻OCH₂CH₂CH₂Cl, generated by deprotonation of 3-chloro-1-propanol with n-BuLi. The cationic nitrile complexes trans-[Pt(CF₃)(NCR)(PPh₃)₂]BF₄ (R=CH3, C₆H₅) react with 1 equiv, of ⁻ OCH2CH2CH2Cl to give a mixture of products, including the corresponding oxazine derivatives trans-[Pt(CF₃){ CH₂}(PPh₃)₂]BF₄ (5 and 6), the chloro complex _trans- [Pt(CF₃)Cl(PPh₃)₂] and free oxazine H2. For short reaction times (c. 5–15 min) the oxazine complexes 5 and 6 could be isolated in modest yield (37–49%) from the reaction mixtures and they could be separated from the corresponding chloro complex (yield 40%) by taking advantage of the higher solubility of the latter derivative in benzene. For longer reaction times (> 2 h), trans-[Pt(CF₃)Cl(PPh₃)₂] was the only isolated product. Complex 6 was crystallographically characterized and it was found to contain also crystals of trans- [PtCl{ H₂}(PPh₃)₂]BF₄, which prevented a more detailed analysis of the bond lengths and angles within the metal coordination sphere. The 1,3-oxazine ring, which shows an overall planar arrangement, is characterized by high thermal values of the carbon atoms of the methylene groups indicative of disordering in this part of the molecule in agreement with fast dynamic ring processes suggested on the basis of ¹H NMR spectra. It crystallizes in the trigonal space group P , with a=22.590(4), b=15.970(3) Å, γ=120°, V=7058(1) ų and Z=6. The structure was refined to R=0.059 for 3903 unique observed (I3σ(I)) reflections. A mechanism is proposed for the conversion of nitrile ligands to oxazines in Pt(II) complexes.     

Quantifying the trans influence of triphenylarsine. Crystal and molecular structures of cis-[PtCl2(SMe2)(AsPh3)] and cis-[PtCl2(AsPh3)2]·CHCl3

Reaction between a mixture of cis-trans-[PtCl₂(SMe₂)₂] and 1 equiv. AsPh₃ in chloroform gives cis-[PtCl₂(SMe₂)(AsPh₃)] crystallizing in P2₁/n with a=10.397(2), b=14.876(3), c=13.956(3) Å, β=90.86(3)° and Z=4. Selected geometrical parameters are PtAs 2.3531(10), PtS 2.262(2), PtCl (trans to S) 2.301(2), PtCl (trans to As) 2.328(2) Å and SPtAs 88.85(6), SPtCl(2) 90.77(8), AsPtCl(1) 91.07(6) and ClPtCl 89.42(7)°. cis-[PtCl₂(AsPh₃)₂]·CHCl₃ crystallizes in P2₁/c with a=20.557(4), b=9.5951(19), c=20.147(4) Å, β=96.77(3)° and Z=4. Selected geometrical parameters are PtAs(1) 2.3599(9), PtAs(2) 2.3770(9), PtCl(1) (trans to As(1)) 2.3515(18), PtCl(2) (trans to As(2)) 2.3251(18) Å and AsPtAs 97.87(3), As(1)PtCl(2) 88.67(5), As(2)PtCl(1) 84.30(5) and ClPtCl 89.32(7)°. By comparison with related structures from the literature the following trans influence series was established PMe₂Ph>PPh₃>AsPh₃≈SbPh₃>Me₂SO≈SMe₂≈SPh₂>NH₃≈olefin>Cl⁻>MeCN.     

Tetrachloroplatinate(II) and hexachloroplatinate(IV) salts of N,N,N′,N′-tetramethylethylenediammonium: significant differences in the conformation of the cation, as shown by infrared and x-ray diffraction data

The structures of (H₂tmen)[PtCl₄], (1), (H₂tmen = N,N,N′,N′-tetramethylethylenediammonium), [triclinic, P ; A = 7.344(3), B = 8.345(3), C = 6.216(2) Å, α = 84.53(3), β = 109.22(3), γ = 69.43(3)°, Z = 1] and (H₂tmen)[PtCl₆], (2), [monoclinic, P2₁/a; A = 14.409(4), B = 12.736(7), C = 8.601(3) Å, β = 99.58(3)°, Z = 4] were determined from diffractometric data by Patterson and Fourier methods and refined by full-matrix least-squares to R = 0.027 and 0.039 for (1) and (2) respectively. In both cases the anions and cations are joined in polymeric chains through hydrogen bonds involving the protonated nitrogens and the co-ordinated chlorine atoms. The square-planar [PtCl₄]²⁻ and octahedral [PtCl₆]²⁻ anions are centrosymmetric; the H₂tmen²⁺ cations are centrosymmetric in (1) with a N-C-C-N dihedral angle of exactly 180°, while in (2) the dihedral angle is 166°. The different symmetry of the organic moieties/C_i and C₁ in (1) and (2) respectively] results in a different i.r. spectrum which is more complex the lower the symmetry; moreover the spectrum of a KBr pellet of (2) changes with time, finally resembling that of (1) and of the (H₂tmen)Cl₂ salt.     

Pressure-tuning infrared spectra of the three Magnus’ Green salts, [Pt(NH3)4][PtCl4], [Pt(ND3)4][PtCl4] and [Pt(NH3)4][PtBr4]

Pressure-tuning infrared spectra (up to ca. 40 kbar) are reported for Magnus’ Green salt, [Pt(NH₃)₄][PtCl₄] and two of its derivatives, [Pt(ND₃)₄][PtCl₄] and [Pt(NH₃)₄][PtBr₄]. The spectroscopic data indicate that there is restricted rotation of the coordinated ammonia groups about the Pt-N bonds in the complexes. It is possible that this restricted rotation is due to the presence of weak hydrogen bonding to the halogens, i.e., N-H?X (X = Cl, Br) interactions.     

Preparation of mono- or di-metal indenyl-iridium edrivatives and of tri-metal iridium-platinum complexes

Treatment of [IrCl(C₂H₄)₄] with K(C₉H₇) (C₉H₇ =indenyl) gives [Ir(C₂H₄)₂(η-C₉H₇)]. This compound is converted quantitatively into [Ir(CO)₂(η-C₉H₇)] by treatment with carbon monoxide. By reacting together these two iridium complexes [Ir₂(μ-CO)(CO)₂(ηC₉H₇)₂] has been obtained. The compound [Ir(CO)₂(η-C₉H₇)] reacts with [Pt(C₂H₄)₂{P(cyclo-C₆H₁₁)₃}] to give the complex [Ir₂Pt(CO)₃{P(cyclo-C₆H₁₁)₃}(η-C₉H₇)₂]. Protonation of the latter affords the salt [Ir₂Pt(μ-H)(CO)₃{P(cyclo-C₆H₁₁)₃}(μ-C₉H₇)₂] [BF₄]. The main features of the molecular structure of these complexes have been established by IR and NMR spectroscopy.     

Synthesis of new platinum(II) complexes containing hybrid thioether-pyrazole ligands: Structural analysis by H and C{H} NMR spectroscopy and X-ray crystal structures

Treatment of the ligands 1,8-bis(3,5-dimethyl-1-pyrazolyl)-3,6-dithiaoctane (bddo), 1,9-bis(3,5-dimethyl-1-pyrazolyl)-3,7-dithianonane (bddn), and 1,6-bis(3,5-dimethyl-1-pyrazolyl)-2,5-dithiahexane (bddh) with several platinum starting materials as K₂PtCl₄, PtCl₂, [PtCl₂(CH₃CN)₂] and [PtCl₂(PhCN)₂] was developed under different conditions. The reactions did not yield pure products. The ratio of the NSSN, NS, SS, NN, and 2NS isomers has been calculated through NMR experiments. Treatment of the mixtures of complexes with NaBPh₄ affords [Pt(NSSN)](BPh₄)₂ (NSSN = bddo, bddn). These Pt(II) complexes have been characterised by elemental analyses, conductivity measurements, IR and ¹H and ¹³C NMR spectroscopy. The X-ray structures of the complexes [Pt(NSSN)](BPh₄)₂ (NSSN = bddo, bddn) have also been determined. In these complexes, the metal atom is tetracoordinated by the two azine nitrogen atoms of the pyrazole rings and two thioether sulfur atoms. When the [Pt(NSSN)](BPh₄)₂ (NSSN = bddo, bddn) complexes were heated under reflux in a solution of Et₄NBr in CH₂Cl₂/CH₃OH (1:1), a mixture of isomers was obtained.