Danila B. Vasilchenko

Speciation of platinum(IV) in nitric acid solutions.

The speciation of platinum(IV) ions in nitric acid (6-15.8 M) solutions of H2[Pt(OH)6] has been studied by (195)Pt NMR and Raman spectroscopy. Series of aqua-hydroxo-nitrato complexes [Pt(L)(x)(NO3)(6-x)] (L = H2O or OH(-); x = 0, ..., 6) were found to exist in such solutions. The pair additivity model of chemical shifts and statistical theory were used to assign signals in NMR spectra to particular [Pt(L)(x)(NO3)(6-x)] species. Mononuclear hexanitratoplatinates(IV) have been isolated in solid state in substantial yield as pyridinium salt (PyH)2[Pt(NO3)6] and characterized by single-crystal X-ray diffraction. Aging of the platinum nitric acid solutions for more than 5-6 h results in oligomerization of [Pt(L)(x)(NO3)(6-x)] species and the formation of oligonuclear aqua-hydroxo-nitrato complexes with OH(-) and NO3(-) bridging ligands. Oligomeric platinum(IV) complexes with two and four nuclei were unambiguously detected by NMR on (195)Pt -enriched samples. Oligomers with even higher nuclearity were also detected. Dimeric anions [Pt2(μ-OH)2(NO3)8](2-) have been isolated as single crystals of tetramethylammonium salt and characterized by X-ray diffraction.

Polynuclear Hydroxido-Bridged Complexes of Platinum(IV) with Terminal Nitrato Ligands

For the first time the polynuclear hydroxido-bridged platinum(IV) nitrato complexes with nuclearity higher than two were isolated from nitric acid solutions of [Pt(H2O)2(OH)4] and crystallized as supramolecular compounds of macrocyclic cavitands cucurbit[n]uril (CB[n], n = 6,8) and 18-crown-6 ether: [Pt4(μ3-OH)2(μ2-OH)4(NO3)10]·CB[6]·25H2O (I), [Pt6(μ3-OH)4(μ2-OH)6(NO3)12](NO3)2·CB[8]·50H2O (II), and [H3O⊂18-crown-6]2[Pt2(μ2-OH)2(NO3)8][Pt4(μ3-OH)2(μ2-OH)4(NO3)10] (III). The isolation of the compounds in the single crystalline state allows the determination of the structure of the tetranuclear and hexanuclear complexes [Pt4(μ3-OH)2(μ2-OH)4(NO3)10] and [Pt6(μ3-OH)4(μ2-OH)6(NO3)12](2+), which have been previously unknown in the solid state. Stability of Ptx(OH)y cores of the polynuclear nitrato complexes toward alkaline hydrolysis was verified by (195)Pt NMR spectroscopy. Analysis of (195)Pt NMR spectra of the compound III reveals that addition of every Pt(μ-OH)2Pt ring results in ∼260 ppm downfield shift relative to the mononuclear form, which allows the prediction of signal positions for complexes of higher nuclearity.

Spectroscopic and DFT Study of RhIII Chloro Complex Transformation in Alkaline Solutions

The hydrolysis of [RhCl6]3- in NaOH-water solutions was studied by spectrophotometric methods. The reaction proceeds via successive substitution of chloride with hydroxide to quantitatively form [Rh(OH)6]3-. Ligand substitution kinetics was studied in an aqueous 0.434-1.085 M NaOH matrix in the temperature range 5.5-15.3 °C. Transformation of [RhCl6]3- into [RhCl5(OH)]3- was found to be the rate-determining step with activation parameters of ΔH† = 105 ± 4 kJ mol-1 and ΔS†= 59 ± 10 J K-1 mol-1. The coordinated hydroxo ligand(s) induces rapid ligand substitution to form [Rh(OH)6]3-. By simulating ligand substitution as a dissociative mechanism, using density functional theory (DFT), we can now explain the relatively fast and slow kinetics of chloride substitution in basic and acidic matrices, respectively. Moreover, the DFT calculated activation energies corroborated experimental data that the kinetic stereochemical sequence of [RhCl6]3- hydrolysis in an acidic solution proceeds as [RhCl6]3- → [RhCl5(H2O)]2- → cis-[RhCl4(H2O)2]-. However, DFT calculations predict in a basic solution the trans route of substitution [RhCl6]3- → [RhCl5(OH)]3- → trans-[RhCl4(OH)2]3- is kinetically favored.

Crystal Structure and Properties of [Rh 2 (H 2 O) 8 (μ-OH) 2 ](NO 3 ) 4 ·4H 2 O

A procedure to synthesize (μ-hydroxo)bis-pentaaquarhodium(III) nitrate tetrahydrate [Rh2(H2O)8(μ-OH)2](NO3)4·4H2O from potassium hexachlororhodiate(III) is elaborated. The compound is isolated into the solid phase and structurally characterized. The crystallographic data are as follows: a = 5.8763(2) Å, b = 9.4749(4) Å, c = 9.6249(3) Å, α = 79.905(1)°, β = 84.324(1)°, γ = 82.922(1)°, space group P-1, Z = 1, ρcalc = 2.240 g/cm3. The compound is soluble in water, ethanol, and acetone. Hydrolysis takes place in concentrated nitric acid with the formation of mononuclear aqua- and aquanitrate complexes. Thermal decomposition of the salt at a temperature above 580 °C leads to the formation of a single product–rhodium(III) oxide.

Crystal structures of cis -diiododiammine platinum and trans -diazidodiammine platinum

Platinum(II) complexes cis-[Pt(NH3)2I2] (1) and trans-[Pt(NH3)2(N3)2] (2) are structurally characterized separately for the first time. The crystallographic data are as follows: for 1, a = 7.0065(6) Å, b = 6.8714(6) Å, c = 7.4106(8) Å, β = 108.432(7)°, space group P21/m, Z = 2, ρcalc = 4.739 g/cm3; for 2, a = 8.1337(5) Å, b = 11.5821(7) Å, c = 6.9705(5) Å, β = 107.256(2)°, space group P21/c, Z = 4, ρcalc = 3.318 g/cm3. Platinum atoms have a square planar environment; the main structure-forming factor is the presence of intermolecular hydrogen bonds forming chain motifs in the structure of 1 and a threedimensional framework in the structure of 2.