Tricarbonylrhenium(I) complexes with the N,6-dimethylpyridine-2-carbothioamide ligand: combined experimental and calculation studies

Abstract

A new series of tricarbonyl complexes of rhenium(I) in the “2 + 1” system with the bidentate ligand N,6-dimethylpyridine-2-carbothioamide ((CH₃)NC₅H₄-CS-NH-CH₃, MeLH(Me)_NS) and a monodentate ligand (halides Cl, Br, or I, and the pseudohalide NCS anion) was synthesized. The use of mixed ligands led to the formation of neutral tricarbonylrhenium(I) complexes [Re(CO)₃(MeLH(Me)_NS)X] (X = Cl, Br, I, NCS) (1–4). Single-crystal X-ray diffraction was used to determine the crystal structures of all four compounds and those results were compared with molecular structures obtained from DFT calculations using the PBE0/def2-TZVPD approach. The complexes were also characterized by spectroscopic (FT-IR, NMR, and UV–vis) and analytical (HPLC, TGA, EA, ESI-MS) techniques. IR and UV–vis spectra were also calculated by DFT and TD-DFT methods. The cytotoxicity of these complexes was estimated using human ovarian cancer cell lines (A2780 and A2780cis), cervical cancer cells (HeLa), and non-cancerous human embryonic kidney cells (Hek-293). The toxicity of most complexes was moderate or low toward cancer cell lines (IC₅₀ = 46–231 μM) and similar against non-cancerous cells (IC₅₀ = 41-121 μM). Only the complex with chlorido ligand remarkably inhibited growth of ovarian cancer cells (IC₅₀ = 3 and 12 μM for A2780 and A2780cis, respectively). The cytotoxicity of 1 was higher than that of cisplatin.     

Investigation of desolvation process in lanthanide dinicotinates

The desolvation process in lanthanide pyridine-3,5-dicarboxylates of the formulae [Tb₂pdc₃(dmf)₂]·dmf (1), [Ho₂pdc₃(dmf)₂]·dmf (2), [Erdc₃(dmf)₂]·dmf (3), and [Yb₂pdc₃(dmf)₂]·dmf (4) where pdc-C₅H₃N(COO)₂²⁻, dmf-N,N′-dimethylformamide) has been investigated by means of the TG–DSC, TG–FTIR, IR and XRD methods. Heating of the complexes in the range 30–260 °C lead to evolution of weakly bonded dmf molecules included in the channels as well those directly bonded with lanthanide atoms. The kinetic analysis revealed a multistep desolvation pattern.     

Dinuclear copper(II) complexes of Fenoprofen: synthesis,spectroscopic, thermal,and SOD-mimic activity studies

Three dinuclear copper(II) complexes with the anti-inflammatory drug Fenoprofen [Hfen, 2-(3-phenoxyphenyl)propionic acid] and nitrogen donors of general formula [Cu₂(fen)₄(L)] _n were prepared from [Cu₂(fen)₄(dmf)₂]·2H₂O (1) [dmf?=?N,N′-dimethylformamide; L?=?4,4′-bipyridine (2), pyrazine (3), and 2,5-dimethylpyrazine (4)]. The new complexes were characterized by chemical analysis, spectroscopic, and thermogravimetric techniques. Antioxidant properties of 1–4 were evaluated for superoxide-dismutase-mimic activity employing the XTT method. Complex 2 presented the highest antioxidant activity (IC₅₀?=?0.260?µmol?L^?1). Anti-inflammatory properties of 2 were evaluated employing carrageenan-induced paw edema in mice, revealing that the Fenoprofen–copper(II) complex containing 4,4′-bipyridine does not present enhanced anti-inflammatory activity compared to the uncomplexed parent drug Fenoprofen calcium salt.     

Light-induced cis/trans isomerization of cis-[Pd(L-S,O)2] and cis-[Pt(L-S,O)2] complexes of chelating N,N-dialkyl-N′-acylthioureas: key to the formation and isolation of trans isomers

Irradiation cis-[M(Lⁿ-S,O)₂] complexes (M = Pt^II, Pd^II) derived from N,N-dialkyl-N′-benzoylthioureas (HLⁿ) with various sources of intense visible polychromatic or monochromatic light with λ < 500 nm leads to light-induced cis?→?trans isomerization in organic solvents. In all cases, white light derived from several sources or monochromatic blue-violet laser 405 nm light, efficiently results in substantial amounts of the trans isomer appearing in solution, as shown by ¹H NMR and/or reversed-phase HPLC separation in dilute solutions at room temperature. The extent and relative rates of cis/trans isomerization induced by in situ laser light (λ = 405 nm) of cis-[Pd(L²-S,O)₂] was directly monitored by ¹H NMR and ¹⁹⁵Pt NMR spectroscopy of selected cis-[Pt(L-S,O)₂] compounds in chloroform-d; both with and without light irradiation allows the δ(¹⁹⁵Pt) chemical shifts cis/trans isomer pairs to be recorded. The cis/trans isomers appear to be in a photo-thermal equilibrium between the thermodynamically favored cis isomer and its trans counterpart. In the dark, the trans isomer reverts back to the cis complex in what is probably a thermal process. The light-induced cis/trans process is the key to preparing and isolating the rare trans complexes which cannot be prepared by conventional synthesis as confirmed by the first example of trans-[Pd(L-S,O)₂] characterized by single-crystal X-ray diffraction, deliberately prepared after photo-induced isomerization in acetonitrile solution.     

Synthesis,cytotoxicity, and interaction with DNA of platinum(II) complexes of (1R,2R)-N1-2-amyl-1,2-diaminocyclohexane

(1R,2R)-N¹-2-amyl-1,2-diaminocyclohexane, which has an amyl substituent as compared with 1,2-diaminocyclohexane, was used as the carrier group to construct three platinum(II) complexes. MTT assay revealed that the complexes showed decent cytotoxicity against all of the four tested tumor cell lines with the IC₅₀ values ranging from 1.08 to 253.36 μM. Particularly, the IC₅₀ values of 2 against A549 and HCT-116 reached 3.32 and 1.08 μM, respectively, which were much lower than those of cisplatin and oxaliplatin. Flow cytometry demonstrated that 2 inhibited HepG2 cells proliferation and caused cytotoxicity by inducing apoptosis and arresting cells in the G2 phase. Furthermore, agarose gel electrophoresis showed that 2 had the ability to interact with DNA in a manner different from cisplatin and oxaliplatin, indicating the carrier ligand with an alkyl moiety had an influence on the action mode of the complex.     

New Ni(II) complexes involving symmetrical bidentate N,O-donor Schiff base ligands: synthesis at ambient temperature,crystal structures,electrochemical study,antioxidant and cytotoxic activities

A new series of Ni(II) complexes, [Ni(L¹)₂] (1), [Ni(L²)₂] (2), [Ni(L³)₂] (3), and [Ni(L⁴)₂] (4), were synthesized at ambient temperature. The bidentate Schiff base ligands HL^1?4 have been obtained by the condensation reaction of 2-hydroxybenzaldehyde, 5-bromo-2-hydroxybenzaldehyde, 3-methoxy-2-hydroxy-benzaldehyde, and 4-methoxy-2-hydroxy-benzaldehyde, respectively, with 2-methoxyethylamine. The newly synthesized complexes were characterized by elemental analyses, FT-IR and UV–vis spectroscopy. The crystal structures of mononuclear Ni(II) complexes 2 and 3 were determined by the single-crystal X-ray diffraction technique. Electrochemical properties of the complexes were investigated in acetonitrile. The antioxidant properties of the Schiff base ligands and complexes were evaluated by two in vitro tests, DPPH radical scavenging and reducing power. The compounds were screened for their in vitro anticancer potential using gastric cancer cell lines by MTT assay. All ligands and complexes showed considerable cytotoxic activity against cancer cell lines (IC₅₀ = 0.2516–5.468 μg·mL^?1). The most promising result was achieved for complex 1 with the best IC₅₀ value of 0.2516 μg·mL^?1. It was found that the proliferation rate of MKN-45 cells decreased after treatment with the complexes in a dose-dependent way.     

NMR and kinetic studies of the interactions of [Au(cis-DACH)Cl2]Cl and [Au(cis-DACH)2]Cl3 with potassium cyanide in aqueous solution

The interactions of [Au(cis-DACH)Cl₂]Cl and [Au(cis-DACH)₂]Cl₃ [where cis-DACH is cis-1,2-diaminocyclohexane] with enriched KCN were carried out in CD₃OD and D₂O, respectively. The reaction pathways of these complexes were studied by ¹H, ¹³C, ¹⁵N NMR, UV spectrophotometry, and electrochemistry. The kinetic data for the reaction of cyanide with [Au(cis-DACH)₂]Cl₃ are k = 18 M^?1s^?1, ?H^≠ = 11 kJ M^?1, ?S^≠ = ?185 JK^?1 M^?1, and E_a = 13 kJ M^?1 with square wave voltammetric (SWV) peak +1.35 V, whereas the kinetic data for the reaction of cyanide ion with [Au(cis-DACH)Cl₂]Cl are k = 148 M^?1s^?1, ?H^≠ = 39 kJM^?1, ?S^≠ = ?80 JK^-1 M^?1, and E_a = 42 kJM^?1 along with SWV peak +0.82 V, indicating much higher reactivity of [Au(cis-DACH)Cl₂]Cl toward cyanide than [Au(cis-DACH)₂]Cl₃. The interaction of these complexes with potassium cyanide resulted in an unstable [Au(¹³CN)₄]^? species which readily underwent reductive elimination reaction to generate [Au(¹³CN)₂]^? and cyanogen.     

Hexakis(dimethylformamide)iron(II) complex cation in hexahalorhenate(IV)-based salts: synthesis,X-ray structure and magnetic properties

Abstract

Two iron(II)-rhenium(IV) compounds of general formula [Fe^II(dmf)₆][Re^IVX₆] [X = Cl (1) and Br (2); dmf = N,N-dimethylformamide] have been prepared and characterized. X-ray powder diffraction measurements on samples of 1 and 2 support the same structure for both systems. The crystal structure of 1 was determined by single-crystal X-ray diffraction. 1 crystallizes in the triclinic system with space group Pī. Each iron(II) is six-coordinate and bonded to six oxygens from six dmf molecules building a distorted octahedral environment. Rhenium(IV) is six-coordinate by six halide anions in an almost regular octahedral geometry. The magnetic properties were investigated from variable-temperature magnetic susceptibility measurements performed on microcrystalline samples of 1 and 2, whose experimental data were reproduced by a model of two isolated paramagnetic centers [S = 2 (Fe^II) and S = 3/2 (Re^IV)] with large values of zero-field splitting (zfs) parameter.     

Synthesis,characterization, antibacterial,and cytotoxic activities of organotin(IV) complexes derived from N(4)-cyclohexylthiosemicarbazone: X-ray crystal structure of [Ph2SnCl(L)]

Reaction of organotin(IV) chloride(s) with 2-benzoylpyridine-N(4)-cyclohexylthiosemicarbazone, [HL] (1) yielded [MeSnCl₂(L)] (2), [BuSnCl₂(L)] (3), [Me₂SnCl(L)] (4), and [Ph₂SnCl(L)] (5). The ligand (1) and its organotin(IV) complexes have been characterized by CHN analyses, molar conductivity, UV-Vis, FT-IR, ¹H, ¹³C, and ¹¹⁹Sn NMR spectral studies. The molecular structure of 5 was also determined by X-ray diffraction. There are two independent molecules in the asymmetric unit and the central tin(IV) atom is six-coordinate in distorted octahedral geometry. The ligand (1) and complexes were screened for their in vitro antibacterial activities. The cytotoxic activities of 1–5 were tested against A2780 and A2780/Cp8 cancer cell lines. The compounds have better antibacterial activities than the free ligand; 2–5 are more potent cytotoxic agents than 1, while the diphenyltin(IV) 5 is more active with IC₅₀ values of 0.05 and 0.54?µmol?L^?1 against A2780 and A2780/Cp8 cell lines, respectively.     

Synthesis,characterization, DNA binding studies and in vitro cytotoxicity of platinum(II)-dihalogenido complexes containing bidentate chelating N-donor ligands

Platinum(II) complexes, [Pt(L_x)X₂] (1–6), where X = Br or I and L_x = 2,2′-bipyridine or 1,10-phenanthroline derivatives (5,5′-dimethyl-2,2′-bipyridine (5-Mebpy), 4,4′-dimethyl-2,2′-bipyridine (4-Mebpy), and 5-amino-1,10-phenanthroline (5-NH₂phen)) were prepared. The complexes were characterized by the elemental analysis, mass spectrometry, infrared, and multinuclear (¹H, ¹³C and ¹⁹⁵Pt) 1-D and 2-D NMR spectroscopies, and by single-crystal X-ray analysis of [Pt(4-Mebpy)I₂] (4). All the platinum(II) complexes (1–6) were evaluated for in vitro cytotoxicity against human cancer cell lines A2780 and A2780R, and against non-malignant MRC5 cell line. All the complexes were nontoxic up to the 50 μM concentration, although they were found to readily bind to calf-thymus DNA (CT-DNA), as determined by spectrophotometric titration (K_b ≈ 10⁷ M^?1) and ethidium bromide displacement assay.     

Synthesis and spectral characterization of platinum(II) complexes containing eugenol,a natural allylphenol

For the first time, eugenol, a natural bioactive allylphenol, was introduced into coordination with platinum(II) by replacement of ethylene from Zeise’s salt with eugenol (Eug). The obtained complex, K[PtCl₃(Eug)] (1), was used as the key compound for preparation of the series of trans-[PtCl₂(Eug)(Amine)] (2–11), [PtCl(Eug)(8-O-quinoline)] (12) and [PtCl(Eug)(2-O₂C-quinoline)] (13). The synthesized complexes were characterized by elemental analyses, IR, ¹H NMR, ¹³C NMR, HSQS, HMBC, NOESY, and MS spectra. In 1–13 eugenol coordinates with Pt(II) at ethylenic double bond of the allyl group, the donor N of the amines is in trans-position in comparison with the double bond. A display of the trans-effect on the chemical shift of ¹H and ¹³C was remarked. Seven complexes were tested for cell in vitro cytotoxicity on human cancer cells. Complexes 3 and 12 exhibit high activities on Hep-G2 with IC₅₀ = 3.12 and 5.29 μM; 12 gives high activity against KB, Lu and MCF-7 with IC₅₀ = 0.43, 2.95 and 1.84 μM, respectively. Most of these IC₅₀ are lower than those of cisplatin.     

Syntheses,crystal structures and photophysical properties of d10 transition-metal (Ag+, Cu+, Cd2+ and Zn2+) coordination complexes based on a thiophene-containing heterocyclic thioamide

Four d¹⁰ transition-metal coordination complexes 1–4 (1: [Ag₂(TPT)₂(TPTH)₂]; 2: [Cu₆(TPT)₆]·2DMF; 3: [Cd(TPT)₂(TPTH)]·CH₃CH₂OH, 4: [Zn(TPT)₂]_n) have been constructed from a newly designed heterocyclic thioamide ligand, TPTH (TPTH = 4-(thiophen-2-yl)-pyrimidine-2-thiol). All complexes have been structurally elucidated by single crystal X-ray diffraction analyses. Except for 4, which shows a one-dimensional (1-D) chain structure, 1–3 are all discrete coordination complexes featuring dinuclear, hexanuclear and mononuclear entities, respectively. Their photophysical properties have been evaluated in the solid state at room temperature by UV–vis diffuse reflectance and luminescence spectra. Among them, 2 exhibits a strong red luminescence (λ_em = 699 nm) with a remarkable red-shift of the maximum emission compared to that of the TPTH ligand (λ_em = 536 nm). The red emission observed with 2 is ascribed to a LMCT (ligand-to-metal charge transfer) transition which agrees with the DFT calculations.     

Chemie polyfunktioneller Moleküle, 94 Chrom- und Wolfram-pentacarbonylderivate des 4-Methyl-1,2,6-triphosphatricyclo[2.2.1.02,6]heptans (P3-Nortricyclans)

The P₃-nortricyclane 4-methyl-1,2,6-triphosphatricyclo[2.2.1.0^2,6]heptane, CH₃C(CH₂P)₃, (1), is synthesized in a better yield than earlier described from P₄, a Na/K alloy, and CH₃C(CH₂Br)₃ in boiling 1,2-dimethoxyethane. It reacts withM(CO)₅ thf (M=Cr, W) in the molar ratios of 1:1, 1:2, and 1:3 to form the pentacarbonylmetal complexes CH₃C(CH₂P)₃[M(CO)₅] _n [n=1, 2, 3;M=Cr (a), W (b)], (2 a, b–4 a, b).1 gives with Mo(CO)₅ thf only mixtures of CH₃C(CH₂P)₃[Mo(CO)₅] _n andcis-Mo(CO)₄ derivatives, which were identified by their infrared active A₁ v(CO) modes at 2075 and 2025 cm^–1.All the new compounds have been characterized also by their¹H{³¹P},³¹P{¹H} NMR, IR,Raman, and mass spectra.

     

两种3D微孔Zn-MOF对水溶液中Fe3+、Cr2O72-和丙酮分子的荧光传感

通过溶剂热法合成了2种三维微孔锌金属有机框架材料,其分子式为[Zn₃(DBA)(OH)(1,10-phen)₂]_n(1)和{[Zn₂(HDBA)(4,4''-bipy)_1.5]·H₂O}_n(2)(H₅DBA=3,5-二(2'',4''-对羧基苯基)苯甲酸;1,10-phen=1,10-菲咯啉;4,4''-bipy=4,4''-联吡啶)。结构分析表明,配合物1为三核锌基金属单元的三维微孔骨架,配合物2为双核锌基的微孔结构。与2相比,配合物1在水中具有较强的发光性能,可作为检测Fe³⁺、Cr₂O₇^2-和丙酮分子的发光传感器,具有较高的选择性和灵敏度。     

Reaction of Os3(μ-Cl)2(CO)10 with Ph2PCH2PPh2. The formation of a novel 12-membered macrocycle containing C, P, Cl, and Os atoms in the ring

The reaction of Os₃(μ-Cl)₂(CO)₁₀ (1) with Ph₂PCH₂PPh₂ (dppm) in a toluene solution at 65°C results in novel osmium complexes [Os₃(μ-Cl)₂(CO)₉]₂(dppm) (2) and [Os₃(μ-Cl)₂(CO)₈]₂(dppm)₂ (3). Compounds 2 and 3 were characterized by¹H and³¹P NMR, and IR spectroscopy and their structures were established by X-ray analysis. In both compounds, dppm is a bridging ligand between the two cluster units. Molecule3 can be considered as an unusual 12-membered macrocycle containing C, P, Cl, and Os atoms in the ring. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1844–1851, September, 1998.     

Supramolecular inclusion of a pillared double-layered host by an anion-directed second-sphere coordination

In this paper, we have illustrated the utilisation of a second-sphere coordination approach to construct supramolecular inclusion solids with varieties of guest molecules. A flexible molecule N,N,N′,N′-tetra-p-methylbenzyl-ethylenediamine (L1) bearing doubly protonated H-bond donors was designed, capable of forming N–H…Cl hydrogen bonds with a crystallographically unique chloride anion, to construct an anion-directed ligand. The pillared double-layered host framework was constructed by an anion-directed ligand and primary coordination sphere [CoCl₄]^2 ?  through weak C–H…Cl hydrogen-bonding interactions. A variety of guest molecules, such as p-anisaldehyde, 1,4-dimethoxy-2,5-bis(methoxymethyl)benzene, can be included, leading to the formation of novel supramolecular inclusion solids: [L1]·4[H]⁺·[CoCl₄]^2 ? ·2Cl^? ·1.5[C₈H₈O₂]·0.25[CH₃OH] (1) and [L1]·4[H]⁺·[CoCl₄]^2 ? ·2Cl^? ·1.5[C₁₂H₂₀O₄]·0.5[CH₃OH] (2).

We have presented herein the utilisation of a second-sphere coordination approach to construct supramolecular inclusion solids with a variety of guest molecules. A novel type of a pillared double-layered host framework was constructed by a second-sphere coordination between the anion-directed ligand (L1 = N,N,N′,N′-tetra-p-methylbenzyl-ethylenediamine) and [CoCl₄]^2 ?  through weak C–H…Cl hydrogen-bonding interaction, and a variety of guest molecules, such as p-anisaldehyde, 1,4-dimethoxy-2,5-bis(methoxymethyl)benzene, can be included, leading to the formation of supramolecular inclusion solids: [L1]·4[H]⁺·[CoCl₄]^2 ? ·2Cl^? ·1.5[C₈H₈O₂]·0.25[CH₃OH] (1) and [L1]·4[H]⁺·[CoCl₄]^2 ? ·2Cl^? ·1.5[C₁₂H₂₀O₄]·0.5[CH₃OH] (2)

     

Syntheses,structural determination,and binding studies of nine-coordinate multinuclear (mnH)2[EuIII(egta)]2·6H2O and binuclear (mnH)4[EuIII2(dtpa)2]·6H2O

Two lanthanide complexes, (mnH)₂[Eu^III(egta)]₂·6H₂O (1) (H₄egta = ethyleneglycol-bis-(2aminoethylether)-N,N,N′,N′-tetraacetic acid) and (mnH)₄[Eu^III₂(dtpa)₂]·6H₂O (2) (H₅dtpa = diethylenetriamine-N,N,N′,N″,N″-pentaacetic acid), have been synthesized and characterized by FT-IR spectroscopy, thermal analysis, and single-crystal X-ray diffraction. X-ray diffraction reveals that 1 is multinuclear nine-coordinate and crystallizes in the monoclinic crystal system with space group C2/c. The obtained cell dimensions are a = 38.513(3)?Å, b = 13.5877(8)?Å, c = 8.7051(5)?Å, β = 99.6780(10)°, and 4490.6(5)?ų. Each methylamine (mnH⁺) cation in 1, through hydrogen bonds, connects three adjacent [Eu^III(egta)]^? anions. The [Eu^III(egta)]^? anions connect one another forming a 1-D multinuclear zigzag chain structure along the c-axis. Complex 2 is nine-coordinate binuclear structure with tricapped trigonal prismatic conformation and crystallizing in the monoclinic crystal system, but with space group P2₁/n. The obtained cell dimensions are a = 9.9132(8)?Å, b = 24.1027(18)?Å, c = 10.7120(10)?Å, β = 109.1220(10)°, and 2418.2(3)?ų. For 2, there are two kinds of methylamine cations (mnH⁺) connecting [Eu^III₂(dtpa)₂]^4? complex anions and lattice waters through hydrogen bonds, leading to formation of a 2-D ladder-like layer structure.     

Crystal structure and spectroscopic behavior of three new tris-oxalatoferrate(III) salts

A new general synthetic procedure for preparation of Na₃[Fe(C₂O₄)₃]·5H₂O (1), Rb₃[Fe(C₂O₄)₃]·3H₂O (2), and Cs₃[Fe(C₂O₄)₃]·2H₂O (3) was developed. The crystal structures of these salts have been determined by single crystal X-ray diffraction. Salt 1 crystallizes in the monoclinic space group C2/c with Z = 8, salt 2 in P2₁/c with Z = 4, and salt 3 in P2₁/n with Z = 4. The three new salts and K₃[Fe(C₂O₄)₃]·3H₂O, prepared for comparative purposes, were further characterized by infrared and ⁵⁷Fe-Mössbauer spectroscopy. These spectra are discussed in comparison with those of related oxalato complexes.     

Accurate prediction of 195Pt-NMR chemical shifts for hydrolysis products of [PtCl6]2− in acidic and alkaline aqueous solutions by non-relativistic DFT computational protocols

The ¹⁹⁵Pt-NMR chemical shifts of all possible hydrolysis products of [PtCl₆]^2? in acidic and alkaline aqueous solutions are calculated employing simple non-relativistic density functional theory computational protocols. Particularly, the GIAO-PBE0/SARC-ZORA(Pt) ∪ 6-31 + G(d)(E) computational protocol augmented with the universal continuum solvation model (SMD) performs the best for calculation of the ¹⁹⁵Pt-NMR chemical shifts of the Pt(IV) complexes existing in acidic and alkaline aqueous solutions of [PtCl₆]^2?. Excellent linear plots of δ_calcd(¹⁹⁵Pt) chemical shifts versus δ_exptl(¹⁹⁵Pt) chemical shifts and δ_calcd(¹⁹⁵Pt) versus the natural atomic charge Q_Pt are obtained. Very small changes in the Pt–Cl and Pt–O bond distances of the octahedral [PtCl₆]^2?, [Pt(OH)₆]^2?, and [Pt(OH₂)₆]⁴⁺ complexes have significant influence on the computed σ^{iso 195}Pt magnetic shielding tensor elements of the anionic [PtCl₆]^2? and the computed δ ¹⁹⁵Pt chemical shifts of [Pt(OH)₆]^2? and [Pt(OH₂)₆]⁴⁺. An increase of the Pt–Cl and Pt–O bond distances by 0.001 Å (1 mÅ) is accompanied by a downfield shift increment of 17.0, 19.4, and 37.6 ppm mÅ^?1, respectively. Counter-anion effects in the case of the highly positive charged complexes drastically improve the accuracy of the calculated ¹⁹⁵Pt chemical shifts providing values very close to the experimental ones.