Structures and excitation energies of ozone-water clusters O3(H2O)n (n = 1-4)

Hybrid density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations have been carried out for ozone-water clusters O₃(H₂O)_n (n = 1-4) in order to obtain hydration effects on the absorption spectrum of ozone. The first water molecule in n = 1 is bound to the ozone molecule by an oxygen orientation form in which the oxygen atom of H₂O orients the central oxygen atom of O₃. In n = 2, the water dimer is bound to O₃ and then the cyclic structure is formed as the most stable structure. For n = 3 (or n = 4), the cyclic water trimer (or tetramer) is bound by a hydrogen bond to the ozone molecule. The TD-DFT calculations of O₃(H₂O)_n (n = 0-4) show that the first and second excitation energies of O₃ are blue-shifted by the interaction with the water clusters. The magnitude of the spectral shift is largest in n = 2, and the shifts of the excitation energies are +0.07 eV for S₁ and +0.13 eV for S₂ states. In addition to the spectral shifts (S₁ and S₂ states), it is suggested that a charge-transfer band is appeared as a low-lying excited state above the S₁ and S₂ states. The origin of the spectrum shifts was discussed on the basis of theoretical results.     

Crystal structure, optical, magnetic, and photochemical properties of the complex pentakis(dimethyl sulfoxide)nitrosylchromium(2+) hexafluorophosphate

The nitrosyl complex [Cr(dmso)₅(NO)](PF₆)₂ (1) (dmso = dimethyl sulfoxide) has been prepared by the solvolysis of [Cr(NCCH₃)₅(NO)](PF₆)₂ in neat dmso. The optical absorption spectrum of 1 in dmso shows maxima at 734, 567, 450, 413, and 337 nm. Continuous photolysis of 1 with λ = 365-580 nm light in dmso solution results in a release of NO with quantum yield, Φ, in the range 0.034-0.108 mol Einstein⁻¹. Irradiation of a deoxygenated CH₃CN solution of [Cr(NCCH₃)₅(NO)](PF₆)₂ in the presence of excess of [Fe(S₂CNEt₂)₂] results in a transfer of NO to the iron centre as shown from the characteristic EPR spectrum of [Fe(S₂CNEt₂)₂(NO)] with A_iso(¹⁴N) = 12.2 × 10⁻⁴ cm⁻¹. The EPR parameters of 1 were determined: g_iso, g_‖ and g_⊥ : 1.96725, 1.91881(4) and 1.992763(2); A_iso(⁵³Cr), A_‖ (⁵³Cr) and A_⊥(⁵³Cr): 22.8 × 10⁻⁴, 39 × 10⁻⁴ and 15.8 × 10⁻⁴ cm⁻¹; A_iso(¹⁴N), A_‖ (¹⁴N) and A_⊥(¹⁴N): 5.9 × 10⁻⁴, 2 × 10⁻⁴ and 7.540(4) × 10⁻⁴ cm⁻¹.     

Capturing the spin state diversity of iron(III)-aryl porphyrins: OLYP is better than TPSSh

DFT calculations with a variety of exchange-correlation functionals, including PW91, OLYP, TPSSh, B3LYP and B3LYP*, have been carried out on the low-energy spin states of chloroiron(III) porphyrin and four aryliron(III) porphyrins, viz. Fe^III(P)Ph (S = 1/2), Fe^III(P)C₆F₅ (S = 5/2), Fe^III(P)(3,4,5-C₆F₃H₂) (S = 1/2), Fe^III(P)(2,4,6-C₆F₃H₂) (S = 5/2), where the expected spin states have been indicated within parentheses. Qualitatively, OLYP reproduces all the expected ground spin states. B3LYP appears to have some difficulty yielding the observed sextet ground states. B3LYP*, TPSSh and PW91 all fail to reproduce the sextet ground states, the latter two by rather large margins of energy. As far as this study is concerned, the overall performance of the functionals appears to be OLYP/OPBE > B3LYP > B3LYP* >> TPSSh > PW91/BLYP/BP86/TPSS.     

Experimental and DFT studies on the DNA-binding trend and spectral properties of complexes [Ru(bpy)2L] (L = dmdpq, dpq, and dcdpq)

The trend in DNA-binding affinities and the spectral properties of a series of Ru(II) polypyridyl complexes, [Ru(bpy)₂(dmdpq)]²⁺ (1), [Ru(bpy)₂(dpq)]²⁺ (2), [Ru(bpy)₂(cndpq)]²⁺ (3) (bpy = 2,2′-bipyridine; dpq = dipyrido[3,2-d:2′,3′-f]quinoxaline; dmdpq = di-methyl-dpq; dcdpq = di-cyano-dpq), have been experimentally and theoretically investigated. The DNA-binding constants K_b of the complexes were determined systematically with spectrophotometric titration. The density functional theory (DFT) and time-dependent DFT (TDDFT) calculations were carried out for these complexes. The experimental results show that these complexes bind to DNA in intercalation mode, and the order of their intrinsic DNA-binding constants K_b is K_b(1) < K_b(2) ? K_b(3). The substituents on the intercalative ligands of the complexes play a very important role in the control of DNA-binding affinities of the complexes, in particular, the stronger electron-withdrawing substituent (-CN) on the intercalative ligand can greatly improve the DNA-binding property of the derivative complex. The trend in DNA-binding affinities as well as the spectral properties of metal-ligand charge-transition (¹MLCT) of this series of complexes can be reasonably explained by applying the DFT and TDDFT calculations and the frontier molecular orbital theory.     

Structures of homoleptic eight- and nine-coordinate uranium(IV) perchlorate complexes with sulfoxide molecules as ligands

Homoleptic eight- and nine-coordinate U(IV) perchlorate complexes with sulfoxide ligands have been characterized crystallographically. Crystals of [U(dmso)₈](ClO₄)₄ · 0.75CH₃NO₂, [U(dmso)₉](ClO₄)₄ · 4dmso (dmso = dimethyl sulfoxide), and [U(tmso)₈](ClO₄)₄ · 2tmso (tmso = tetramethylene sulfoxide) were found to have dodecahedral, tricapped trigonal prismatic, and square antiprismatic geometries, respectively. Average U-O bond distances in [U(dmso)₈](ClO₄)₄ · 0.75CH₃NO₂, [U(dmso)₉](ClO₄)₄ · 4dmso, and [U(tmso)₈](ClO₄)₄ · 2tmso are 2.35(3), 2.41 (4), and 2.35(3) Å, respectively. Furthermore, it was found that [U(dmso)₈]⁴⁺ is in equilibrium with [U(dmso)₉]⁴⁺ in CH₃NO₂ solution containing dmso. Thermodynamic parameters for such an equilibrium are as follows: K (25 °C) = 3.4 ± 0.2 dm³ mol⁻¹, ΔH = −54.9 ± 4.5 kJ mol⁻¹, and ΔS = −174 ± 15 J K⁻¹ mol⁻¹.     

Crystal structure and spectroscopic properties of trans-bis(nicotinato)(1,4,8,11-tetraazacyclotetradecane)chromium(III) perchlorate

The trans-[Cr(cyclam)(nic-O)₂]ClO₄ (cyclam = 1,4,8,11-tetraazacyclotetradecane; nic-O = O-coordinated nicotinate) has been prepared and structurally characterized by single-crystal X-ray diffraction at 150 K. The chromium atom is in a tetragonally compressed octahedral environment with four N atoms of the macrocyclic ligand in equatorial positions and two O-bonded nicotinates in trans axial positions. The macrocyclic cyclam adopts the centrosymmetric trans-III configuration with six- and five-membered chelate rings in chair and gauche conformation, respectively. The IR and visible spectral properties are consistent with the result of X-ray crystallography. The resolved band maxima of the electronic d-d spectrum are fitted with secular determinant for quartet state energy of d³ configuration in tetragonal field including configurational interaction. It is found that the nitrogen atoms of the cyclam ligand are a strong σ-donors and that O-bonded nicotinato group has strong σ- and π-donor characteristics toward the chromium(III) ion.     

Remarkable chiral and luminescent properties of novel Yb(III) and Eu(III) complexes containing BINAPO ligand

Lanthanide complexes are of great importance for their prospective applications in wide range of science and technology. Chiral lanthanide complexes can constitute stereo-discriminating probes in biological media, owing to the luminescent properties of the rare-earth ions. Sensitized emission with narrow bandwidth, having fast radiation rate and high emission quantum efficiency are the main perspective for synthesizing the complexes. Attention has been given on remarkable chirality with high dissymmetry factors (g = Δε_ext/ε_max) of the complexes. For this purpose, beta-diketonato ligands with chiral BINAPO (1,1′-binapthyl phosphine oxide) ligand were chosen to achieve the goal. The complexes [Ln(TFN)₃(S-BINAPO)](TFN = 4,4,4-trifluoro-1(2-napthyl)-1,3-butanedione), [Ln(HFT)₃(S-BINAPO)] (HFT = 4,4,5,5,6,6,6-heptafluoro-1-(2-thienyl)-1,3-hexanedione) and [Ln(HFA)₃(S-BINAPO)](hfa = hexafluoroacetylacetonate) (where Ln = Yb, Eu) were synthesized. The complex, [Eu(TFN)₃(S-BINAPO)] gives strong red emission at 615 nm with narrow emission band (<10 nm) when excited by 465 nm light with quantum efficiency 86%. The dissymmetry factors (g = Δε_ext/ε_max) corresponding to the ⁷F₁ → ⁵D₀ transition at 590 nm is 0.091 for [Eu(TFN)₃(S-BINAPO)] and for [Yb(hfa)₃(S-BINAPO)](hfa = hexafluoroacetylacetonate) corresponding to the ²F_7/2 → ²F_5/2 transitions is 0.12, are among the largest values for both Eu and Yb complexes to date, respectively. The Eu complexes, [Eu(HFT)₃(S-BINAPO)] and [Eu(TFN)₃(S-BINAPO)] are found to be spontaneously emissive, showing bright red emission, when placed in sunlight or even in the laboratory when light is switched on.     

The McClure and Weiss models of Fe–O2 bonding for oxyhemes, and the HbO2 + NO reaction

For the Fe–O₂(S = 0) linkages of oxyhemes, valence bond (VB) structures are re-presented for the McClure [Fe^II(S = 1) + O₂(S = 1)], Pauling–Coryell [Fe^II(S = 0) + O₂*(S = 0)], and Weiss [Fe^III(S = ½) + O₂ ^?(S = ½)] models of bonding. The VB structures for the McClure and Weiss models are of the increased-valence type, with more electrons participating in bonding than occur in their component Lewis structures. The Fe–O bond number and O–O bond order for the McClure structure are correlated with measured Fe–O and O–O bond lengths for oxymyoglobin. Back-bonding from O ₂ ^? to Fe^III of the Weiss structure gives a restricted form of the McClure structure. The McClure and Weiss increased-valence structures are used to provide VB formulations of mechanisms for the oxyhemoglobin + NO reaction. The products of these two formulations are Hb⁺ and NO₃ ^? (where Hb is hemoglobin) and Hb⁺ and OONO^?, respectively. Because Hb⁺ and NO₃ ^? are the observed products, they provide an experimental procedure for distinguishing the McClure and Weiss models. It is also shown that the same type of agreement between McClure-type theory and experiment occurs for oxycoboglobin + NO, cytochrome P450 monooxygenases, and related hydrogen atom transfer reactions. In the appendices, the results of density functional theory and multireference molecular orbital calculations for oxyhemes are related to one formulation of the increased-valence wavefunction for the McClure model, and theory is presented for the calculation of approximate weights for the Lewis structures that are components of the McClure increased-valence structure.     

Synthesis of ruthenium(II) monosubstituted squarates: 1. Procedural considerations

Attempted syntheses of ruthenium(II) monosubstituted squarate complexes in acetonitrile using cis-[RuCl₂(dmso)₄] and anisole-, methoxy-, methyl- and diphenylamino-squarate ligands, respectively, resulted in the formation in each case of the monomer cis, fac-Ru(CH₃CN)Cl₂(dmso)₃ (1) with the ruthenium atom in a distorted octahedral environment. A second crop of crystals harvested from the reaction with the methoxysquarate ligand was identified as the oxalato-bridged dimer [{cis-(CH₃CN)(Cl)(dmso)₂Ru}₂(μ-C₂O₄)] (2). When cis-[RuCl₂(dmso)₄] and methylsquarate were reacted in aqueous solution instead of acetonitrile, the dimer [{fac-(Cl)(dmso)₃Ru}₂(μ-C₂O₄)] (3) was produced. The dimers 2 and 3 are formed from oxidation/ring opening of the methoxy- and methyl-squarate ligands, respectively. Use of the salts of these ligands instead of their non-ionised forms under different reaction conditions, afforded [Na] fac-[RuCl₃(dmso)₃] (4) and [(C₄H₉)₄N]₂[(C₄O₄)(C₄H₂O₄)₂] (7), respectively, which were shown to be products of competing reactions. The information acquired from these failed attempts has provided the basis for the development of a strategy to overcome these problems and lead to a successful synthetic route to ruthenium(II) monosubstituted squarates.     

Long-distance magnetic coupling in dinuclear copper(II) complexes with oligo-para-phenylenediamine bridging ligands

Two novel dinuclear copper(II) complexes of formulae [Cu₂(tren)₂(bpda)](ClO₄)₄ (2) and [Cu₂(tren)₂(tpda)](ClO₄)₄ (3) containing the tripodal tris(2-aminoethyl)amine (tren) terminal ligand and the 4,4′-biphenylenediamine (bpda) and 4,4″-p-terphenylenediamine (tpda) bridging ligands have been synthesized and structurally, spectroscopically, and magnetically characterized. Their experimentally available electronic spectroscopic and magnetic properties have been reasonably reproduced by DFT and TDDFT calculations. Single crystal X-ray diffraction analysis of 2 shows the presence of dicopper(II) cations where the bpda bridging ligand adopts a bismonodentate coordination mode toward two [Cu(tren)]²⁺ units with an overall non-planar, orthogonal anti configuration of the N-Cu-N threefold axis of the trigonal bipyramidal Cu^II ions and the biphenylene group. The electronic absorption spectra of 2 and 3 in acetonitrile reveal the presence of four moderately weak d-d transitions characteristic of a slightly distorted trigonal bipyramid stereochemistry of the Cu^II ions. TDDFT calculations on 2 identify these transitions as those taking place between the four lower-lying, doubly occupied a₂ (d_yz)², b₂ (d_xz)², b₁ (d_xy)², and a₁ (d_x²-y²)² orbitals and the upper, singly occupied a₁ (d_z²)¹ orbital of each trigonal bipyramidal Cu^II ion. Variable-temperature magnetic susceptibility measurements of 2 and 3 show the occurrence of moderate (J = −8.5 cm⁻¹) to weak intramolecular antiferromagnetic couplings (J = −2.0 cm^-1) [H = −JS₁·S₂ with S₁ = S₂ = S_Cu = ½] inspite of the relatively large copper-copper separation across the para-substituted biphenylene- (r = 12.3 Å) and terphenylenediamine (r = 16.4 Å) bridges, respectively. DFT calculations on 2 and 3 support the occurrence of a spin polarization mechanism for the propagation of the exchange interaction between the two unpaired electrons occupying the d_z² orbital of each trigonal bipyramidal Cu^II ion through the predominantly π-type orbital pathway of the oligo-p-phenylenediamine bridges, as reported earlier for the parent compound [Cu₂(tren)₂(ppda)](ClO₄)₄·2H₂O (1) with the 1,4-phenylenediamine (ppda) bridging ligand. Finally, a rather slow exponential decay of the antiferromagnetic coupling (-J) with the number of phenylene repeat units, -(C₆H₄)_n- (n = 1-3), has been found both experimentally and theoretically along this series of oligo-p-phenylenediamine-bridged dicopper(II) complexes. These results further support the ability of linear π-conjugated oligo-p-phenylene spacers to transmit the exchange interaction between the unpaired electrons of the two Cu^II centers with intermetallic distances in the range of 7.5-16.4 Å.     

Dinuclear alkoxo-bridged copper(II) coordination polymers: Syntheses, structural and magnetic properties

The alkoxo-bridged dinuclear copper(II) complexes [Cu₂(ap)₂(NO₂)₂] (1), [Cu₂(ap)₂(C₆H₅COO)₂] (2) and [Cu₂(ap)₂μ-1,3-C₆H₄(COO)₂(dmso)₂]·dmso (3) (ap = 3-aminopropanolato and dmso = dimethyl sulfoxide) have been synthesized via self-assembly from copper(II) perchlorate, 3-aminopropanol as main chelating ligand and nitrite and isophthalate anions as spacers and benzoate anion as auxiliary ligand. Complexes 1 and 3 crystallize as 2D and 1D coordination polymers, respectively, and their structures consist of dinuclear [Cu₂(ap)₂]²⁺ units connected with nitrite and isophthalate ligands. The adjacent dinuclear units of 2 and 1D polymers of 3 are further connected by hydrogen bonds resulting in the formation of 2D layers. The variable temperature crystallographic measurements of 1 at 100, 173 and 293 K indicate the static Jahn-Teller distortion with librational disorder in the nitrite group. Experimental magnetic studies showed that complexes 1-3 exhibit strong antiferromagnetic couplings. The values of the magnetic exchange coupling constant for 1-3 are well reproduced by the theoretical calculations.     

Photolysis of the ion pair [Pt(NH3)5Cl]S2O8: reduction of platinum(IV) induced by outer-sphere charge transfer excitation

The ion pair [Pt^IV(NH₃)₅Cl]³⁺S₂O₈²⁻ shows a S₂O₈²⁻ → [Pt(NH₃)₅Cl]³⁺ outer-sphere charge transfer (OSCT) absorption at λ_max=267 nm. OSCT excitation leads to the reduction of Pt(IV) by S₂O₈²⁻ to Pt(II) with φ=3×10⁻³ at λ_irr=280 nm.     

Synthesis, characterization and in vitro cytotoxicity studies of platinum(IV) complexes with thiouracil ligands

Reactions of [PtMe₃(bpy)(Me₂CO)][BF₄] (2) with the thionucleobases 2-thiouracil (s²Ura), 4-thiouracil (s⁴Ura) and 2,4-dithiouracil (s²s⁴Ura) resulted in the formation of complexes of the type [PtMe₃(bpy)(L-κS)][BF₄] (L = s²Ura, 3; s⁴Ura, 4; s²s⁴Ura, 5). The complexes were characterized by NMR spectroscopy (¹H, ¹³C, ¹⁹⁵Pt), IR spectroscopy as well as microanalyses. The coordination through the C4S groups (4, 5) was additionally confirmed by DFT calculations, where it was shown that these complexes [PtMe₃(bpy)(L-κS⁴)]⁺ (L = s⁴Ura, s²s⁴Ura) are about 5.8 (4b) and 3.3 kcal/mol (5b), respectively, more stable than the respective complexes, having thiouracil ligands bound through the C2X groups (X = O, 4a; S, 5a). For [PtMe₃(bpy)(s²Ura-κS²)][BF₄] (3) no preferred coordination mode could be assigned solely based on DFT calculations. Analysis of NMR spectra showed the κS² coordination. In vitro cytotoxic studies of complexes 3−5 on nine different cell lines (8505C, A253, FaDu, A431, A549, A2780, DLD-1, HCT-8, HT-29) revealed in most cases moderate activities. However, 3 and 5 showed significant activity towards A549 and A2780, respectively, possessing IC₅₀ values comparable to those of cisplatin. Cell cycle perturbations and trypan blue exclusion test on cancer cell line A431 using [PtMe₃(bpy)(s²s⁴Ura-κS⁴)][BF₄] (5) showed induction of apoptotic cell death. Furthermore, the reaction of [PtMe₃(OAc-κ²O,O′)(Me₂CO)] (6) with 4-thiouracil yielded the dinuclear complex [(PtMe₃)₂(μ-s⁴Ura_-H)₂] (7), which has been characterized by microanalysis, NMR (¹H, ¹³C, ¹⁹⁵Pt) and IR spectroscopy as well as ESI mass spectrometry. X-ray diffraction analysis of crystals yielded in an isolated case exhibited the presence of a hexanuclear thiouracilato platinum(IV) complex, possessing each three different kinds of methyl platinum(IV) moieties and 4-thiouracilato ligands. This exhibited the ability of 4-thiouracil platinum(IV) complexes to form multinuclear complexes.     

Complexes of N-thiophosphorylthioureas RNHC(S)NHP(S)(OiPr)2 (HL) (R = pyridin-2-yl, pyridin-3-yl, 6-amino-pyridin-2-yl) with copper(I): Crystal structures of Cu(PPh3)nL (n = 1, 2)

Reaction of the potassium salts of N-thiophosphorylated thioureas of common formula RNHC(S)NHP(S)(OiPr)₂ [R = pyridin-2-yl (HL^a), pyridin-3-yl (HL^b), 6-amino-pyridin-2-yl (HL^c)] with Cu(PPh₃)₃I in aqueous EtOH/CH₂Cl₂ leads to mononuclear [Cu(PPh₃)₂L^a,b-S,S′] (1, 2) and [Cu(PPh₃)L^c-S,S′] (3) complexes. Using copper(I) iodide instead of Cu(PPh₃)₃I, polynuclear complexes [Cu_n(L-S,S′)_n] (4-6) were obtained. The structures of these compounds were investigated by IR, ¹H, ³¹P{¹H} NMR spectroscopy, ES-MS and elemental analyses. The crystal structures of Cu(PPh₃)₂L^b (2) and Cu(PPh₃)L^c (3) were determined by single-crystal X-ray diffraction.     

Theoretical studies on DNA-binding, DNA-photocleavage and spectral properties of Co(III) complexes [Co(phen)2(L)] (L = pip, hpip, hnaip)

Theoretical studies on the DNA-binding, DNA-photocleavage and spectral properties of Co(III) polypyridyl complexes [Co(phen)₂(L)]³⁺ (L = pip, hpip, hnaip) have been carried out, using the density functional theory (DFT), Hartree-Fock (HF) and configuration interaction singles (CIS) methods. The optimized geometric structures of these Co(III) complexes in aqueous solution are more close to experimental data than those in vacuo at the B3LYP/LanL2DZ level. Based on the optimized geometric structures in solution, the electronic structures of these Co(III) complexes were analyzed and the trend in the DNA-binding constants (K_b) was reasonably explained. In particular, via the analysis of natural charges of the complexes in ground state and excited state, it is very interesting to find the following: under UV or visible light irradiation, the Co(Ш) polypyridyl complexes undergo an intra-molecular electron transfer from S₀ state to T₁ state, and the positive charges on the main-ligand in the T₁ state are greatly increased, so as to form a radical cation with strong oxidation ability. Meanwhile, the change in geometry of the complexes under light irradiation also helps to the radical cation easily approaching and further oxidating DNA-base-pairs. These results offer the theoretical explanation for the photo-induced oxidation-reduction mechanism which was experimentally proposed on DNA-photocleavage by Co(Ш) polypyridyl complexes. In addition, the electronic absorption spectra of these complexes were calculated and simulated in aqueous solution using the time dependent DFT (TDDFT) method, in satisfying agreement with experimental results, and the properties of experimental absorption bands have been theoretically explained in detail.     

EPR and H NMR spectroscopy and DFT study of pentaammineruthenium(III)phenylcyanamide complexes

The EPR and ¹H NMR spectroscopy of seven [Ru(NH₃)₅L]²⁺ complexes, where L = 3,5-dimethoxyphenylcyanamide (MeO₂pcyd), 3,4,5-trimethoxyphenylcyanamide (MeO₃pcyd), 4-nitrophenylcyanamide (NO₂pcyd), 2,3-dichlorophenylcyanamide (Cl₂pcyd), 2,4,6-trichlorophenylcyanamide (Cl₃pcyd), 2,3,5,6-tetrachlorophenylcyanamide (Cl₄pcyd) and pentachlorophenylcyanamide (Cl₅pcyd), was performed. EPR spectra of the complexes showed an axial signal with g_|| and g_⊥ at high and low field, respectively. The g_|| axis is suggested to lie along the Ru-cyanamide bond. Gas-phase DFT calculations of [Ru(NH₃)₅ phenylcyanamide]²⁺ showed spin density localized mostly on the phenylcyanamide ligand, in disagreement with EPR data. DFT/polarizable continuum model (PCM, water solvation) calculations shifted spin density towards ruthenium so that spin density was shared between ruthenium and phenylcyanamide ligand. Proton contact shifts were determined from NMR and EPR data and were used to estimate spin density distributions on phenyl ring carbons. The results showed that the DFT/PCM calculation overestimated spin density on phenyl ring carbons by approximately one order of magnitude. Donor-acceptor interactions between the solute and solvent that are not fully accounted for in the DFT/PCM method are suggested to stabilize the Ru(III) oxidation state.     

Antisymbiosis. Preferential coordination of anionic oxygen versus neutral sulfur donor atoms of methylsulfanyl- or methylsulfinyl-acetato, 2-benzoato and 2-phenolato to the cis-Pt(PPh3)2 and Pt(dppe) residues

The interaction of an excess of the title ligands L⁻ with the cis-Pt(phos)₂ moieties gives compounds a-bcis-[Pt(L-O)₂(phos)₂] (a, phos = P(Ph)₃; b, phos = 1/2 dppe), in which O- is preferred to S-coordination. Such preference is confirmed by the fact that the same products are obtained by reaction of excess of L⁻ with the previously reported a-d complexes [Pt(L-O,S)(phos)₂]⁺, (c, phos = PPh₃, d, phos = 1/2 dppe), for which chelate ring opening occurs with rupture of Pt-S rather than Pt-O bonds. Compound a can be obtained also by oxidative addition of HL to [Pt(PPh₃)₃]. The Pt-O bonds in compounds a-d are stable towards substitution by Me₂SO, pyridine and tetramethylthiourea. Substitution of L’s occurs with N,N′-diethyldithiocarbamate, which forms a very stable chelate with Pt(II). Thiourea and N,N′-dimethylthiourea also react, because they give rise to cyclometallated products [Pt(phos)₂(NRC(S)NHR)]⁺ (R = H, CH₃), with one ionised thioamido group, as revealed by an X-ray investigation of [Pt(PPh₃)₂(NHC(S)NH₂)]⁺. The preference of O versus S coordination, as well as the stability of the Pt-O bonds, are discussed in terms of antisymbiosis.     

Preparation and structural organisation of heteroleptic tetraphenylantimony(V) complexes comprising unidentately and bidentately coordinated O,O′-dialkyldithiophosphate groups: Multinuclear (C, P) CP/MAS NMR and single-crystal X-ray diffraction studies

O,O′-dipropyldithiophosphate and O,O′-di-iso-butyldithiophosphate (Dtph) tetraphenylantimony(V) complexes of the general formula [Sb(C₆H₅)₄{S₂P(OR)₂}] (R = C₃H₇, i-C₄H₉) were prepared and studied by means of ¹³C, ³¹P CP/MAS NMR spectroscopy and single-crystal X-ray diffraction. Distorted octahedral and trigonal bipyramidal molecular structures have been established for prepared complexes. These unexpected structural distinctions between chemically related compounds are defined by the principally different coordination modes of O,O′-dipropyldithiophosphate and O,O′-di-iso-butyldithiophosphate ligands in their molecular structures (i.e., S,S′-bidentate chelating and S-unidentately coordinated, respectively). To characterise quantitatively phosphorus sites in both species of dithiophosphate ligands, ³¹P chemical shift anisotropy parameters (δ_aniso and η) were calculated from spinning sideband manifolds in MAS NMR spectra. The ³¹P chemical shift tensors for the bidentate chelating and unidentately coordinated dithiophosphate ligands display a profoundly rhombic and nearly axially symmetric characters, respectively.     

Electrochemical reduction of rhenium(V) dithiocarbamate complexes trans-Re2O3(S2CNR2)4 in nonaqueous media

The electrochemistry for the reduction of tetrakis(dialkyl- and diphenyldithiocarbamato)-μ-oxodioxodirhenium complexes trans-Re₂O₃(S₂CNR₂)₄ (R = methyl, ethyl, propyl, butyl and phenyl) was investigated in seven nonaqueous solvents. The complexes underwent a reversible reduction involving one- electron at a platinum electrode to [Re₂O₃(S₂CNR₂)₄]⁻, which decomposed with the cleavage of the μ-oxo bridge to form ReO(S₂CNR₂)₂, R₂CNS₂⁻ and other rhenium complexes. The redox potential E^o′ of [Re₂O₃(S₂CNR₂)₄]^0/− couples and the stability of the reduction product [Re₂O₃(S₂CNR₂)₄]⁻ depend on the R group. The E^o′ are appreciably solvent-dependent. The difference in E^o′ with solvents could be interpreted in terms of the solubility parameters.