Heteroleptic lanthanide terphenyl/tris(pyrazolyl)borate compounds of ytterbium

The synthesis and structural characterization of the two novel unsolvated heteroleptic ytterbium compounds DanipYb(Tp^Me,Me)Cl (1) and DanipYb(Tp^Me,Me)CH₂SiMe₃ (2) by simple salt metathesis reaction is reported [Danip = 2,6-di(o-anisol)phenyl); Tp^Me,Me = hydrotris(3,5-dimethyl-pyrazolyl)borate]. In the molecular structure of 2 a flexible bonding mode of the donor-functionalized terphenylic ligand is observed.     

Synthesis and structural analysis of calix[4]arene-supported iron(III) complexes

The paper describes the reactivity of calix[4]arene dialkyl- or -silylethers H₂R₂calix, R=Me (1), Bz (2), or SiMe₃ (3) (p-tert.butyl-calix[4]arene=H₄calix), towards the iron(III) complex [FeCl(NSiMe₃)₂(thf)] 4. Bis(silylation) of H₄calix was achieved using a mixture of NEt₃ and Me₃SiCl as silylating agent, which is probably the most convenient and cheapest way for the preparation of H₂(Me₃Si)₂calix 3. [FeCl(N{SiMe₃}₂)₂(thf)] 4 has been obtained from the reaction of [FeCl₃] and commercially available K[N(SiMe₃)₂] in THF. The reactions of 4 with H₂Me₂calix and H₂Bz₂calix afford mononuclear iron(III) chloro compounds [FeCl(R₂calix)] 5 (R=Me) and 6 (R=Bz). The usage of calix[4]arene silyl ether 3 leads to a dinuclear complex [Fe₂({Me₃Si}calix)₂] 7, presumably under Me₃SiCl cleavage of a mononuclear calixarene iron(III) chloro complex. The calix[4]arene ether stabilized iron(III) chloro complexes are susceptible to nucleophilic substitution reactions, as exemplified by the reaction of 5 with sodium azide yielding an azido complex [Fe(N₃)(Me₂calix)] 8. The molecular structures of 4, 5, 6, 7, and 8 in the solid state have been determined by X-ray diffraction.     

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.     

Synthesis and structure of heteroleptic ytterbium (II) tetrahydroborate complexes

The synthesis and characterization of (Tp^tBu,Me)Yb(BH₄)(THF)_n (n = 0, 3; n = 1, 4) complexes are reported. The compounds represent rare examples of lanthanide (II) tetrahydroborate complexes. The X-ray crystal structure of complex 4 has been determined and it shows a monomeric, formally seven coordinate ytterbium center, bearing one κ³ bonded Tp^tBu,Me ligand, a tetrahydroborate ligand and a coordinated THF molecule. The tetrahydroborate ligand binds in a κ³ fashion, via three bridging hydrogen atoms. IR spectroscopy data are consistent with the solid-state structure and the corresponding BD₄ analog of 4 shows the expected IR isotope shifts. The ¹H NMR spectra of 3 and 4 shows one set of resonances each for the BH₄ and the pyrazolylborate ligands indicating dynamic solution behavior. For complex 3, although X-ray quality crystals could not be obtained, the IR and NMR data are consistent with its formulation as the solvent-free analog of complex 4 with κ³-bonded BH₄ ligand.     

Rhodium and iridium olefin complexes with bulky cyclopentadienyl and hydrotris(pyrazolyl)borate ligands

The synthesis of a series of rhodium and iridium complexes bearing bulky cyclopentadienyl or hydro(trispyrazolyl)borate ligands is described. The rhodium cyclopentadienyl and hydrotris(pyrazolyl)borate diene compounds, [(η⁵-C₅Me₄Bu^t)Rh(η⁴-2,3-MeRC₄H₄] (R = H, 1; Me, 2) and Tp^MsRh(η⁴-2,3-MeRC₄H₄) (R = H, 3; Me, 4; Tp^Ms is hydrotris(3-mesitylpyrazol-1-yl)borate), respectively, have been prepared from the corresponding Rh(I) diene precursors and Zn(C₅Me₄Bu^t)₂ (for 1 and 2), or TlTp^Ms (for 3 and 4), as effective C₅Me₄Bu^t or Tp^Ms transfer reagents. In contrast with these results, attempts to obtain a bis(ethylene) derivative of the Tp^tolIr(I) unit (Tp^tol stands for hydrotris(3-p-tolylpyrazol-1-yl)borate) have provided instead the Ir(III) complex [(κ⁴-N,N′,N″,C-Tp^tol)-Ir(C₂H₅)(C₂H₄)] (5), whose formation requires C-H bond activation of a molecule of ethylene and of one of the Tp^tolp-tolyl substituents. In refluxing toluene 5 experiences metalation of a second p-tolyl substituent to give [(κ⁵-N,N′,N″,C,C′-Tp^tol)-Ir(C₂H₄)] (6), which features unusual κ⁵-Tp^tol coordination. The latter compound reacts with carbon monoxide to yield the corresponding carbonyl, 7.     

Synthesis and structures of aryloxo- and binaphthoxogermanium(IV) alkyl iodide complexes

The germanium(II) aryloxide complexes (S)-[Ge{O₂C₂₀H₁₀-(SiMe₂Ph)₂-3,3′}{NH₃}] (1) and [Ge(OC₆H₃Ph₂-2,6)₂] (2) react with either Bu^tI or MeI to yield the corresponding germanium(IV) compounds (S)-[Ge{O₂C₂₀H₁₀-(SiMe₂Ph)₂-3,3′}{Bu^t}{I}] (3), (S)-[Ge{O₂C₂₀H₁₀-(SiMe₂Ph)₂-3,3′}{Me}{I}] (4), [Ge(OC₆H₃Ph₂-2,6)₂(Bu^t)(I)] (5), and [Ge(OC₆H₃Ph₂-2,6)₂(Me)(I)] (6). Compound 6 reacts with 2,6-diphenylphenol to yield [Ge(OC₆H₃Ph₂-2,6)₃(Me)] (7), while 3-5 do not. The X-ray crystal structures of 3-5 and 7 were determined, and 3-5 represent the first structurally characterized germanium(IV) species having germanium bound to both oxygen and iodine.     

Syntheses, crystal structures, and characterization of heteronuclear complexes based on a versatile ligand with both acetylacetonate and bis(2-pyridyl) units

A new type of multidentate ligand with both acetylacetonate and bis(2-pyridyl) units on the 1,3-dithiole moiety, 3-[2-(dipyridin-2-yl-methylene)-5-methylsulfanyl-[1,3]dithiol-4-ylsulfanyl]-pentane-2, 4-dione (L), has been prepared. Through reactions of the ligand with Re(CO)₅X (X = Cl, Br), new rhenium(I) tricarbonyl complexes ClRe(CO)₃(L) (2) and BrRe(CO)₃(L) (3), have been obtained. With the use of 2 or 3 as the precursors, the further reactions with (Tp^Ph2)Co(OAc)(Hpz^Ph2) (Tp^Ph2 = hydrotris(3,5-diphenylpyrazol-1-yl)borate); Hpz^Ph2 = 3,5-diphenyl-pyrazole) or M(OAc)₂(M = Mn, Zn), afford four new heteronuclear complexes: ClRe(CO)₃(L)Co(Tp^Ph2) (4), BrRe(CO)₃(L)Co(Tp^Ph2) (5), [ClRe(CO)₃(L)]₂Mn(CH₃OH)₂ (6) and [ClRe(CO)₃(L)]₂Zn(CH₃OH)₂ (7), respectively. Crystal structures of complexes 2 and 4-7 have been determined by X-ray diffraction. Their absorption spectra, photoluminescence and magnetic properties have been studied.     

Zinc(II) complexes based on sterically hindered hydrotris(pyrazolyl)borate ligands: Synthesis, reactivity and solid-state structures

The coordination chemistry and reactivity of zinc(II) complexes supported by monoanionic hydrotris(pyrazolyl)borate ligands substituted by 3,3,3-mesityl groups (Tp^Ms) and 3,3,5-mesityl groups (Tp^Ms∗) have been investigated. Salt metathesis of ZnCl₂, ZnEt₂, and Zn(OAc)₂ with Tl[Tp^Ms] or Tl[Tp^Ms∗] cleanly afforded the corresponding compounds Tp^MsZnCl (1), Tp^MsZnEt (2), Tp^Ms∗ZnEt (3), and Tp^MsZnOAc (5). Compound 3 slowly disproportionates in benzene solution to afford the bis(ligand) complex (κ²-Tp^Ms∗)₂Zn (4). Acetate complex 5 as well as Tp^MsZnOCOPh (6) and [Tp^Ms∗ZnOAc]₂ (7) were alternatively prepared by acidolysis of the parent ethyl complexes (2, 3) with the corresponding carboxylic acid. No reaction was observed between 2 and 3 and alcohols (ROH; R = Et, iPr, Bn), while salt metathesis reactions of ZnEt(OR) with Tl[Tp^Ms] led to 2 instead of the desired zinc-alkoxide complex. Compounds 1-7 were characterized by elemental analysis, ¹H and ¹³C NMR spectroscopy, as well as by X-ray diffraction studies for 1, 2, 4, 5 and 7. The former compounds adopt a monomeric structure in the solid state while [Tp^Ms∗ZnOAc]₂ (7) exists as an anti-syn bridged acetate dimer. Complex 4 is four-coordinated, featuring a rare bidentate coordination mode of the Tp^Ms∗ ligands. The results are rationalized in terms of the variable steric constraint around the zinc atom provided by the Tp^Ms and Tp^Ms∗ ligands.     

Diverse reactivity of stereoisomers containing quadruply bonded dimolybdenum with oxygen: formation of [{Mo(η-N,N′-diisopropylbenzamidinato)oxo}2(μ-acetato)2(μ-oxo)]

The reaction of quadruply bonded dimolybdenum complex, [Mo₂(μ-OAc)₄] (1), with lithiated amidinato, Li[(NⁱPr)₂CR] (R = ^tBu; 2a, Me; 2b, Ph; 2c), was investigated. The reaction of 1 with 2a afforded the dark-red solid, whereas the product was so highly unstable that the product was not able to be characterized. In the case of acetamidinato 2b, lantern-type mixed-ligand quadruply bonded dimolybdenum complex, [Mo₂(μ-OAc){μ-(NⁱPr)₂CMe}₃] (3), was obtained as a yellow solid. In the reaction with benzamidinato 2c, symmetrical lantern-type dimolybdenum complex, [Mo₂(μ-OAc)₂ {μ-(NⁱPr)₂CPh}₂] (4), was isolated as a yellow solid. In the latter reaction, intermediary red compound (5), which is considered to be stereoisomer of 4 possessing non-lantern-type skeleton, was formed. However, isolation of 5 as a single component was not successful due to isomerization to 4. Complex 5 readily reacted with dry oxygen to give dimolybdenum(V) complex, [{Mo(η-(NⁱPr)₂CPh)oxo}₂ (μ-OAc)₂(μ-oxo)] (6), as a red solid. These complexes were characterized spectroscopically as well as, in some cases, by X-ray analyses.     

1,2-Borotropic shifts and B-N bond cleavage reactions in molybdenum hydrotris(3-isopropylpyrazolyl)borate chemistry: Mixed-valence MoMo2 and pyrazole-rich oxo-Mo complexes

Red-black [Tp^iPr∗Mo^VO]₂(μ-O)(μ-Mo^VIO₄) (1, Tp^iPr∗ = hydrobis(3-isopropylpyrazolyl)(5-isopropylpyrazolyl)borate) has been isolated as a by-product in the synthesis of NEt₄[Tp^iPrMo(CO)₃] (Tp^iPr = hydrotris(3-isopropylpyrazolyl)borate) and characterized by spectroscopic and X-ray crystallographic techniques. The trinuclear, mixed-valence complex contains two distorted octahedral anti-Tp^iPr∗Mo^VO centers bridged by bent oxo (Mo-O-Mo av. 158.7°) and tetrahedral κO,κO′-molybdate ligands. The complex contains a six-membered, non-planar Mo₃(μ-O)₃ core and two 1,2-borotropically-shifted Tp^iPr∗ ligands (with the shifted pyrazolyl trans to Mo^V=O). Aerial decomposition of solid NEt₄[Tp^iPrMo(CO)₃] produces sky-blue, diamagnetic Tp^iPrMoO(ⁱPrpz)(ⁱPrpzH) (2, ⁱPrpz^- = 3-isopropylpyrazolate, ⁱPrpzH = 3-isopropyl-2H-pyrazole). Molecules of 2 feature a tridentate fac-Tp^iPr ligand and mutually cis terminal oxo (MoO = 1.665(2) Å) and monodentate ⁱPrpz⁻ and ⁱPrpzH ligands. The latter are formed by B-N bond cleavage of Tp^iPr. The complex can also be synthesized by reacting NEt₄[Tp^iPrMo(CO)₃] with excess 3-isopropylpyrazole and dioxygen at 100 °C. Cleavage of the B-N bond(s) of Tp^iPr was also observed in the formation of Tp^iPrMoO(SPh)(ⁱPrpzH) (3) as a by-product in the synthesis of Tp^iPrMoO₂(SPh). In the monohydrate, 3 exhibits a distorted octahedral geometry defined by a tridentate fac-Tp^iPr ligand and mutually cis terminal oxo (MoO = 1.676(3) Å) and monodentate SPh⁻ and ⁱPrpzH ligands. The pyrazole β-NH group is observed to participate in a hydrogen-bond to the lattice water molecule. The complex can be synthesized in high yield by reducing Tp^iPrMoO₂(SPh) by HSPh or PPh₃ in the presence of excess 3-isopropylpyrazole.     

Linear and bent oxo-bridged dinuclear rhenium(V) complexes with terminal and bridging pyrazole ligands

The [ReOX₃(AsPh₃)(OAsPh₃)] (X = Cl or Br) complexes react with two equivalents of 3,5-dimetylopyrazole (3,5-Me₂pzH) in acetone at room temperature to give [{Re(O)X₂(3,5- Me₂pzH)₂}₂(μ-O)] (1 and 2). In the case of [ReOBr₃(AsPh₃)(OAsPh₃)], a small quantity of the dinuclear rhenium complex [{Re(O)Br(3,5-Me₂pzH)}₂(μ-O)(μ-3,5-Me₂pz)₂] (3) has been isolated next to the main product 2. Treatment of [ReOX₃(PPh₃)₂] compounds with two equivalents of 3,5-Me₂pzH in acetone at room temperature leads to the isolation of symmetrically substituted dinuclear rhenium complexes [{Re(O)X(PPh₃)}₂(μ-O)(μ-3,5-Me₂pz)₂] (4 and 5). Refluxing of [ReO(OEt)X₂(PPh₃)₂] complexes with 3,5-Me₂pzH in ethanol affords unsymmetrically substituted dinuclear rhenium [{Re(O)X(PPh₃)}(μ-O)(μ-3,5-Me₂pz)₂{Re(O)X(3,5- Me₂pzH)}] complexes (6 and 7). The complexes obtained in these reactions have been characterised by IR, UV-Vis, ¹H and ³¹P NMR. The crystal and molecular structures have been determined for 1, 2, 3, 4, 6 and 7 complexes.     

Synthesis and properties of new trinuclear Mo(II) complexes containing imidazole and benzimidazole ferrocene units

The reaction of FcCOCl (Fc = (C₅H₅)Fe(C₅H₄)) with benzimidazole or imidazole in 1:1 ratio gives the ferrocenyl derivatives FcCO(benzim) (L1) or FcCO(im) (L2), respectively. Two molecules of L1 or L2 can replace two nitrile ligands in [Mo(η³-C₃H₅)(CO)₂(CH₃CN)₂Br] or [Mo(η³- C₅H₅O)(CO)₂(CH₃CN)₂Br] leading to the new trinuclear complexes [Mo(η³-C₃H₅)(CO)₂(L)₂Br] (C1 for L = L1; C3 for L = L2) and [Mo(η³-C₅H₅O)(CO)₂(L)₂Br] (C2 for L = L1; C4 for L = L2) with L1 and L2 acting as N-monodentade ligands. L1, L2 and C2 were characterized by X-ray diffraction studies. [Mo(η³-C₅H₅O)(CO)₂(L1)₂Br] was shown to be a trinuclear species, with the two L1 molecules occupying one equatorial and one axial position in the coordination sphere of Mo(II). Cyclic voltammetric studies were performed for the two ligands L1 and L2, as well as for their molybdenum complexes, and kinetic and thermodynamic data for the corresponding redox processes obtained. In agreement with the nature of the frontier orbitals obtained from DFT calculations, L1 and L2 exhibit one oxidation process at the Fe(II) center, while C1, C3, and C4 display another oxidation wave at lower potentials, associated with the oxidation of Mo(II).     

Selective synthesis of triangular cluster oxido-sulfidocomplexes of Mo and W: High yield preparations of [Mo3O2S2(H2O)9], [W3O2S2(H2O)9], [W2MoO2S2(H2O)9] and their derivatization

Reaction of [Mo₂O₂(μ-S)₂(H₂O)₆]²⁺ with Mo(CO)₆ or metallic Mo under hydrothermal conditions (140 °C, 4 M HCl) gives oxido-sulfido cluster aqua complex [Mo₃(μ₃-S)(μ-O)₂(μ-S)(H₂O)₉]⁴⁺ (1). Similarly, [W₃(μ₃-S)(μ-O)₂(μ-S)(H₂O)₉]⁴⁺ (2) is obtained from [W₂O₂(μ-S)₂(H₂O)₆]²⁺ and W(CO)₆. While reaction of [Mo₂O₂(μ-S)₂(H₂O)₆]²⁺ with W(CO)₆ mainly proceeds as simple reduction to give 1, [W₂O₂(μ-S)₂(H₂O)₆]²⁺ with Mo(CO)₆ produces new mixed-metal cluster [W₂Mo(μ₃-S)(μ-O)₂(μ-S)(H₂O)₉]⁴⁺ (3) as main product. From solutions of 1 in HCl supramolecular adduct with cucurbit[6]uril (CB[6]) {[Mo₃O₂S₂(H₂O)₆Cl₃]₂CB[6]}Cl₂⋅18H₂O (4) was isolated and structurally characterized. The aqua complexes were converted into acetylacetonates [M₃O₂S₂(acac)₃(py)₃]PF₆ (M₃ = Mo₃, W₃, W₂Mo; 5a-c), which were characterized by X-ray single crystal analysis, electrospray ionization mass spectrometry and ¹H NMR spectroscopy. Crystal structure of (H₅O₂)(Me₄N)₄[W₃(μ₃-S)(μ₂-S)(μ₂-O)₂(NCS)₉] (6), obtained from 2, is also reported.     

Synthesis and reactivity of five- and six-coordinate hydrido(vinyl) iridium(III) complexes

The reaction of the dihydrido iridium(III) precursor [IrH₂(Cl)(PiPr₃)₂] (5) with internal alkynes RCC(CO₂Me) (R = Me, CO₂Me) afforded the five-coordinate hydrido(vinyl) complexes [IrH(Cl){(E)-C(R)CH(CO₂Me)}(PiPr₃)₂] (6, 7), via insertion of the alkyne into one of the IrH bonds. Compounds 6 and 7 are also accessible by careful hydrogenation of the alkyne iridium(I) derivatives trans-[IrCl{RCC(CO₂Me)}(PiPr₃)₂] (9, 10), the latter being prepared from in situ generated trans-[IrCl(C₈H₁₄)(PiPr₃)₂] and RCC(CO₂Me). UV irradiation of 6 (R = CO₂Me) led to the formation of the isomer [IrH(Cl){κ²(C,O)-C(CO₂Me)CHC(OMe)O}(PiPr₃)₂] (3) having the vinyl ligand coordinated in a bidentate fashion. While 6 reacted with acetonitrile and CO to afford the six-coordinate iridium(III) compounds [IrH(Cl){(E)-C(CO₂Me)CH(CO₂Me)}(L′)(PiPr₃)₂] (11, 12), treatment of 6 with LiC₅H₅ gave the half-sandwich-type complex [(η⁵-C₅H₅)IrH{(E)-C(CO₂Me)CH(CO₂Me)}(PiPr₃)] (13) by, the loss of one PiPr₃. The reaction of 3 with CO under pressure resulted in the formation of [IrH(Cl){(Z)-C(CO₂Me)CH(CO₂Me)}(CO)(PiPr₃)₂] (14) in which, in contrast to the stereoisomer 12, the two CO₂Me substituents are trans disposed.     

Synthesis and crystal structure of a salicylatooxovanadium(V) complex of an aminebis(phenolate) ligand: Kinetic studies on its formation from corresponding alkoxo complexes

Synthesis and single crystal X-ray structures of H₂L¹ and VO(L¹)(HL) [H₂L¹ = N,N-bis(2-hydroxy-3,5-ditertiarybutyl)-N′,N′-dimethylethylendiamine) or simply aminebis(phenol) and H₂L = salicylic acid) are reported here. The complex [VO(L¹)(HL)] is in distorted octahedral geometry under O₄N₂ donor environment where the basal core is defined by O(1), O(3), O(2) and N(5) atoms and two axial coordinates are occupied by O(4), an alkoxo-group and N(1), an imino-nitrogen atom. The electron spray mass spectrometric study on [VO(L¹)(HL)] in MeCN clearly points out the existence of single species in solution. Again, the ⁵¹V NMR of the bulk polycrystalline sample reveals that the complex [VO(L¹)(HL)] mainly exists in three out of four possible isomers. The formation of [VO(L¹)(HL)] from both [VO(L¹)(OMe)] and [VO(L¹)(OEt)] was followed kinetically by reacting with salicylic acid in MeCN. The presence of isosbestic point indicates a clean conversion of the reactants to product.     

Oxygenation of a low valent rhodium complex, TpRh(dppe): sequential conversion of molecular oxygen into peroxo and hydroperoxo complexes and characterization of the peroxo species

Sequential conversion of molecular oxygen into peroxo- and hydroperoxo-metal species involved in an effective O₂-activation is verified for the Tp^iPr2Rh system by isolation and characterization of the intermediates. O₂-treatment of the Rh(I) precursor, Tp^iPr2Rh(dppe) (1), in the presence of 3,5-diisopropylpyrazole (H-pz^iPr2) gives the κ²-peroxometal complex, Tp^iPr2(H-pz^iPr2)Rh(κ²-O₂) (2), which is subsequently converted to the hydroperoxo complex, Tp^iPr2(H-pz^H2)(pz^H2)Rh-OOH (4), upon treatment with pyrazole (H-pz^H2). The peroxo species 2 and 4 have been characterized by spectroscopic and crystallographic methods and it is revealed that, in the present N-rich coordination system, the basic peroxo ligands (O₂, OOH) form hydrogen-bonding interactions with the proximal N- and NH-functional groups.     

A series of oxo-vanadium(IV) complexes containing mixed ligands of poly(pyrazolyl)borate and organic carboxylic acid: Synthesis, structural characterization and primary study of bromination reaction activities

A series of oxo-vanadium(IV) complexes: Tp^∗VO(pzH^∗)(CH₃COO) (1), Tp^∗VO(pzH^∗)(CCl₃COO) (2), Tp^∗VO(pzH^∗)(C₆H₅COO) (3), Tp^∗VO(pzH^∗)(m-NO₂-C₆H₄COO)·CH₃CN (4) and [Tp^∗VO(pzH^∗)(H₂O)]⁺[m-NO₂-C₆H₄-SO₃]⁻·CH₃OH (5) (Tp^∗ = hydrotris(3,5-dimethylpyrazolyl)borate; pzH^∗ = 3,5-dimethylpyrazole) are synthesized in methanol solution under physiological conditions. They are characterized by elemental analysis, IR, UV-Vis and X-ray crystallography. Structural analyses show that the vanadium atoms in complexes 1-5 are all in a distorted-octahedral environment with the N₄O₂ donor set, and intra- or inter-hydrogen bonding linkages have been also observed in each complex. Bromination reaction activity of the complexes has been evaluated by the method with phenol red as organic substrate in the presence of H₂O₂, Br⁻ and phosphate buffer, indicating that they can be considered as potential functional model vanadium-dependent haloperoxidases. In addition, thermal analysis and quantum chemistry calculations were also performed and discussed in detail.     

Syntheses, characterization and DNA binding of mono- and diruthenium(II) complexes containing 2,2′-bis(1,2,4-triazino[5,6-f]phenanthren-3-yl)-4,4′-bipyridine and 2,2′-bipyridine ligands

A novel bridging ligand 2,2′-bis(1,2,4-triazino[5,6-f]phenanthren-3-yl)-4,4′-bipyridine (btpb) and its mononuclear ruthenium(II) complex [Ru(bpy)₂(btpb)]²⁺ (Rubtpb; bpy = 2,2′-bipyridyl) and dinuclear ruthenium(II) complex [Ru(bpy)₂(btpb)Ru(bpy)₂]⁴⁺ (Ru₂btpb) have been synthesized and characterized by elemental analyses, fast atom bombardment or electrospray mass spectra, ¹H NMR, and electronic spectroscopy. Binding behaviors of the mono- and dinuclear complexes with calf thymus DNA (CT-DNA) have been investigated by absorption spectra, viscosity measurements, and equilibrium dialysis experiments. As the concentration of DNA is increased, the electronic absorption spectra bands at the metal-ligand charge transfer of the mononuclear complex Rubtpb at 501.0 nm exhibit hypochromism of about 17.4% and bathochromism of 2.0 nm, the dinuclear complex Ru₂btpb at 511.0 nm exhibits hypochromism of about 24.8% and bathochromism of 1.0 nm. The increasing amounts of the complexes on the relative viscosities of CT-DNA are much smaller than that of the classic intercalators. The experiments suggest that the Rubtpb and Ru₂btpb may be bound to DNA by non-intercalating binder.     

Synthesis and structural studies of dimolybdenum(V), palladium(II) and dicopper(I) complexes that contain mixed pyridyl-iso-propylphosphine ligands

The reaction of Mo₂(μ-O₂CCH₃)₄ with 2-pyridyl(diisopropylphosphino)methane (NP) affords the dimolybdenum(V) complex Mo₂(μ-O)₂O₂Cl₂(η²-NP)₂ (1). Complexes of the related 2-pyridylbis(diisopropylphosphino)methane ligand (NP²) have been isolated, namely, a mixed bromo/chloro complex of composition PdBr_1.09Cl_0.91(η²-NP²) (2) and the dicopper(I) complex [Cu₂(μ-η³-NP²)₂](BF₄)₂ (3). The structures of 1, 2 and 3 have been established by X-ray crystallography.     

Synthesis and characterisation of bis(2,2′-bipyridine)(4-carboxy-4′-(pyrid-2-ylmethylamido)-2,2′-bipyridine)ruthenium(II) di(hexafluorophosphate): Comparison of spectroelectrochemical properties with related complexes

The new complex, [Ru^II(bpy)₂(4-HCOO-4′-pyCH₂ NHCO-bpy)](PF₆)₂ · 3H₂O (1), where 4-HCOO-4′-pyCH₂NHCO-bpy is 4-(carboxylic acid)-4′-pyrid-2-ylmethylamido-2,2′-bipyridine, has been synthesised from [Ru(bpy)₂(H₂dcbpy)](PF₆)₂ (H₂dcbpy is 4,4′-(dicarboxylic acid)-2,2′-bipyridine) and characterised by elemental analysis and spectroscopic methods. An X-ray crystal structure determination of the trihydrate of the [Ru(bpy)₂(H₂dcbpy)](PF₆)₂ precursor is reported, since it represented a different solvate to an existing structure. The structure shows a distorted octahedral arrangement of the ligands around the ruthenium(II) centre and is consistent with the carboxyl groups being protonated. A comparative study of the electrochemical and photophysical properties of [Ru^II(bpy)₂(4-HCOO-4′-pyCH₂NHCO-bpy)]²⁺ (1), [Ru(bpy)₂(H₂dcbpy)]²⁺ (2), [Ru(bpy)₃]²⁺ (3), [Ru(bpy)₂Cl₂] (4) and [Ru(bpy)₂Cl₂]⁺ (5) was then undertaken to determine their variation upon changing the ligands occupying two of the six ruthenium(II) coordination sites. The ruthenium(II) complexes exhibit intense ligand centred (LC) transition bands in the UV region, and broad MLCT bands in the visible region. The ruthenium(III) complex, 5, displayed overlapping LC bands in the UV region and a LMCT band in the visible. 1, 2 and 3 were found, via cyclic voltammetry at a glassy carbon electrode, to exhibit very positive reversible formal potentials of 996, 992 and 893 mV (versus Fc/Fc⁺) respectively for the Ru(III)/Ru(II) half-cell reaction. As expected the reversible potential derived from oxidation of 4 (−77 mV (versus Fc/Fc⁺)) was in excellent agreement with that found via reduction of 5 (−84 mV (versus Fc/Fc⁺)). Spectroelectrochemical experiments in an optically transparent thin-layer electrochemical cell configuration allowed UV-Vis spectra of the Ru(III) redox state to be obtained for 1, 2, 3 and 4 and also confirmed that 5 was the product of oxidative bulk electrolysis of 4. These spectrochemical measurements also confirmed that the oxidation of all Ru(II) complexes and reduction of the corresponding Ru(III) complex are fully reversible in both the chemical and electrochemical senses.