Synthesis, structures and in vitro cytotoxicity of some cationic cis-platinum(II) complexes containing chelating thiocarbamates

The thiocarbamates 4-RC₆H₄NHC(S)NR₂′ (R = H, Cl; R′ = Me, Et), 4-ClC₆H₄NHC(S)NR (NR = 2-pyridylpiperazine) react with cis-[PtCl₂(PTA)₂] (PTA = 1,3,5-triaza-7-phosphaadamantane) in the presence of base to afford the monocationic platinum(II) complexes cis-[Pt{SC(NR₂′) = NC₆H₄R}(PTA)₂]⁺ (R = H, Cl; R′ = Me, Et), cis-[Pt{SC(NR) = NC₆H₄Cl}(PTA)₂]⁺ (NR = 2-pyridylpiperazine), which were isolated as their PF₆ salts in high yields. The complexes were fully characterised spectroscopically and also by X-ray crystallography. Cytotoxicity of these complexes was studied in vitro in three human cancer cell lines (CH1, A549 and SW480) using the MTT assay.     

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.     

C-ansa-zirconocene complexes with O/S donor ligands: Novel homoleptic six coordinate 4-mercaptophenolate complex of Zr(IV)

New C-ansa-zirconocene complexes containing methoxythiophenolate and mercaptophenolate ligands have been synthesized and characterized. The reaction of (HSC₆H₄-n-OMe) (n = 2, 3 or 4) with [Zr{(t-Bu)HC(η⁵-C₅Me₄)(η⁵-C₅H₄)}Me₂] (1) led to the formation of monosubstituted complexes [Zr{(t-Bu)HC(η⁵-C₅Me₄)(η⁵-C₅H₄)}Me(κ,S-SC₆H₄-n-OMe)] (n = 2 (2); n = 3 (3)) and the disubstituted complex [Zr{(t-Bu)HC(η⁵-C₅Me₄)(η⁵-C₅H₄)}(κ,S-SC₆H₄-4-OMe)₂] (4). The complexes [Zr{(R)HC(η⁵-C₅Me₄)(η⁵-C₅H₄)}(κ,O-OC₆H₄-4-SH)₂] (R = t-Bu (6); R = CH₂CHCH₂ (7)) and [Zr(η⁵-C₅H₄)₂(OC₆H₄-n-SH)₂] (n = 3 (9); n = 4 (10)) have been synthesized using the corresponding dimethyl zirconocene and mercaptophenol. However, the reaction of [Zr{(t-Bu)HC(η⁵-C₅Me₄)(η⁵-C₅H₄)}Cl₂] (11) with 4-mercaptophenol in the presence of NEt₃ led to the formation of the first example of a homoleptic six-coordinate mercaptophenolate complex of zirconium, namely [HNEt₃]₂[Zr(κ,O-OC₆H₄-4-SH)₆] (12). Complex 12 can be obtained in higher yield by the reaction of ZrCl₄ with six equivalents of 4-mercaptophenol and NEt_3. The reaction of 12 with [Zr(η⁵-C₅H₄)₂Cl₂] gave the unexpected disubstituted complex [Zr(η⁵-C₅H₄)₂(OC₆H₄-4-SH)₂] (10). The molecular structures of 4 and 12 have been determined by single-crystal X-ray diffraction studies.     

Formation and structural chemistry of the unusual cyanide-bridged dinuclear species [Ru2(NN)2(CN)7] (NN = 2,2′-bipyridine or 1,10-phenanthroline)

Crystallisation of simple cyanoruthenate complex anions [Ru(NN)(CN)₄]²⁻ (NN = 2,2′-bipyridine or 1,10-phenanthroline) in the presence of Lewis-acidic cations such as Ln(III) or guanidinium cations results, in addition to the expected [Ru(NN)(CN)₄]²⁻ salts, in the formation of small amounts of salts of the dinuclear species [Ru₂(NN)₂(CN)₇]³⁻. These cyanide-bridged anions have arisen from the combination of two monomer units [Ru(NN)(CN)₄]²⁻ following the loss of one cyanide, presumably as HCN. The crystal structures of [Nd(H₂O)_5.5][Ru₂(bipy)₂(CN)₇] · 11H₂O and [Pr(H₂O)₆][Ru₂(phen)₂(CN)₇] · 9H₂O show that the cyanoruthenate anions form Ru-CN-Ln bridges to the Ln(III) cations, resulting in infinite coordination polymers consisting of fused Ru₂Ln₂(μ-CN)₄ squares and Ru₄Ln₂(μ-CN)₆ hexagons, which alternate to form a one-dimensional chain. In [CH₆N₃]₃[Ru₂(bipy)₂(CN)₇] · 2H₂O in contrast the discrete complex anions are involved in an extensive network of hydrogen-bonding involving terminal cyanide ligands, water molecules, and guanidinium cations. In the [Ru₂(NN)₂(CN)₇]³⁻ anions themselves the two NN ligands are approximately eclipsed, lying on the same side of the central Ru-CN-Ru axis, such that their peripheries are in close contact. Consequently, when NN = 4,4′-^tBu₂-2,2′-bipyridine the steric bulk of the t-butyl groups prevents the formation of the dinuclear anions, and the only product is the simple salt of the monomer, [CH₆N₃]₂[Ru(^tBu₂bipy)(CN)₄] · 2H₂O. We demonstrated by electrospray mass spectrometry that the dinuclear by-product [Ru₂(phen)₂(CN)₇]³⁻ could be formed in significant amounts during the synthesis of monomeric [Ru(phen)(CN)₄]²⁻ if the reaction time was too long or the medium too acidic. In the solid state the luminescence properties of [Ru₂(bipy)₂(CN)₇]³⁻ (as its guanidinium salt) are comparable to those of monomeric [Ru(bipy)(CN)₄]²⁻, with a ³MLCT emission at 581 nm.     

Synthesis of [SnPh2(SR)2] SR = SC6F4-4-H, SC6F5: Reactivity towards group 10 transition metal complexes

The organometallic tin(IV) complexes [SnPh₂(SR^F)₂] SR^F = ⁻SC₆F₄-4-H (1), ⁻SC₆F₅ (2), were synthesized and their reactivity with [MCl₂(PPh₃)₂] M = Ni, Pd and Pt explored. Thus, transmetallation products were obtained affording polymeric [Ni(SR^F)(μ-SR^F)]_n, monomeric cis-[Pt(PPh₃)₂(SC₆F₄-4-H)₂] (3) and cis-[Pt(PPh₃)₂(SC₆F₅)₂] (4) and dimeric species [Pd(PPh₃)(SC₆F₄-4-H)(μ-SC₆F₄-4-H)]₂ (5) and [Pd(PPh₃)(SC₆F₅)(μ-SC₆F₅)]₂ (6) for Ni, Pt and Pd, respectively. The crystal structures of complexes 1, 2, 3, 4 and 6 were determined.     

Synthesis, structures and in vitro cytotoxicity of some platinum(II) complexes containing thiocarbamate esters

The thiocarbamate esters 4-RC₆H₄NHC(S)OMe (R = H, Cl, OMe, NO₂, Me) react with cis-[PtCl₂(PTA)₂] (PTA = 1,3,5-triaza-7-phosphaadamantane) in the presence of base to afford the platinum(II) complexes trans-[Pt{SC(OMe)NC₆H₄R}₂(PTA)₂] (R = H, Cl, OMe, NO₂, Me) in high yields. The complexes were fully characterised spectroscopically and, in case of the NO₂ derivate, by X-ray crystallography. Cytotoxicity of these complexes was studied in vitro in four human cancer cell lines (CH1, HT29, A549, SK-OV-3) using the MTT assay. The results show that the Cl substituted derivate is the most potent of these compounds in vitro. Moreover, this derivative is capable of partially circumventing primary cisplatin resistance in ovarian and colon carcinoma cells.     

New aryl phosphinite ligands avoiding ortho-metallation: Synthesis and molecular structures of trans-[PdCl2(PPh2OR)2] and trans-[Rh(CO)Cl(PPh2OR)2] (R = 2,4,6-Me3C6H2; 2,6-Ph2C6H3)

The new aryl phosphinites PPh₂OR (R = 2,4,6-Me₃C₆H₂, 1; R = 2,6-Ph₂C₆H₃, 2) have been prepared from chlorodiphenylphosphine and the corresponding phenols. In these ligands, the ortho-positions of the aromatic phosphite function are blocked by methyl and phenyl substituents, which allows coordination to metal centres without ortho-metallation. Thus, reaction with [PdCl₂(cod)] leads to the complexes trans-[PdCl₂(PPh₂OR)₂] (R = 2,4,6-Me₃C₆H₂, 3; R = 2,6-Ph₂C₆H₃, 4), while the reaction with [Rh₂(CO)₄Cl₂] gives trans-[Rh(CO)Cl(PPh₂OR)₂] (R = 2,4,6-Me₃C₆H₂, 5; R = 2,6-Ph₂C₆H₃, 6). The single-crystal X-ray structure analyses of 3 and 5 confirm the trans-coordination of the new ligands in these square-planar complexes.     

Mixed-valency with cyanides as terminal ligands: Diruthenium(III,II) complexes with the 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine bridge and variable co-ligands (CN vs. bpy or NH3)

New diruthenium complexes (PPN)₄[(NC)₄Ru(μ-bptz)Ru(CN)₄], (PPN)₄1, and [(bpy)₂Ru(μ-bptz)Ru(CN)₄], 2, (PPN⁺ = bis(triphenylphospine)iminium; bptz = 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine; bpy = 2,2′-bipyridine), were synthesised and characterised by spectroscopic and electrochemical techniques. The comproportionation constant K_c = 10^7.0 of the mixed-valent species [(NC)₄Ru(μ-bptz)Ru(CN)₄]³⁻ as obtained by oxidation of 1⁴⁻ in CH₃CN is much lower than the K_c = 10^15.0 previously detected for [(H₃N)₄Ru(bptz)Ru(NH₃)₄]⁵⁺, reflecting the competition between CN⁻ and bptz for the π-electron density of the metals. Comparison with several other bptz-bridged diruthenium(II,III) complexes reveals an approximate correlation between K_c and the diminishing effective π acceptor capacity of the ancillary terminal ligands. In addition to the intense MLCT absorption at λ_max = 624 nm, the main IVCT (intervalence charge transfer) band of 1³⁻ was detected by spectroelectrochemistry at λ_max = 1695 nm (in CH₃CN; ε = 3200 M⁻¹ cm⁻¹). The experimental band width at half-height, Δν_1/2 = 2700 cm⁻¹, is slightly smaller than the theoretical value Δν_1/2 = 3660 cm⁻¹, calculated from the Hush approximation for Class II mixed-valent species. In agreement with comparatively moderate metal-metal coupling, the mixed-valent intermediate 1³⁻ was found to be EPR silent even at 4 K. The unsymmetrical mixed-valent complex [(bpy)₂Ru^II(μ-bptz)Ru^III(CN)₄]⁺, obtained in situ by bromine oxidation of 2 in CH₃CN/H₂O, displays a broad NIR absorption originating from an IVCT transition at λ_max = 1075 nm (ε ≈ 1000 M⁻¹ cm⁻¹, Δν_1/2 ≈ 4000 cm⁻¹). In addition, the lifetime of the excited-state of the mononuclear precursor complex [Ru(bptz)(CN)₄]²⁻ was measured in H₂O by laser flash photolysis; the obtained value of τ = 19.6 ns reveals that bptz induces a metal-to-ligand electronic delocalisation effect intermediate between that induced by bpy and bpz (bpz = 2,2′-bipyrazine) in analogous tetracyanoruthenium complexes.     

Ditopic tris(2-mercaptoimidazol-1-yl)borate ligands and their coordination behavior toward [Ru(p-cymene)]

The ditopic tris(2-mercaptoimidazol-1-yl)borate ligand K₂[(mt^Et)₃B-B(mt^Et)₃] cannot be prepared from B₂(NMe₂)₄/4 Hmt^Et/2 Kmt^Et, because the stable intramolecular diadduct (mt^Et)B(μ-mt^Et)₂B(mt^Et) is generated instead (Hmt^Et = 2-mercapto-1-ethylimidazole). Introduction of a meta- or para-phenylene spacer between the two boron atoms precludes the 2-mercaptoimidazol-1-yl groups from adopting a bridging position so that the potassium salts K₂[(mt^Et)₃B-(m-C₆H₄)-B(mt^Et)₃] and K₂[(mt^Et)₃B-(p-C₆H₄)-B(mt^Et)₃] become readily accessible. These ligands react with [(p-cym)RuCl₂]₂ to give the dinuclear Ru^II complexes [(p-cym)Ru(mt^Et)₃B-(m-C₆H₄)-B(mt^Et)₃Ru(p-cym)]Cl₂ and [(p-cym)Ru(mt^Et)₃B-(p-C₆H₄)-B(mt^Et)₃Ru(p-cym)]Cl₂ (p-cym = p-cymene). After the exchange of the Cl⁻ counterions for [PF₆]⁻, both complexes have been crystallized and structurally characterized by X-ray diffraction.     

Single molecule magnet: Heterodinuclear cyano-bridged cubic cluster [(Tp)8Fe4Ni4(CN)12] (Tp = hydrotris(1-pyrazolyl)borate)

The octanuclear cyano-bridged cluster [(Tp)₈Fe₄Ni₄(CN)₁₂] · H₂O · 24CH₃CN (1) (Tp = hydrotris(1-pyrazolyl)borate) showing magnetic properties of single-molecule magnet has been synthesized by reaction of [fac-Fe(Tp)(CN)₃]⁻ with {(Tp)Ni(NO₃)} species formed from an equimolar reaction mixture of Ni(NO₃)₂ · 6H₂O and KTp in MeCN. The X-ray analysis of 1 shows molecular cube structure in which Fe^III and Ni^II ions reside in alternate corners. The average intramolecular Fe?Ni distance is 5.124 Å. Out-of-phase ac susceptibility and reduce magnetization measurements show that 1 is a single molecule magnet with ground spin state S = 6 and spin reversal energy barrier U = 14 K. Magnetic hysteresis loops were also observed by applying fast sweeping field.     

Novel Pt(II) and Pt(IV) complexes with 3-amino-5-methyl-5-(4-pyridyl)-2,4-imidazolidenedione. Synthesis, physicochemical, chemometric and pharmacological investigation

Platinum(II) and platinum(IV) complexes with 3-amino-5-methyl-5-(4-pyridyl)-2,4-imidazolidenedione (L) with general formulaе cis-[PtL₂X₂]·nH₂O and [PtL₂Cl₄], where X = Cl⁻, Br⁻, I⁻ and n = 2-4) were synthesized. The novel compounds were fully characterized by elemental analysis, IR, ¹H, ¹³C, ¹⁹⁵Pt NMR spectra, thermal analysis and molar conductivity. The geometry of Pt(II) complexes and of the organic ligand in the gas phase were optimized using the hybrid DFT method B3LYP with LANL2DZ and 6-31G** basis sets. Some physicochemical parameters as dipole moment, HOMO, LUMO energies and ESP charges were calculated. The comparison of the bond length and angles, obtained from the X-ray analysis and DFT calculations is realized. The cytotoxic effects of these complexes in human T-cell leukemia KE-37 (SKW-3) are reported.     

The cyanocarbanion (C[C(CN)2]3) as monodentate ligand: Synthesis, structure and magnetic properties of [Mn2(bpym)3(tcpd)2(H2O)2] (tcpd = (C[C(CN)2]3) and bpym = 2,2′-bipyrimidine)

One-pot reaction between MnCl₂·4H₂O, K₂tcpd (tcpd²⁻ = [C₁₀N₆]²⁻ = (C[C(CN)₂]₃)²⁻ = 2-dicyanomethylene-1,1,3,3-tetracyanopropanediide anion) and 2,2′-bipyrimidine (bpym = C₈H₆N₄) in aqueous solution yields the new compound [Mn₂(bpym)₃(tcpd)₂(H₂O)₂] (1). The molecular structure of 1 consists of a centrosymmetrical binuclear complex which includes unprecedented unidentate tcpd ligands with two bidentate and a bis-chelate bpym units. Examination of the intermolecular distances reveals that the dinuclear units are held together by hydrogen bonds involving coordinated water molecules and two nitrile groups of the tcpd ligand, giving rise to a 2D structure overall. Variable-temperature magnetic susceptibility data show the occurrence of slight antiferromagnetic coupling (J = −0.58 cm⁻¹) between the Mn(II) ions through bridging bpym (the exchange Hamiltonian being defined as ).     

Multinuclear magnetic resonance study of Pt(II) compounds with sulfoxide ligands and crystal structures of complexes of the types [Pt(R2SO)X3] and Pt(R2SO)2Cl2

Pt(II) complexes of the types K[Pt(R₂SO)X₃], NR₄[Pt(R₂SO)X₃] and Pt(R₂SO)₂Cl₂ (where X = Cl or Br) were characterized by multinuclear magnetic resonance spectroscopy (¹⁹⁵Pt, ¹H and ¹³C). In ¹⁹⁵Pt NMR, the chloro ionic compounds have shown signals between −2979 and −3106 ppm, while the cis disubstituted complexes were observed at higher fields, between −3450 and −3546 ppm. The signal of the compound trans-Pt(DPrSO)₂Cl₂ was found at higher field (−3666 ppm) than its cis analogue (−3517 ppm), since π-back-donation is considerably less effective in the trans geometry. In ¹H NMR, a single signal was observed for the sulfoxide in [Pt(DMSO)Cl₃]⁻, but for the other more sterically hindered ligands, two series of resonances were observed for the protons in α and β positions. The coupling constant ³J(¹⁹⁵Pt-¹H) are between 15 and 33 Hz. The ¹³C NMR results were interpreted in relation to the concept of inversed polarization of the π sulfoxide bond. The ²J(¹⁹⁵Pt-¹³C) values vary between 35 and 66 Hz, while a few ³J(¹⁹⁵Pt-¹³C) couplings were observed (13-26 Hz). The crystal structures of five monosubstituted ionic compounds N(n-Bu)₄[Pt(TMSO)Cl₃], N(Me)₄[Pt(DPrSO)Cl₃], K[Pt(EMSO)Cl₃], K[Pt(TMSO)Br₃] · H₂O and N(Et)₄[Pt(DPrSO)Br₃] and one disubstituted complex cis-Pt(DBuSO)₂Cl₂ were determined. The trans influence of the different ligands is discussed.     

Interaction of free functional group with platinum(II) center in cyclometalated complexes: A structural and photophysical property investigation

A series of flexible multidentate ligands containing N,P-donor, 2-[N-(diphenylphosphino)methyl]amino-pyridine (L¹), 2-[N-bi-(diphenylphosphino) methyl]amino-pyridine (L²), 2-[N-(diphenylphosphino)methyl]amino-7-methyl-1,8-naphthyridine (L³) and 4-[(N-diphenylphosphino)methyl]amino-pyridine) (L⁴) have been synthesized. The mono- and dinuclear cyclometalated platinum(II) complexes [Pt(C^N^N)L¹]ClO₄ (HC^N^N = 6-phenyl-2,2′-bipyridine), [Pt₂(C^N^N)₂L¹](ClO₄)₂, [Pt₂(C^N^N)₂L²](ClO₄)₂, [Pt(C^N^N)L³]ClO₄ and [Pt₂(C^N^N)₂L⁴](ClO₄)₂ were prepared and their structures determined by X-ray crystal analysis. These complexes exhibit long-lived bright orange emissions ranging from 560 to 610 nm in the solid state at room temperature. In solution, dinuclear complexes have emissions with higher quantum yields than mononuclear complexes. This can be attributed to intramolecular interaction of free functional group with Pt(II) at axial position, resulting in the quenching of phosphorescence for platinum(II) complexes in the ³MLCT excited state.     

Reactivity study of arene(azido)ruthenium N∩O-base complexes with activated alkynes

Substitution reaction of chloro η⁶-arene ruthenium N∩O-base complexes [(η⁶-arene)Ru(N∩O)Cl] [N∩O = pyrazine-2-carboxylic acid (pca-H), 8-hydroxyquinoline (hq-H); arene = p-ⁱPrC₆H₄Me, N∩O = hq (1); arene = C₆Me₆, N∩O = hq (2)] with NaN₃ yield the neutral arene ruthenium azido complexes of the general formula [(η⁶-arene)Ru(N∩O)N₃] [N∩O = pca, arene = p-ⁱPrC₆H₄Me (3), arene = C₆Me₆ (4); N∩O = hq, arene = p-ⁱPrC₆H₄Me (5), arene = C₆Me₆ (6)]. These complexes undergo [3 + 2] dipolar cycloaddition reaction with activated alkynes dimethyl and diethyl acetylenedicarboxylates to yield the arene triazole complexes [(η⁶-arene)Ru(N∩O){N₃C₂(CO₂R)₂}] [N∩O = pca, R = Me, arene = p-ⁱPrC₆H₄Me (7), C₆Me₆ (8); R = Et, arene = p-ⁱPrC₆H₄Me (9), C₆Me₆ (10); N∩O = hq, R = Me, arene = p-ⁱPrC₆H₄Me (11) C₆Me₆ (12); R = Et, arene = p-ⁱPrC₆H₄Me (13), C₆Me₆ (14)]. On the bases of proton NMR study, in the above triazole complexes N(2) isomers are assigned with dimethylacetylenedicarboxylate whereas N(1) isomers with diethylacetylenedicarboxylate. All complexes have been characterized by IR and NMR spectroscopy as well as by elemental analysis. The molecular structures of the azido complexes [(η⁶-p-ⁱPrC₆H₄Me)Ru(pca)N₃] (3), [(η⁶-p-ⁱPrC₆H₄Me)Ru(hq)N₃] (5) and [(η⁶-C₆Me₆)Ru(hq)N₃] (6) have been established by single crystal X-ray diffraction studies.     

Short-bite aminobis(phosphonite) containing olefinic functionalities, PhN{P(OC6H3(OMe-o)(C3H5-p))2}2: Synthesis and transition metal complexes

Short-bite aminobis(phosphonite) containing olefinic functionalities, PhN{P(OC₆H₃(OMe-o)(C₃H₅-p))₂}₂ (1) was synthesized by reacting PhN(PCl₂)₂ with eugenol in the presence of triethylamine. The ligand 1 acts as a bidentate chelating ligand toward metal complexes [M(CO)₄(C₅H₁₀NH)₂] forming [M(CO)₄{η²-PhN{P(OC₆H₃(OMe-o)(C₃H₅-p))₂}₂}] (M = Mo, 2; W, 3). The reaction between 1 and [CpFe(CO)₂]₂ leads to the cleavage of one of the P-N bonds due to the metal assisted hydrolysis to give a mononuclear complex [CpFe(CO){P(O)(OC₆H₃(OMe-o)(C₃H₅-p))₂}{PhN(H)(P(OC₆H₃(OMe-o)(C₃H₅-p))₂)}] (4). Treatment of 1 with gold(I) derivative, [AuCl(SMe₂)] resulted in the formation of a dinuclear complex, [(AuCl)₂{PhN{P(OC₆H₃(OMe-o)(C₃H₅-p))₂}₂}] (5) with a Au···Au distance of 3.118(2) Å indicating the possibility of aurophilic interactions. An equimolar reaction between 1 and [Ru(η⁶-p-cymene)Cl₂]₂ afforded a tri-chloro-bridged bimetallic complex [(η⁶-p-cymene)Ru(μ-Cl)₃Ru{PhN(P(OC₆H₃(OMe-o)(C₃H₅-p))₂)₂}Cl] (6). The crystal structures of 1-3 and 5 were established by single crystal X-ray diffraction studies.     

Synthesis and characterization of Pt(II) and Pt(II)/Ru(II) complexes with the bidentate bridging ligand dipyrido(2,3-a:3′,2′-h)phenazine (dpop)

Three new complexes [Pt(dpop)(Cl)₂], [(Cl)₂Pt(dpop)Pt(Cl)₂] and [(bpy)₂Ru(dpop)Pt(Cl)₂](PF₆)₂ (dpop = dipyrido(2,3-a:3′,2′-h)phenazine) were prepared and studied. The electronic absorption spectra of the complexes display Pt dπ → dpop π* and Ru dπ → dpop π* MLCT transitions at longer wavelengths than for previously reported similar complexes. Results of cyclic voltammograms show reversible dpop centered reductions while for the mixed metal [(bpy)₂Ru(dpop)Pt(Cl)₂]²⁺ an irreversible Pt(II) oxidative wave precedes the Ru(II) oxidation/reduction couple. Spectroelectrochemical results show that all oxidative and reductive processes are completely reversible. The [(Cl)₂Pt(dpop)Pt(Cl)₂] complex cleaves in solution with pseudo-first order kinetics resulting in loss of the Pt dπ → dpop π* MLCT transition at 545 nm.     

Cobalt(II) and nickel(II) coordination polymers constructed from P,P′-diphenylmethylenediphosphinic acid (H2pcp) and 4,4′-bipyridine (bipy): Structural isomerism in [Co(pcp)(bipy)0.5(H2O)2]

The P,P′diphenylmethylenediphosphinic acid (H₂pcp) reacts with Co(ClO₄)₂ · 6H₂O and 4,4′-bipyridine to give a mixture of two polymeric isomers of formula [Co(pcp)(bipy)_0.5(H₂O)₂], {red (1) and pink (2)} and the new violet hybrid [Co(Hpcp)₂] (3). The pure red and violet species have been obtained by the reaction of H₂pcp with Co(CH₃COO)₂ · 4H₂O and bipy or with Co(ClO₄)₂ · 6H₂O, respectively. The analogous reaction of Ni(CH₃COO)₂ · 4H₂O or Ni(ClO₄)₂ · 6H₂O with H₂pcp and bipy affords only the [Ni(pcp)(bipy)_0.5(H₂O)₂] species (4). The two cobalt isomers present different structural arrangements. Whereas the red isomer (1) shows an undulated 2D layered structure, the pink one (2) forms an infinite monodimensional strand. Both the architectures extend to higher dimensions through hydrogen bonding interactions. The nickel derivative is isomorphous with the red cobalt isomer. The violet [Co(Hpcp)₂] (3), which is isomorphous with the complexes of the reported series [M(Hpcp)₂], M = Ca(II), Mg(II), presents a monodimensional polymeric structure. Compounds 1 and 4 show a very similar thermal behaviour, the two water molecules being lost in the temperature range 25-150 and 160-320 °C, respectively. Temperature dependent X-ray powder diffractometry (TDXD) has been performed on compound 1 in order to follow the structural transformations that occur during the heating process.     

Taniaphos and Walphos ligands: Oxidative electrochemistry and complexation. Synthesis, characterization, oxidative electrochemistry and X-ray structures of [(Taniaphos/Walphos)MCl2] (M = Pd or Pt)

The oxidative electrochemistry of chiral, bidentate ferrocenylphosphines, five Taniaphos and seven Walphos ligands, was studied in methylene chloride. In general, two waves of varying reversibility were observed. Complexes of the general type [(phosphine)MCl₂] (phosphine = Taniaphos or Walphos; M = Pd or Pt) were prepared and characterized by NMR. Upon coordination, the oxidative electrochemistry of the ligands was greatly simplified. The X-ray structures of a Taniaphos platinum complex as well as a palladium and a platinum complex with a Walphos ligand were determined.     

Ru2(CO)4(OOCR)2L2 sawhorse-type complexes containing axial 5-(4-pyridyl)-10,15,20-triphenylporphyrin ligands

The thermal reaction of Ru₃(CO)₁₂ with various carboxylic acids (benzoic, 4-hydroxyphenylacetic, ferrocenic, stearic, oleic, 4-(octadecyloxy)benzoic) in refluxing tetrahydrofuran, followed by addition of 5-(4-pyridyl)-10,15,20-triphenylporphyrin (L), gives the dinuclear complexes Ru₂(CO)₄(OOCR)₂L₂ (1: R = -C₆H₅, 2: R = -CH₂-p-C₆H₄OH, 3: R = -C₅H₄FeC₅H₅, 4: R = -(CH₂)₁₆CH₃, 5: R = -(CH₂)₇CHCH(CH₂)₇CH₃, 6: R = -p-C₆H₄O(CH₂)₁₇CH₃). Complexes 1-6 were characterised by IR, NMR, and ESI-MS as well as by elemental analysis. The UV-Vis spectra show the Soret band centred at 417 nm and the Q bands at 515, 550, 590 and 645 nm, respectively.