From the {Cu(μ2-S)N}4 butterfly architecture to the {Cu(μ3-S)N}12 double wheel

Copper(I) complexes with {Cu(μ₂-S)N}₄ and {Cu(μ₃-S)N}₁₂ core portions of butterfly-shaped or double wheel architectures have been isolated in the reaction of Cu(I) with the Schiff base ligand C₆H₄(CHNC₆H₄S)₂, “iso-abt”, under different conditions. containing the tetranuclear electroneutral complex is formed by the reaction of CuI in acetonitrilic solution and recrystallization from DMF, whereas containing dodecanuclear wheels is accessible starting from CuBF₄. Complexes 2 and 4 represent the first examples of cyclic complexes with the same overall stoichiometry but different ring sizes. The ligand induces two different coordination environments around copper(I) by switching between μ₂- and μ₃-sulfur bridging modes.     

Photochemical reactions of trans-[Ru(NH3)4L(NO)] complexes

The photochemical behavior of a series of trans-[Ru(NH₃)₄L(NO)]³⁺ complexes, where L=nitrogen bound imidazole, L-histidine, 4-picoline, pyridine, nicotinamide, pyrazine, 4-acetylpyridine, or triethylphosphite is reported. In addition to ligand localized absorption bands (<300 nm), the electronic spectra of these complexes are dominated by relatively low intensity bands assigned as ligand field (LF) and metal to ligand (d_π → NO) charge transfer (MLCT) transitions. Irradiation of aqueous solutions of these complexes with near-UV light (300-370 nm) labilizes NO, i.e.,

     

The preparation, characterisation and low temperature X-ray structure of Ru6(η-μ4-CO)2(CO)13(η6-C6Me6)

The new organometallic cluster (η²-μ₄-CO)₂(CO)₁₃(η⁶-C₆Me₆) has been prepared by the thermolysis of Ru₃(CO)₁₂ with hexamethylbenzene in octane and characterised by a single crystal X-ray diffraction study. It is isostructural with the known cluster Ru₆(η²-μ₄-CO)₂(CO)₁₃(η⁶-C₆H₃Me₃) and the metal core constitutnts the same tetrahedral Ru₄ unit with two edge-bridging Ru atoms. The mesitylene derivative has been shown to undergo rearrangement to afford the octahedral carbido cluster Ru₆C(CO)₁₄(η⁶-C₆H₃Me₃), but this conversion is not observed for the new hexamethylbenzene derivative.     

Synthesis and structures of the cuboidal iron-sulfur-nitrosyl-phosphine clusters [Fe4S3(NO)4(PR3)3] (R = Et, Pr, C6H11)

A series of cuboidal iron-sulfur clusters [Fe₄S₃(NO)₄(PR₃)₃]^0,1+ (R = Et, Prⁱ, Cy) were synthesized by two routes: reductive desulfurization of [Fe₄S₄(NO)₄] by tertiary phosphines, and substitution of triphenylphosphine in [Fe₄4S₃(NO)₄(PPh₃)₃] by a more basic phosphine. The structures of 3[Fe₄S₃(NO)₄(PEt₃)₃] · 0.5Et₂O, [Fe₄S₃(NO)₄(PEt₃)₃] [Fe₄S₃(NO)₇] and partially substituted [Fe₄S₃(NO)₄(PPh₃)_2⁻ (PPrⁱ₃)] have been determined by X-ray diffraction in order to define the cuboidal Fe₄S₃ core, previously known only in Roussin's black anion and its reduced form, [Fe₄S₃(NO)₇7]^1−,2−, and as a part of the iron-molybdenum cofactor of nitrogenase.     

Comparison in halide binding ability between the unsaturated clusters [Pd3(μ-dppm)3(CO)] and [PdPtCo(μ-dppm)2(CO)3(CNBu)] (dppm = Ph2PCH2PPh2)

The trinuclear clusters [Pd₃(μ-dppm)₃(CO)]²⁺ and [PtPdCo(μ-dppm)₂(CO)₃(CN^tBu)]⁺ exhibit a large and a small cavity, respectively, formed by the phenyl rings of the bridging diphosphine ligands. Their binding constants (K₁₁) with halide ions (X⁻) were obtained by UV-Vis spectroscopy. The binding ability varies as I⁻ > Br⁻ > Cl⁻, and [Pd₃(μ-dppm)₃(CO)]²⁺ > [ptPdCo(μ-dppm)₂-(CO)₃(CN^tBu)]⁺. The MO diagram for the related cluster [Pd₂Co(μ-dppm)₂(CO)₄]⁺ has been addressed theoretically in order to predict the nature of the lowest energy electronic bands. For this class of compounds, the lowest energy bands are assigned to charge transfers from the Co center to the Pd₂ centers.     

Dinitrosyl iron complexes [E5Fe(NO)2] (E = S, Se): A precursor of Roussin’s black salt [Fe4E3(NO)7]

[PPN][Se₅Fe(NO)₂] (1) and [K-18-crown-6-ether][S₅Fe(NO)₂] (2′) were synthesized and characterized by IR, UV-Vis, EPR spectroscopy, magnetic susceptibility, and X-ray structure. [PPN][Se₅Fe(NO)₂] easily undergoes ligand exchange with S₈ and (RS)₂ (R = C₇H₄SN (5), o-C₆H₄NHCOCH₃ (6), C₄H₃S (7)) to form [PPN][S₅Fe(NO)₂] and [PPN][(SR)₂Fe(NO)₂]. The reaction displays that [E₅Fe(NO)₂]⁻ (E = Se (3), S (4)) facilely converts to [Fe₄E₃(NO)₇]⁻ by adding acid HBF₄ or oxidant [Cp₂Fe][BF₄] in THF, respectively. Obviously, complexes 1 and 2′ serve as the precursors of the Roussin’s black salts 3 and 4. The electronic structure of {Fe(NO)₂}⁹ core of [Se₅Fe(NO)₂]⁻ is best described as a dynamic resonance hybrid of {Fe⁺¹(NO)₂}⁹ and {Fe⁻¹(NO⁺)₂}⁹ modulated by the coordinated ligands. The findings, EPR signal of g = 2.064 for 1 at 298 K, implicate that the low-molecular-weight DNICs and protein-bound DNICs may not exist with selenocysteine residues of proteins as ligands, since the existence of protein-bound DNICs and low-molecular-weight DNICs in vitro has been characterized with a characteristic EPR signal at g = 2.03. In addition, complex 2′ treated human erythroleukemia K562 cancer cells exposed to UV-A light greatly decreased the percentage survival of the cell cultures.     

Reaction of [Pt{Fe(CO)3(NO)}2(PhCN)2] with diphenyl(2-pyridyl)phosphine selenide. Crystal structure of [(CO)3Fe(μ3-Se){Pt(CO)P(2-C5H4N)Ph2}2] and its theoretical study

The reaction between the linear trinuclear complex [Pt{Fe(CO)₃(NO)}₂(PhCN)₂] and Ph₂(2-C₅H₄N)PSe led to the isolation and characterization of the 46-electron cluster [(CO)₃Fe(μ₃-Se){Pt(CO)P(2-C₅H₄N)Ph₂}₂] (1), whose structure has been determined by X-ray diffraction methods. The cluster typology, which consists of an open triangle Pt---Fe---Pt capped by a μ₃-Se atom, is rather rare. The chemical bonding in 1 and in similar systems has been analyzed through density functional theory (DFT) and qualitative MO approaches. A strict analogy with the well understood L₂M(μ-acetylene)ML₂ systems is invoked by considering 1 as formed by the (CO)₃FeSe tetrahedral unit stabilized by sidewise interactions of the triple bond with two d¹⁰-L₂M fragments. Otherwise, the 18-electron (CO)₃FeSe monomer is unstable as an isolate molecule. This is confirmed by our DFT calculations that indicate how the well characterized dimer (CO)₃Fe(μ-Se₂)Fe(CO)₃ lies as much as, approximately, 58 kcal mol⁻¹ deeper in energy. Finally, by considering an analogy with [L₂M(μ-dichalcogen)ML₂]^{0, +2} redox systems (M=Pd, Pt), reduction of 1 to a dianion has been hypothesized and the structure of the latter has been tentatively explored by DFT calculations.     

Dinuclear sulfide–thiolate complexes [Pt2(μ-S)(μ-SR)(PPh3)4] as cationic metalloligands

The cationic monoalkylated derivatives of the well-known metalloligand [Pt₂(μ-S)₂(PPh₃)₄], viz. [Pt₂(μ-S)(μ-SR)(PPh₃)₄]⁺ (R = n-Bu, CH₂Ph) are themselves able to act as metalloligands towards the Ph₃PAu⁺ and R′Hg⁺ (R′ = Ph or ferrocenyl) fragments, by reaction with Ph₃PAuCl or R′HgCl, respectively. The resulting dicationic products [Pt₂(μ-SR)(μ-SAuPPh₃)(PPh₃)₄]²⁺ and [Pt₂(μ-SR)(μ-SHgR′)(PPh₃)₄]²⁺ are readily isolated as their hexafluorophosphate salts, and have been fully characterised by spectroscopic techniques and an X-ray structure determination on [Pt₂(μ-SR)(μ-SHgFc)(PPh₃)₄](PF₆)₂.     

The coordination chemistry of cationic main group clusters: syntheses and structures of [Fe3(Se2)2(CO)10] and [Fe4(Se2)3(CO)12]

The reactions of the polysulfur and selenium cationic clusters S₈²⁺ and Se₈²⁺ with various iron carbonyls were investigated. Several new chalcogen containing iron carbonyl cluster cations were isolated, depending on the nature of the counteranion. In the presence of SbF₆⁻ as a counterion, the cluster [Fe₃(E₂)₂(CO)₁₀] [SbF₆]₂·SO₂ (E = S, Se) could be isolated from the reaction of E₈²⁺ and excess iron carbonyl. The cluster is a picnic-basket shaped molecule of two iron centers linked by two Se₂ groups, with the whole fragment capped by an Fe(CO)₄ group. Crystallographic data for C₁₀O₁₂Fe₃Se₄Sb₂F₁₂S (I): space group monoclinic P2₁/c, A = 11.810(9), b = 24.023(6), c = 10.853(7) Å, β = 107.15(5)°, V = 2942(3) ų, Z = 4, R = 0.0426, R_w = 0.0503. When Sb₂F₁₁⁻ is present as the counterion, or Se₄[Sb₂F₁₁]₂ is used as the cluster cation source, a different cluster can be isolated, which has the formula [Fe₄(Se₂)₃(CO)₁₂] [SbF₆]₂·3SO₂. The dication contains two Fe₂Se₂ fragments bridged by an Se₂ group. Crystallographic data for C₁₂O₁₈Fe₄Se₆Sb₂F₁₂S₃ (III): space group triclinic , b = 18.400(9), C = 10.253(4) Å, = 93.10(4), β = 103.74(3), γ = 93.98(3)°, V = 1995(1) ų, Z = 2, R = 0.0328, R_w = 0.0325. The CO stretches in the IR spectrum all show a large shift to higher wavenumbers, suggesting almost no τ backbonding from the metals. This also correlates with the observed bond distances. All the compounds are extremely sensitive to air and water, and readily lose SO₂ when removed from the solvent. Thus all the crystals were handled at −100°C. The clusters seem to be either insoluble or unstable in all solvents investigated.     

New precursors in the chemistry of IVB transition metal alkoxides V. Synthesis and molecular structure of Zr3Fe(μ4-O)(μ2-OC3H7)6-(OC3H7)4(acac)3

The reaction of iron(III) acetylacetonate with zirconium(IV) n-propanolate in n-propanol leads to a tetranuclear species Zr₃FeO(OC₃H₇)₁₀(acac)₃. This compound crystallizes in the triclinic system (space group P ): a = 12.426(2), b = 12.977(2), c = 20.129(4) Å, α = 91.55(1), β = 97.90(1), γ = 100.53(1)°. The structure consists of discrete tetranuclear molecules. The metal atoms design an almost perfect tetrahedron around a four-fold coordinated oxygen atom. The zirconium atoms are in a seven-fold coordination and the iron atom in a five-fold coordination.     

Cis- and trans-titanium complexes with doubly silyl-bridged dicyclopentadienyl ligands: molecular structure of [(TiCl)2(μ-O){(SiMe2)2(η-C5H3)2}]2(μ-O)2

The reaction of TiCl₄ with Li₂[(SiMe₂)₂(η⁵-C₅H₃)₂] in toluene at room temperature afforded a mixture of cis- and trans-[(TiCl₃)₂{(SiMe₂)₂(η⁵-C₅H₃)₂}] in a molar ratio of 1/2 after recrystallization. The complex trans-[(TiCl₃)₂{(SiMe₂)₂(η⁵-C₅H₃)₂}] was hydrolyzed immediately by the addition of water to THF solutions to give trans-[(TiCl₂)₂(μ-O){(SiMe₂)₂(η⁵-C₅H₃)₂}] as a solid insoluble in all organic solvents, whereas hydrolysis of cis-[(TiCl₃)₂{(SiMe₂)₂(η⁵-C₅H₃)₂}] under different conditions led to the dinuclear μ-oxo complex cis-[(TiCl₂)₂)(μ-O){(SiMe₂)₂(η⁵-C₅H₃)₂}] and two oxo complexes of the same stoichiometry [(TiCl)₂(μ-O){(SiMe₂)₂(η⁵-C₅H₃)₂}]₂(μ-O)₂ as crystalline solids. Alkylation of cis- and trans-[(TiCl₃)₂{(SiMe₂)₂(η⁵-C₅H₃)₂}] with MgCIMe led respectively to the partially alkylated cis-[(TiMe₂Cl)₂{(SiMe₂)₂(η⁵-C₅H₃)₂}] and the totally alkylated trans-[(TiMe₃)₂{(SiMe₂)₂(η⁵-C₅H₃)₂}] compounds. The crystal and molecular structure of the tetranuclear oxo complex [(TiCl)₂(μ-O){(SiMe₂)₂(η⁵-C₅H₃)₂}]₂(μ-O)₂ was determined by X-ray diffraction.     

The structure of the dichromium compound Cr2(μ-OH)2(μ-3,5Cl2-form)2(η-3,5Cl2-form)2

With exposure to trace amounts of air and moisture, the Cr₂(II, II) complex Cr₂(μ-3,5Cl₂-form)₄, where 3,5Cl₂-form is [(3,5-Cl₂C₆H₃)NC(H)N(3,5-Cl₂C₆H₃)⁻], undergoes an oxidative addition reaction. Structural information from the X-ray crystal structure of the edge-sharing bioctahedral (ESBO) Cr₂(III, III) product Cr₂(μ-OH)₂(μ-3,5Cl₂-form)₂(η²-3,5Cl₂-form)₂ (1) indicates 1 has a significantly longer Cr–Cr distance [2.732(2) Å] than Cr₂(μ-3,5Cl₂-form)₄ [1.9162(10) Å], but the shortest Cr–Cr distance in an ESBO Cr₂(III, III) complex recorded to date.     

Reinvestigation of the visible absorption bands of the 2,2′-bipyrimidine complexes W(CO)4(bpym) and (μ-bpym)[M(CO)4]2 (M=Mo, W) with resonance Raman spectroscopy; the emission spectrum of (μ-bpym)[Mo(CO)4]2

The character of the two lowest energy transitions of W(CO)₄(bpym) and (μ-bpym)[M(CO)₄]₂ (M=Mo, W) were established with resonance Raman spectroscopy. According to these spectra the two bands belong to MLCT transitions to different π* orbitals of the bpym ligand. Contrary to expectations it is not the first (lowest energy) but the second and more intense electronic transition which, according to the resonance Raman spectra, is directed to the lowest lying π* orbital (b_2u*, LUMO) of these complexes. This interpretation explains the different band intensities and the untypically low g values of the ESR signals of corresponding anion radicals. Excitation of (μ-bpym)[Mo(CO)₄]₂ in CH₂Cl₂ at 400 nm produced a weak emission with an onset at 700 nm. According to the excitation spectrum, this emission originates from the lowest MLCT-excited state of the complex.     

Synthesis and properties of the dichloro [tetramethyl (trifluoromethyl)cyclopentadienyl]ruthenium dimer: X-ray structure of [M2(η-C5Me4CF3)2Cl2(μ-Cl)2] (M=Ru, Rh)

The reaction of RuCl₃(H₂O), with C₅Me₄CF₃J in refluxing EtOH gives [Ru₂(η⁵-C₅Me₁CF₂)₂ (μ-Cl₂] (20 in 44% yield. Dimer 2 antiferromagnetic (−2J=200 cm¹). The crystal structures of 2 (rhombohedral system, R3 space group, Z=9, R=0.0589) and [Rh₂(η⁵-C₅Me₄CF₃(₂Cl₂(μ-Cl)₂] (3) (rhombohedral system. space group, Z = 9, R = 0.0641) were solved; both complexes have dimeric structures with a trans arrangement of the η⁵-C₅Me₄CF₄ rings. Comparison of the geometry of 2 and 3 with those of the corresponding η⁵-C₅Me₅ complexes shows that lowering the ring symmetry causes significant distortion of the M₂(μ-Cl)₂ moiety. The analysis of the MCl₃ fragment conformations in 2 and 3 and in the η⁵-C₅ME₅ analogues shows that they are correlated with the M---M distances. The Cl atoms are displaced by Br on reaction of 2 with KBr in MeOH to give the diamagnetic dimer [Ru₂(η⁵-C₅Me₄CF₃)₂Br₂ (μ-Br₂] (4). Complex 2 reacts with O₂ in CH₂Cl₂ solution at ambient temperature to form a mixture of isomeric η⁶-fulvene dimers [Ru₂(η⁶-C₅Me₃CF₃ = CH₂)₂Cl₂(μ-Cl)₂] (5). Reactions of 5 with CO and allyl chloride give Ru(η⁵-C₅Me₃CF₃CH₂Cl)(CO)₂Cl (6) and Ru(η⁵-C₅Me₃CF₃CF₃CH₂Cl)(η³-C₃H₅)Cl₂ (7) respectively.     

Pressure-tuning infrared spectra of the three Magnus’ Green salts, [Pt(NH3)4][PtCl4], [Pt(ND3)4][PtCl4] and [Pt(NH3)4][PtBr4]

Pressure-tuning infrared spectra (up to ca. 40 kbar) are reported for Magnus’ Green salt, [Pt(NH₃)₄][PtCl₄] and two of its derivatives, [Pt(ND₃)₄][PtCl₄] and [Pt(NH₃)₄][PtBr₄]. The spectroscopic data indicate that there is restricted rotation of the coordinated ammonia groups about the Pt-N bonds in the complexes. It is possible that this restricted rotation is due to the presence of weak hydrogen bonding to the halogens, i.e., N-H?X (X = Cl, Br) interactions.     

A new example of a tetranuclear iron(III) cluster containing the [Fe4O2] core: preparation, X-ray crystal structure, magnetochemistry and Mössbauer study of [Fe4O2(O2CMe)6(N3)2(phen)2]

Two synthetic procedures have been employed that allow access to the new tetranuclear cluster [Fe₄O₂(O₂CMe)₆(N₃)₂(phen)₂] (1), where phen is 1,10-phenanthroline. Complex 1 · 3MeCN displays an unusual structural asymmetry (observed for the second time) in its [Fe₄O₂]⁸⁺ core that can be considered as a hybrid of the bent (butterfly) and planar dispositions of four metal ions seen previously in such compounds with transition metals. Complex 1 has been characterized by variable-temperature magnetic susceptibility studies, and by IR and variable-temperature ⁵⁷Fe Mössbauer spectroscopies. Magnetochemical data reveal a diamagnetic ground state (S=0) with antiferromagnetic body-body and body-wingtip interactions between the iron(III) ions of the butterfly core (J_bb=−11 cm⁻¹, J_wb=−70 cm⁻¹). Magnetochemical and Mössbauer studies on 1 show that its structural asymmetry has practically no influence on these properties compared with the more symmetric types.     

Olefin versus sulfur coordination of benzo[b]thiophene (BT) in Cp(CO)2Re(η:η-μ2-BT)Cr(CO)3

Reactions of Cr(CO)₃(η⁶-BT), in which the Cr is π-coordinated to the benzene ring of benzo[b]thiophene (BT), with Cp′(CO)₂Re(THF), where Cp′ = η⁵-C₅H₅ or η⁵-C₅Me₅, give the products Cp′(CO)₂Re(η²:η⁶-μ₂-BT)Cr(CO)₃ in which the Cr remains coordinated to the benzene ring and Re is bound to the C(2)=C(3) double bond. An X-ray diffraction study of Cp(CO)₂Re(η²:η⁶-μ₂-BT)Cr(CO)₃ (3) provides details of the geometry. This structure contrasts with that of the Cp′(CO)₂Re(BT) complexes that exist as mixtures of isomers in which the BT is coordinated to the Re through either the double bond (2,3-η²) or the sulfur (η¹(S)). Thus, the electron-withdrawing Cr(CO)₃ group in 3 stabilizes the 2,3-η² mode of BT coordination to the Cp′(CO)₂Re fragment. Implications of these results for catalytic hydrodesulfurization of BT are discussed. Crystal data for 3: triclinic, space group

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