Tetranuclear manganese(III) clusters containing both carboxylate and phosphonate bridging ligands

This paper reports two tetranuclear manganese clusters, namely, [Mn₄O₂(O₂CCH₃)₄(O₃PC₆H₁₁)₂(phen)₂] (1) and [Mn₄O₂(O₂CPh)₄ (O₃PC₆H₁₁)₂(bpy)₂] (2). Both contain a butterfly-like [Mn₄(μ₃-O)₂]⁸⁺ core. The neighboring Mn atoms within the core are bridged by the carboxylate groups, forming approximately a plane. The phosphonate ligands locate above and below the plane, and cap on top of the Mn₃O triangles by using its three phosphonate oxygen atoms. The magnetic measurements of complexes 1 and 2 reveal that dominant antiferromagnetic interactions are propagated between the magnetic centers.     

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.     

Seven organic-inorganic hybrid compounds constructed from 2,4,6-tris-(pyridyl)-1,3,5-triazine and polyoxometalates

Seven new organic-inorganic hybrid compounds containing inorganic polyoxometalates and trigonal organic ligand 2,4,6-tris-(3/4-pyridyl)-1,3,5-triazine (3/4-tpt), namely [Mo₈O₂₆M(Htpt)₂(H₂O)₂]_n (M = Zn (1), Co (2), Ni (3)), [Mo₈O₂₆Cu(Htpt)₂(H₂O)₂]_n·2nH₂O (4), [Mo₈O₂₆(H₂tpt)₂]·6H₂O (5), [Mn(Mo₄O₁₃)(4-tpt)₂]_n (6) and [Fe₃(Mo₄O₁₅)(3-tpt)]_n·nH₂O (7), were synthesized hydrothermally and characterized by EA, IR, TG, and PXRD techniques. Single crystal X-ray structural analysis revealed that compounds 1-4 are 1-D coordination polymers constructed from [Mo₈O₂₆]⁴⁻ cluster and [M(Htpt)₂(H₂O)₂]⁴⁺ fragments. Compound 5 is an isolated cluster composed of [Mo₈O₂₆]⁴⁻ anion and monodentate H₂tpt²⁺ cation. 3-Tpt ligands in 1-5 are partially protonated and act as monodentate ligands. Octamolybdates adopt β- and γ-[Mo₈O₂₆]⁴⁻ structural mode in compounds 1-4 and 5, respectively. In compound 6, each [Mo₄O₁₃]²⁻ tetramer links four Mn(II) ions to form a 2-D wave-like polymeric layer. The 2-D [MnMo₄O₁₃] bimetallic layers are pillared by neutral 4-tpt bidentately to generate a 3-D metal-organic framework. Compound 7 is a 3-D coordination polymer constructed from 2-D [Fe₃(Mo₄O₁₅)] bimetallic polymeric layer and pillared by neutral tridentate 3-tpt. These compounds are thermal stable under 250 °C. The compounds 1 and 5 display luminescence with emission maximum at 481 and 442 nm, respectively.     

Synthesis, crystal structures, electrochemical and magnetic properties of polynuclear {Fe4} and {Fe8Na4} carboxylate/picolinate clusters

Reaction of sodium picolinate with Fe^III oxo-centered carboxylate triangles in MeCN in the presence of PPh₄Cl yields (PPh₄)[Fe₄O₂(O₂CR)₇(pic)₂] (R = Ph (1), Bu^t (2)). Omitting the phosphonium cation produces [Fe₈Na₄O₄(O₂CPh)₁₆(pic)₄(H₂O)₄] (3), which contains two Fe₄Na₂ units bridged by two picolinate ligands. X-ray crystal structures of 1 and 3 are reported.Voltammetric profiles in MeCN show four one-electron reduction steps for complexes 1 and 2. Variable-temperature magnetic susceptibility measurements in polycrystalline samples of 1 and 3 reveal strong antiferromagnetic couplings leading to S = 0 ground states.     

Mono- and dinuclear (o-thioetherphenolato)-copper(II) complexes. Structural models for galactose oxidase

Three new o-thioetherphenol ligands have been synthesized: 1,2-bis(3,5-di-tert-butyl-2-hydroxyphenylsulfanyl)ethane (H₂bse), 1,2-bis(3,5-di-tert-butyl-2-hydroxyphenylsulfanyl)benzene (H₂bsb), and 4,6-di-tert-butyl-2-phenylsulfanylphenol (Hpsp). Their complexes with copper(II) were prepared and investigated by UV-Vis-, EPR-spectroscopy; their electro- and magnetochemistry have also been studied: [Cu^II(psp)₂] (1), [Cu^II₂(bse)₂] (2), [Cu^II₂(bsb)₂] (3), [Cu^II(bsb)(py)₂] (4). The crystal structures of the ligands H₂bse, H₂bsb, Hpsp and of the complexes 1, 2, 3, 4 have been determined by X-ray crystallography.     

Synthesis and characterization of four cubical molybdenum(V) tetramers and their catalytic properties for the epoxidation of cis-cyclooctene using H2O2

Molybdenum tetramers: Mo₄(μ³-O)₄[μ-O₂P(CH₂Cl)₂]₄O₄ (1), Mo₄(μ³-O)₄(μ-O₂P(CH₂OH)₂)₄O₄ (2), Mo₄(μ³-O)₄[μ-O₂P(PhOMe)₂]₄O₄ (3), and Mo₄(μ³-O)₄[μ-O₂P(o-C₆H₄(CH₂)₂)]₄O₄ (4) have been synthesized and characterized by IR, UV-Vis, and ³¹P NMR spectroscopy. Molybdenum tetramers 1 and 4 along with the ligands L2A and L4 were structurally characterized by single crystal X-ray crystallography. An infinite 2D polymeric sheet was formed via inter and intra hydrogen bonds in the crystals of L2A. The crystals of L4 consist of infinite polymeric chains formed through hydrogen bonding. All molybdenum tetramers were tested as catalysts for the epoxidation of cis-cyclooctene in the presence of H₂O₂. Compounds 1 and 2 resulted in more than 80% epoxide after 24 hours at 70 °C, and displayed superior catalytic activities over compounds 3 and 4 under identical conditions. The superior catalytic activities of compounds 1 and 2 may be attributed to their better solubility in the ethanol/H₂O₂ system.     

Synthesis, crystal structure and magnetic properties of cubane and linear trinuclear nickel complexes formed by 3,5-dichloro-2-hydroxybenzylaminoacetic acid

The reaction of Ni(ClO₄)₂·6H₂O with 3,5-dichloro-2-hydroxy-benzylaminoacetic acid (H₂dchaa), NaN₃ and triethylamine in methanol solution or water solution under solvothermal methods leads to the formation of two completely different Ni^II compounds: [HN(C₂H₅)₃]₈·[Ni₄(dchaa)₄(N₃)₄]₂ (1) and [HN(C₂H₅)₃]₂·[Ni₃(dchaa)₄(H₂O)₄]₂·(H₂O)₂ (2). The complexes 1 and 2 have been characterized by elemental analyses, IR spectra and single-crystal X-ray diffraction. Structure analyses reveal that complex 1 is a cubane cluster, while the complex 2 is a linear trinuclear cluster. The magnetic investigation shows that complexes 1 and 2 exhibit a ferromagnetic coupling between Ni^II ions. Ac susceptibilities of 1 and 2 reveal no frequency-dependent out-of-phase signals and the corresponding magnetic properties were discussed.     

Biotechnological application of homo- and heterotrinuclear iron(III) furoates for cultivation of iron-enriched Spirulina

New trinuclear iron(III) furoates with the general formula [Fe₃O(α-fur)₆(R-OH)₃]X, where α-fur C₄H₃OCOO, R = CH₃ (1), C₂H₅ (2), n-C₃H₇ (3), n-C₄H₉ (4), X = NO₃⁻ (1-4); [Fe₃O(α-Fur)₆(DMF)(CH₃OH)₂]NO₃ (5); [Fe₃O(α-Fur)₆(H₂O)(CH₃OH)₂]Cl (6); [Fe₂MO(α-Fur)₆(L)(H₂O)₂], where L = THF (7-9), DMF (10-12), M = Mn²⁺ (7, 10), Co²⁺ (8, 11), Ni²⁺ (9, 12) and [Fe₂MO(α-Fur)₆(3Cl-Py)₃], where M = Mn²⁺ (13), Co²⁺ (14), Ni²⁺ (15); have been prepared and investigated by Mössbauer and IR spectroscopy. The X-ray crystal structure for the 1·2CH₃OH complex indicates that it crystallizes in the monoclinic crystal system (P2₁/n) and has a structure typical of μ₃-O-bridged trinuclear iron(III) compounds. Coordination compounds 1, 4, 7, 8 can be used as regulators of the biochemical composition of cyanobacterium Spirulina platensis biomass. The supplementation of these compounds, in concentrations exceeding 5-10 mg/l, increases the content of iron, amino acids, peptides and carbohydrates in Spirulina.     

Syntheses, structures and magnetic properties of heterobimetallic complexes based on a new tetracyanometalate precursor

A new mononuclear tetracyanometallic complex, (n-Bu₄N)[(dbphen)Fe(CN)₄] (1, dbphen = 5,6-dibromo-1,10-phenanthroline), has been prepared by reacting [(dbphen)Fe^II(py)₂(SCN)₂] and KCN in water and further oxidized with chlorine. With the use of 1 as building block, two trinuclear Fe₂M complexes, [(dbphen)₂Fe₂(CN)₈Cu(Me₃tacn)]·3H₂O (2), [(dbphen)₂Fe₂(CN)₈Ni(dabhctd)]·2H₂O (3) and a chain complex of squares [(dbphen)₂Fe₂(CN)₈Co(MeOH)₂]_n (4), have been synthesized and structurally characterized. Magnetic studies show ferromagnetic coupling between Fe^III and M^II (M = Cu, 2; Ni, 3) ions bridged by cyanides in complexes 2 and 3, while complex 4 exhibits meta-magnetic behavior.     

Iron(III), chromium(III) and cobalt(II) complexes with squarate: Synthesis, crystal structure and magnetic properties

The preparation and variable temperature-magnetic investigation of three squarate-containing complexes of formula [Fe₂(OH)₂(C₄O₄)₂(H₂O)₄]·2H₂O (1) [Cr₂(OH)₂(C₄O₄)₂(H₂O)₄]·2H₂O (2) and [Co(C₄O₄)(H₂O)₄]_n (3) [H₂C₄O₄ = 3.4-dihydroxycyclobutene-1,2-dione (squaric acid)] together with the crystal structures of 1 and 3 are reported. Complex 1 contains discrete centrosymmetric [Fe₂(OH)₂(C₄O₄)₂(H₂O)₄] diiron(II) units where the iron pairs are joined by a di-μ-hydroxo bridge and two squarate ligands acting as bridging groups through adjacent oxygen atoms. Two coordinated water molecules in cis position complete the octahedral environment at each iron atom in 1. The iron-iron distance with the dinuclear unit is 3.0722(6) Å and the angle at the hydroxo bridge is 99.99(7)°, values which compare well with the corresponding ones in the isostructural compound 2 (2.998 Å and 99.47°) whose structure was reported previously. The crystal structure of 3 contains neutral chains of squarato-O¹,O³-bridged cobalt(II) ions where four coordinated water molecules complete the six-coordination at each cobalt atom. The cobalt-cobalt separation across the squarate bridge is 8.0595(4) Å. A relatively important intramolecular antiferromagnetic coupling occurs in 1 whereas it is very weak in 2, the exchange pathway being the same [J = −14.4 (1) and −0.07 cm⁻¹ (2), the spin Hamiltonian being defined as ]. A weak intrachain antiferromagnetic interaction between the high-spin cobalt(II) ions occurs in 3 (J = −0.30 cm⁻¹). The magnitude and nature of these magnetic interactions are discussed in the light of their respective structures and they are compared with those reported for related systems.     

Supramolecular architectures built of triangular molybdenum(IV) heterometallic clusters encapsulating novel water clusters

The hydrothermal reaction of the dimolybdenum(V) Na₂[Mo₂O₃S(HNTA)₂] · 6H₂O (1) and the lanthanide(III) ion yield the neutral trimolybdenum(IV) heterometalic cluster, [(H₂O)₈NdMo₃O₃S(HNTA)₂(NTA)] · 7H₂O (2) (NTA = nitrilotriacetato ligand). The addition reaction of Ag⁺ and [Mo₃O₄(C₂O₄)₃(H₂O)₃]²⁻ affords the anionic heterometallic cluster in N(C₂H₅)₄[Ag(H₂O)₃Mo₃O₄(C₂O₄)₃(H₂O)₃] · 5H₂O (3). The H-bonded self-assemblies of the resulting asymmetric and larger heterometallic clusters form the 2D layered structure and 3D supramolecular open framework in 2 and 3, respectively, with larger pores to be stabilized by water clusters. These water clusters appear as (H₂O)₄ and (H₂O)₁₈ in 2 and (H₂O)₂₂ in 3.     

Tungsten complexes of aromatic and aliphatic thioaldehydes

Reaction of PPN[W(CO)₃(R₂PC₂H₄PR₂)(SH)] (PPN=Ph₃PNPPh₃; R=Me, 1; R=Ph, 2) with aromatic aldehydes in the presence of trifluoroacetic acid gave tungsten complexes of thiobenzaldehydes mer-[W(CO)₃(R₂PC₂H₄PR₂)(η²-SCHR^′)] (R=Me, 3a-3f; R=Ph, 4a-4e) in high yields. Analogous complexes of aliphatic thioaldehydes mer-[W(CO)₃(Me₂PC₂H₄PMe₂)(η²-SCHR^′)] (3g-3l) could only be obtained from the highly electron-rich thiolate complex 1. The structure of 3i (R^′=i-Bu) was determined by X-ray crystallography. In solution the complexes 3 and 4 are in equilibrium with small quantities of their isomers fac-[W(CO)₃(R₂PC₂H₄PR₂)(η²-SCHR^′)]. Reaction of complexes 3 with dimethylsulfate followed by salt metathesis with NH₄PF₆ gave the alkylation products mer-[W(CO)₃(Me₂PC₂H₄PMe₂)(η²-MeSCHR^′)]PF₆ (5a-5l) as mixtures of E and Z isomers. The methylated thioformaldehyde complex mer-[W(CO)₃(Me₂PC₂H₄PMe₂)(η²-MeSCH₂)]PF₆ (5m) was prepared similarly. Nucleophilic addition of hydride (from LiAlH₄) to 5 initially gave thioether complexes mer-[W(CO)₃(Me₂PC₂H₄PMe₂)(MeSCH₂R^′)] (mer-6) which rapidly isomerized to fac-[W(CO)₃(Me₂PC₂H₄PMe₂)(MeSCH₂R^′)] (fac-6).     

Solid state coordination chemistry of the oxovanadium-diphosphonate system: Structural consequences of aryl tethers on materials of the type cation/VxOy/diphos, where cation = organoammonium and diphos = 1,4-phenyldiphosphonic acid

Hydrothermal reactions of V₂O₅, 1,4-phenyldiphosphonic acid and an appropriate organoamine, in the presence of HF as solubilizer, were exploited to prepare a series of materials of the general type [organoammonium cation]_n[V_xO_y(H_mO₃PC₆H₄PO₃H_p)₃]. Compound 1, [H₃N(CH₂)₄NH₃][V₂O₄(O₃PC₆H₄PO₃)], exhibits a one-dimensional V-P-O substructure, linked through the phenyl tethers of the ligand into a layer. Compound 1 is a unique example of a V(V)-diphosphonate phase. Compounds 2 and 3, [H₃N(CH₂)₂NH₃][V₂O₂(O₃PC₆H₄PO₃H)₂] and [H₂pip][V₂O₂(O₃PC₆H₄PO₃H)₂] (H₂pip = piperazinium), exhibit identical two dimensional substructures, constructed from ribbons connected through the phenyl tethers of the ligands. The three-dimensional framework of [H₃N(CH₂)₇NH₃]₂[V₃O₄(O₃PC₆H₄PO₃)₂] (4) consists of V-P-O layers characterized by trinuclear V(IV)-oxide subunits and 9 and 12 polyhedral connect rings; the layers are buttressed by the phenyl spacers to provide the typical “pillared” layer structure common to metal diphosphonate materials. Compound 5, [H₂dabco][V₂F₃O₂(O₃PC₆H₄PO₃H)]·H₂O, is also three-dimensional with oxyfluoro-vanadium(IV) chains linked through the diphosphonate ligands into a framework structure with void spacers to accommodate the {H₂dabco}²⁺ cations (dabco = diamino bicyclo octane). The magnetic properties of 2-5 reflect the structural characteristics of the materials.     

Speciation, stability constants and structures of complexes of copper(II), nickel(II), silver(I) and mercury(II) with PAMAM dendrimer and related tetraamide ligands

The acid-base properties and Cu(II), Ni(II), Ag(I) and Hg(II) binding abilities of PAMAM dendrimer, L, and of the simple model compounds, the tetraamides of EDTA and PDTA, L¹, were studied in solution by pH-metric methods and by ¹H NMR and UV-Vis spectroscopy. PAMAM is hexabasic and six pK_a values have been determined and assigned. PAMAM forms five identifiable complexes with copper(II), [CuLH₄]⁶⁺, [CuLH₂]⁴⁺, [CuLH]³⁺, [CuL]²⁺ and [CuLH_-1]⁺ in the pH range 2-11 and three with nickel(II), [NiLH]³⁺, [NiL]²⁺ and [NiLH_-1]⁺ in the pH range 7-11. The complex [CuLH₄]⁶⁺, which contains two tertiary nitrogen and three amide oxygen atoms coordinated to the metal ion, is less stable than the analogous EDTA and PDTA tetraamide complexes [CuL¹]²⁺, which contain two tertiary nitrogen and four amide oxygen atoms, due to ring size and charge effects. With increasing pH, [CuLH₄]⁶⁺ undergoes deprotonation of two coordinated amide groups to give [CuLH₂]⁴⁺ with a concomitant change from O-amide to N-amidate coordination. Surprisingly and in contrast to the tetraamide complexes [CuL¹]²⁺, these two deprotonation steps could not be separated. As expected the nickel(II) complexes are less stable than their copper(II) analogues. The tetra-N-methylamides of EDTA, L¹(b), and PDTA form mononuclear and binuclear complexes with Hg(II). In the case of L¹(b) these have stoichiometries HgL¹(b)Cl₂, [HgL¹(b)H₋₂Cl₂]²⁻, [Hg₂L¹(b)Cl₂]²⁺, Hg₂L¹(b)H₋₂Cl₂ and [Hg₂L¹(b)H₋₅Cl₂]³⁻. Based on ¹H NMR and pH-metric data the proposed structure for HgL¹(b)Cl₂, the main tetraamide ligand containing species in the pH range <3-6.5, contains L¹(b) coordinated to the metal ion through the two tertiary nitrogens and two amide oxygens while the structure of [HgL¹(b)H₋₂Cl₂]²⁻, the main tetraamide ligand species at pH 7.5-9.0, contains the ligand similarly coordinated but through two amidate nitrogen atoms instead of amide oxygens. The proposed structure of [Hg₂L¹(b)Cl₂]²⁺, a minor species at pH 3-6.5, also based on ¹H NMR and pH-metric data, contains each Hg(II) coordinated to a tertiary amino nitrogen, two amide oxygens and a chloride ligand while that of [Hg₂L¹(b)H₋₅Cl₂]³⁻, contains each Hg(II) coordinated to a tertiary amino nitrogen, two amidate nitrogens, a chloride and a hydroxo ligand in the case of one of the Hg(II) ions. The parent EDTA and PDTA amides only form mononuclear complexes. PAMAM also forms dinuclear as well as mononuclear complexes with mercury(II) and silver(I). In the pH range 3-11 six complexes with Hg(II) i.e. [HgLH₄Cl₂]⁴⁺, [HgLH₃Cl₂]³⁺, [Hg₂LCl₂]²⁺, [Hg₂LH₋₁Cl₂]⁺, [HgLH₋₁Cl₂]⁻ and [HgLH₋₂Cl₂]²⁻ were identified and only two with Ag(I), [AgLH₃]⁴⁺ and [Ag₂L]²⁺. Based on stoichiometries, stability constant comparisons and ¹H NMR data, structures are proposed for these species. Hence [HgLH₄Cl₂]⁴⁺ is proposed to have a similar structure to [CuLH₄]⁶⁺ while [Hg₂LCl₂]²⁺has a similar structure to [Hg₂L¹(b)H₋₅Cl₂]³⁻.     

Initial employment of pyridine-2-amidoxime in zinc(II) chemistry: Synthetic, structural and spectroscopic studies of mononuclear and dinuclear complexes

The first employment of pyridine-2-amidoxime [(py)C(NH₂)NOH] in zinc(II) chemistry is reported. The syntheses, crystal structures, and spectroscopic characterization are described for complexes [Zn(O₂CR)₂{(py)C(NH₂)NOH}₂] (R = Me; 1, Ph; 2), [Zn₂(acac)₂{(py)C(NH₂)NO}₂] (3), and [Zn(NO₃){(py)C(NH₂)NOH}₂](NO₃) (4). The reactions between Zn(O₂CR)₂·2H₂O (R = Me, Ph) or Zn(NO₃)₂·5H₂O and two equivalents of (py)C(NH₂)NOH in MeOH led to mononuclear compounds 1, 2 and 4, respectively. All three complexes contain two neutral N,N′-chelating (η²) (py)C(NH₂)NOH ligands, coordinated through the N_pyridyl and N_oxime atoms. In contrast, the use of Zn(acac)₂·H₂O in place of Zn(O₂CR)₂·2H₂O gives the dinuclear compound 3, which instead contains the anionic, η¹:η¹:η¹:μ bridging form of the organic ligand; the Zn^II atoms are doubly bridged by the diatomic oximate groups of the (py)C(NH₂)NO⁻ groups. Strong intra- and intermolecular hydrogen bonding interactions provide appreciable thermodynamic stability and interesting supramolecular chemistry for compounds 1-4. The photoluminescence properties of complexes 1-4 recorded in the solid state at room temperature are also presented.     

Bioinspired FeIIICdII and FeIIIHgII complexes: synthesis, characterization and promiscuous catalytic activity evaluation

In this work we report on the synthesis, crystal structure, and physicochemical characterization of the novel dinuclear [Fe^IIICd^II(L)(μ-OAc)₂]ClO₄·0.5H₂O (1) complex containing the unsymmetrical ligand H₂L = 2-bis[{(2-pyridyl-methyl)-aminomethyl}-6-{(2-hydroxy-benzyl)-(2-pyridyl-methyl)}-aminomethyl]-4-methylphenol. Also, with this ligand, the tetranuclear [Fe₂^IIIHg₂^II(L)₂(OH)₂](ClO₄)₂·2CH₃OH (2) and [Fe^IIIHg^II(L)(μ-CO₃)Fe^IIIHg^II(L)](ClO₄)₂·H₂O (3) complexes were synthesized and fully characterized. It is demonstrated that the precursor [Fe^III₂Hg^II₂(L)₂(OH)₂](ClO₄)₂·2CH₃OH (2) can be converted to (3) by the fixation of atmospheric CO₂ since the crystal structure of the tetranuclear organometallic complex [Fe^IIIHg^II(L)(μ-CO₃)Fe^IIIHg^II(L)](ClO₄)₂·H₂O (3) with an unprecedented {Fe^III(μ-O_phenoxo)₂(μ-CO₃)Fe^III} core was obtained through X-ray crystallography. In the reaction 2 → 3 a nucleophilic attack of a Fe^III-bound hydroxo group on the CO₂ molecule is proposed. In addition, it is also demonstrated that complex (3) can regenerate complex (2) in aqueous/MeOH/NaOH solution. Magnetochemical studies reveal that the Fe^III centers in 3 are antiferromagnetically coupled (J = − 7.2 cm^− 1) and that the Fe^III-OR-Fe^III angle has no noticeable influence in the exchange coupling. Phosphatase-like activity studies in the hydrolysis of the model substrate bis(2,4-dinitrophenyl) phosphate (2,4-bdnpp) by 1 and 2 show Michaelis-Menten behavior with 1 being ~ 2.5 times more active than 2. In combination with k_H/k_D isotope effects, the kinetic studies suggest a mechanism in which a terminal Fe^III-bound hydroxide is the hydrolysis-initiating nucleophilic catalyst for 1 and 2. Based on the crystal structures of 1 and 3, it is assumed that the relatively long Fe^III…Hg^II distance could be responsible for the lower catalytic effectiveness of 2.     

A kinetic study on pyridine exchange reactions at a bis(μ-acetato)(μ-oxo)diruthenium(III) center: effects of monodentate and bidentate N-heterocyclic ligands cis to the oxo bridge

A series of (μ-oxo)bis(μ-acetato)diruthenium(III) complexes containing two pyridine (py) ligands and varied N-heterocyclic ligands in the positions trans and cis to μ-O, respectively, have been prepared to study py/py-d₅ exchange reactions using ¹H NMR spectroscopy. The diruthenium(III) complexes under investigation are [Ru₂(μ-O)(μ-CH₃COO)₂(py)₆](PF₆)₂ (1), [Ru₂(μ-O)(μ-CH₃COO)₂(bpy)₂(py)₂](PF₆)₂ (2), [Ru₂(μ-O)(μ-CH₃COO)₂(acpy)₄(py)₂](FF₆)₂ (3), and [Ru₂(μ-O)(μ-CH₃COO)₂(dmbpy)₂(py)₂](PF₆)₂ (4), where bpy=2,2′-bipyridine, acpy=4-acetylpyridine, and dmbpy=4,4′-dimethyl-2,2′-bipyridine. Pseudo-first order rate constants for the ligand-exchange reactions are 10⁻⁶−10⁻⁵ s⁻¹ for 1-4 in CD₃CN at 298 K. It is found that the rate of the py/py-d₅ exchange reactions is controlled by the electronic nature of the cis-oriented ancillary ligands, while the exchange mechanisms are tuned principally by the ligand steric factors. The activation parameters (ΔH^‡ and ΔS^‡) indicate that exchange reactions proceed through the dissociative (D) or the interchange dissociative (I_d) mechanism for 1 and 3. Negative ΔS^‡ values observed for 2 and 4 suggest a significant contribution of incoming ligands to the exchange pathway. The kinetic and thermodynamic parameters for the diruthenium series and the corresponding data for Ru-based oxo bridged trinuclear complexes established previously are compared and discussed.     

Titanium and vanadium complexes with tetraphenylimidodiphosphinate

Treatment of [Ti(OPrⁱ)₂Cl₂] with K(tpip) (tpip⁻ = [N(PPh₂O)₂]⁻) followed by chlorination with HCl afforded cis-[Ti(tpip)₂Cl]₂ (1). Reduction of 1 with Na/Hg in THF gave [Ti(tpip)₃] (2), which could also be prepared from [TiCl₃(THF)₃] and K(tpip). Recrystallization of [V(O)(tpip)₂] (3) from CH₂Cl₂-Et₂O in air afforded trinuclear [{V(O)}₃(μ-tpip)₃(μ-O)₃] (4). Treatment of [Cr(NBu^t)₂Cl₂] and [Cr(NBu^t)Cl₃(dme)] (dme = 1,2-dimethoxyethane) with [Ag(tpip)]₄ led to isolation of [Cr(tpip)₃] (6) and [Cr(NBu^t)(tpip)₂Cl] (7), respectively. The Ti- and V-tpip complexes are capable of catalyzing oxidation of sulfides with tert-butyl hydroperoxide and H₂O₂. The crystal structures of 1, 2, and 4 have been determined.     

Metal-regulated assemblies of Cu, Ni, and Zn complexes with isoquinoline-3-carboxylate displaying diverse supramolecular networks

Three distinct coordination complexes, viz. {[Cu(μ-L)₂] · (H₂O)₄}_n (1), [Ni(L)₂(CH₃OH)₂] (2), and [Zn(L)₂(H₂O)₂] · (H₂O)₂ (3), have been prepared by the reactions of metal nitrates with isoquinoline-3-carboxylic acid (HL). X-ray single-crystal diffraction suggests that 1 is a 1D chain coordination polymer in which the Cu^II ions are connected by carboxylates, whereas complexes 2 and 3 represent discrete mononuclear species. In all the cases, the coordination entities are further organized via hydrogen-bonding interactions to generate multifarious supramolecular networks. Remarkably, a well-resolved 1D water morphology is observed for the first time in the crystalline lattice of 1 along [1 0 0], which consists of edge-sharing tetrameric subunits and stabilized by the metal-organic host surroundings.     

Synthesis, characterization and antibacterial activity of Fe, Co, Cu and Zn complexes probed by transmission electron microscopy

We synthesized iron(III), cobalt(II), copper(II) and zinc(II) complexes [Fe^III(HBPClNOL)Cl₂]·H₂O (1), [Co^II(H₂BPClNOL)Cl₂] (2), [Cu^II(H₂BPClNOL)Cl]Cl·H₂O (3), and [Zn^II(HBPClNOL)Cl] (4), where H₂BPClNOL is the ligand (N-(2-hydroxybenzyl)-N-(2-pyridylmethyl)[(3-chloro)(2-hydroxy)]propylamine). The complexes obtained were characterized by elemental analysis, IR and UV-visible spectroscopies, electrospray ionization mass spectrometry (ESI-MS), tandem mass spectrometry (MS/MS), and cyclic voltammetry. X-ray diffraction studies were performed for complexes (3) and (4) revealing the presence of mononuclear and dinuclear structures in solid state for (3). However, the zinc complex is mononuclear in solid state. Biological studies of complexes (1)-(4) were carried out in vitro for antimicrobial activity against nine Gram-positive bacteria (Staphylococcus aureus strains RN 6390B, COL, ATCC 25923, Smith Diffuse, Wood 46, enterotoxigenic S. aureus FRI-100 (SEA+), FRI S-6 (SEB+) and SEC FRI-361) and animal strain S. aureus LSA 88 (SEC/SED/TSST-1+). The following sequence of inhibition promoted by the complexes was observed: (4) > (2) > (3) > (1), showing the effect of the metal on the biological activity. To directly observe the morphological changes of the internal structure of bacterial cells after the treatment, transmission electron microscopy (TEM) was employed. For the most active complex [Zn^II(HBPClNOL)Cl] (4), granulation deposits around the genetic material and internal material leaking were clearly detected.