Lipoxygenase pathway in brown algae: The biosynthesis of novel oxylipins ‘ectocarpins’ by hydroperoxide bicyclase CYP5164A3 of Ectocarpus siliculosus

The sequence encoding the CYP5164A3 of the brown alga Ectocarpus siliculosus (Stramenopiles, SAR) was heterologously expressed in E. coli cells. The resulting recombinant CYP74 clan-related protein CYP5164A3 possessed a selective activity towards the α-linolenic acid 13(S)-hydroperoxide (13-HPOTE) and eicosapentaenoic acid 15(S)-hydroperoxide (15-HPEPE). The major products were the heterobicyclic oxylipins. For instance, the 13-HPOTE was converted into plasmodiophorols A, B, and C formed at about 14:3:2 ratio. Plasmodiophorols A-C have been recently described as the products of enzyme hydroperoxide bicyclase CYP50918A1 of cercozoan Plasmodiophora brassicae (Rhizaria, SAR). Furthermore, an unknown compound 1 was detected. Purified product 1 (Me) was identified as a novel substituted 3-propenyl-6-oxabicyclo[3.1.0]hexane based on its MS and NMR spectral data. Conversion of 15-HPEPE by CYP5164A3 resulted in products 7 and 8, analogous to plasmodiophorols A and B. This work uncovered the CYP5164A3 as the first hydroperoxide bicyclase in brown algae. Apparently, this enzyme plays a crucial role in the biosynthesis of heterobicyclic oxylipins like hybridalactone, ecklonilactones, and related natural products, widespread in brown algae.     

The “heterolytic hydroperoxide lyase” is an isomerase producing a short-lived fatty acid hemiacetal

To elucidate the reaction mechanism of hydroperoxide lyase (HPL), the enzyme from guava (Psidium guajava) fruits, was incubated for 10–60 s at 0 °C with 13-HPOT. The products were rapidly extracted and derivatized by trimethylsilylation. Two trapping products, namely the trimethylsilyl ether/ester derivatives of the hemiacetal 12-(1′-hydroxy-3′-hexenyloxy)-9,11-dodecadienoic acid and the enol (9Z,11E)-12-hydroxy-9,11-dodecadienoic acid, were detected by gas chromatography-mass spectrometry (GC-MS) analyses. The structural assignments were supported by mass spectra recorded for (a) hydrogenated products; (b) products biosynthesized from [9,10,12,13,15,16] 13-HPOT or [¹⁸O₂]13-HPOT; (c) chemically prepared reference compounds. Kinetic experiments showed that the hemiacetal and enol were both unstable and transiently appearing compounds (half-lives, ca. 20 s and 2 min, respectively). Hemiacetal and enol biosynthesized from [¹⁸O₂]13-HPOT retained two and one ¹⁸O atoms, respectively, whereas no ¹⁸O was incorporated from [¹⁸O]water. The data demonstrated that: (1) the true enzymatic product formed from 13-HPOT in the presence of HPL is a short-lived hemiacetal; (2) the hemiacetal spontaneously dissociates into (3Z)-hexenal and the unstable enol form of (9Z)-12-oxo-9-dodecenoic acid; (3) the enzymatic isomerization of 13-HPOT into the hemiacetal occurs homolytically.     

Oxylipin biosynthesis in spikemoss Selaginella moellendorffii: Molecular cloning and identification of divinyl ether synthases CYP74M1 and CYP74M3

Nonclassical P450s of CYP74 family control the secondary conversions of fatty acid hydroperoxides to bioactive oxylipins in plants. At least ten genes attributed to four novel CYP74 subfamilies have been revealed by the recent sequencing of the spikemoss Selaginella moellendorffii Hieron genome. Two of these genes CYP74M1 and CYP74M3 have been cloned in the present study. Both recombinant proteins CYP74M1 and CYP74M3 were active towards the 13(S)-hydroperoxides of α-linolenic and linoleic acids (13-HPOT and 13-HPOD, respectively) and exhibited the activity of divinyl ether synthase (DES). Products were analyzed by gas chromatography–mass spectrometry. Individual oxylipins were purified by HPLC and finally identified by their NMR data, including the ¹H NMR, 2D-COSY, HSQC and HMBC. CYP74M1 (SmDES1) specifically converted 13-HPOT to (11Z)-etherolenic acid and 13-HPOD to (11Z)-etheroleic acid. CYP74M3 (SmDES2) turned 13-HPOT and 13-HPOD mainly to etherolenic and etheroleic acids, respectively. CYP74M1 and CYP74M3 are the first DESs detected in non-flowering plants. The obtained results demonstrate the existence of the sophisticated oxylipin biosynthetic machinery in the oldest taxa of vascular plants.     

The "heterolytic hydroperoxide lyase" is an isomerase producing a short-lived fatty acid hemiacetal

To elucidate the reaction mechanism of hydroperoxide lyase (HPL), the enzyme from guava (Psidium guajava) fruits, was incubated for 10-60 s at 0 degrees C with 13-HPOT. The products were rapidly extracted and derivatized by trimethylsilylation. Two trapping products, namely the trimethylsilyl ether/ester derivatives of the hemiacetal 12-(1'-hydroxy-3'-hexenyloxy)-9,11-dodecadienoic acid and the enol (9Z,11E)-12-hydroxy-9,11-dodecadienoic acid, were detected by gas chromatography-mass spectrometry (GC-MS) analyses. The structural assignments were supported by mass spectra recorded for (a) hydrogenated products; (b) products biosynthesized from [9,10,12,13,15,16] 13-HPOT or [(18)O(2)]13-HPOT; (c) chemically prepared reference compounds. Kinetic experiments showed that the hemiacetal and enol were both unstable and transiently appearing compounds (half-lives, ca. 20 s and 2 min, respectively). Hemiacetal and enol biosynthesized from [(18)O(2)]13-HPOT retained two and one (18)O atoms, respectively, whereas no (18)O was incorporated from [(18)O]water. The data demonstrated that: (1) the true enzymatic product formed from 13-HPOT in the presence of HPL is a short-lived hemiacetal; (2) the hemiacetal spontaneously dissociates into (3Z)-hexenal and the unstable enol form of (9Z)-12-oxo-9-dodecenoic acid; (3) the enzymatic isomerization of 13-HPOT into the hemiacetal occurs homolytically.     

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.     

Epoxyalcohol synthase of Ectocarpus siliculosus. First CYP74-related enzyme of oxylipin biosynthesis in brown algae

Enzymes of CYP74 family play the central role in the biosynthesis of physiologically important oxylipins in land plants. Although a broad diversity of oxylipins is known in the algae, no CYP74s or related enzymes have been detected in brown algae yet. Cloning of the first CYP74-related gene CYP5164B1 of brown alga Ectocarpus siliculosus is reported in present work. The recombinant protein was incubated with several fatty acid hydroperoxides. Linoleic acid 9-hydroperoxide (9-HPOD) was the preferred substrate, while linoleate 13-hydroperoxide (13-HPOD) was less efficient. α-Linolenic acid 9- and 13-hydroperoxides, as well as eicosapentaenoic acid 15-hydroperoxide were inefficient substrates. Both 9-HPOD and 13-HPOD were converted into epoxyalcohols. For instance, 9-HPOD was turned primarily into (9S,10S,11S,12Z)-9,10-epoxy-11-hydroxy-12-octadecenoic acid. Both epoxide and hydroxyl oxygen atoms of the epoxyalcohol were incorporated mostly from [¹⁸O₂]9-HPOD. Thus, the enzyme exhibits the activity of epoxyalcohol synthase (EsEAS). The results show that the EsEAS isomerizes the hydroperoxides into epoxyalcohols via epoxyallylic radical, a common intermediate of different CYP74s and related enzymes. EsEAS can be considered as an archaic prototype of CYP74 family enzymes.     

Acidic 1,3-propanediaminetetraacetate zinc complexes as a probe of water soluble coordination polymers

In a very acidic solution, potassium 1,3-propanediaminetetraacetate zinc chloride K_2n[ZnCl₂(1,3-H₂pdta)ZnCl₂]_n (1) and its substituted iodide [ZnI₂(H₂O)(1,3-H₄pdta)]_n (2) (H₄pdta = 1,3-propanediaminetetraacetatic acid, C₁₁H₁₈N₂O₈) were isolated. The former was obtained from the reaction of zinc chloride and H₄pdta in pH ∼1.5. Further substitution of 1 results in the formation of iodide 2 with the addition of potassium iodide in acidic solution of pH 0.5. Complex 1 consists of a dimeric anionic unit [ZnCl₂(1,3-H₂pdta)ZnCl₂]²⁻ with strong intra-molecular hydrogen bonds [N1?O2 2.648(4); N1?O4 2.710(4) Å]. In neutral complex 2, an 1,3-pdta ligand links each monomeric unit [Zn(H₂O)I₂] to generate an infinite 1D chain, which extents into a 3D supramolecular structure by very strong inter-molecular hydrogen bonds the [O4?O2b 2.50 (1) Å, bx, y, z + 1]. 1 is soluble in water at room temperature, which is traced by ¹³C NMR experiment.     

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.     

Epoxyalcohol synthase activity of the CYP74B enzymes of higher plants

The CYP74B subfamily of fatty acid hydroperoxide transforming cytochromes P450 includes the most common plant enzymes. All CYP74Bs studied yet except the CYP74B16 (flax divinyl ether synthase, LuDES) and the CYP74B33 (carrot allene oxide synthase, DcAOS) are 13-hydroperoxide lyases (HPLs, synonym: hemiacetal synthases). The results of present work demonstrate that additional products (except the HPL products) of fatty acid hydroperoxides conversion by the recombinant StHPL (CYP74B3, Solanum tuberosum), MsHPL (CYP74B4v1, Medicago sativa), and CsHPL (CYP74B6, Cucumis sativus) are epoxyalcohols. MsHPL, StHPL, and CsHPL converted the 13-hydroperoxides of linoleic (13-HPOD) and α-linolenic acids (13-HPOT) primarily to the chain cleavage products. The minor by-products of 13-HPOD and 13-HPOT conversions by these enzymes were the oxiranyl carbinols, 11-hydroxy-12,13-epoxy-9-octadecenoic and 11-hydroxy-12,13-epoxy-9,15-octadecadienoic acid. At the same time, all enzymes studied converted 9-hydroperoxides into corresponding oxiranyl carbinols with HPL by-products. Thus, the results showed the additional epoxyalcohol synthase activity of studied CYP74B enzymes. The 13-HPOD conversion reliably resulted in smaller yields of the HPL products and bigger yields of the epoxyalcohols compared to the 13-HPOT transformation. Overall, the results show the dualistic HPL/EAS behaviour of studied CYP74B enzymes, depending on hydroperoxide isomerism and unsaturation.     

Hydrogen-bonding assemblies constructed from metalloligand building blocks and H2O

New hydrogen-bonding assemblies were synthesized from the reaction of a metalloligand, [Cu(2,4-pydca)₂]²⁻ (L^Cu) (2,4-pydca = 2,4-pyridinedicarboxylate), with a Fe^II ion or an imidazole in an aqueous medium and crystallographically characterized. The obtained compounds, [Fe(H₂O)₆][Cu(2,4-pydca)₂] (1) and [Cu(2,4-pydca)(imidazole)₂] · 2H₂O (2), have metalloligand dimer units, [Cu₂(2,4-pydca)₄]⁴⁻ and [Cu₂(2,4-pydca)₂(imidazole)₄], respectively, each of which assembles by π-π (1) and hydrogen-bonding (2) interactions to form 1-D metalloligand arrays. The 1-D metalloligand arrays are linked by rich hydrogen-bonding interactions via H₂O molecules.     

Synthesis and X-ray characterization of nickel(II) arsenatotungstate complexes: isolation of an intermediate leading to the formation of a sandwich-type polyoxometalate

The nickel arsenatotungstate K₁₀[As₂W₁₉(H₂O){Ni(H₂O)}₂O₆₇]·18H₂O (1) has been synthesized. Due to its instability in water, attempts to obtain crystals of 1 suitable for X-ray diffraction have failed. The stabilization of the [As₂W₁₉(H₂O){Ni(H₂O)}₂O₆₇]¹⁰⁻ core has been reached by synthesizing the analogue mixed {CsK} salt. The crystal structure of Cs₆K₂[Ni(H₂O)₆][As₂W₁₉(H₂O){Ni(H₂O)}₂O₆₇]·17H₂O (2) has been resolved. It consists of two [α-AsW₉O₃₃]⁹⁻ sub-units linked via a belt containing a tungsten and two nickel cations. Comparison of infrared and electronic absorption spectroscopic data for 1 and 2 has confirmed the structure proposed for 1. The instability of 1 led us to investigate the behavior of 1 in water. UV-Vis spectroscopy revealed that the formation of this complex is a multi-step reaction. An intermediate, the complex K₈[Ni(H₂O)₆]_1.5[As₂W₁₉(H₂O){K(H₂O)}{Ni(H₂O)₄}O₆₇]·21H₂O (3), has been isolated and characterized by elemental analysis, UV-Vis and infrared spectroscopies, and X-ray diffraction. In 3, the two vacant sites of the [As₂W₁₉O₆₇]¹⁴⁻ anion are occupied by a nickel and a potassium, forming a {WNiK} belt. It follows that the stability of 2 in water is due to the large ionic radius of Cs⁺, which prevents the inclusion of the alkaline cation into the cavity of the [As₂W₁₉O₆₇]¹⁴⁻ anion. The complex 3 represents a unique example of a fully characterized intermediate leading to the formation of a sandwich-type polyoxometalate.     

Expanding the 4,4′-bipyridine ligand: Structural variation in {M(pytpy)2}2+ complexes (pytpy = 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine,M = Fe,Ni, Ru) and assembly of the hydrogen-bonded,one-dimensional polymer {[Ru(pytpy)(Hpytpy)]}n3n+

The solid state structures of [Ni(1)₂][NO₃]₂ · 2MeOH · 2H₂O, [Fe(1)₂][ClO₄]₂ · 2MeOH · 0.5H₂O, [Ru(1)₂][PF₆]₂ and [Ru(1)₂][PF₆][NO₃] (1 = 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine) are presented and the structural variation observed for the {M(1)₂}²⁺ unit is discussed. Protonation of the pendant pyridine group in [Ru(1)₂]²⁺ leads to the formation of a hydrogen-bonded, one-dimensional polymer [{Ru(1)(H1)}_n]³ⁿ⁺ exemplifed by the solid-state structure of [{Ru(1)(H1)}{Fe(NCS)₆} · 1.25H₂O]_n.     

The hydrogen bonding effect on the halobismuthate(III) geometry: thermal,spectroscopic and structural properties of halobismuthate complexes of 4,6-dimethylpyrimidine-2(1H)-thione

Reactions involving Bi(III) halides and 4,6- dimethylpyrimidine-2(1H)-thione (L) in HX solution result in the formation of [HL]₃[BiX₆]·2H₂O (X=C1, Br) and [HL]₃[Bi₂I₉]. These compounds together with the organic molecule in the form of the hydrochloride, (HLCl) were characterized by means of spectroscopic and thermogravimetric measurements. For HLCl·H₂O (1) and [HL]₃[BiCl₆]·2H₂O (2), X-ray structures were determined. In 1, which crystallizes in the space group Pca2₁, with four molecules in the cell, the structure consists of roughly planar protonated organic molecules stacked along the [100] axis and built up by hydrogen bonds involving chlorine atoms and water molecules. For 2, the space group is P2₁/n, Z=4, the structure contains [BiCl₆]³⁻ anions, protonated organic molecules stacked along the [010] axis and water molecules which form strong hydrogen bonds with the [BiCl₆]³⁻ anions. The final R indices are 0.0320 and 0.0465 for 1 and 2, respectively.     

Ternary copper(II) complexes with hippurate derivatives and 1,10-phenanthroline: Synthesis and biological activity

Several new Cu-hippurate derivative-phenanthroline ternary complexes have been prepared. The X-ray structure of one of them, [Cu(hip)(phen)₂]⁺·(hip⁻) (2) (where hip is hippurate and phen is 1,10-phenanthroline) has been solved. The structure of this new compound shows important differences (3D-pattern) to other similar related complexes (2D-pattern). A study of the biological activity of [Cu(hip)(phen)₂]⁺·(hip⁻)·2H₂O (2), [Cu(BGG)(phen)₂]⁺·(BGG⁻)·6H₂O (3), [Cu(B^IGG)₂(phen)](H₂O) (4) and [Cu(I-hip)(bpy)₂]⁺·(I-hip⁻)·3.5H₂O (5) (where I-hip is ortho-iodohippurate, BGG corresponds to benzoylglycilglycine, and B^IGG is ortho-iodobenzoylglycilglycine) is included and compared with the anti-proliferative activity of [Cu(I-hip)(phen)₂]⁺·(I-hip⁻)·7H₂O (1) previously described, resulting in a greater cytotoxic activity of the compounds with 1,10-phenanthroline instead of those with 2,2′-bipyridyl, in the same way that removing iodine substitution or lengthening the peptidic chain diminishes the activity of compounds compared with 1. The presence of an ortho-iodine group and the direct bond between Ar-CO and glycine moieties yield to the best results.     

Sesquiterpene biosynthesis: The biosynthesis of quadrone and terrecyclic acid

Feeding of [1-¹³C]- and [1,2-¹³C₂]acetates to cultures of Aspergillus terreus gave labeled quadrone (1) and terrecyclic acid (2) which were analyzed by high-field ¹³C NMR. The patterns of enhancements and couplings were used not only in the analysis of the biosynthetic origins of the two metabolites, but also in the assignment of the ¹³C spectra themselves. The latter assignments were confirmed and further extended by extensive analysis by a combination of ¹H COSY, ¹H¹³C heteroCOSY, and difference NOE spectra of quadrone. The biosynthetic pathway was further probed by incorporation of [3,4-¹³C₂]mevalonate, revealing that formation of 1 and 2 involves cleavage of the 3,4-bond of one of the three mevalonte precursors. The results are consistent with the formation of quadrone and terrecyclic acid by cyclization of farnesyl pyrophosphate (8).     

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.     

Racemic twin crystals containing left- and right-handed polyoxometalate chains induced by the asymmetric coordination of metal-organic units

Two racemic twin crystals containing left- and right-handed polyoxometalates (POMs) chains [Cu(en)₂][Cu(en)₂(H₂O)]₂ [SiW₁₁CuO₃₉] · 5H₂O (D-1 and L-1; en = ethylenediamine) have been synthesized and structurally characterized. Both chiral compounds (D-1 and L-1) were constructed from the achiral building blocks [SiW₁₁CuO₃₉]⁶⁻ and [Cu(en)₂(H₂O)_n]²⁺ (n = 0 or 1). The structural chirality is induced by the [Cu(en)₂(H₂O)_n]²⁺ units asymmetrically coordinated on the chainlike [SiW₁₁CuO₃₉]_n⁶ⁿ⁻ polyoxoanions, leading to the whole molecules crystallized in the chiral P1 space group. The chiroptical activities of D-1 and L-1 were confirmed by the solid-state circular dichroism spectroscopy. Their electrochemical and electrocatalytic properties were also investigated.     

Syntheses, structures and properties of three nonmetal borates with salicylic acid and organic amines

Three new borates containing nonmetal compounds, [C₄H₁₂N][BO₄(C₇H₄O)₂] (1), [C₈H₂₀N][BO₄(C₇H₄O)₂] (2) and [C₆H₁₈N₂]_0.5[BO₄(C₇H₄O)₂] (3) have been prepared, aiming at the formation of extended supramolecular networks with organic-inorganic hybrid materials of salicylic acid and boric acid. The corresponding compounds have been characterized by chemical and spectroscopic techniques. X-ray diffraction analyses of available single crystals revealed that the molecular structures of the three compounds have the same isolated [BO₄(C₇H₄O)₂]⁻ anion. The [BO₄(C₇H₄O)₂]⁻ anion with a distorted BO₄ tetrahedron is formed by bidentate coordination of the B atom to two salicylic acid molecules via the O atoms of the central carboxyl and α-hydroxyl groups. The three compounds display violet luminescence with emission maxima around 365 nm.     

Polyoxometalate cluster [V12B18O60H6] functionalized with the copper(II) bis-ethylenediamine complex

Three compounds based on the polyoxometalate building block [V₁₂B₁₈O₆₀H₆], (Na)₁₀[(H₂O)V₁₂B₁₈O₆₀H₆]·18H₂O (1), Na₈[Cu(en)₂]₂[V₁₂B₁₈O₆₀H₆](NO₃)₂·14.7H₂O (2), Na₇[Cu(en)₂]₂[V₁₂B₁₈O₆₀H₆](NO₃)·15.5H₂O (3), (en = ethylenediamine), have been hydrothermally synthesized and characterized by single-crystal X-ray diffraction analysis and TGA. Compound 1 consists of polyoxovanadium borate [V₁₂B₁₈O₆₀H₆] clusters which are surrounded by sodium countercations in octahedral sites, stabilized by electrostatic interactions with the oxygen atoms of both vanadium and boron centres. However, compounds 2 and 3 correspond to more complicated structures, constructed from the same polyoxometalate clusters, which are interconnected by [Cu(en)₂]²⁺ moieties via the terminal oxygen atoms of the polyoxoanions, generating one-dimensional structures. The functionalization of this polyoxovanadium borate cluster has been obtained by the use of [Cu(en)₂]²⁺ complex ions, thus demonstrating the capacity of the terminal oxygen atoms of the cluster to bind transition metal centres. The structural stability of the [V₁₂B₁₈O₆₀H₆] cluster permits the formation of functionalized polyoxometalate clusters, generating various crystalline lattices.     

Synthesis and characterization of transition metal complexes bearing tetrafluoro-4-pyridyl substituent on the cyclopentadienyl ring

The reaction of sodium cyclopentadienide (NaCp) with pentafluoropyridine gives Na[4-(C₅F₄N)C₅H₄] (^PyFCpNa, 1) contaminated with starting NaCp from which pure 1 could be extracted with Et₂O. Hydrolysis of 1 and subsequent crystallization gives pure Diels-Alder dimer 1,4-bis(tetrafluoro-4-pyridyl)tricyclo[5.2.1.0^2,6]deca-3,8-diene (2). The reactions of 1 with FeCl₂, [MnBr(CO)₅], CoBr₂, [Ni(NH₃)₆]Cl₂, [TiCl₄(THF)₂] and [CpTiCl₃] cleanly affords the corresponding metallocenes [Fe(^PyFCp)₂] (3), [(^PyFCp)Mn(CO)₃] (5), [Co(^PyFCp)₂] (6), [Ni(^PyFCp)₂] (8), [(^PyFCp)₂TiCl₂] (9) and [(^PyFCp)(Cp)TiCl₂] (10), respectively. Tetrafluoro-4-pyridyl-substituted ferrocene 3 and [Fe(^PyFCp)(Cp)] (4) can be alternatively prepared by the reaction of the respective lithioferrocenes with C₅F₅N in THF. Air-oxidation of complex 6 affords the corresponding cobaltocenium salt [Co(^PyFCp)₂]PF₆ (7). All prepared compounds were characterized spectroscopically and by elemental analysis. The crystal structures of 3-7 were determined, revealing extensive arene π?π stacking and C-H?F-C contacts. Electrochemical studies supported with the spectroscopic data of the prepared metallocene complexes evidenced strong electron-withdrawing nature of the tetrafluoro-4-pyridyl substituent.