The Syntheses and Vibrational Spectra of O-16- and O-18-Enriched cis-MO2 (M=Mo, W) Complexes

In this contribution, we report convenient synthetic approaches for obtaining O-16/O-18-enriched dioxidometal(VI) complexes, MO2(L) (W, Mo), with a linear, tetradentate amine phenolate ligand N,N-dimethyl-N,N-bis(2-hydroxy-3,5-dimethylbenzyl)ethylenediamine (H2L) and describe their characterization by IR and Raman spectroscopy complemented by DFT computational analysis. The isotopologues of WO2(L) were made of tungsten(VI) trisglycolate W(eg)(3) (eg=1,2-ethanediolate dianion) and ligand H2L in the presence of either H-2[O-16] or H-2[O-18], whereas (MoO2)-O-16(L) was made using Na(2)MoO(4)2H(2)O which was converted to (MoO2)-O-18(L) by oxido substitution using H-2[O-18]. The complementary IR and Raman analyses show the (MO2)(s) and (MO2)(a) at 934 and 899cm(-1) for (WO2)-O-16(L) and at 914 and 898cm(-1) for (MoO2)-O-16(L), respectively. In the vibrational spectra of the O-18 substituted derivatives, the (MO2)(s) were shifted to lower energy by 43cm(-1) for (WO2)-O-18(L) and by 41cm(-1) for (MoO2)-O-18(L) whereas asymmetric MO2 stretches in the IR were partially overlapped by an organic ligand related stretch. However, Raman spectroscopy, accompanied by DFT calculations, allowed the deciphering the (MO2)(a) shifts of 47cm(-1) for (WO2)-O-18(L) and 31cm(-1) for (MoO2)-O-18(L)

Bioinspired Mo, W and V complexes bearing a highly hydroxyl- functionalized Schiff base ligand

A series of bioinspired dioxidomolybdenum(vi), dioxidotungsten(vi) and oxidovanadium(v) complexes [MoO2(H2LSaltris], [WO2(H2LSaltris] and [VO(HLSaltris)](2) were prepared by the reaction of a hydroxyl-rich Schiff base proligand N-(1,3-dihydroxy-2-(hydroxymethyl)propan 2 yl) 3,5 di-tert butylsalicylaldimine (H4LSaltrisc) with metal precursors in methanol solutions. Molybdenum and tungsten complexes crystallize as mononuclear molecules, whereas the vanadium complex forms dinuclear units. From the complexes, [VO(HLSaltris)](2) shows activity in the oxidation of 4-tert-butylcatechol and 3,5-di-tert-butylcatechol, mimicking the action of the dicopper enzyme catechol oxidase

Reactions of a Dioxidomolybdenum(VI) Complex with Thionation Reagents-Formation of Mo(IV) Species with Sulfur Donors

Molecular molybdenum complexes with sulfur donor ligands are generally studied as soluble model compounds for molybdenum enzymes essential for life. The dioxidomolybdenum(VI) complex with tetradentate aminobisphenolate ligand undergoes a reaction with thionation reagent P2S5 or its organic derivative, Lawesson's reagent, to yield stable Mo(IV) aminobisphenolate complexes, where pristine oxido ligands have been replaced by bidentate sulfur donors tetrasulfide, S-4(2-) or (4-methoxyphenyl)phosphonotrithioate residue derived from Lawesson's reagent. This is in contrast to the behaviour of analogous dioxidotungsten(VI) complex, which, under similar conditions, yields W(VI) S-2 systems. The overall cis,trans,cis geometry of the parent dioxidomolybdenum(VI) aminobisphenolate is retained, namely, the neutral nitrogen donors are in cis positions, phenolate oxygens are trans to each other and sulfur donors are cis. Although formally Mo(IV), thus d(2) system, the studied complexes have diamagnetic singlet electron configurations as a result of the axially compressed octahedral structures

Integration of catalyst and nucleophile in oxometal aminobis(phenolate) complexes with ammonium iodide pendant arm groups

An amine bisphenol ligand with an ammonium iodide group in the pendant arm (H2L) reacts with V, Mo and U oxometal precursors to form oxovanadium(V), dioxomolybdenum(VI) and dioxouranium(VI) species, respectively. In methanol solutions, vanadium(V) and molybdenum(VI) form 1:1 complexes [VO(OMe)(L)]I·2MeOH and [MoO2(L)(H2O)]I·2MeOH, where the cationic charge in the pendant arm is counterbalanced by an iodide anion. Uranium(VI) forms a complex in which the anionic charge of uranate complex unit is compensated by the cationic pendant arm. The complex crystallises as a co-crystal containing a neutral ligand precursor, namely [UO2(L)(OAc)]·[H2L]I·4MeOH. The oxovanadium(V) complex combines a Lewis acid, i.e. a pentacoordinated metal centre with a Lewis basic iodide moiety, which makes it a suitable catalyst for the coupling of CO2 with styrene oxide. The role of the ammonium moiety of the ligand is to carry the iodide nucleophile in the reaction.</p

Single crystal X-ray structural dataset of 1,2,4-dithiazolium tetrafluoroborate

Herein, we present the crystallographic dataset of 1,2,4-dithiazolium tetrafluoroborate. Single crystal X-ray structural analysis evidences that the 1,2,4-dithiazolium ring is almost planar. The 1,2,4-dithiazolium and tetrafluoroborate ions contribute in hydrogen bonding wherein the N-H·N hydrogen bonding in 1,2,4-dithiazolium dimer forms an eight-membered pseudo ring with the R 2 2 ( 8 ) Etter's graph set. The information provided in this data contributes to the understanding of structural chemistry and hydrogen bonding interactions in dithiazole derivatives.© 2022 The Author(s).</p

Series of Near-IR-Absorbing Transition Metal Complexes with Redox Active Ligands

New soluble and intensely near-IR-absorbing transition metal (Ti, Zr, V, Ni) complexes were synthesized using a redox non-innocent N,N'-bis(3,5-di-tertbutyl-2-hydroxy-phenyl) -1,2-phenylenediamine (H4L) as a ligand precursor. In all the complexes, ([Ti(L-ox)(2), [Zr(L-ox)(2)], [V(L-sq1)(HLox)] and [Ni(HLox)(2)], two organic molecules coordinate to the metal center as tri- or tetradentate ligands. The solid-state structures of the complexes were determined using single crystal XRD, and the compounds were further characterized with Electrospray Ionisation Mass Spectrometry (ESI-MS). Thermoanalytical measurements indicated the thermal stabilities of the complexes. All compounds absorb strongly in the near-IR region and show very interesting magnetic and electrochemical properties. Moreover, it was shown that the V and Ni complexes can also convert absorbed near-IR photons to (un)paired electrons, which indicates great promise in photovoltaic applications

A diamagnetic iron complex and its twisted sister - structural evidence on partial spin state change in a crystalline iron complex

We report here the syntheses of a diamagnetic Fe complex [Fe(HL)2] (1), prepared by reacting a redox non-innocent ligand precursor N,N′-bis(3,5-di-tert-butyl-2-hydroxy-phenyl)-1,2-phenylenediamine (H4L) with FeCl3, and its phenoxazine derivative [Fe(L′)2] (2), which was obtained via intra-ligand cyclisation of the parent complex. Magnetic measurements, accompanied by spectroscopic, structural and computational analyses show that 1 can be viewed as a rather unusual Fe(III) complex with a diamagnetic ground state in the studied temperature range due to a strong antiferromagnetic coupling between the low-spin Fe(III) ion and a radical ligand. For a paramagnetic high-spin Fe(II) complex 2 it was found that, when crystalline, it undergoes a thermally induced process where 25% of the molecules in the material change to a diamagnetic low-spin ground state below 100 K. Single crystal X-ray studies conducted at 95 K afforded detailed structural evidence for this partial change of spin state of 2 showing the existence of crystallographically distinct molecules in a 3 : 1 ratio which exist in high- and low-spin states, respectively. Also, the magnetic behaviour of 2 was found to be related with the crystallinity of the material as demonstrated by near-IR radiation to unpaired electrons conversion ability of amorphous sample of 2. </p

Dioxomolybdenum(VI) and -Tungsten(VI) Amino Bisphenolates as Epoxidation Catalysts

Low-cost metallate salts Na2MO4·2H2O (M = molybdenum, tungsten) react with a tridentate amine bisphenol bis(2-hydroxy-3-tert-butyl-5-methylbenzyl)methylamine (H2ONOtBu) under ambient conditions in acidic methanol solutions. The reactions lead to the formation of isostructural dioxo complexes [MO2(ONOtBu)(MeOH)]·MeOH in convenient yields. Spectral data as well as X-ray analyses reveal these complexes to be isostructural. Both compounds were tested as catalysts for epoxidation of olefins using cis-cyclooctene, cyclohexene, norbornene and styrene as substrates and tert-butyl hydroperoxide and hydrogen peroxide as oxidants. The molybdenum complex catalyses selectively the oxidation of cis-cyclooctene and norbornene to corresponding epoxides, whereas oxidation of cyclohexene and styrene lead low yields as the epoxidations were associated with the formation of other oxidation products. Corresponding tungsten complex shows lower activity for epoxidation of norbornene and practically no activity for other olefins. Both complexes can also catalyse the conversion of benzoin to benzil using dimethyl sulphoxide as an oxidant, while the molybdenum complex shows higher activity.peerReviewe

Oxidovanadium(V) amine bisphenolates as epoxidation, sulfoxidation and catechol oxidation catalysts

Air-stable oxidovanadium(V) complexes with tetradentate amine bisphenolate ligands were made by the reaction of VOSO4·xH2O and ligand precursors in MeOH solutions. Isolated compounds were studied as catechol oxidase models as well as catalysts for epoxidation and sulfoxidation reactions. All compounds can catalyse such oxidation reactions without notable structure-activity correlations. The 51V NMR studies indicate that the complexes turn to the number of different species during the catalytic experiments.peerReviewe