Bridging Fragment Research Articles

Impact of Structural Flexibility of Amine Moieties as Bridges for Redox-Active Sites on Secondary Battery Performance.

Although environmentally benign organic cathode materials for secondary batteries are in demand, their high solubility in electrolyte solvents hinders broad applicability. In this study, a bridging fragment to link redox-active sites is incorporated into organic complexes with the aim of preventing dissolution in electrolyte systems with no significant performance loss. Evaluation of these complexes using an advanced computational approach reveals that the type of redox-active site (i. e., dicyanide, quinone, or dithione) is a key parameter for determining the intrinsic redox activity of the complexes, with the redox activity decreasing in the order of dithione>quinone>dicyanide. In contrast, the structural integrity is strongly reliant on the bridging style (i. e., amine-based single linkage or diamine-based double linkage). In particular, owing to their rigid anchoring effect, diamine-based double linkages incorporated at dithione sites allow structural integrity to be maintained with no significant decrease in the high thermodynamic performance of dithione sites. These findings provide insights into design directions for insoluble organic cathode materials that can sustain high performance and structural durability during repeated cycling.

The disposition of bridge hydrogen bond in the homopolar-diborane and its derivatives

Compounds that comprehend less valence electrons are designated as electron deficient and atoms involved in such compounds occasionally form three-center-two-electron (3c-2e-) bonds to engross all of their available valence orbitals in bonding. Hence, in this study, calculations using M06-2X, MP2, and CCSD(T) method with the inclusion of def2-TZVP basis sets are exploited to reconnoiter the authentic bonding portrayal in diborane (DB) and its derivatives. Molecular electrostatic potential (MEP) analysis on the basis of vSmax and vSmin values indicates that there is a charge transfer between a π-hole that encompasses one monomer and the most negative region of another monomer that results in the formation of bridge bonds between two monomers. QTAIM investigation directed towards the charge depletion at bridging fragment in all the complexes and disclosed the polar covalent nature of bridge hydrogen bond. Additionally, ETS-NOCV examination suggests that charge flow from bridge to boron atom of all the complexes. Additionally, the bonding found to be more through orbital interactions compared to electrostatic interactions.

Non-sterical stabilization of one-electron-oxidized NiSalen complex by thiophene core

A combined theoretical/experimental study of the new thiophene-based NiSalen complex with unconjugated bridging fragment. This complex demonstrates unusual stability of the oxidized form, which is not typical for this class of compounds.

Chalcogen stabilized trimetallic clusters: synthesis, structures, and bonding of [(Cp*M)3(E)6+m(BH)n] (M = Nb or Ta; E = S or Se; m = 0 or 1 or 2; n = 0 or 1).

In an effort to isolate the chalcogen-rich niobium analogue of [(Cp*Ta)3(μ-S)3(μ3-S)3BH], the room temperature reaction of [Cp*NbCl4] (Cp* = η5-C5Me5) with Li[BH2S3] was carried out. Although the objective of isolating the niobium analogue was not achieved, the reaction yielded a homocubane-type cluster [(Cp*Nb)3(μ-S)3(μ3-S)3(μ-S)BH], 1, and a hexa-sulfido cluster [(Cp*Nb)3(μ-S)6], 2. Cluster 1 is a notable example of a homocubane-type cluster in which one of the vertices of the homocubane is missing. Compound 1 may be considered as a hypo-electronic cluster with an electron count of 64 cve (cve = cluster valence electrons), whereas compound 2 shows the presence of two doubly bridging η1-S around each Nb-Nb bond. On the other hand, the room temperature reaction of [Cp*TaCl4] with selenaborate ligand, [LiBH2Se3], led to the formation of [(Cp*Ta)3(μ-Se)4{μ-Se2(Se2)}], 3. Compound 3 is one of the rarest examples having a Ta3Se6 core structure with a unique diselenide bridging fragment. The presence of a short Se-Se bond of this diselenide unit makes this molecule of further interest. All these compounds were characterized by 1H, 11B{1H} and 13C{1H} NMR spectroscopy, infrared spectroscopy, mass spectrometry, and single-crystal X-ray crystallography. Density functional theory (DFT) calculations were carried out to provide insight into the bonding and electronic structures of these chalcogen-rich trimetallic clusters.

Photo- and ionochromic thienyl(coumarinyl)thiazoles

Thienyl (6-methoxycoumarinyl)thiazoles containing various amino groups in bridging fragment were synthesized. In the ring-opened form, the dihetarylethenes display fluorescence with quantum yields of 0.012–0.015. Irradiation of their solutions with light of 365 or 436 nm results in the formation of non-fluorescent ring-closed isomers. Re-opening of the cyclohexadiene ring occurs under exposure to visible light (λ > 500 nm). The prepared compounds represent bifunctional chemosensors – “naked-eye” chromogenic for F− anions (change of the solution color from yellow to brown-red) and fluorogenic for Hg2+ cations (with CHEQ effect).

On the Magnetic Coupling and Spin Crossover Behavior in Complexes Containing the Head-to-Tail [FeII2(μ-SCN)2] Bridging Unit: A Magnetostructural Experimental and Theoretical Study.

A new dinuclear complex [{Fe(tpc-OBn)(NCS)(μ-NCS)}2] (1) based on the tripodal tpc-OBn ligand (tpc-OBn = tris(2-pyridyl)benzyloxymethane), containing bridging μ-κN:κS-SCN and terminal κN-SCN thiocyanate ligands, has been prepared and characterized by single crystal X-ray diffraction, magnetic studies, and DFT theoretical calculations. This complex represents the first example of dinuclear FeII complex with double μ-κN:κS-SCN bridges in a head-to-tail configuration that exhibits ferromagnetic coupling between metal ions (JFeFe = +1.08 cm-1). Experimental and theoretical magnetostructural studies on this kind of infrequent FeII dinuclear complex containing a centrosymmetrically [Fe2(μ-SCN)2] bridging fragment show that the magnitude and sign of the magnetic coupling parameter, JFeFe, depend to a large extent on the Fe-N-C (α) angle, so that JFeFe decreases linearly when α decreases. The calculated crossover point below which the magnetic interactions change from ferromagnetic to antiferromagnetic is found at 162.3°. In addition, experimental results obtained in this work and those reported in the literature suggest that large Ntripodal-FeII distances and bent N-bound terminal κN-SCN ligands favor the high spin state of the FeII ions, while short Ntripodal-FeII distances and almost linear Fe-N-C angles favor a stronger ligand field, which enables the FeII ions to show spin crossover (SCO) behavior.

Controlled and Reversible Stepwise Growth of Linear Copper(I) Chains Enabled by Dynamic Ligand Scaffolds.

Reversible stepwise chain growth in linear CuI assemblies can be achieved by using the dynamic, unsymmetric naphthyridinone-based ligand scaffolds L1 and L2. With the same ligand scaffolds, the length of the linear copper chain can be varied from two to three and four copper atoms, and the nuclearity of the complex is easily controlled by the stepwise addition of a CuI precursor to gradually increase the chain length, or by the reductive removal of Cu atoms to decrease the chain length. This represents a rare example of a stepwise controlled chain growth in extended metal atom chains (EMACs). All complexes are formed with excellent selectivity, and the mutual transformations of the complexes of different nuclearity were found to be fast and reversible. These unusual rearrangements of metal chains of different nuclearities were achieved by a stepwise "sliding" movement of the naphthyridinone bridging fragment along the metal chain.

Controlled and Reversible Stepwise Growth of Linear Copper(I) Chains Enabled by Dynamic Ligand Scaffolds

AbstractReversible stepwise chain growth in linear CuI assemblies can be achieved by using the dynamic, unsymmetric naphthyridinone‐based ligand scaffolds L1 and L2. With the same ligand scaffolds, the length of the linear copper chain can be varied from two to three and four copper atoms, and the nuclearity of the complex is easily controlled by the stepwise addition of a CuI precursor to gradually increase the chain length, or by the reductive removal of Cu atoms to decrease the chain length. This represents a rare example of a stepwise controlled chain growth in extended metal atom chains (EMACs). All complexes are formed with excellent selectivity, and the mutual transformations of the complexes of different nuclearity were found to be fast and reversible. These unusual rearrangements of metal chains of different nuclearities were achieved by a stepwise “sliding” movement of the naphthyridinone bridging fragment along the metal chain.

Obvious modulation of rectifying performance by conjugation breaking of the bridging fragment in donor–bridge–acceptor molecular diodes

Large modulation of rectifying performance is obtained by breaking conjugation of the bridging fragment in donor–bridge–acceptor molecular diodes.

Palladium allylic complexes with enantiopure bis(diamidophosphite) ligands bearing a cyclohexane-1,2-diamine skeleton as catalysts in the allylic substitution reaction

A series of cationic allyl palladium complexes [Pd(η3-CH3-C3H5)(P-P)]X (X = PF6, 2a-c, 2e; and X = BPh4, 3a, 3b, 3d, 3e) and [Pd(η3-1,3-Ph2-C3H3)(P-P)]X (X = PF6, 6b; and X = BPh4, 7a) have been prepared. The bis(diamidophosphite) ligands (P-P) contain a diazaphospholidine terminal fragment derived from (R,R)- and (S,S)-N,N’-dibenzyl- and (R,R)-N,N’-dimethyl-cyclohexane-1,2-diamines and dialcoxy bridging fragment derived from (R,R)- and (S,S)-butanediol, (R,R)-cyclohexanediol, (4R,5R)- and (4S,5S)-4,5-di(hydroxymethyl)-2,2-dimethyl-1,3-dioxolane and (R)- and (S)-binaphthol. Complexes [Pd(η3-CH3-C3H5l)P2]X (X = PF6, 4f, 4g; and X = BPh4, 5f), where P are monodentate diamidophosphite ligands with diazaphospholidine heterocyclic backbone obtained from (R,R)- and (S,S)-N,N’-dibenzylcyclohexane-1,2-diamine and alcoxy groups coming from (R)-phenyl-ethanol and (S)-borneol have been also prepared. Neutral palladium complexes [PdCl2(P-P)] (1a, 1c) were synthesized to prove the C2 symmetry of the P-P ligand. The new compounds were fully characterized in solution by NMR spectroscopy. The X-ray crystal structure determination for 2e-(R,R,Ral,Ral;R,R) and 1a-(S,S;Sal,Sal;S,S) has been achieved.The new allyl-palladium complexes were applied in the asymmetric allylic substitution reaction of the benchmark substrate rac-3-acetoxy-1,3-diphenyl-1-propene with dimethyl malonate and benzylamine as nucleophiles in order to test their catalytic potential. The best results were obtained with the 3a-(R,R;Ral,Ral;R,R) precursor (up to 84% ee) while complexes with the e ligand derived from the (R,R)-N,N’-dimethylcyclohexane-1,2-diamine terminal fragment resulted inactive in the process. The influence of the nature and the absolute configuration of both the bridging and the terminal fragments of the bis(diamidophosphite) ligand on the asymmetric induction is discussed. A preliminary study of the anion effect (PF6− vs. BPh4-) on the activity and the enantioselectivity of the Pd-catalysed allylic substitution has also been performed.

New rhenium(III) semiclathrochelates with biorelevant apical substituents: Synthesis, X-ray structure and reactivity

One-pot reduction–condensation of K2ReCl6, dimethylglyoxime and phenylboronic acid anhydride in the presence of metallic silver gave the mixture of the boron-capped tris-dioximate rhenium(III) semiclathrochelate with its reduced diimine-iminoximate derivatives, resulted from the side ligand-centered domino-reaction; one of them was characterized by single crystal X-ray diffraction. Its rhenium(III) cation coordinates two boron-bridged iminooximate moieties and one non-bridged imine chelate ligand. Third oxygen atom of the boron-containing bridging fragment is also coordinated to this ion, thus giving a capped trigonal-prismatic (TP) ReN6O‐ coordination polyhedron in which the Re–O distance is substantially smaller than the Re–N ones {1.966(8) and 2.029(11)–2.099(11)Å, respectively}. Template condensation of ReCl3((C6H5)3P)2(CH3CN) with cyclohexane-1,2-dione dioxime (nioxime) and 3-formylphenylboronic acid afforded a formyl-terminated rhenium(III) tris-nioximate, undergoing a further H+-catalyzed condensation with isoniazid to give the semiclathrochelate hydrazone with apical functionalizing vector substituent. As follows from single crystal X-ray diffraction data, the ReN6Cl‐ coordination polyhedron of the former formyl-terminated complex possesses a geometry of a capped TP with the distortion angle φ equal to 5.0° and with the Re–Cl distance (2.4040(9)Å) that is substantially greater than the Re–N ones (2.046(3)–2.127(3)Å). The attempted capping of this formylphenylboron rhenium(III) complex with IGe(CF3)3 resulted in its transmetallation, leading to the germanium-capped semiclathrochelate. The analogous boron-capped semiclathrochelates with apical hexadecyl and cholesteryl groups were prepared using the direct template condensation of nioxime and hexadecylboronic acid on a rhenium(III) ion as a matrix, and by capping of the non-macrocyclic rhenium(III) tris-nioximate with cholesterylboronic acid, respectively.

Photochromic and fluorescent 5-coumarinyl-4-pyrrolylthiazoles

New dihetarylethenes of 5-coumarinyl-4-pyrrolylthiazole chemotype depending on the nature of the substituent at the bridging fragment are capable of either photochromic modulation of the fluorescent properties or emission with anomalous Stokes shift due to the ESIPT-effect.

Tetrakis(ferrocenylethynyl)ethene: Synthesis, (Spectro)electrochemical and quantum chemical characterisation

Tetrakis(ferrocenylethynyl)ethene (1) has been prepared in four steps from ethynyl ferrocene (2). In a dichloromethane solution containing 10−1 M NBu4[PF6], only a single oxidation process is observed by cyclic voltammetry, corresponding to the independent oxidation of the four ferrocenyl moieties. However, in dichloromethane containing 10−1 M NBu4[BArF4] electrolyte, where [BArF4]– is the weakly associating anion [B{C6H3(CF3)2-3,5}4]–, four distinct oxidation processes are resolved, although further spectroelectrochemical investigation revealed essentially no through bond interaction between the individual ferrocenyl moieties. Quantum chemical treatment of 1 identified several energetic minima corresponding to different relative orientations of the ferrocenyl moieties and the plane of the all-carbon bridging fragment. Further computational investigation of the corresponding monocation [1]+ supported the notion of charge localisation with no evidence for significant through bond electronic interactions.

An experimental and theoretical magneto-structural study of polynuclear Ni(II) complexes assembled from a versatile bis(salicylaldehyde)diamine polytopic ligand.

Six novel Ni(II) complexes, ranging from mononuclear to tetranuclear, have been prepared from the polytopic symmetrical Mannich base ligand N,N'-dimethyl-N,N'-bis(2-hidroxy-3-formyl-5-bromo-benzyl)ethylenediamine (H2L) and different anionic coligands: [Ni(H2L)(NO3)(H2O)]NO3·H2O (), [Ni2(μ-L)(acac)2(H2O)]·CH3CN (), [Ni2(μ-L)(μ-OAc)(NCS)] (), [Ni3(μ-L)2(μ-OH2)2(H2O)(CH3CN)](NO3)2·4CH3CN (), [Ni4(μ-L)2(μ-OAc)2(μ-OCH3)2]·6H2O·2CH3OH () and [Ni4(μ-L)2(μ-OAc)2(μ-N3)2]·2H2O·CH3OH (). These complexes have been characterized by single crystal X-ray diffraction, magnetic measurements and DFT theoretical calculations. The structural analysis of these complexes reveals that the anionic coligand and reaction conditions play a fundamental role in determining their final structures and magnetic properties. Compound contains a monomeric cationic unit with the nickel ion coordinated in the external O4 site of the compartmental ligand H2L, which acts in a neutral zwitterionic form. Complexes and are dinuclear Ni2 neutral entities, in which the Ni(II) ions are connected through two μ-phenoxido bridging groups. The Ni(O)2Ni bridging fragment in is almost planar, whereas in is bent due to the additional presence of a syn-syn acetate bridge connecting the Ni(II) atoms. Complex has a bent trinuclear structure with double μ-phenoxido/μ-water bridges between the central and terminal nickel atoms. Complexes and are Ni4 complexes with defective dicubane structures, in which triple μ-phenoxido/μ1,1,1-X/syn-syn acetate and double μ-phenoxido/μ1,1,1-X mixed bridges connect central and terminal Ni(II) atoms, whereas double μ1,1,1-X bridging ligands link the central Ni(II) ions (X = methoxido and azido groups for and , respectively). Magnetic susceptibility measurements reveal that complex shows a moderate antiferromagnetic interaction between the Ni(II) ions through the double di-μ-phenoxido bridge, leading to a S = 0 ground state. Compared to , complex shows a much weaker magnetic exchange interaction due the counter-complementarity effect provoked by the additional presence of the syn-syn acetate bridging group, as well as the non-planarity of the bridging fragment. In complex , the double μ-phenoxido/μ-water mixed bridges lead to very weak antiferromagnetic interactions between the central and external Ni(II) ions. Overall ferromagnetic interactions are found for , and , although in not all the magnetic pathways transmit ferromagnetic interactions. A detailed analysis of the magnetic exchange interactions transmitted through the different pathways as well as DFT calculations on the X-ray structures of compounds were performed to support the magneto-structural data of these compounds.

Bimetallic ruthenium complexes bridged by divinylphenylene bearing oligo(ethylene glycol)methylether: synthesis, (spectro)electrochemistry and the lithium cation effect

A series of 1,4-disubstituted ruthenium-vinyl complexes, (E,E)-[{(PMe3)3(CO)ClRu}2(μ-HC=CH-Ar-CH=CH)], in which the 1,4-diethenylphenylene bridge bears two oligo(ethylene glycol)methyl ether side chains at different positions (2,5- and 2,3-positions), were prepared. The respective products were characterized by elemental analyses and NMR spectroscopy. The structures of complexes 1b and 1e were established by X-ray crystallography. The electronic properties of the complexes were investigated by cyclic voltammetry, and IR and UV-vis/NIR spectroscopies. Electrochemical studies showed that the 2,5-substituents better stabilized the mixed-valence states; the electrochemical behavior was greatly affected by lithium cations, especially complex 1g with 2,3-substituents, which was further supported by IR and UV-vis/NIR spectra changes. Spectroelectrochemical studies showed that the redox chemistry was dominated by the non-innocent character of the bridging fragment.

Anion controlled structural and magnetic diversity in unusual mixed-bridged polynuclear Ni(II) complexes with a versatile bis(2-methoxy phenol)diamine hexadentate ligand. An experimental and theoretical magneto-structural study.

This work reports the syntheses, crystal structures, magnetic properties and DFT calculations of six novel polynuclear NiII compounds [Ni2(μ-HL1)2(μ-N3)]N3·(CH3OH)2·2H2O (1), [Ni2(μ-HL1)2(μ-N3)][Na2Ni2(μ-L1)2(μ-N3)2(CH3OH)(N3)]·4CH3OH (2), [Ni4(μ-L1)2(μ-N3)4(CH3OH)2]·2CH3OH (3), [Na2Ni4(μ-L1)2(μ-OAc)2(μ-N3)4(CH3OH)4]·2CH3OH (4), [Ni4(μ-L1)2(μ-Cl)2(Cl)2] (5), and [Ni3(μ-L1)2(acac)2(H2O)2] (6), with uncommon structures and rare mixed-bridges between NiII ions, which were prepared from the versatile polytopic Mannich base ligand N,N′-dimethyl-N,N′-bis(2-hydroxy-3-methoxy-5-methylbenzyl)ethylenediamine (H2L1). The anionic coligand (azide, chloride, acetate and acetylacetonate) and reaction conditions play crucial roles in determining the final structure of these compounds and consequently their magnetic properties. Compound 1 contains a Ni2 cationic unit with rare di-μ-phenoxido/μ1,1-azide triple mixed bridges whereas complex 2 is made from the same Ni2 cationic unit as 1, cocrystallized with Na2Ni2 neutral units, in which double μ1,1,1-azide bridges connect the NiII and NaI anions. Complexes 3 and 4 are Ni4 complexes with defective dicubane and linear structures, respectively. Complex 3 has two distinct types of mixed bridges, μ-phenoxido/μ1,1,1-azido and μ1,1-azido/μ1,1,1-azido and a double di-μ1,1,1-azido bridge, the latter connecting the face-sharing NiII ions. In 4, rare μ-phenoxido/μ1,1-azide/syn–syn acetate triple mixed bridges connect central and terminal NiII atoms whereas a double μ1,1-azide planar bridging fragment links the central NiII ions. Complex 5 has a defective-dicubane structure with double μ-phenoxido/μ3-chloro mixed bridges and di-μ3-chloro bridges, whereas complex 6 has a bent structure with very uncommon single μ-phenoxido bridges. The analysis of the magnetic properties reveals that in complexes 1–4 all magnetic pathways transmit ferromagnetic interactions leading to S = 2 ground states for 1 and 2 and S = 4 ground states for 3 and 4. In complex 5, the double μ-phenoxido/μ3-chloro mixed bridges and di-μ3-chloro bridges mediate antiferro- and ferromagnetic interactions, respectively, giving rise to a S = 0 ground state. Complex 6 shows antiferromagnetic interactions between the NiII ions through single μ-phenoxido bridging groups, leading to an S = 1 ground state. DFT calculations on the X-ray structures and model compounds were performed to support the magneto-structural data of the above compounds.

Bifunctional ZnIILnIII Dinuclear Complexes Combining Field Induced SMM Behavior and Luminescence: Enhanced NIR Lanthanide Emission by 9-Anthracene Carboxylate Bridging Ligands

There were new dinuclear Zn(II)-Ln(III) complexes of general formulas [Zn(μ-L)(μ-OAc)Ln(NO3)2] (Ln(III) = Tb (1), Dy (2), Er (3), and Yb (4)), [Zn(μ-L)(μ-NO3)Er(NO3)2] (5), [Zn(H2O)(μ-L)Nd(NO3)3]·2CH3OH (6), [Zn(μ-L)(μ-9-An)Ln(NO3)2]·2CH3CN (Ln(III) = Tb (7), Dy (8), Er (9), Yb(10)), [Zn(μ-L)(μ-9-An)Yb(9-An)(NO3)3]·3CH3CN (11), [Zn(μ-L)(μ-9-An)Nd(9-An)(NO3)3]·2CH3CN·3H2O (12), and [Zn(μ-L)(μ-9-An)Nd(CH3OH)2(NO3)]ClO4·2CH3OH (13) prepared from the reaction of the compartmental ligand N,N',N″-trimethyl-N,N″-bis(2-hydroxy-3-methoxy-5-methylbenzyl)diethylenetriamine (H2L), with ZnX2·nH2O (X = NO3(-) or OAc(-)) salts, Ln(NO3)3·nH2O, and, in some instances, 9-anthracenecarboxylate anion (9-An). In all these complexes, the Zn(II) ions invariably occupy the internal N3O2 site whereas the Ln(III) ions show preference for the O4 external site, giving rise to a Zn(μ-diphenoxo)Ln bridging fragment. Depending on the Zn(II) salt and solvent used in the reaction, a third bridge can connect the Zn(II) and Ln(III) metal ions, giving rise to triple-bridged diphenoxoacetate in complexes 1-4, diphenoxonitrate in complex 5, and diphenoxo(9-anthracenecarboxylate) in complexes 8-13. Dy(III) and Er(III) complexes 2, 8 and 3, 5, respectively, exhibit field induced single molecule magnet (SMM) behavior, with Ueff values ranging from 11.7 (3) to 41(2) K. Additionally, the solid-state photophysical properties of these complexes are presented showing that ligand L(2-) is able to sensitize Tb(III)- and Dy(III)-based luminescence in the visible region through an energy transfer process (antenna effect). The efficiency of this process is much lower when NIR emitters such as Er(III), Nd(III), and Yb(III) are considered. When the luminophore 9-anthracene carboxylate is incorporated into these complexes, the NIR luminescence is enhanced which proves the efficiency of this bridging ligand to act as antenna group. Complexes 2, 3, 5, and 8 can be considered as dual materials as they combine SMM behavior and luminescent properties.

Family of Carboxylate- and Nitrate-diphenoxo Triply Bridged Dinuclear NiIILnIII Complexes (Ln = Eu, Gd, Tb, Ho, Er, Y): Synthesis, Experimental and Theoretical Magneto-Structural Studies, and Single-Molecule Magnet Behavior

Seven acetate-diphenoxo triply bridged M(II)-Ln(III) complexes (M(II) = Ni(II) and Ln(III) = Gd, Tb, Ho, Er, and Y; M(II) = Zn(II) and Ln(III) = Ho(III) and Er(III)) of formula [M(μ-L)(μ-OAc)Ln(NO(3))(2)], one nitrate-diphenoxo triply bridged Ni(II)-Tb(III) complex, [Ni(μ-L)(μ-NO(3))Tb(NO(3))(2)]·2CH(3)OH, and two diphenoxo doubly bridged Ni(II)-Ln(III) complexes (Ln(III) = Eu, Gd) of formula [Ni(H(2)O)(μ-L)Ln(NO(3))(3)]·2CH(3)OH have been prepared in one pot reaction from the compartmental ligand N,N',N"-trimethyl-N,N"-bis(2-hydroxy-3-methoxy-5-methylbenzyl)diethylenetriamine (H(2)L). Moreover, Ni(II)-Ln(III) complexes bearing benzoate or 9-anthracenecarboxylate bridging groups of formula [Ni(μ-L)(μ-BzO)Dy(NO(3))(2)] and [Ni(μ-L)(μ-9-An)Dy(9-An)(NO(3))(2)]·3CH(3)CN have also been successfully synthesized. In acetate-diphenoxo triply bridged complexes, the acetate bridging group forces the structure to be folded with an average hinge angle in the M(μ-O(2))Ln bridging fragment of ~22°, whereas nitrate-diphenoxo doubly bridged complexes and diphenoxo-doubly bridged complexes exhibit more planar structures with hinge angles of ~13° and ~2°, respectively. All Ni(II)-Ln(III) complexes exhibit ferromagnetic interactions between Ni(II) and Ln(III) ions and, in the case of the Gd(III) complexes, the J(NiGd) coupling increases weakly but significantly with the planarity of the M-(O)(2)-Gd bridging fragment and with the increase of the Ni-O-Gd angle. Density functional theory (DFT) theoretical calculations on the Ni(II)Gd(III) complexes and model compounds support these magneto-structural correlations as well as the experimental J(NiGd) values, which were found to be ~1.38 and ~2.1 cm(-1) for the folded [Ni(μ-L)(μ-OAc)Gd(NO(3))(2)] and planar [Ni(H(2)O)(μ-L)Gd(NO(3))(3)]·2CH(3)OH complexes, respectively. The Ni(II)Dy(III) complexes exhibit slow relaxation of the magnetization with Δ/k(B) energy barriers under 1000 Oe applied magnetic fields of 9.2 and 10.1 K for [Ni(μ-L)(μ-BzO)Dy(NO(3))(2)] and [Ni(μ-L)(μ-9-An)Dy(9-An)(NO(3))(2)]·3CH(3)CN, respectively.

Interrelation between the chemical structure and antioxidant properties of N-substituted amides of salicylic acid

The kinetics of the initiated oxidation of a model lipid (methyl oleate has been investigated in the presence of a group of new “hybrid” structures, namely, N-substituted amides of salicylic acid whose structure contains an amide residue conjugated with, or separated by a bridging fragment (three methylene groups) from, an N-phenolic substituent. The compounds also differ in the degree of screening of the OH groups. The process was initiated by thermal decomposition of azobisisobutyronitrile at 60°C (initiation rate of wi = 4.2 × 10−8 mol L−1 s−1) or by UV irradiation (γ = 313−365 nm, wi = 0.6 × 10−8 mol L−1 s−1). The compounds examined exhibit antiradical activity owing to the presence of the phenolic hydroxyl groups. N-substituted salicylamides efficiently inhibit the overall methyl oleate oxidation process and are comparable in activity with dibunolum and α-tocopherol or are superior to them. The structures in which the residues of salicylamide and sterically hindered phenol are separated by the bridging fragment are particularly efficient. The advantages of the salicylamides absorbing at 300–365 nm manifest themselves in UV-initiated oxidation. The peroxidase activity of the N-substituted salicyl acid derivatives is determined by the structure of the amide moiety. The compounds examined here are new, promising, effective antioxidants, whose particular structural fragments act via different mechanisms in oxidation.

Novel titanium(iv) complexes with 2,4-di-tert-butyl-6-(1,1,1,3,3,3-hexafluoro-2-hydroxypropan-2-yl)phenol in ethene polymerization

Dinuclear (2) and mononuclear dichloride complexes (3) of titanium(iv) isopropoxide with a bidentate phenol alcohol ligand, viz., 2,4-di-tert-butyl-6-(1,1,1,3,3,3-hexafluoro-2-hydroxy-propan-2-yl)phenol, were obtained. The structures of the complexes were confirmed by X-ray diffraction. The dimeric structure of complex 2 is typical of alkoxy compounds and contains the bridging fragment Ti(μ-OPri)2Ti; the coordination polyhedron of the Ti atom is a distorted tetragonal pyramid. In complex 3, the Ti atom has a distorted octahedral environment made up of the O atoms of the ligand, the Cl atoms, and the O atoms of two coordinated propan-2-ol molecules. The catalytic properties of complexes 2 and 3 in ethene polymerization were studied with such promoters as polymethylaluminoxane (MAO), trimethylaluminum, triisobutylaluminum, diethylaluminum chloride, and Et2AlCl-MgBu2. Both the complexes were catalytically active (635 and 540 kg of polyethylene (PE)/(mol of Ti) h atm, respectively) only in the presence of the binary promoter Et2AlCl-MgBu2. The dichloride complexes obtained from a lithium or magnesium salt of the same ligand and TiCl4 without separation from lithium and magnesium chlorides formed as by-products were catalytically active in the presence of MAO, Bui 3Al, and Me3Al. For the catalytic system containing the dichloride complex and MgCl2, the best promoter is Me3Al (1082 kg of PE/(mol of Ti) h atm). The polymer obtained on all the catalytic systems is linear polyethylene characterized by high molecular weight (Mw = = 593900–2000000 g mol−1) and high polydispersity indices (Mw/Mn = 2.8–15). Various conjectures were made about why lithium and magnesium chlorides have the promoting effects.