Tripodal Ligand Research Articles

The Influence of MWCNTs Amounts and PVP Aqueous Solutions on the Properties of PVA/PVP/MWCNTs Nanocomposite Membranes

In this article, the surface functionalization of multi-walled carbon nanotubes (MWCNTs) is performed using a tris(2-aminoethyl)amine (TAA) to generate functional moieties (−NH2) on the surface. The functionalized MWCNTs (f-MWCNTs) are incorporated in the blend polymers of polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) to fabricate a nanocomposite membrane via phase inversion process, which are named PVA/PVP/f-MWCNT. The nanocomposite membranes are characterized by a field emission scanning electron microscopy (FE-SEM), fourier transform infrared spectrometer (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), water contact angle. The FE-SEM images show that the PVA/PVP/f-MWCNTs nanocomposite membrane consisting 0.01 g of f-MWCNTs exhibits a uniform morphology and good dispersion of f-MWCNTs. The X-ray results demonstrate that the incorporation of f-MWCNTs has successfully changed the structural properties of the nanocomposite membranes. TGA analysis indicates that the PVA/PVP/f-MWCNTs nanocomposite membranes exhibit higher thermal properties than the pristine PVA/PVP blend membrane. The weight loss within 420 °C–550 °C is increased from 34.62 to 55.66% with increasing the PVP content from 1 wt% to 8 wt%, respectively. The contact angle measurements indicate that addition of f-MWCNTs to the PVA/PVP blend membrane has improved hydrophilic properties.

Experimental and theoretical magnetostructural studies on discrete heterometallic cyanide-bridged dinuclear FeIIIMnII and tetranuclear FeIII2CuII2 complexes bearing tripodal pyrazolyl borate and tetradentate phenolate-based ligands.

Two new complexes [FeIII(Tp)(CN)2(μ-CN)MnIICl(HL1)]·3DMF (1) and {[FeIII(Tp)(CN)(μ2-NC)2CuII(HL2)](ClO4)}2·6DMF (2) (HL1 = 2-((((1-methylbenzimidazol-2-yl)methyl)(pyridin-2-ylmethyl)amino)methyl)phenol and HL2 = 2-(((pyridin-2-ylmethyl)(quinolin-2-ylmethyl)-amino)methyl)phenol) have been synthesized and characterized by elemental analysis and IR and UV/vis spectroscopy. Structural analysis revealed that 1 is a discrete dinuclear coordination complex and 2 is a discrete tetranuclear coordination complex. In complex 1, each MnII is in a distorted octahedral MN4OCl environment where coordination is satisfied by three nitrogen atoms and one oxygen atom of the ligand, and a chloride group and one nitrogen atom from cyanide. In complex 2, each Cu is in a distorted octahedral MN5O environment where coordination is satisfied by three nitrogen atoms and one oxygen atom of the ligand, and two nitrogen atoms from two cyanides. Direct current (dc) variable-temperature magnetic susceptibility measurements on polycrystalline samples of 1 and 2 were carried out in the temperature range of 1.8-300 K. Investigation of the magnetic properties reveals the occurrence of weak antiferromagnetic coupling between the low-spin FeIII (S = 1/2) ions and high-spin MnII (S = 5/2) ions in 1, while 2 exhibits ferro- and antiferromagnetic coupling between the metal ions in the tetranuclear CuII2FeIII2 unit. DFT calculations show ferromagnetic coupling in both complexes, although this appears to be weak in the case of complex 1. In addition, magnetostructural correlations reveal the magnetic behavior against Mn-N-C and Fe-C-N angles in 1 and Cu-N-C and Fe-C-N angles in 2.

Structural characterization and solvent vapor sorption of two solvent-dependent Zn(ii) supramolecular architectures based on a flexible tripodal thioether-based pyridyl ligand and a dicarboxylate-based ligand

Two solvent-dependent 3D supramolecular architectures, constructed by doubly-interpenetrating layered 2D MOF and triply-interpenetrating 3D MOF, respectively, showed interesting reversible solvent vapor ad-/desorption behaviors.

Construction of ZnII/CdII-based MOFs containing a tripodal aromatic carboxylate ligand with unequal arms and their fluorescence detection for Cu2+ and Fe3+ cations

Four MOFs have been synthesized and characterized. The luminescent sensing investigation indicates that compound 1 exhibits extremely sensitive and selective detection of Cu2+ and compounds 2–4 show extremely sensitive and selective detection of Fe3+.

Assembly of an iron-based complex into a metal-organic framework: a space confinement strategy for isolation of mono-iron complexes to protect from dimerization.

Non-heme mononuclear iron complexes, especially when supported by tripodal tetradentate ligands, show promising C-H bond activation efficiency in catalytic reactions. Nevertheless, they intrinsically decay readily to their dinuclear form, and the dimerization process is inevitable in homogenous solution, which dramatically hinders their further application. Hence, we demonstrate that the mononuclear iron complex [(TPA)FeII-2L]2+ (L = labile ligands, mainly solvent molecules) was successfully encapsulated in a highly robust metal-organic framework UiO-66 via a two-step "ship-in-a-bottle" strategy. The nearly perfect size matching of the octahedral cages of the host UiO-66 provides ideal space confinement for the guest complex to protect from dimerization and dramatically increases the mono-nuclear complex stability compared to its un-confined state. The successful encapsulation of [(TPA)FeII-2L]2+ in UiO-66 was verified thoroughly by spectroscopy, microscopy, N2 adsorption, and electrochemistry characterization techniques. This work shows that encapsulating an unstable molecular complex in MOFs via a two-step "ship-in-a-bottle" strategy highlights opportunities for extending the heterogenization of homogeneous complexes.

Mononuclear nickel(ii)-flavonolate complexes of tetradentate tripodal 4N ligands as structural and functional models for quercetin 2,4-dioxygenase: structures, spectra, redox and dioxygenase activity.

Three new nickel(ii)-flavonolate complexes of the type [Ni(L)(fla)](ClO4) 1-3, where L is the tripodal 4N ligand tris(pyrid-2-ylmethyl)amine (tpa, L1) or (pyrid-2-ylmethyl)bis(6-methylpyrid-2-ylmethyl)amine (6-Me2-tpa, L2) or tris(N-Et-benzimidazol-2-ylmethyl)amine (Et-ntb, L3), have been isolated as functional models for Ni(ii)-containing quercetin 2,4-dioxygenase. Single crystal X-ray structures of 1 and 3 reveal that Ni(ii) is involved in π-back bonding with flavonolate (fla-), as evident from enhancement in C[double bond, length as m-dash]O bond length upon coordination [H(fla), 1.232(3); 1, 1.245(7); 3, 1.262(8) Å]. More asymmetric chelation of fla- in 3 than in 1 [Δd = (Ni-Ocarbonyl - Ni-Oenolate): 1, 0.126; 3, 0.182 Å] corresponds to lower π-delocalization in 3 with electron-releasing N-Et substituent. The optimized structures of 1-3 and their geometrical isomers have been computed by DFT methods. The HOMO and LUMO, both localized on Ni(ii)-bound fla-, are highly conjugated bonding π- and antibonding π*-orbitals respectively. They are located higher in energy than the Ni(ii)-based MOs (HOMO-1, dx2-y2; HOMO-2/6, dz2), revealing that the Ni(ii)-bound fla- rather than Ni(ii) would undergo oxidation upon exposure to dioxygen. The results of computational studies, in combination with spectral and electrochemical studies, support the involvement of redox-inactive Ni(ii) in π-back bonding with fla-, tuning the π-delocalization in fla- and hence its activation. Upon exposure to dioxygen, all the flavonolate adducts in DMF solution decompose to produce CO and depside, which then is hydrolyzed to give the corresponding acids at 70 °C. The highest rate of dioxygenase reactivity of 3 (kO2: 3 (29.10 ± 0.16) > 1 (16.67 ± 0.70) > 2 (1.81 ± 0.04 × 10-1 M-1 s-1)), determined by monitoring the disappearance of the LMCT band in the range 440-450 nm, is ascribed to the electron-releasing N-Et substituent on bzim ring, which decreases the π-delocalization in fla- and enhances its activation.

In silico capture and activation of methane with light atom molecules.

Methane (CH4) can be captured in silico with a light atom molecule containing only C, H, Si, O, and B atoms, respectively. A tripodal peri-substituted ligand system was employed, namely, [(5-Ph2B-xan-4-)3Si]H (1, xan = xanthene), which after hydride abstraction (1+) carries four Lewis acidic sites within the cationic cage structure. In a previous study, this system was shown to be able to capture noble gas atoms He-Kr (Mebs & Beckmann 2022). In the corresponding methane complex, 1+CH4, a polarized Si+⋯CH4 contact of 2.289 Å as well as series of (H3)CH⋯O/CPh hydrogen bonds enforce spatial CH4 fixation (the molecule obeys C3-symmetry) and slight activation. A trigonal-pyramidal Si-CHeq3-Hax local geometry is thereby approached with Hax-C-Heq angles decreased to 103.7°. All attempts to replace the Lews acidic -BPh2 fragments in 1 with basic -PR2 (R = Ph, tBu) fragments indeed increased intra-molecular hydrogen bonding between host molecule and CH4, and thus caused stronger activation of the latter, however ultimately resulted in the formation of energetically favorable quenched structures with short P-Si contacts, making CH4 binding hard to achieve. The electronic situation of two hypothetic methane complexes, 1+CH4 and [(5-tBu2P-xan-4-)3SiCH4]+ (2+CH4), was determined by a set of calculated real-space bonding indicators (RSBIs) including the Atoms-In-Molecules (AIM), non-covalent interactions index (NCI), and electron localizability indicator (ELI-D) methods, highlighting crucial differences in the level of activation. The proposed ligand systems serve as blueprints for a more general structural design with adjustable trigonal ligand systems in which central atom, spacer fragment, and functional peri-partner can be varied to facilitate different chemical tasks.

Two Cu(i) coordination polymers based on a new benzimidazolyl-tetrazolyl heterotopic ligand for visible-light-driven photocatalytic dye degradation

Two Cu(i) CPs based on a new heterotopic tripodal ligand were constructed and their visible-light-driven photocatalytic performance were studied.

Cobalt-based tripodal complexes as molecular catalysts for photocatalytic CO2 reduction.

Construction of artificial photosynthetic systems including CO2 reduction is a promising pathway to produce carbon-neutral fuels and mitigate the greenhouse effect concurrently. However, the exploitation of earth-abundant catalysts for photocatalytic CO2 reduction remains a fundamental challenge, which can be assisted by a systematic summary focusing on a specific catalyst family. Cobalt-based complexes featuring tripodal ligands should merit more insightful discussion and summarization, as they are one of the most examined catalyst families for CO2 photoreduction. In this feature article, the key developments of cobalt-based tripodal complexes as molecular catalysts for light-driven CO2 reduction are discussed to offer an upcoming perspective, analyzing the present progress in electronic/steric tuning through ligand modification and dinuclear design to achieve a synergistic effect, as well as the bottlenecks for further development.

Copper Complexes of Silicon Pyridine-2-olates RSi(pyO)3 (R = Me, Ph, Bn, Allyl) and Ph2Si(pyO)2

The organosilicon pyridine-2-olates 1a–1d (RSi(pyO)3, R = Me (a), Ph (b), Bn (c), Allyl (d); pyO = pyridine-2-olate) may serve as tripodal ligands toward CuCl with formation of complexes of the type RSi(μ2-pyO)3CuCl (2a–2d). In addition, for R = Allyl, formation of the more stable isomer 2d′ (κO-pyO)Si(μ2-pyO)2(μ2-Allyl)CuCl was observed. In the presence of dry air (as a source of oxygen), reactions of 1a–1d and CuCl afforded Cu(II) complexes RSi(μ2-pyO)4CuCl (3a–3d); 3a–3c in good yield, and 3d only as a side product. Reaction of Ph2Si(pyO)2 (4) and CuCl in equimolar ratio afforded, depending on reaction conditions, a series of (CuCl)n-ladder-type oligonuclear Cu(I) complexes Ph2Si(μ2-pyO)2(CuCl)n(μ2-pyO)2SiPh2 (n = 2 (52), 3 (53), 4 (54)). In all of the above compounds, the pyO group is Si–O bound and, in the case of μ2 coordination, Cu–N bound. All new compounds (1c, 1d, 2b, 2c, 2d, 2d′, 3b, 3c, 3d, 52, 53, 54) were characterized by single-crystal X-ray diffraction, and further characterization includes solution 1H, 13C, 29Si NMR spectroscopy (1c, 1d, 2b, 2c, 2d’, 53, 54), solid-state 29Si (2b, 2c, 2d′, 53, 54) and 63Cu NMR spectroscopy (2c, 2d′) as well as computational analyses of the isomerization of the couple 2d, 2d′.

Investigations on the Reactivity of Copper(I) Complexes with a N3S Thioether Ligand System

AbstractIn the active site of several copper monooxygenases, thioether residues are coordinated through the sulfur atom, e. g. dopamine‐β‐monooxygenase (DβM). The reaction of dioxygen with a series of copper(I) complexes with thioether groups in tripodal ligands based on either derivatives of tris(2‐pyridylmethyl)amine (TMPA) or a guanidine system were investigated by low‐temperature stopped‐flow measurements. The formation of labile intermediates, an end‐on superoxido complex, and μ‐1,2‐trans‐peroxido copper(II) complexes were spectroscopically detected and a kinetic analysis allowed the calculation of activation parameters for these reactions supporting the postulated mechanism. Most interesting was the finding that replacing the ethyl group in the tren‐guanidine derivative (TMGEt)2(SEtEt)N with a methyl group allowed a dramatic increase in the stability of the formed superoxido copper complex. Measurements with ozone were performed in order to find an alternative way to obtain and stabilize the labile intermediates.

Extraction of Np(IV/VI) from nitric acid medium using three different tripodal diglycolamide ligands in ionic liquid: Batch extraction, spectroscopic and electrochemical investigations

Complexation of Np(IV) and Np(VI) ions was studied in a room temperature ionic liquid (C4mim.NTf2) using three tripodal ligands with an ‘N’ atom, a ‘C’ atom and a benzene ring at the center, which are termed as LI, LII and LIII, respectively . The studies include solvent extraction, visible-near infrared (vis-NIR) spectroscopy, and cyclic voltammetry. The trend of the extraction of Np4+ was LIII > LII > LI, which resembled that reported before in a mixture of molecular diluents but with about 10 times higher ligand concentration. Np(VI) was extracted to a much lower extent than Np(IV). Slope analysis of Np(IV) extraction suggested formation of Np(NO3)4.L species for LII and LIII, while a cationic species of the type [Np(NO3)2.L]2+ was seen for LI. On the other hand, for Np(VI), formation of NpO2(NO3)2.L species was proposed for LI and LIII and [NpO2(NO3).L]+ for LII. All the extracted species conform to a ‘solvation’ type extraction except for Np(IV) with LI and Np(VI) with LII which point to a ‘cation-exchange’ mechanism. The complexation of the metal ions with the tripodal ligands was supported by peak shifts in the vis-NIR as well as the cyclic voltammetric studies.

Combined Reprocessability and Self-Healing in Fluorinated Acrylic-Based Covalent Adaptable Networks (CANs)

Combining reprocessing and self-healing in one material provides an opportunity for the development of sustainable materials with enhanced mechanical properties. We developed fluorinated acrylic-based covalent adaptable networks (CANs) capable of self-healing and reprocessing by copolymerizing (2-acetoacetoxy)ethyl methacrylate (AAEMA), 2,2,2-trifluoroethyl methacrylate (TFEMA), and n-butyl acrylate (nBA), followed by cross-linking with tris(2-aminoethyl) amine (TREN). These materials exhibit the maximum stress at break of about 16 MPa and the storage modulus of ∼2.6 GPa in the −60 to 25 °C range. Capable of complete recovery of mechanical properties, these materials are reprocessable by compression molding at 120 °C. The recovery of physical and chemical properties involves the exchange reactions between vinylogous urethane linkages and primary amines. Upon multicycle reprocessing, junction densities and stored entropic energy are also recovered and preserved. These CANs self-heal under ambient conditions. Upon damage, initially C═O groups of vinylogous urethanes respond to perturbation by conformational changes, followed by the (E) → (Z) isomerization of C═C bonds accompanied by the conformational rearrangements of the CF3 and CH2 moieties. This reversible process leads to the recovery of dipolar interactions that facilitates self-healing under ambient conditions. The concept of equipping materials with dynamic cross-linking and self-healing attributes can be extended to other systems.

Experimental and theoretical studies on coordination of a flexible cyclohexane based C3-symmetric tripodal ligand with iron, aluminum and gallium

The use of a cyclohexane ring in the centre of a C3 symmetric tripodal ligand with a suitable spacer can flip between the axial and equatorial forms due to low transition energy and can facilitate the formation of stable metal complexes. Keeping this perspective in view, a new chelator, N,N′,N″-((1R,3R)-cyclohexane-1,3,5-triyl)tris(8-hydroxyquinoline-2-carboxamide), TACH2COX, comprising of a cis,cis-1,3,5-trisaminocyclohexane(TACH) as central unit and three quinolinols joined through amide linkage is developed. The brown-colored ligand has been characterized through melting point, IR, NMR (1H, 13C), ESI mass, and absorption spectroscopy. The solution coordination chemistry of the newly synthesized ligand is studied by its interaction with three bio-relevant metal ions: iron(III), aluminum (III) and gallium(III) through spectroelectrochemical technique. The high metal–ligand formation constants of the ligand indicate that TACH2COX is one of the strong metal chelators amid synthetic chelators. The structure and bonding of the complexes have been established through DFT studies. The molecular modeling studies reveal that the tripodal ligand binds to the metal ions by coordination of the ligand through three sets of N, O-coordination sites on, each from one pendant showing distorted octahedral geometry. The NBO, EDA, ETS-NOCV analysis, and absorption spectra of the ligand and its metal complexes are also described.

Coordination-driven Synthesis of a Self-assembled Architecture Bearing Urea Groups from a Triply Helical Fe(II) Complex of a Tripodal Ligand and a Pd(II) Complex

Triply helical iron(II) complexes of a tripodal 2,2′-bipyridine ligand bearing 4-pyridyl urea groups have undergone coordination-driven self-assembly with palladium(II)-bis(1,3-diphenylphosphinopropane), dppp, units affording the 2:3 complex in an almost quantitative yield. In the coordination-driven self-assembled architecture, the 4-pyridyl moieties of the iron(II)-tris(2,2′-bipyridine) complexes coordinated to the palladium(II) cations ligated by dppp.

2,2’-Dipyridylamine: A tripod ligand enabling practical access to diaryl ethers via Cu-catalyzed coupling reaction

2,2’-dipyridylamine (DPA) is hereby firstly reported as a novel and efficient tridentate ligand for promoting copper(I)-catalyzed C-O/S coupling reactions of abundant aryl bromines with related phenols or thiophenols. The key to this very discovery is the identification of an N-donor tripod ligand (DPA), and such a reaction allows the conversion of simple starting materials to complex diaryl ethers or diaryl thioethers, which are important synthetic intermediates in the preparation of bioactive molecules.

Framework robustness in early d-block metal complexes with tripodal polyalcohol ligands

While performing our research on the tetranuclear “star-shaped” complexes formulated as [M3M'(LR)2(dpm)6], where M, M' are first-row d-block metals; H3LR is a tripodal alcohol, RC(CH2OH)3, with R = Et, Me or Ph; and Hdpm = dipivaloylmethane, we isolated a series of binuclear, alkoxide-bridged chelate complexes of titanium and chromium upon spontaneous deprotonation of the polyalcohol. In the titanium system, both [TiIII2Cl4(H2LEt)2]·4thf and [TiIV2Cl4(HLEt)2]·2thf were identified; they present analogous binuclear frameworks but distinct metal oxidation states and polyalcohol deprotonation degrees. Four similar CrIII2 compounds were also isolated, differing in the tripodal R groups and cocrystallized solvent or proligand molecules. The products were characterized by single-crystal X-ray diffraction analysis and spectroscopic, thermogravimetric and magnetic measurements. Cocrystallization influences the nature, strength and pattern of intermolecular interactions. Among the binuclear MIII products, all those containing solvating tetrahydrofuran, [M2Cl4(H2LR)2]·x thf (R = Et, Ph; x = 4 or 5 respectively), lose solvent upon gradual polyalcohol deprotonation, mild heating or vacuum drying. The versatile tripodal skeleton assembles the alkoxide-bridged M2 units (M = TiIII/IV or CrIII) in various experimental conditions, including air or inert atmosphere and non-protic or protic media, and confers remarkable robustness to the final binuclear aggregates.

Rotating magnetocaloric effect in highly anisotropic TbIII and DyIII single molecular magnets

The magnetocaloric effect (MCE) was investigated in highly anisotropic single crystals of two single molecule magnets (SMMs): [LnIII(ZnIIL)2]CF3SO3, where Ln = Tb, Dy and L = tripodal hexadentate Schiff base ligand. The structure of these paramagnetic compounds consists of identically oriented linear trinuclear clusters in a trigonal system with an easy direction c∥Zn–Ln–Zn array and a hard plane ab⊥Zn–Ln–Zn array. The magnitude of MCE measured for c∥H was significantly greater than MCE for ab∥H at a wide temperature range regardless of the studied SMM. Therefore, the rotating magnetocaloric effect (RMCE) was evaluated. The maxima of the magnetic entropy change for RMCE were obtained at 2.0 K and moderate fields: 3.9 J K−1 kg−1 at µ0H = 1.3 T for Ln = Tb and 3.3 J K−1 kg−1 at µ0H = 1.1 T for Ln = Dy. The relative efficiency of RMCE compared to the MCE measured in c∥H was as high as 99% at low magnetic fields.

The Anion-Directed Self-Assembly of tubular helical silver (I)-Based coordination polymers and the adsorption properties of hazardous substances

The controlled synthesis of topologically-structured helical coordination polymers (CPs) using versatile organic linkers and a metal centre, has recently attracted considerable attention. In this study, we design and synthesize a flexible tripodal ligand L1 (where L1 = 1, 3, 5-tris(2-pyridylsulfanylmethyl)-2, 4, 6-triethylbenzene) with an N, S cooperative chelation coordination geometry. In combination with silver salts in the presence of anions (nitrate and hexafluorophosphate), silver(I)-based tubular-shaped coordination polymers 1 ([Ag(NO3)(DMF)L12]n) and 2 ({[Ag(CH3CN)L12]•PF6}n) were precisely constructed through cooperative Ag-N/Ag-S and anion coordination interactions, which influenced the helical structures. Both single-stranded helical silver (I)-based CPs were characterised by NMR, PXRD, XPS, and FT-IR spectroscopy. CPs 1–2 have an irregular tube-like channel within their crystal structure which can capture iodine (adsorption capacity 0.27 g/g) and MnO4¯anions (0.25 eq. PF6¯ anions were exchanged) from their aqueous, or hexane, solution.

Hydrogen-bonded helix formation by N-brigded tripodal ligand

Hydrogen-bonded helix formation by a simple N-bridged tripodal ligand is reported. The ligand has been synthesized by reduction of product formed through substitution reaction of tris(2-chloroethyl) amine hydrochloride by hydroxybenzaldehyde. The reported ligand has been characterized by 1H NMR, 13C NMR, IR and mass spectra. Crystal structure has been characterized by single crystal X-ray diffraction and thermogravimetric analysis.