# Transition Metal Chemistry

## Current research reports and chronological list of recent articles..

Transition Metal Chemistry is an international scientific journal dealing with all aspects of the preparation of transition metal-based compounds of all kinds, their structural, physical, kinetic and biological properties, their use in chemical synthesis as well as their application in the widest context, their role in naturally occurring systems and more.

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## Transition Metal Chemistry - Abstracts

Template-directed assembly of two cadmium diphosphonates with or without the luminescent sensing ability for Hg2+

### Abstract

By using 2, 2'-biimidazole (2, 2′-biim) and 2, 2′-bipyridine (2, 2′-bipy) as structure-directing agents (SDAs), two cadmium diphosphonates, [Cd2(H2L)2(H2O)] (1) and [Cd5(HL)2(H2L)2]·4H2O (2) (H4L = 4–F–C6H4CH2N(CH2PO3H2)2), have been hydrothermally synthesized. The introduction of different N-heterocyclic aromatic SDAs results in the diverse structures, thermal stabilities, and luminescent properties. Structural analyses reveal that both 1 and 2 show three-dimensional (3D) supramolecular structures wherein the adjacent layers are further connected by moderately π–π stacking interactions or hydrogen-bond interactions. Among them, the thermal stability of 1 is higher than 2. Surprisingly, 1 displays excellent luminescent performance, whereas 2 shows no luminescent signal. Based on the intense luminescence of 1, it can serve as a high selectively and sensitively luminescent sensor for Hg2+ with a low detection limit of 3.1 × 10–7 M in aqueous solution. Additionally, the probable sensing mechanism for 1 has also been investigated in detail, which can be assigned to the weak interaction between the uncoordinated O sites from the H2L2– ligands and Hg2+.

### Graphical abstract

Two cadmium diphosphonates with different structures and luminescent properties have been hydrothermally obtained by using N–heterocyclic aromatic (2, 2′–biim and 2, 2′‒bipy) compounds as SDAs. 1 displays excellent luminescent performance, whereas 2 shows no luminescent signal. Furthermore, 1 can serve as a luminescent sensor for Hg2+ in water

Datum: 02.08.2022

Antiferromagnetically coupled iso-structural CrIII, MnIII and FeIII complexes of a tetradentate Schiff base ligand derived from o-phenylenediamine

### Abstract

Three isostructural, Iron(III), Manganese(III) and Chromium complexes, with a tetradentate Schiff base ligand (H2L2) from o-phenylenediamine and o-vanillin having the general formulae, [M(H2L2)(C2H3O2)(H2O)], where M = Cr, Mn, Fe) have been prepared. The complexes were then subsequently characterized by physico-chemical and spectroscopic methods and further investigated for their magnetic nature. All the complexes are neutral mononuclear species and crystallize in a triclinic space group P-1(2). Single-crystal diffraction studies reveal that the ligand, H2L2, coordinates to the central metal ion in a tetradentate fashion through both the azomethine nitrogen and the deprotonated phenolic oxygen generating neutral complexes. One of the acetate counter anions and a water molecule is involved in the coordination, generating a distorted octahedral geometry in all the complexes. Temperature dependence magnetic susceptibility was measured in a squid magnetometer in the temperature range 300–1.8 K and reveals that all of the three complexes show antiferromagnetic behavior in the temperature range studied. The experimental susceptibility data fitting, by considering the intermolecular interactions, enabled to estimate the magnetic anisotropy D and lead to the parameters (D =  + 0.14 cm−1 and zJ =  − 0.35 cm−1) for FeIII and (D =  − 3.95 cm−1; E =  + 0.54 cm−1; zJ =  − 0.35 cm−1) for MnIII ions. This study is aiming and boosting to 'open up' our interest to focus more on mononuclear complexes with SMM character with first-row transition metals, which will be more interesting as far as the application side is concerned.

Datum: 02.08.2022

### Abstract

To further develop the active site mimics of azadithiolate-bridged [FeFe]-hydrogenases, a series of new diiron azadithiolate complexes [{(μ-SCH2)2N(C6H4CH2CH2OC(O)R)}Fe2(CO)6] (R = CH2C6H4Me-p, 2; C6H5, 3; CH3, 4) bearing bridgehead N-derivation were successfully prepared by facile esterification reaction of parent complex [{(μ-SCH2)2N(C6H4CH2CH2OH)}Fe2(CO)6] (1) and different carboxyl compounds RCO2H in the presence of 4-dimethylaminopyridine (DMAP) as catalyst and dicyclohexylcarbodiimide (DCC) as dehydrating reagent. Complexes 2–4 have been fully characterized by means of elemental analysis, FT-IR and NMR (1H, 13C) spectroscopies, and especially for 2 by X-ray crystallography. Further electrochemical and electrocatalytic properties of target complexes 24 and reference analogue 1 were studied and compared in the absence and presence of acetic acid (HOAc) as a proton source by cyclic voltammetry (CV), indicating that they may be considered as the active biomimetic electrocatalysts for proton reduction to hydrogen (H2).

Datum: 01.08.2022

Stabilized catalyst comprising nickel and supported 12-tungstophosphoric acid: synthesis, characterization and aqueous-phase Suzuki–Miyaura cross-coupling

### Abstract

This work describes a simple impregnation and soaking method for designing of stabilized nickel exchanged supported 12-tungstophosphoric acid, its characterization and use as a heterogeneous catalyst for carrying out Suzuki–Miyaura (SM) cross-coupling in aqueous medium. The influence of various reaction parameters was screened for maximum conversion, and the catalyst was found to exhibit an excellent activity (89% conversion) with a very small amount of active species (0.26 mol% of Ni) under mild conditions. The catalyst was retrieved by centrifugation, reactivated by heating at 100 °C only and reused without exhibiting any significant change in conversion up to three catalytic runs. The stability of the regenerated catalyst was confirmed by FT-IR, XPS and TEM analysis.

### Graphical abstract

Datum: 22.07.2022

Three Keggin-based complexes modified by an asymmetric ligand: structures, electrochemical, photocatalytic and fluorescence sensing properties

### Abstract

By using an asymmetric ligand with triazole and imidazole groups, three Keggin-based complexes were obtained, [Cu(HMET)4(H2O)2](PMo12O40)2·2H2O (1), [Cu3(HMET)4Cl2(H2O)2(XM12O40)2]·4H2O (X = Si, M = W 2, X = Ge, M = Mo 3) (MET = 4-(2-imidazol-1-yl-ethyl)-4H-[1,3,4]triazole). Complex 1 contains discrete Keggin anions and mono-nuclear [Cu(MET)4(H2O)2]2+ clusters. Complexes 2 and 3 are isostructural with tri-nuclear Cu clusters linked by Keggin anions to construct a 1D chain. The 1- to 3-CPEs show electrocatalytic properties and can also act as nitrite amperometric sensors. Complexes 13 exhibit photocatalytic activities for degradation of MB. Complexes 1– 3 own fluorescence sensing properties for detecting Hg2+ ions.

### Graphical abstract

By using an asymmetric ligand three POM-based complexes were constructed. The 1– to 3–CPEs exhibit good electrocatalytic activities and can be used as nitrite amperometric sensors. The title complexes show good photocatalytic activities for degradation of MB. Moreover, complexes 13 can act as fluorescence sensors to selectively detect Hg2+.

Datum: 20.07.2022

Synthesis, structural characterization and anticancer properties of p-cymene Ru(II) complexes with 2-(N-methyl-1H-1,2,4-triazol-3-yl)pyridines

### Abstract

The structures of new p-cymene Ru(II) complexes with 2-(1-methyl-1H-1,2,4-triazol-3-yl)pyridine and 2-(1-methyl-1H-1,2,4-triazol-5-yl)pyridine were established based on the results of elemental analysis; IR and NMR spectra; and X-ray diffraction studies. Their anticancer activity, tested on human ovarian cancer cell lines A2780 (cisplatin-sensitive) and A2780cis (cisplatin-resistant), is also reported.

### Graphical abstract

Datum: 12.07.2022

Synthesis of nickel-doped titanium-oxo clusters with enhanced visible-light photocatalytic activity

### Abstract

Two new Ni-doped titanium-oxo clusters of the formula [Ni2Ti4(μ3-O)2(μ2-O)2(BA)12(CH3CN)(H2O)]∙CH3CN (Ti4Ni2BA12; BA = benzoate) and [Ni2Ti4(μ3-O)2(μ2-O)2(O2CtBu)6(MA)4(OQ)2] (Ti4Ni2OQ2; MA = methylacrylate, HOQ = 8-hydroxyquinoline) were synthesized. Single-crystal X-ray diffraction analyses show that the two clusters have similar Ti4Ni2 cluster core consisting of a {Ti4(μ3-O)2(μ2-O)2} ring connected with two Ni atoms. The clusters were functionalized with benzoate and 8-quinolinolate ligands, respectively. Compared to benzoate ligand, the coordination of 8-quinolinolate to the cluster core in Ti4Ni2OQ2 leads to enhanced visible-light absorption due to the ligand-to-metal charge transfer transition. In the photocatalytic tests, Ti4Ni2OQ2 exhibits remarkably promoted catalytic performance for visible-light-driven photocatalytic oxidative desulfurization of dibenzothiophene.

Datum: 04.07.2022

Synthesis, characterization and antileishmanial activity of copper(II) and zinc(II) complexes with diamine ligands

### Abstract

A new set of copper- and zinc-diamine (N-alkylated (L1) and N,N'-dialkylated (L2)) complexes, [Cu(L1)2(NO3)2] (1), [Cu(L1)2(Cl)2].5H2O (2), [Cu(L2)2(NO3)2] (3), [Cu(L2)2(Cl)2] (4), [Zn(L1)2(C2H3O2)2] (5), [Zn(L1)2(Cl)2] (6), [Zn(L2)2(C2H3O2)2] (7), [Zn(L2)2(Cl)2] (8) were prepared by a reaction of the N-alkylated (L1) and N,N'-dialkylated (L2) with their respective copper and zinc salts under mild conditions. The metal complexes were fully characterized by physicochemical and spectroscopic methods. All new metal compounds exhibited significant biological activity against Leishmania amazonensis promastigotes when compared to the free ligands (L1 and L2).

Datum: 01.06.2022

Four bimetallic ammonium formate frameworks: structures, magnetism and dielectricity

### Abstract

The synthesis, crystal structures, magnetic and dielectric properties of four ammonium bimetallic formate frameworks [AI][GaIIICoII(HCOO)6] for AI = CH3NH3+ (1), (CH3)2NH2+ (2), CH3CH2NH3+ (3) and (CH3CH2)2NH2+ (4) have been reported. They are isomorphic and crystallize in the trigonal P $$\bar{3}$$ 1c space group at both 110 and 293 K. The structures possess [GaIIICoII(HCOO)6] anionic metal formate frameworks of binodal (412·63)(49·66) topology, in which the disordered ammonium cations are located in the cavities. The magnetic data of complex 2 was fitted by the one-ion approximation for CoII ion with spin–orbit coupling in Oh symmetry giving λ = − 102.7 cm−1. The dielectric studies of 1 and 2 showed that the dielectric abnormality was caused by the weakening of the movement of the ammonium cations with the decrease in temperature. The activation energies for the motions of ammonium cations in 1 and 2 were determined to be 3.00 and 3.19 × 103 K, respectively.

Datum: 01.06.2022

Advances in value-added aromatics by oxidation of lignin with transition metal complexes

### Abstract

Lignin is the second most abundant component in biomass, considered as the most abundant and available renewable source of aromatics in Nature. The depolymerization of lignin presents a sustainable way for producing value-added aromatic chemical platforms. Among all the transformation strategies, the catalytic oxidation transformation of lignin toward the production of highly functionalized aromatic chemicals is an efficient way for high-value chemicals. Herein, we review various transition metal complexes used for the effective transformation of lignin and lignin model compounds to aromatic building blocks, which involves metal porphyrins, metal salens, vanadium complexes, methyltrioxo rhenium and other highly elaborated complexes. The corresponding mechanisms are included. Based on the catalytic systems, challenges and future directions are discussed.

Datum: 01.06.2022

Synthetic and ESI mass spectrometric investigations of Pt, Pd, Ir, Ru and Rh complexes of a polyether-functionalised thiourea ligand

### Abstract

Reaction of PhNCS with the polyetheramine Jeffamine® M600 H2NCHMeCH2(OCHMeCH2)nOCH2CH2OMe gave the polyether-functionalised thiourea PhNHC(S)NHCHMeCH2(OCHMeCH2)nOCH2CH2OMe. Neutral bis(phosphine) platinum(II) and palladium(II) complexes [M{SC(NPh)N(CHMeCH2(OCHMeCH2)nOCH2CH2OMe)}(PPh3)2], containing the thiourea dianion ligand, were prepared by reaction of [MCl2(PPh3)2] (M = Pt, Pd) with the thiourea and Me3N base in refluxing methanol. Closely related cationic complexes containing thiourea monoanion ligands were isolated by addition of NaBPh4 to the reaction mixtures. Corresponding organo-ruthenium, -iridium and -rhodium complexes were prepared by the reaction of [(η6-p-cymene)RuCl2]2 or (Cp*MCl2)2 (M = Ir, Rh; Cp* =  $$\eta$$ 5-C5Me5) with the thiourea. Positive-ion ESI mass spectrometry was shown to be a convenient and powerful technique for the investigation of these complexes. A model Rh complex was also prepared from the short-chain analogue PhNHC(S)NHCH2CH2OMe.

Datum: 01.06.2022

Asymmetrically tetra-substituted phthalocyanine derivatives: synthesis, photophysical and photochemical properties

### Abstract

The syntheses of highly soluble asymmetrically substituted metal free and zinc phthalocyanine derivatives bearing three 4-(4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenoxy) and one 4-(2-(benzo[d]thiazol-2-yl)phenoxy) groups or bearing one 4-(4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenoxy) and three 4-(2-(benzo[d]thiazol-2-yl)phenoxy) groups were reported for the first time in this study. The successful synthesis of phthalocyanines was achieved through the common statistical condensation method utilizing two different phthalonitriles named as 4-(4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenoxy)phthalonitrile and 4-(2-(benzo[d]thiazol-2-yl)phenoxy)phthalonitrile. The asymmetrical phthalocyanines were characterized by spectroscopic methods. Moreover, the aggregation behavior, photophysical and photochemical properties of the substituted A3B type asymmetrical metal free and Zn (II) phthalocyanines were investigated in DMF. The asymmetrical Zn (II) phthalocyanine complexes produced highly singlet oxygen and appropriate fluorescence behavior in DMF suggesting that they can be suitable candidates as Type II photosensitizers in photodynamic therapy (PDT) applications.

Datum: 01.06.2022

N3/4-pyridinyl Schiff base copper(II) benzoate complexes: synthesis, crystal structures and ring-opening polymerization studies

### Abstract

Five benzoate complexes of copper(II) were synthesized by the reaction of N-donor Schiff base ligands with copper(II) acetate and benzoate co-ligands. All complexes were characterized by physicochemical, spectroscopic techniques and single-crystal X-ray diffraction studies. Crystal structure analysis revealed mononuclear complexes Cu(C6H5COO)2(L1)2·H2O (1) with a square pyramidal geometry and Cu(Me-C6H5COO)2(L2)2·2H2O (3) with a distorted octahedral geometry around the Cu(II) center. Three other complexes [Cu(C6H5COO)2(L2)]2·(2), [Cu(Me-C6H5COO)2(L3)]2·(4) and [Cu(C6H5COO)2(L4)]2·(5) all adopted a paddlewheel conformation in which the two Cu(II) centers each have a square pyramidal geometry. All complexes were found to be active as catalyst in ring-opening polymerization of ɛ-caprolactone (ε-CL), yielding low molecular weight polymers of about 2200 g mol−1 to 3870 g mol−1. The activity of complex 4 increased with the addition of different alcohol co-initiators except in t-butanol where a reduction was obtained arguably due to steric hindrance.

Datum: 01.03.2022

Manganese(II)-based coordination polymer as a bi-responsive luminescent sensor for highly selective detection of picric acid and CrO42− ion

### Abstract

A novel luminescent coordination polymer (CP) {Mn(H2abtc)(DMF)(H2O)2·2H2O}n (1), (H4abtc = 3,3′,5,5′-azobenzenete-tracarboxylic acid), has been successfully prepared by the solvothermal reaction of H4abtc and MnCl2·4H2O, which has been further characterized by single-crystal X-ray diffraction, elemental analysis, thermogravimetric analysis (TGA), infrared (IR) spectrum and powder X-ray diffraction (PXRD). 1 can serve as a potential dual response luminescence sensor for picric acid (PA) and CrO42− via luminescence quenching with good selectivity and sensitivity. The quenching behavior of PA toward 1 can be ascribed to the combined effects of electron and resonance energy transfer mechanisms. And the quenching phenomenon of CrO42− to 1 can be explained by the electron transfer mechanism.

### Graphical abstract

A novel luminescent Mn(II)-based coordination polymer 1 has been successfully prepared. 1 can serve as a potential dual response luminescence sensor for Picric acid (PA) and CrO42− with good selectivity and sensitivity.

Datum: 01.03.2022

A family of 1D coordination polymers based on Ln–Cu 15-metallacrown-5 units with two topological sorting: syntheses, structures, and single-chain magnet behaviour

### Abstract

Three one-dimensional coordination polymers based on Ln–Cu 15-metallacrown-5 units were self-assembled via covalent bonds between pyrazine hydroxamic acid ligands and Cu atoms in the adjacent MC units. Due to the presence of different coordination anion ligands, complexes TbIII (1) and GdIII (2) show zig-zag-like topological structures, while complex DyIII (3) displays wheatear-like topological structure. The frequency dependence of the out-of-phase reveals that complexes 1 and 2 show slow relaxation of the magnetization, and complex 3 displays single-chain magnet behaviour.

Datum: 01.03.2022

Synthesis, characterization and catalytic transfer hydrogenation properties of Ru(II) complexes

### Abstract

Three half-sandwich Ru(II) complexes with the general formulae of [Ru( $$\eta$$ 6-p-cymene)(L)Cl2] (where L: 2a (diethyl-4-aminobenzylphosphonate), 2b (4-aminoethylbenzoate) and 2c (4-methoxybenzylamine) containing an aniline ligands were synthesized and their structures were characterized. The Crystal structure of complex [Ru( $$\eta$$ 6-p-cymene)(2c)Cl2] was investigated by single crystal X-ray diffraction studies. Each Ru(II) ion in both complexes is coordinated with a 6-p-cymene nitrogen atom, two chloride and aniline derivatives. This results in a distorted piano-stool geometry. The catalytic performances of the complexes were investigated in transfer hydrogenation reactions. The complexes catalyze the transfer hydrogenation of cyclohexanone and 2-hexanone in the presence of a base. For 2-hexanone to 2-hexanol reduction, complex [Ru( $$\eta$$ 6-p-cymene)(2a)Cl2] showed the highest conversion rate (at the end of 6 h) with 97% conversion. The complexes were found to be more active catalysts in the transfer hydrogenation of cyclohexanone than that of 2-hexanone.

Datum: 01.03.2022

Stereoselective homo- and co-polymerization of lactides and ε-caprolactone catalysed by highly active racemic zinc(II) pyridyl complexes

### Abstract

A series of Zn(II) chlorido complexes (1′5′) supported by N,N′-bidentate N-(pyridin-2-ylethyl)amine ligands have been synthesized. Zn(II) alkyl and alkoxy complexes 1′-Me5′-Me and 1′-OBn5′-OBn were synthesized in situ by first reacting complexes 1′5′ with methyl lithium and subsequently with benzyl alcohol. Both species 1′-Me5′-Me and 1′-OBn5′-OBn showed excellent catalytic activity in ring-opening polymerization (ROP) of cyclic esters with the alkoxyl species performing better. The ROP reactions exhibited pseudo-first-order kinetics with respect to monomer concentration. Polymer molecular weights increased as ligand steric hindrance decreased and they lie between 3096 and 8837 g mol−1 and relatively high molecular weight distributions with dispersity (Ð) values ca. 2 were observed. The poly(rac-lactide) polymers were predominantly heterotactic, while poly(ʟ-lactides) formed were largely isotactic. All polymerization reactions proceeded through coordination insertion mechanism followed by hydrolysis of the metal. Notably, the stereogenic centres of the ligand skeleton influenced control of polymer stereochemistry. Random copolymerization of ε-caprolactone (ε-CL) and lactides (LA) resulted in block gradient copolymers. The sequential addition of lactides after ε-CL gave diblock PCL-b-PLA, and reversing monomer addition did not form any copolymer.

### Graphical abstract

Datum: 01.03.2022

Synthesis, characterization, and electrochemistry of SNS cobalt(II) tridentate complexes

### Abstract

The preparation of two cobalt(II) complexes that contain a tridentate ligand with sulfur, nitrogen, and sulfur donor atoms is described. The tridentate ligand precursors are based on bis-imidazole or bis-triazole moieties. The complex based on a bis-imidazole precursor was green in color and was prepared in 93.3% yield. The complex based on a bis-triazole precursor was blue-green in color and was prepared in 69.8% yield. Single-crystal structures of both complexes were obtained. Both complexes contain [BF4] as the counter-anion. Based on the single-crystal structure, the molecular geometry around the cobalt(II) center is distorted tetrahedral. EPR spectra were obtained for both complexes at 4 K. Each complex has axial symmetry for its electron density and each cobalt(II) complex has S = 3/2. For the complex based on a bis-imidazole precursor, the UV–Vis peaks were observed at 696 nm, 629 nm, 585 (sh) nm, and 375 (sh) nm. For the complex based on bis-triazole, UV–Vis peaks were observed at 681, 613, 570, 243, 239, 236, 233, 230, 227, and 210 nm. Cyclic voltammetry spectra were obtained for both complexes. Both the ligand precursor and the cobalt(II) complexes are redox active. All of the redox waves were irreversible.

Datum: 01.03.2022

Synthesis, crystal structure, and photocatalytic property of heterometallic calcium‒titanium oxo cluster with high aqueous stability

### Abstract

A new heterometallic calcium‒titanium oxo cluster formulated as [Ca2Ti8(μ3-O)8(AcO)2(OiPr)2(BA)16]·4H2O (BA = benzoate) was synthesized and structurally characterized by single-crystal X-ray diffraction analysis. The cluster core contains a crown-ether-like Ti8O8 ring with two Ca atoms embedded in it. Due to the unique {Ti8Ca2O8} core structure and the coordination with sixteen bridging benzoate ligands, this cluster exhibits high structural stability in aqueous solutions with a wide pH range. Photocatalytic experiments for the degradation of methyl orange demonstrate the high photocatalytic activity and good recycling stability of the cluster.

### Graphical abstract

Datum: 01.01.2022

Diarylazooxime complex of cobalt(III): synthesis, structure, ligand redox, DFT calculations and spectral characteristics

### Abstract

By using a multifunctional diarylazooxime ligand LNOH 1, incorporating electron deficient azo chromophore in conjunction with a pendant π-electron-rich naphthyl group, the trans dichloro bis complex of type [CoIII(LNOH)(LNO−)Cl2] 2 has been synthesized. The structure of the chelate has been determined by X-ray crystallography, thereby authenticating the presence of oxime-oximato hydrogen bond within the coordinated moiety. The stability of this complex is attributed to intra-molecular hydrogen bonding as well as due to strong Phπ–Phπ stacking interactions. The complex has been characterized by several spectroscopic techniques, and their electrochemical properties have been reported. These are further complemented by theoretical studies in the form of DFT and TDDFT. The visible excitation for the complex arises from mainly mixed singlet manifold 1ILCT and 1LLCT transitions.

### Graphical abstract

Datum: 01.01.2022

Category: Current Chemistry Research

Last update: 28.03.2018.