Neutral Mononuclear Complexes Research Articles

Why are the luminescent properties of the mononuclear and binuclear Eu/Tb-2-hydroxybenzoate complexes with 1,10-phenanthroline so different? An experimental-theoretical study

This study presents a comprehensive investigation into the structural and luminescent properties of lanthanide 2-hydroxybenzoate compounds, focusing on Eu3+ and Tb3+ ions in both single and mixed systems. The X-ray structures of (Hphen)2[Eu2(2-OHBz)8(H2O)2]·2H2O (1a·2H2O) and [Eu(2-OHBz)3(phen)2]·PhMe (2a·PhMe) were determined, where 2-OHBz: 2-hydroxybenzoate and phen: 1,10-phenantroline, revealing triclinic crystal structures with distinct coordination geometries. Compound 1a·2H2O displayed a centrosymmetric dinuclear anion with a coordination number of eight for each Eu3+ center, while compound 2a·PhMe exhibited a neutral mononuclear complex with a decacoordinated Eu3+ center. A comparative analysis of luminescent properties between these compounds unveiled significant differences in the nonradiative decay rates of the 5D0 level of Eu3+ ions, suggesting potential luminescence-quenching channels. The investigation is extended to mixed Eu3+-Tb3+ systems, demonstrating efficient Tb3+ to Eu3+ energy transfer, especially at room temperature. Three models, including two novel ones proposed in this study, were considered to rationalize energy transfer in the mixed systems. Our theoretical-experimental investigation reveals that variations in lifetimes of the emitting level 5D0 of Eu-2-OHBz mononuclear and binuclear complexes, or mixed Eu/Tb-2-OHBz complexes, with 1,10-phenanthrolines, primarily result from multiphonon decay processes; however, low-energy ligand-to-metal charge transfer (LMCT) states play a key role in suppressing luminescence in the binuclear complex compare to the mononuclear ones.

Mononuclear Rare-Earth Metalloligands Exploiting a Divergent Ligand.

Rare-earth tris-diketonato [RE(dike)3pyterpy] metalloligands can be prepared reacting at room temperature [RE(dike)3dme] (dme = 1,2-dimethoxyethane; dike = tta with Htta = 2-thenoyltrifluoroacetone and RE = La, 1; Y, 2; Eu, 3; Dy, 4; or dike = hfac with Hhfac hexafluoroacetylacetone, and RE = Eu, 5; Tb, 6; Yb 7) with 4'-(4‴-pyridil)-2,2':6',2″-terpyridine (pyterpy). The molecular structures of 1, 5, 6, and 7 have been studied through single-crystal X-ray diffraction showing mononuclear neutral complexes with the rare-earth ion in coordination number nine and with a muffin-like coordination geometry. [RE(tta)3pyterpy] promptly reacts with [M(tta)2dme] with formation of [Mpyterpy2][RE(tta)4]2 (M = Zn, RE = Y, 8; M = Co, RE = Dy, 9). Consistently, [Zn(hfac)2dme] reacts at room temperature with 2 equiv of pyterpy yielding [Znpyterpy2][hfac]2 10 that easily can be transformed by reaction with 2 equiv of [Eu(hfac)3] in [Znpyterpy2][Eu(hfac)4]2 11 that has been structurally characterized. Finally, 1, 2, 3, 5, and 7 metalloligands react at room temperature in few minutes with [PtCl(μ-Cl)PPh3]2 yielding the heterometallic molecular complexes [RE(dike)3pyterpyPtCl2PPh3] (dike = tta, RE = La, 12; Y, 13; Eu; 14; dike = hfac, RE = Eu, 15; Yb, 16).

Molybdenum(VI) complexes with ligands derived from 5-(2-pyridyl)-2H-tetrazole as catalysts for the epoxidation of olefins

The development of effective catalytic epoxidation processes that are an alternative to stoichiometric non-selective oxidation routes is important to meet environmental sustainability goals. In this work, molybdenum(VI) compounds bearing 5-(2-pyridyl)−2H-tetrazole derivatives as organic components, namely the ionic and neutral mononuclear complexes (H2ptz)[MoO2Cl2(ptz)] (1) and [MoO2Cl2(tBu-ptz)] (2), and the new Lindqvist-type polyoxometalate (POM) [tBu-Hptz]2[Mo6O19] (3), where Hptz = 5-(2-pyridyl)tetrazole and tBu-ptz = 2-tert-butyl-5-(2-pyridyl)−2H-tetrazole, were studied as epoxidation catalysts using readily available and relatively ecofriendly hydroperoxide oxidants, namely hydrogen peroxide and tert-butyl hydroperoxide (TBHP). The prepared catalysts were very active. For example, 100% cis-cyclooctene conversion and 100% epoxide selectivity were reached at 1 h for 1 and 3, and 10 min for 2 (with TBHP). Catalytic and characterization studies indicated that the mononuclear complexes suffered chemical transformations under the reaction conditions, whereas 3 was structurally stable. This POM acted as a homogeneous catalyst and could be recycled by employing an ionic liquid solvent. The POM can be synthesized from 2 under different conditions, including those used in the catalytic process. Moreover, 3 was an effective epoxidation catalyst for a biobased substrate scope that included fatty acid methyl esters and the terpene dl-limonene.

Synthesis and molecular structure of arene ruthenium(II) complexes containing benzhydrazone derivative ligands with antibacterial and antioxidant properties

A suitable method for the synthesis of ruthenium(II) arene benzhydrazone complexes (1–6) of the general formula [(η6-arene)Ru(L)Cl] (arene = p-cymene or benzene; L= bidentate substituted benzhydrazone derivatives) has been described. The composition of all the complexes have been established by IR, UV-Vis and NMR spectroscopies and ESI-MS. Ruthenium precursors [(η6-arene)RuCl2]2 (arene = p-cymene or benzene) on reacting with benzhydrazone derivative ligands (L1, L2 and L3) resulted in the formation of mononuclear neutral complexes (1-6). All the neutral complexes were further reacted with NaN3 to yield azido complexes (7-12). Then, the binding modes of the benzhydrazone derivatives to the metal center for complexes (1, 5, 6, 7 and 9) have been confirmed by single-crystal X-ray diffraction studies. Further, their in-vitro antibacterial activity against gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli, Klebsiella pneumoniae) strains have been evaluated for the complexes (1-6) and their ligands. An anti-bacterial study revealed that complex 1 and complex 6 have magnificent activity against S. aureus, E. coli and K. pneumoniae. For antioxidant properties, all the complexes showed a higher percentage of DPPH radical scavenging activity than the ligands.

Structural diversity of 9,10-phenanthrenequinone molecular complexes with metal halides

A series of metal halide complexes with 9,10-phenanthrenequinone (PQ) have been synthesized and characterized in detail. An interaction of PQ with metal halides leads to molecular complexes with general formula (PQ)•MXn (MXn = ZnI2, CdI2, HgBr2, InI3). The molecular structures of these complexes have been established by single-crystal X-ray analysis. The metal type determines the resulting molecular structure: the reaction product of PQ with ZnI2 is neutral mononuclear complex ((PQ)•ZnI2 (1) or (PQ)2ZnI2 (2) depending on the synthesis conditions), CdI2 produces with PQ a 1D-coordination polymer [(PQ)•CdI2]n (3), HgBr2 coordinates two PQ ligands with the formation of (PQ)2HgBr2 (4) while indium complex with PQ has an ionic nature [(PQ)2InI2]+[InI4]− (5). The instant reduction accompanies the reaction of PQ with MgI2 and GaI3; unstable monoradical species (PSQ)MgI and (PSQ)GaI2 (where PSQ is an anion-radical of PQ) have been detected using EPR spectroscopy.

Mono and dinuclear ruthenium, rhodium and iridium metal complexes containing N-acylhydrazone moiety: Synthesis and in vitro biological studies

Half-sandwich mono and dinuclear ruthenium, rhodium and iridium complexes (1–9) have been synthesized with ligands L1 {N'-(9H-fluoren-9-ylidene) thiophene-2-carbohydrazide}, L2 {N'-(9H-fluoren-9-ylidene)-3-methoxybenzohydrazide} and L3 {N'-(9H-fluoren-9-ylidene) isonicotinohydrazide}. The neutral mononuclear bidentate complexes were obtained by treatment of the hydrazone ligands (L1, L2) with metal precursors [(arene)MCl2]2 (arene = p-cymene, Cp*; M = Ru, Rh and Ir) in a 1:2 ratio. Reactions of [(arene)MCl2]2 with L3 in both 1:2 and 1:1 metal dimer to ligand ratios have yielded neutral dinuclear complexes where L3 acts as a tridentate ditopic ligand. Single-crystal X-ray diffraction studies have determined the solid-state structures of eight complexes (1–7, 9). In vitro antibacterial activities of the synthesized ligands and complexes were evaluated against human pathogenic bacteria. These compounds were evaluated for their in vitro antioxidant activity by using the DPPH assay. The binding capacity of complex 2 to SM-DNA was elucidated using fluorescence spectroscopy.

Synthesis, characterization, and crystal structure of LnIII – (1E,2E)-3-(furan-2-yl)-N-(4H-1,2,4-triazol-4-yl)prop-2-en-1-imine

New neodymium (1a) and samarium (1 b) complexes with the general formula [LnIII(NO3)3(H2O)3 L]·L (1) were synthesized based on the previously reported ligand L (L = (1E,2E)-3-(furan-2-yl)-N-(4H-1,2,4-triazol-4-yl)prop-2-en-1-imine) which were investigated by X-ray analysis. Through X-ray studies, it was shown that the Schiff base L coordinates to LnIII via κN-bonding of one of the triazole ring nitrogen atoms as a monodentate ligand, three κ2 OO′-bonded nitrate ions and three κO-bonded water molecules completing the coordination sphere around the LnIII ion, resulting in a tenfold-coordinated LnNO9 unit in a distorted bicapped square antiprismatic geometry. The mononuclear complex units [Ln(NO3)3(H2O)3·L] are linked to the L molecule through intermolecular hydrogen-bonding interactions to form a 2 D polymeric supramolecular architecture. The complexes are neutral and paramagnetic mononuclear complexes, as determined by conductivity and magnetic investigations at room temperature, as well as findings from FT-IR and UV–vis spectroscopy. Finally, thermogravimetric measurements confirm the presence of three water molecules in the coordination sphere. In the visible region, the spectrum of the complex shows typical parity forbidden narrow 4f–4f absorptions originating from the 4 I 9/2 ground state to the various excited states of NdIII.

Synthesis and structural characterization of new gold(I) complexes as bioactive and antitumor agents

New mononuclear gold(I) complexes based on 1-thiocarbamoyl-3,5-diaryl-pyrazoline ligands were synthesized and structurally characterized using X-ray crystallography, 13C and 1H NMR studies, and elemental analysis combined with FT-IR and UV-Vis spectroscopy. Complexes 1–3 were prepared in good yields and characterized by X-ray diffraction as neutral mononuclear complexes of the [Au(L)Cl] type with linear coordination geometry around AuI atoms. The UV-Vis absorption profiles of the compounds prepared exhibited two strong absorption bands between 225 and 400 nm, attributed to HOMO → LUMO electronic transitions of the (M + X)LCT type (charge transfer excitations arising from metal plus halogen to ligand) and mixed XLCT + IL type (charge transfer excitations arising from halogen to ligand plus intraligand), based on DFT studies. Assayed for antitumor activity against B16-F10 murine melanoma cells, 4 T1 murine mammary carcinoma cells, and a normal BHK-21 baby hamster kidney cells line, complexes 1–3 exhibited higher bioactivity and selectivity than their respective free ligands. The preliminary results showed these complexes to be good candidates for the development of new metallodrugs based on gold(I) compounds.

Synthesis, spectral, structural, DFT and NLO studies of cerium(III) and thorium(IV) complexes of 1-(5-(1-(2-aminophenylimino)ethyl)-2,4-dihydroxyphenyl)ethanone

Reactions of cerium(III) and thorium(IV) nitrates with the Schiff base 1-(5-(1-(2-aminophenylimino)ethyl)-2,4-dihydroxyphenyl)ethanone (H2L) gave two neutral mononuclear complexes, [Ce(HL)(NO3)2(H2O)]·EtOH (1) and [Th(HL)(NO3)3(H2O)]·6H2O (2), respectively. The complexes were characterized by elemental and thermal analyses, IR, electronic, 1H NMR and mass spectra, molar conductivity and magnetic susceptibility measurements. Analytical and spectroscopic methods illustrated that the Schiff base acts as a monoanionic tridentate N2O-ligand. This paper shows a correlation between the structure of the cerium(III) and thorium(IV) complexes experimentally and theoretical study on molecular structure, thermo-chemical parameters and the harmonic vibration frequencies of them. The geometrically optimized structures of the complexes are non-planar. HOMO and LUMO gap energy is small, the charge transfer occurring within cerium(III) and thorium(IV) complexes indicates a greater reactivity and conversely, low chemical stability.

Novel Lanthanide (III) Complexes Derived from an Imidazole–Biphenyl–Carboxylate Ligand: Synthesis, Structure and Luminescence Properties

A series of neutral mononuclear lanthanide complexes [Ln(HL)2(NO3)3] (Ln = La, Ce, Nd, Eu, Gd, Dy, Ho) with rigid bidentate ligand, HL (4′-(1H-imidazol-1-yl)biphenyl-4-carboxylic acid) were synthesized under solvothermal conditions. The coordination compounds have been characterized by infrared spectroscopy, thermogravimetry, powder X-ray diffraction and elemental analysis. According to X-ray diffraction, all the complexes are a series of isostructural compounds crystallized in the P2/n monoclinic space group. Additionally, solid-state luminescence measurements of all complexes show that [Eu(HL)2(NO3)3] complex displays the characteristic emission peaks of Eu(III) ion at 593, 597, 615, and 651 nm.

Synthetic route to vanadium(III) dichalcogenidophosphinate complexes, V(S2PPh2)3 and V(Se2PPh2)3: A spectroscopic and structural comparative study with analogous complexes of chromium(III), Cr(E2PPh2)3 (E=S, Se)

AbstractAddition of the potassium dichalcogenidodiphenylphosphinate salts, KE2PPh2 (E=S, Se), to either the THF solvate of vanadium(III) chloride or unsolvated chromium(III) chloride results in rapid ligand substitution and the formation of a series of closely‐related trivalent, neutral mononuclear complexes, M(E2PPh2)3 (M=V, Cr; E=S, Se), isolated in modest to good yield. The metal dichalcogenidophosphinate complexes reported herein were characterized by IR, UV‐vis, and 1H NMR spectroscopies, and their solid‐state molecular structures were determined by single‐crystal X‐ray crystallography. Importantly, the comparative analysis includes the structural and spectroscopic studies of two rare V(III) dithio‐ and diseleno‐phosphinate VE6 cores, as well as, two previously known CrE6 analogues. In the solid‐state the title complexes exhibit trigonal distortion from octahedral with torsion angles ranging from 43(2) to 50.3(6)° and structural parameters consistent with ligation of progressively ‘softer’ chalcogen‐donors.

Complexes of Lanthanide (Dy, Er, Yb) Thiocyanates with Tetramethylphenanthroline. Synthesis, Thermolysis, and SMM Properties

The mononuclear neutral complexes [Ln(Me4Phen)2(H2O)(NCS)3]·Me4Phen·0.75EtOH (Ln = Dy, Er, Yb) were prepared for the first time by the reaction of [Ln(H2O)5(NCS)3]·H2O (Ln = Dy, Er, Yb) with 3,4,7,8-tetramethyl-1,10-phenanthroline (Me4Phen) in ethanol. The products were identified by elemental analysis and powder X-ray diffraction. A thermoanalytical study of the products revealed the transfer of the outer-sphere Me4Phen ligand to the first coordination sphere. The obtained compounds were found to behave as single-molecule magnets.

Ten-Coordinate Lanthanide [Ln(HL)(L)] Complexes (Ln = Dy, Ho, Er, Tb) with Pentadentate N3O2-Type Schiff-Base Ligands: Synthesis, Structure and Magnetism

A series of five neutral mononuclear lanthanide complexes [Ln(HL)(L)] (Ln = Dy3+, Ho3+ Er3+ and Tb3+) with rigid pentadentate N3O2-type Schiff base ligands, H2LH (1-Dy, 3-Ho, 4-Er and 6-Tb complexes) or H2LOCH3, (2-Dy complex) has been synthesized by reaction of two equivalents of 1,1′-(pyridine-2,6-diyl)bis(ethan-1-yl-1-ylidene))dibenzohydrazine (H2LH, [H2DAPBH]) or 1,1′-(pyridine-2,6-diyl)bis(ethan-1-yl-1-ylidene))di-4-methoxybenzohydrazine (H2LOCH3, [H2DAPMBH]) with common lanthanide salts. The terbium complex [Tb(LH)(NO3)(H2O)2](DME)2 (5-Tb) with one ligand H2LH was also obtained and characterized. Single crystal X-ray analysis shows that complexes 1–4 have the composition {[Ln3+(HL)−(L)2−] solv} and similar molecular structures. In all the compounds, the central Ln3+ ion is chelated by two interlocked pentadentate ligands resulting in the coordination number of ten. Each lanthanide ion is coordinated by six nitrogen atoms and four oxygen atoms of the two N3O2 chelating groups forming together a distorted bicapped square antiprismatic polyhedron N6O4 with two capping pyridyl N atoms in the apical positions. The ac magnetic measurements reveal field-induced single-molecule magnet (SMM) behavior of the two dysprosium complexes (with barriers of Ueff = 29 K at 800 Oe in 1-Dy and Ueff = 70 K at 300 Oe in 2-Dy) and erbium complex (Ueff = 87 K at 1500 Oe in 4-Er); complex 3-Ho with a non-Kramers Ho3+ ion is SMM-silent. Although 2-Dy differs from 1-Dy only by a distant methoxy-group in the phenyl ring of the ligand, their dynamic magnetic properties are markedly different. This feature can be due to the difference in long-range contributions (beyond the first coordination sphere) to the crystal-field (CF) potential of 4f electrons of Dy3+ ion that affects magnetic characteristics of the ground and excited CF states. Magnetic behavior and the electronic structure of Ln3+ ions of 1–4 complexes are analyzed in terms of CF calculations.

Synthesis, spectral, magnetic, DFT calculations, antimicrobial studies and phenoxazinone synthase biomimetic catalytic activity of new binary and ternary Cu(II), Ni(II) and Co(II) complexes of a tridentate ONO hydrazone ligand

New mononuclear copper(II), nickel(II) and cobalt(II) hydrazone complexes of 2-cyano-N′-((4-oxo-4H-chromen-3-yl)methylene)acetohydrazide have been synthesized. Structure identification of the prepared complexes was carried out by physicochemical and spectroscopic techniques including elemental analyses, infrared, electronic, mass and electron spin resonance spectra, thermal analysis, conductivity and magnetic susceptibility measurements, powder x-ray diffraction and transmission electron microscope. The isolated binary complexes are neutral mononuclear complexes (with 1:1 and 1:2; M:L stoichiometries) and ternary complexes (with 1:1:1; M:L:L′ stoichiometry). The analytical and spectroscopic techniques illustrated the monoanionic tridentate behavior of the hydrazone ligand with γ-pyrone oxygen, enolic oxygen and azomethine nitrogen coordinating sites. The metal complexes displayed square planar, tetrahedral and octahedral geometries. Density Functional Theory calculations were carried out for the chelating agent and its copper(II) chelates. The phenoxazinone synthase activity of the binary copper(II) complexes was studied and discussed. The antimicrobial activity of the hydrazone ligand and its complexes was evaluated toward some sorts of Gram–positive bacteria, Gram–negative bacteria, yeast and fungus.

Monomeric and tetrameric mercury(II) complexes with iodo and N2O2/N3O ligands: Structure and blue luminescence

The reaction of mercury(II) iodide and potential tetradentate ligand N-(2-pyridylmethyl)iminodiethanol (H2pmide) or N,N-bis(2-pyridylmethyl)-2-aminoethanol (bpaeOH) leads to the isolation of monomeric complex [Hg(H2pmide)(I)2] (1) and tetrameric {[Hg2(bpaeOH)2][Hg2I7]I} (2). The crystal structures of 1 and 2 have been characterized by single crystal X-ray crystallography. In mononuclear neutral complex 1, the Hg(II) ion is bonded with one H2pmide species and two iodide anions as a distorted square pyramidal structure. 2 is a tetranuclear neutral complex that is composed of two [Hg(bpaeOH)]2+ cations and one [Hg2I7]3− anion as well as additional I− anion. The [Hg2I7]3− species connected to both the [Hg(bpaeOH)]2+ and [Hg(bpaeOH)(I)]+ units on the opposite side, which gives rise to the tetranuclear structure. 1 shows strong fluorescent emission at 412 nm with a blue color in methanol solution, while 2 displays very weak emission at 467 nm in the solid state. Particularly, in the case of 1, quantum yield is ca. 8.1% and fluorescence decay lifetime is ca. 1.95 ns.

Ru, Rh and Ir metal complexes of pyridyl chalcone derivatives: Their potent antibacterial activity, comparable cytotoxicity potency and selectivity to cisplatin

Half sandwich ruthenium, rhodium and iridium complexes containing pyridyl chalcone analogues (L1 and L2) are prepared by the reaction of [(arene)M(µ-Cl)Cl]2 (arene = benzene, p-cymene, Cp*) and (M = Ru, Rh/Ir)] with L1 and L2 in 1:2 (M:L) ratio. Eight neutral mononuclear complexes (1–8) were obtained and characterized using FT-IR, 1H NMR, 13C NMR, ESI mass and UV–Vis spectroscopic methods. The molecular structures of complexes 2, 4, 5 and 7 are established by single crystal X-ray diffraction studies. Antibacterial studies were tested against three strains of bacterial microorganisms Staphylococcus aureus (gram +ve), Klebsiella pneumoniae (gram −ve) and Escherichia coli (gram −ve). Further the cytotoxicity study of the pyridyl chalcone derivatives and their complexes were evaluated against the human colorectal cancer cell lines HT-29, HCT-116 p53+/+, HCT-116 p53−/− and ARPE-19 (non-cancer retinal epithelium).

Synthesis, Structures, Electrochemistry, and Catalytic Activity towards Cyclohexanol Oxidation of Mono-, Di-, and Polynuclear Iron(III) Complexes with 3-Amino-2-Pyrazinecarboxylate

The synthesis and characterization of a set of iron(III) complexes, viz. the mononuclear [Fe(L)3] (1) and [NHEt3][Fe(L)2(Cl)2] (2), the dinuclear methoxido-bridged [Fe(L)2(μ-OMe)]2.DMF.1.5MeOH (3), and the heteronuclear Fe(III)/Na(I) two-dimensional coordination polymer [Fe(N3)(μ-L)2(μ-O)1/2(Na)(μ-H2O)1/2]n (4), are reported. Reactions of 3-amino-2-pyrazinecarboxylic acid (HL) with iron(III) chloride under different reaction conditions were studied, and the obtained compounds were characterized by elemental analysis, Fourier Transform Infrared (FT-IR) spectroscopy, and X-ray single-crystal diffraction. Compound 1 is a neutral mononuclear complex, whereas 2 is mono-anionic with its charge being neutralized by triethylammonium cation. Compounds 3 and 4 display a di-methoxido-bridged dinuclear complex and a two-dimensional heterometallic Fe(III)/Na(I) polynuclear coordination polymer, respectively. Compounds 3 and 4 are the first examples of methoxido- and oxido-bridged iron(III) complexes, respectively, with 3-amino-2-pyrazinecarboxylate ligands. The electrochemical study of these compounds reveals a facile single-electron reversible Fe(III)-to-Fe(II) reduction at a positive potential of 0.08V vs. saturated calomel electrode (SCE), which is in line with their ability to act as efficient oxidants and heterogeneous catalysts for the solvent-free microwave-assisted peroxidative oxidation (with tert-butyl hydroperoxide) of cyclohexanol to cyclohexanone (almost quantitative yields after 1 h). Moreover, the catalysts are easily recovered and reused for five consecutive cycles, maintaining a high activity and selectivity.

Synthesis, Photophysical, Thermal and Crystallographic Studies of 3‐Aminocoumarin Based Monobasic κ3‐O,N,O‐tridentate/ κ2‐N,O‐bidentate Schiff Base Divalent Complexes

AbstractThe reaction of 3‐Amino coumarin based Schiff base ligands HL1 and HL2 with metal acetates in refluxing ethanol affords access to a new series of neutral mononuclear divalent complexes [MII‐κ3‐bis‐O,N,O‐tridentate Schiff base‐ HL1/ HL2] {HL1, MII=Co (1), Ni (2) or Zn (3); HL2, MII=Co (4), Ni (5) or Zn (6)}, [CuII‐κ2‐bis‐N,O‐bidentate Schiff base‐HL1] (7) and [CuII‐κ2‐bis‐N,O‐bidentate Schiff base‐HL2] (8). Compounds were characterized by microanalysis, standard spectroscopic (viz. MALDI‐TOF‐MS, IR, 1H and 13C NMR, UV‐visible absorption and emission) and TGA/DTA methods. The unambiguous crystal structure of HL1, HL2, complexes 2 and 3 was determined crystallographically. The IR, UV‐visible, EPR spectral and magnetic studies clearly suggest the κ3‐O,N,O‐tridentate‐ coordination mode of HL1 and HL2 towards cobalt(II), nickel(II) and zinc(II) metal ions in 1–6 and κ2‐N,O‐bidentate‐coordination mode towards copper(II) metal ions in 7 and 8. Notably, compounds fluoresce a medium to strong emissions in the visible region is observed with concomitant Stokes shifts of ≈ 90 nm. UV‐visible transmittance spectral study reveals the semiconducting nature of HL1, HL2, complexes 1–8 gave with band gap energy of 1.57‐2.24 electron volts. The molecules of HL1, HL2, 2 and 3 are stabilized by various intermolecular CH…π, CH…O and π…π contacts that efficiently managed the growth of self‐assembly in three dimensions and form infinite molecular layers in the solid state.

Synthesis, structural characterization, and luminescence properties of mono- and di-nuclear platinum(II) complexes containing 2-(2-pyridyl)-benzimidazole

The starting complex [Pt(Me)(DMSO)(pbz)] (1, pbz = 2-(2-pyridyl)benzimidazolate) was prepared by a known method using the reaction of [Pt(Me)2(DMSO)2] with Hpbz at room temperature. Reaction of 1 with an equivalent of a phosphine ligand gave the neutral mononuclear complexes [Pt(Me)(L)(pbz)] (2, L = PPh3 and 3, L = PPh2Me). Reaction of 1 with 0.5 equivalent of the linear diphosphine 1,1′–bis(diphenylphosphino)acetylene (dppac) gave the binuclear complex [Pt2(Me)2(μ-dppac)(pbz)2]. Each complex was fully characterized by NMR spectroscopy, X-ray single-crystal crystallography and mass spectrometry. The photophysical properties of the complexes were investigated under different conditions and interpretation was supported by TD-DFT calculations. The low-lying transitions in the absorption and emission spectra were assigned as having LLCT/MLCT (ligand to ligand charge transfer/metal to ligand charge transfer) character. We also describe the luminescence properties of [Pt(Me)(PPh3)(ppy)] and [Pt(Me)(PPh2Me)(ppy)] (ppy is 2-phenylpyridinate), the (N^C−) analogues of 2 and 3.

Dysprosium Thiocyanate Complexes with s-Triazine

The reaction of Dy(NCS)3 · 6H2O with 2,4,6-tris(2-pyridyl)-s-triazine (Tptz) in МеОН, MeCN, and H2O affords mononuclear neutral and ionic thiocyanate complexes with tridentate ligand Tptz: [Dy(H2O)(MeOH)(Tptz)(NCS)3] · Tptz (I), [Dy(Tptz)2(NCS)3] · MeCN (II), and [Dy(H2O)3-(Tptz)(NCS)2] · NCS · Tptz · 1.5H2O · 1.25MeOH (III). Structural features of the synthesized compounds are determined using powder XRD, IR spectroscopy, and thermoanalytical methods (thermogravimetry and differential scanning calorimetry). Compounds II and III exhibit the properties of single-molecule magnets.