Heterocyclic Diimine Research Articles

1,1'-Biisoquinolines-Neglected Ligands in the Heterocyclic Diimine Family That Provoke Stereochemical Reflections.

1,1′-Biisoquinolines are a class of bidentate nitrogen donor ligands in the heterocyclic diimine family. This review briefly discusses their properties and the key synthetic pathways available and then concentrates upon their coordination behaviour. The ligands are of interest as they exhibit the phenomenon of atropisomerism (hindered rotation about the C1–C1′ bond). A notation for depicting the stereochemistry in coordination compounds containing multiple stereogenic centers is developed. The consequences of the chirality within the ligand on the coordination behaviour is discussed in detail.

Photoluminescence of europium and terbium trifluoroacetylacetonates. Participation of LMCT state in processes of the energy transfer to Eu3+ ion

The effect of fluorination on spectroscopic properties of europium and terbium trifluoroacetylacetonates Ln(TFAA)3·2H2O, Ln(TFAA)3·Phen and Ln(TFAA)3·Bpy in the solid state have been investigated. A threefold increase in the luminescence intensity of europium compounds at -CF3 for −CH3 substitution in the β-diketonate ligand was obtained at 77 and 295 K. Different mechanisms of the excitation energy transfer to Ln3+ ions in europium and terbium compounds, which result in a drop in the luminescence efficiency at elevated temperatures, have been analyzed. A key role of ligand-metal charge transfer (LMCT) states in the processes of sensitization of the europium trifluoroacetylacetonates is demonstrated. Expansion of the energy gap between the LMCT state and the lowest triplet state T1 at fluorination gives rise to an increase in the excitation efficiency of the Eu3+ luminescence at 295 K. The back-transfer energy 5D4-T1 in the terbium trifluoroacetylacetonates is the main reason for shortening the 5D4 lifetime and decreasing the luminescence efficiency. The energy dissipation processes in the lanthanide TFAA adducts with heterocyclic diimines are mainly related to the β-diketonate ligand.

Luminescence and energy transfer processes in europium and terbium complexes with 2-substituted cycloalkanones and 1,10-phenanthroline derivatives

Abstract A series of solid lanthanide complexes with 2-substituted cycloalkanones (CA) of the composition Ln(CA)3·Phn and Ln(CA)3·Bpy (Ln = Eu, Tb, Gd) have been synthesized and investigated using luminescence spectroscopy. CA = 2-acetylcyclohexanone (AcCHex), 2-isobutyrylcyclohexanone, 2-acetylcyclopentanone, 2-acetylbutyrolactone, 2-benzoylcyclohexanone, 2-acetyltetralone; Phn = 1,10-phenanthroline (Phen), 4,7-dimethyl-phenanthroline, 3,4,7,8-tetramethyl-phenanthroline, 5-phenyl-phenanthroline, 4,7-diphenyl-phenanthroline; Bpy = 2,2′-bipyridine. Tris and tetrakis compounds Ln(CA)3·2H2O and LnNa(CA)4 were also synthesized. The composition, structure and photophysical properties of the lanthanide cycloalkanonates having oligomethylene chain in the ligand are close to peculiarities of β-diketonates without tethered chain. But the presence of this chain can cause a decrease in the energy of the lowest triplet state of the ligand. The Stark structure of the Eu3+ electronic states in the europium CA adducts with heterocyclic diimines corresponds to the distorted tetragonal anti-prismatic coordination geometry of the luminescence center. The lifetimes of 5D4 (Tb3+) and 5D0 (Eu3+) states at 77 K are 0.55–0.85 ms. The luminescence efficiencies of the lanthanide CA adducts at 77 K are comparable with them for known β-diketonates. The back energy transfer from the 5D4 (Tb3+) state to the lowest triplets of the ligands is the main cause for the decrease in the 5D4 lifetime and the Tb3+ luminescence efficiency at 295 K. In the Ln(AcCHex)3·Phn complexes the energy absorbed by the two ligands is transferred to the lowest triplet state of Phn and then to Ln3+ ion. In other Ln(CA)3·Phen compounds, the energy transfer to Ln3+ ion is carried out through the lowest triplet state of CA, which is located below the Phen triplet. The preliminary data on photochemical stability of the compounds were obtained.

Ruthenium(II) complexes of some simple classic amine ligands

Several new Ru(II) complexes of tris(2-aminoethyl)amine (Tren) and diethylenetriamine (Dien) have been prepared using Ru(PPh3)3Cl2 and [(CH3)4N]2[Ru(Phen)Cl4] (1) as starting materials. The reaction of Tren or Dien with Ru(PPh3)3Cl2 leads to the formation of either the [Ru(Tren)(PPh3)Cl]Cl (2) or the Ru(Dien)(PPh3)Cl2 (4) complex, of which the latter then reacts further with a heterocyclic diimine (N–N) ligand to yield [Ru(Dien)(PPh3)(N–N)]Cl2. Addition of Tren or Dien to solutions of the [(CH3)4N]2[Ru(Phen)Cl4] complex replaces the coordinated chlorides with the N-donor ligand, forming [Ru(Tren)Phen](ClO4)2 (3) and [Ru(Dien)(Phen)Cl]Cl (5) respectively. Redox chemistry shows single-electron Ru(II)→Ru(III) oxidations over a wide range of potentials.

Reversible sigma C-C bond formation between phenanthroline ligands activated by (C5Me5)2Yb.

The electronic structure and associated magnetic properties of the 1,10-phenanthroline adducts of Cp*2Yb are dramatically different from those of the 2,2'-bipyridine adducts. The monomeric phenanthroline adducts are ground state triplets that are based upon trivalent Yb(III), f(13), and (phen(•-) ) that are only weakly exchange coupled, which is in contrast to the bipyridine adducts whose ground states are multiconfigurational, open-shell singlets in which ytterbium is intermediate valent ( J. Am. Chem. Soc 2009 , 131 , 6480 ; J. Am. Chem. Soc 2010 , 132 , 17537 ). The origin of these different physical properties is traced to the number and symmetry of the LUMO and LUMO+1 of the heterocyclic diimine ligands. The bipy(•-) has only one π*1 orbital of b1 symmetry of accessible energy, but phen(•-) has two π* orbitals of b1 and a2 symmetry that are energetically accessible. The carbon pπ-orbitals have different nodal properties and coefficients and their energies, and therefore their populations change depending on the position and number of methyl substitutions on the ring. A chemical ramification of the change in electronic structure is that Cp*2Yb(phen) is a dimer when crystallized from toluene solution, but a monomer when sublimed at 180-190 °C. When 3,8-Me2phenanthroline is used, the adduct Cp*2Yb(3,8-Me2phen) exists in the solution in a dimer-monomer equilibrium in which ΔG is near zero. The adducts with 3-Me, 4-Me, 5-Me, 3,8-Me2, and 5,6-Me2-phenanthroline are isolated and characterized by solid state X-ray crystallography, magnetic susceptibility and LIII-edge XANES spectroscopy as a function of temperature and variable-temperature (1)H NMR spectroscopy.

3-D Framework {[Cu(L)nX][X] (H<sub>2</sub>O)<sub>2</sub>} L= bipy,n=2 Constructed through C-H….Cl Hydrogen Bondings and π-π Interactions

The reaction of copper 2,2-dichloroacetic acid, heterocyclic diimine (bipy) ligands under mildconditions affords one novel supramolecular complexes, [Cu (bipy)2[[H22 (bipy=2,2-bipyridine X=dichloroacetic acid). The compounds were constituted through hydrogen bonding and ππ interactions between the heterocyclic rings.

Crystal Structure and Synthesis of {[Cu(L)nX][X] (H<sub>2</sub>O)<sub>2</sub>} L= benz,n=3

The reaction of copper 2,2-dichloroacetic acid and heterocyclic diimine (benz) ligands under mildconditions affords one supramolecular complexes, [Cu (bipy)2[[H22 (bipy=benz, X=dichloroacetic acid). The compounds involves a regular square based pyramidal one and were constituted through hydrogen bonding and ππ interactions between the heterocyclic rings.

A way of lowering the uncertainty in values of crystal field parameters derived from the spectra of Ln 3+ ions in cubic field with rhombic distortions

Potentialities of increasing the reliability of crystal field parameters (CFPs) obtained from an analysis of Stark splitting of J-states of spin–orbital multiplets 2S+1L J of the Ln 3+ ions in cubic crystal field with rhombic distortions via a reduction of the region of their final fitting are examined. Suggested method of lowering the uncertainty of the CFP consists in determination of the relation of general cubic CFP of the fourth and sixth ranks ( B 4 and B 6) by comparison of a fragment of the experimental Ln 3+ spectrum with well known picture of dependences of Stark splitting of J-states on the relation mentioned. These dependences were calculated many years ago and published as a set of diagrams by K. Lea, M. Leask, W. Wolf, J. Phys. Chem. Solids, 23 (1962) 1381. Cubic parameters derived from the relation determined can be used for a narrowing of the fitting region for the rest of CFP. The method described is applied to the luminescence spectra of dimeric europium carboxylates with heterocyclic diimines. To justify application of this method to the spectra of Eu 3+ ions in crystal field of cubic symmetry with rhombic distortions it was shown that the influence of the second rank components of the crystal field on the relative Stark splitting of J-states of europium ions is minimal for J = 3, 4. In some cases, this peculiarity provides an approach of Stark splitting of the levels with J = 4 in spectra of compounds with rhombic distortions of cubic crystal field to the image of the splitting at an effective field of cubic symmetry. It was demonstrated that for europium complexes under consideration the relation of the general CFP B 4/ B 6 > 119. Consequently, the CFPs of the sixth rank are very small and the region of fitting of the rest of CFP can be appreciably reduced.

Spectral, luminescent, and electrochemical properties of cyclometalated complexes of Rh(III) based on 1-phenylpyrazole with ethylenediamine and heterocyclic diimines

A series of [Rh(ppz)2(N^N)]+ complexes (ppz− is the deprotonated form of 1-phenylpyrazole and (N^N) is ethylenediamine, 2,2′-bipyridyl, 1,10-phenanthroline, 4,7-diphenyl-1,10-phenanthroline, and 2,2′-biquinoline) is obtained and characterized by 1H NMR spectroscopy, electronic absorption and emission spectroscopy, and cyclic voltamperometry. A 0.75-V anodic shift of the ligand-centered reduction potentials of complexes compared to free heterocyclic (N^N) ligands is observed. The vibrationally structured luminescence spectra of complexes are attributed to intraligand spin-forbidden optical transitions localized on the {Rh(N^N)} metal-complex fragments.

Spectroscopic and electrochemical properties of cyclopalladated complexes derived from 2,3-diphenylpyrazine

A comparative study of complexes [Pd(dphpz)(N∧N)]PF6 [dphpz− is the deprotonated form of 2,3-diphenylpyrazine; (N∧N) is ethylenediamine (En), 2,2′-bipyridine (bpy), o-phenanthroline (phen), dipyrido[a,c]phenazine (dppz), 6,7-dicyanopyrido[f,h]quinoxaline (dicnq)] was made, using 1H NMR, electronic absorption, and emission spectroscopy, and also cyclic voltammetry. Steric interaction of the dphpz− phenyl rings leads to significant proton shielding in the carbanionic moiety of the cyclometallated ligand. Introduction of heterocyclic diimines instead of ethylenediamine decreases the desheilding of the dphpz− protons adjacent to the coordination center. Irrespective of the nature of the N∧N ligands, the cyclopalladated complexes are characterized by specific parameters of photo-and electrostimulated electron transfer processes involving the Pd(dphpz) orbitals, namely, by the long-wave absorption band with λmax 395±6 nm and e (2.2±1.2) × 103 1 mol−1 cm−1, the vibrationally structured low-temperature (77 K) luminescence resulting from the spinforbidden optical transfer from the excited to the ground state of the complex (energy E 00 19.27±0.07 kK, lifetime τ 160±30 μs), and the one-electron electroreduction wave with E 1−(2.0±0.1)V. For the [Pd(dphpz)·(N∧N)]+ complexes containing diazine derivatives of phenanthroline (dppz, dicnq), the degradation of the photoexcitation energy from two electronically excited states can occur as isolated process with successive transfer of electrons to the π orbitals localized on the remote moieties: [Pd(dphpz)] and diazine fragments of the N∧N ligands.

Peculiarities of the structure of lanthanide chloride complexes with heterocyclic diimines and the efficiency of energy transfer processes

Two families of lanthanide chlorides LnCl3L2(H2O)n and LnCl3L(H2O)m where L is 1,10-phenanthroline or 2,2′-bipyridine were synthesized. Their luminescence properties were investigated in the solid state and 1-dodecyl-3-methylimidazolium chloride solution. The structural peculiarities of lanthanide chlorides were elucidated by joint analysis of the X-ray, vibrational and luminescence data including the lifetime measurements. As a result the analysis of efficiency of energy transfer processes was performed and the correlation between the structure and the luminescence intensity was demonstrated in the systems studied.

Effect of heterocyclic diimine ligands with donor and acceptor substituents on the spectroscopic and electrochemical properties of Au(III) complexes

The composition, structure, and properties of a series of Au(III) complexes with heterocyclic diimine ligands [Au(N^N)Cl2]+, where (N^N) = 2,2′-bipyridine (Bipy), 4,4′-dimethyl-2,2′-bipyridine (DmBipy), 2,2′-biquinoline (Bqx), 1,10-phenanthroline (Phen), 2,9-dimethyl-1,10-phenanthroline (DmPhen), and 4,7-diphenyl-1,10-phenanthroline (DphPhen), were characterized by 1H NMR, electronic absorption, and emission spectroscopy and also by cyclic voltammetry. The influence of donor and acceptor substituents on the spectroscopic and electrochemical properties of the Au(III) complexes was revealed.

Effect of ligand radicals on vibrational IR, Raman and vibronic spectra of europium β-diketonates

Vibrational IR, Raman spectra and vibronic sidebands of Eu 3+ electronic transitions of europium tris-β-diketonates Eu(β) 3·Ph (β-dipyvaloylmethane (DPM), acetylacetone (AA), benzoylacetone (BA), thenoyltrifluoroacetone (TTFA) and other β-diketones; Ph-methyl-, phenyl-, and nitro-derivatives of 1,10-phenanthroline (Phen)) as well as Eu(β) 3·Bpy and Eu(β) 3·D-Bpy (Bpy- and D-Bpy–H- and D-2,2′-bipyridine) were studied. Effect of ligand radical properties on spectra and manifestation of the reciprocal influence of non-equivalent ligands in spectra are discussed. Dependence of the spectra on electronic density distribution in both ligands as well as on the strength of MO and MN bonds at the variation of radicals of one of the ligands, β or Ph, was examined. Shape of vibronic sidebands was analysed. Behaviour of bands in the middle and far regions of IR spectra of the series Eu(β) 3·Phen and Eu(TTFA) 3·Ph was investigated. Increase of the polarising influence of Eu 3+ ions on Phen and Bpy molecules and strengthening the EuN bonds in TTFA compounds in comparison with DPM compounds were disclosed from the Raman spectra of Eu(β) 3·Phen and Eu(β) 3·Bpy, that is in accordance with properties of β-diketone radicals. Conclusion about weaker EuN bonds in europium β-diketonates with heterocyclic diimines in comparison with corresponding nitrates was derived from the spectra. Spectral data concerning the relative strength of Euligand bonds are in agreement with available X-ray data.

Novel hydrogen-bonded and π–π interaction networks generated from the reaction of copper(II) chloride hydrates with heterocyclic diimines (2,2 ′-bipyridine, 1,10-phenanthroline) and bidentate diamine (ethylenediamine)

The reaction of copper dichloride dihydrate, heterocyclic diimine (bipy, phen) and bidentate diamine (en) ligands under mild conditions affords two novel supramolecular complexes containing Cu IIN 4Cl chromophores, [Cu(en)(bipy)Cl][OH] · (H 2O) 3 ( 1) (en=ethylenediamine, bipy=2,2 ′-bipyridine) and [Cu(phen) 2Cl][OH] · (CH 3OH) 2 · (H 2O) 6 ( 2) (phen=1,10-phenanthroline). Complex 1 involves a Cu IIN 4Cl chromophore with a regular square based pyramidal stereochemistry, while complex 2 involves a regular trigonal bipyramidal one. To our knowledge, 1 is the first example of a Cu IIN 4X complex generated from mixed ligands. Both of the two compounds were constituted through hydrogen bonding and π–π interactions between the heterocyclic rings. The magnetic properties of 2 were studied in the temperature range 5–300 K. The results reveal the occurrence of a weak antiferromagnetic coupling with J=−1.9 cm −1.

Preparation and Spectral Properties of Au(III) Complexes with Heterocyclic Diimine Ligands

Preparation and Spectral Properties of Au(III) Complexes with Heterocyclic Diimine Ligands

Synthesis and Reactivity of [(DMSC)Ti(η2-OCAr2)L2] Complexes (DMSC = Dimethylsilyl-Bridged p-tert-Butylcalix[4]arene Dianion, Ar = Aryl Group, and L2 = Delocalized Diimine)

Reactions of titanapinacolate complexes [(DMSC)Ti(OCAr2CAr2O)] (1, Ar = Ph; 2, Ar = p-MeC6H4; DMSC = 1,2-alternate dimethylsilyl-bridged p-tert-butylcalix[4]arene dianion) with 1 equiv of a delocalized diimine furnished titanium η2-ketone complexes [(DMSC)Ti(η2-OCAr2)L2)] 3−6 (L2 = bpy, dmbpy, or phen). The ketone is weakly bound in 3−6, and it is readily dissociated. The compounds dissolve in aromatic hydrocarbon solvents to give intense green solutions and undergo a photochemically assisted transformation into 1-aza-5-oxa-titanacyclopentene derivatives 8−11, in which C−H activation of the heterocyclic diimine ligand and hydride migration to a Ti-bound ketone to form an alkoxide group has occurred. The reaction of 3−6 with one or more equivalents of appropriate ketone gave 8−11 in high yield. The compounds were characterized by NMR (1H and13C) and microanalysis data, as well as by X-ray crystallography for [(DMSC)Ti{κ3-OC(p-MeC6H4)2C10H7N2}{OCH(p-MeC6H4)2}] (9). The ease of transformation of [(DMSC)Ti{η2...

Vibronic spectra and details of the structure of europium nitrates with derivatives of 1,10-phenanthroline

Luminescence and excitation of luminescence vibronic spectra as well as IR and Raman spectra of europium nitrates with 1,10-phenanthroline derivatives of formula Eu(NO 3) 3.Ph 2 were studied. The effect of size of ligands and their effective charges on crystal structure and, as a consequence, on spectroscopic characteristics was investigated under conditions where one type of ligand (NO 3 − group) is sufficiently rigid. The second ligand, heterocyclic diimine, can change its size and donor-acceptor properties when the substituents are varied. Stark splittings and relative intensities of the Eu 3+ electronic transitions, the behaviour of vibration frequencies, and vibronic interaction were studied. It was demonstrated that nitrates under investigation have identical composition but form two different structural groups with small and bulky phenanthroline derivatives due to the influence of steric factor. All nitrate anions in the compounds are coordinated and the Eu-O (NO 3 −) bonds are relatively strong. The values of the splitting of stretching vibrations of the NO 3 −-anions (▵= ν 4− ν 1) and position of the band of ν(Eu–O) vibration show that the strongest Eu–O bonds are formed in Eu(NO 3) 3.Nphen 2, Eu(NO 3) 3.Tmphen 2 and Eu(NO 3) 3.Dphphen 2 due to high acceptor properties of nitro-phenanthroline and large size of tetramethyl- and diphenyl-phenanthroline molecules. Weak vibronic mixing of electronic and vibronic states was demonstrated in the region of 5D 0– 7F 2 transition of Eu 3+. The vibronic satellites of 5D 0– 7F 0 -transition due to vibrations of the NO 3 −-group borrow about 1–2% of the intensity of the electric-dipole 5D 0– 7F 2 transition yielding the increase of their relative intensity of 100 times in the Stokes sideband.

Spectroscopic and electronic properties of mixed ligand aminoacidatocopper(II) complexes: Molecular structure of [Cu(4,7-dimethyl-1,10-phenanthroline)( l-phenylalaninato)](ClO 4)

Mixed-ligand aminoacidatocopper(II) complexes of the types, [Cu( l-phe)( NN)](ClO 4)· nH 2O [ l-phe= l-phenylalaninato; NN=2,2′-bipyridine ( n=2), 1,10-phenanthroline ( n=2), and 4,7-dimethyl-1,10-phenanthroline (dmphen, n=0)], [Cu(gly)( NN)](ClO 4)· nH 2O [gly=glycinato; NN=2,2′-bipyridine ( n=1), 1,10-phenanthroline ( n=0), neocuproine ( n=0), and ethylenediamine ( n=2)], and [Cu( l-ala)( NN)](ClO 4)· nH 2O [ l-ala= l-alaninato; NN=2,2′-bipyridine ( n=0), 1,10-phenanthroline ( n=1), and neocuproine ( n=2)], have been synthesized and characterized by elemental analyses, and IR, UV–Vis, CD, and EPR spectroscopic measurements. The molecular structure of [Cu( l-phe)(dmphen)](ClO 4) ( 1) has been determined by three-dimensional X-ray diffraction data. Complex 1 consists of discrete perchlorate anions and square planar cationic copper complexes. Based on the spectroscopic data, the structures of the complexes are either square pyramidal or square planar in solid state, whereas they are square pyramidal in solution. The sequence of d orbitals was assigned as d xy ≫ d z 2 > d x 2− y 2 > d yz > d xz for the solution species as deduced from the Gaussian resolved electronic absorption and CD spectroscopic data. Both aminoacidato and heterocyclic diimine ligands do not participate in π-interactions in these complexes.

Electronic and bonding properties of acetylacetonato copper(II) complexes. Molecular structure of [Cu(Acetylacetonato)(1,10-phenanthroline)(ClO 4)(0.5CH 3CN)

The preparation and characterization of mixed ligand complexes, [Cu (acac)(NN)(ClO 4)] (acac = acetylacetonate, NN = N, N, N′, N′-tetramethylethylenediamine, 2,2′-bipyridine, 1,10-phenanthroline (phen), and neocuproine), are reported. The structure of [Cu(acac)(phen)(ClO 4)(0.5CH 3CN)] determined from three-dimensional X-ray diffraction data comprises discrete square pyramidal [Cu(acac)(phen)(ClO 4)] and [Cu (acac)(phen)(CH 3CN)](ClO 4) units, with the perchlorate or the CH 3CN on the apex. The CH 3CN is coordinated in an unusual bent mode with a CuNC angle of 129.2(9)°. Analysis of the electronic spectra of the complexes suggests the sequence of d orbitals as d xy ⪢ d z 2 > d x 2 y − y2 ∼ d xz > d yz. In square pyramidal complexes, acetylcetonate ligands are π donors whilst heterocyclic diimines are not participated in π interactions.

H2O soluble ternary complexes of divalent transition metal ions with AN-(2-acetamido)iminodiacetic acid and heterocyclic diimines

H2O soluble mixed ligand complexes of the type [M-(ADA)B·H2O] where M = NiII or CuII; [ADA]2- = divalent anion of N-(2-acetamido)iminodiacetic acid, B = heterocyclic diimine (2,2'-bipyridyl or 1,10-phenanthroline), were prepared and characterized by elemental and thermal analyses, i.r. and electronic spectra, as well as conductivity measurements. Formation constants for the 1∶1∶1 ternary cobalt(II), nickel(II) and copper(II) complexes formed in solution were determined potentiometrically at 24 °C and μ = 0.1mol dm-3(KNO3).