Spectral and luminescent properties of mono- and binuclear cyclometalated complexes of Pd(II) and Pt(II) based on 4,6-diphenylpyrimidine with ethylenediamine and orthophenanthroline

The [M(N_^∧N)(Hdphpm)]ClO₄ and [(M(N_^∧N))₂(μ-dphpm)](ClO₄)₂ complexes (M = Pd(II), Pt(II); (N_^∧N) is ethylenediamine (En) and orthophenanthroline (Phen); Hdphpm^? and dphpm^2? are the mono- and bisdeprotonated forms of 4,6-diphenylpyrimidine) are obtained and characterized by ¹H NMR spectroscopy and electronic absorption and emission spectroscopy. The magnetic nonequivalence of protons of (N_^∧N) ligands is explained by a difference in the trans-effect of the carbanion and pyrimidine parts of the cyclometalated ligand. The long-wavelength absorption bands and the vibrationally structured luminescence bands of ethylenediamine complexes are attributed to optical transitions in the {M(Hdphpm)} and {M₂(μ-dphpm)} metal-complex fragments. The complexes with orthophenanthroline exhibit two low-energy optical transitions involving π* orbitals localized on the cyclometalated and chelating ligands; the difference in their energies depends on the metal and is much larger for Pt(II) than for Pd(II). It is found that the replacement of Pd(II) by Pt(II) in the [(M(phen))₂(μ-dphpm)]²⁺ complexes changes the direction of the photoexcitation energy degradation due to the energy transfer between the {M₂(μ-dphpm)} bridging fragment and peripheral phenanthroline ligands.     

Spectral and luminescent investigations of ammonia cyclometalated Pt(II) complexes

A method of synthesis of ammonia cyclometalated Pt(II) complexes [Pt(NH₃)₂C∧N]ClO₄, where C∧N is 2-phenylpyridinate or 2-phenylbenzothiazole ion, is developed. The electronic absorption and emission properties of the complexes are studied. It is found that the state responsible for intense long-lived luminescence is the excited charge-transfer state of the ³(d-π*) type, the π* orbital being localized at the corresponding cyclometalating ligand. Formation of platinum blue is observed in air-saturated aqueous solutions of ammonia cyclometalated complexes.     

Optical and spectroscopic properties of substituted oxa- and thiazole luminophores metalated with platinum metals

The cyclometalated [M(pbo)En]PF₆(M = Pd(II), Pt(II)), [M(pbo)₂En]PF₆ (M = Rh(III), Ir(III)), and [Rh(C∧N)₂En]PF₆ ((C∧N)^? are the deprotonated forms of 2-phenylbenzoxazole (pbo), 2,5-diphenyloxazole (dpo), 2-phenylbenzothiazole (pbt), 2-biphenyl-4-yl-5-phenyloxazole (bpo), and 2-biphenyl-4-yl-6-phenylbenzoxazole (bpbo) and En is ethylenediamine) complexes are studied by ¹H NMR spectroscopy, IR spectroscopy, and electronic absorption and emission spectroscopy. Metalation of luminophores leads to the formation of five-membered {M(C∧N)} cycles in the composition of plane-square and octahedral complexes of the cis-C,C structure. In addition to the intraligand (IL) π-π* optical transitions in the UV region, the complexes are characterized by long-wavelength metal-to-ligand charge-transfer (MLCT) absorption bands in the region of 366–416 nm. The phosphorescence of the complexes in the visible region (482–531 nm) is attributed to radiative transition from the mixed IL/MLCT electronically excited state. The temperature quenching of the phosphorescence of complexes is attributed to the thermally activated population of metal-centered electronically excited states with subsequent nonradiative deactivation.     

Optical properties of bicyclometalated Ir(III) and Rh(III) complexes of benzo[h]quinoline with (N∧S)− and (N∧O)− chelating ligands

[M(bzq)₂(N∧X)] complexes (M = Rh(III), Ir(III); (bzq)^? is the deprotonated form of benzo[h]quinoline, and (N∧X)^? are 2-thiolpyridine, 2-hydroxypyridine, and 2-thiolbenzothiazole ions) are studied by absorption and emission spectroscopy and voltammetry. The long-wavelength absorption bands of [Rh(bzq)₂(N∧X)] in the range of 420–424 nm are attributed to the optical metal-to-ligand charge transfer (MLCT) transitions, while the low-temperature (77 K) phosphorescence in the range of 490–610 nm is assigned to the intraligand (IL) transition of the {Rh(bzq)₂} metal-complex fragment. The phosphorescence of the [Ir(bzq)₂(N∧X)] complexes in liquid solutions in the range of 585–675 nm is assigned to the radiative MLCT transition, while the low-temperature (77 K) phosphorescence occurs from the thermally nonequilibrium MLCT and IL excited states of the {Ir(bzq)₂} metal-complex fragment.     

Optical, spectroscopic, and electrochemical properties of cyclometalated complexes of platinum metals based on 2-tolylpyridine and benzo[h]quinoline in ethylenediamine

Cyclometalated [M(C∧N)En]PF₆ (M = Pd(II), Pt(II)) and [M(C∧N)₂En]PF₆ (M = Rh(III), Ir(III)) complexes ((C∧N)^? corresponds to the deprotonated forms of 2-tolylpyridine and benzo[h]quinoline, and En is ethylenediamine) are studied by ¹H NMR spectroscopy, electronic absorption and emission spectroscopy, and voltammetry. Metalation of heterocyclic ligands leads to the formation of five-membered {M(C∧N)} cycles in the composition of square planar and octahedral complexes of the cis-C,C structure. Correlation of the energy positions of the long-wavelength metal-to-ligand charge-transfer absorption bands with the difference between the potentials of one-electron waves of metal-centered oxidation and ligand-centered reduction of complexes is shown. The phosphorescence of the complexes in the visible region of 469–524 nm is attributed to the radiative transition from the metal-modified intraligand excited state. The temperature quenching of the phosphorescence of complexes is attributed to the thermally activated population of metal-centered electronically excited states with subsequent nonradiative deactivation.     

Optical and electrochemical characteristics of ethylenediamine complexes of Pt(II) and Ir(III) with metalated 2-phenyl- and 2-naphthylbenzothiazole

The cyclometalated complexes [Pt(С^N)En]PF₆ and [Ir(C^N)₂En]PF₆ ((C^N)^– are deprotonated forms of 2-phenylbenzothiazole or 2-naphthylbenzothiazole and En is ethylenediamine) are studied by ¹Н NMR, IR, electronic absorption, and emission spectroscopy, as well as by voltammetry. Metalation of heterocyclic ligands leads to the formation of five-membered {M(C^N)} cycles in the composition of squareplanar Pt(II) complexes and octahedral Ir(III) complexes of the cis-С,С structure. A bathochromic shift of the metal-to-cyclometalated ligand charge transfer bands and a decrease in the potential difference between the single-electron waves of metal-centered oxidation and ligand-centered reduction of complexes upon substitution of 2-phenylbenzothiazole by 2-naphthylbenzothiazole and of Pt(II) by Ir(II) are shown. The phosphorescence of complexes in the visible region is assigned to the radiative transition from the metal-modified intraligand electronic excited state.     

Optical properties of cyclometalated Pd(II) and Rh(III) complexes based on 2-(4-biphenylyl)-6-phenylbenzoxazole luminophore with ethylenediamine

Using the methods of electronic absorption and emission spectroscopy, we have studied the optical properties of cyclometalated [Pd(C??N)En]CH₃COO and [Rh(C??N)₂En]Cl complexes of 2-(4-biphenylyl)-6-phenylbenzoxazole luminophore with ethylenediamine. We have shown that, along with a bathochromic shift of intraligand spin-allowed ??-??* optical transitions by 1000?C1800 cm^?1, complexes are characterized by the occurrence of long-wavelength bands of a mixed nature (intraligand-metal-ligand charge transfer) in the range of 369??392 nm and by competing intraligand fluorescence (419?C423 nm) and phosphorescence (511?C532 nm) processes under low-temperature (77 K) photoexcitation.     

Optical and electrochemical properties of cyclometalated Rh(III) complexes based on 4,6-diphenylpyrimidine with ethylenediamine, 2,2′-bipyridyl,and 1,10-phenanthroline

The [Rh(Hdp)₂(N∧N)]ClO₄ complexes (Hdp⁻ is the monodeprotonated form of 4,6-diphenylpyrimidine and (N∧N) is ethylenediamine, 2,2′-bipyridyl, and 1,10-phenanthroline) are synthesized and characterized by ¹H and ¹³C NMR, IR, electronic absorption, and emission spectroscopy, as well as by cyclic voltammetry. The magnetic equivalence of two cyclometalated 4,6-diphenylpyrimidine ligands in the composition of complexes points to the cis position of metalated phenyl rings in the inner sphere. Quasi-reversible one-electron reduction waves are attributed to the ligand-centered electron transfer to the π* antibonding orbital of heterocyclic ligands, while irreversible oxidation waves are associated with electron detachment from the Rh-C σ bonding orbital of the {Rh(Hdp)₂} metal-complex fragment. The characteristic long-wave-length absorption bands and the vibrationally structured phosphorescence bands of complexes are assigned to the spin-allowed and spin-forbidden charge-transfer optical transitions between the σ_Rh-C and π_Hdp* orbitals localized on the {Rh(Hdp)₂} fragment of the complex.     

The Effect of Hg(II) on the Optical Characteristics of Cycloiridated 2-Phenylbenzothiazole Complexes with Chelating Ligands Containing Sulfur Donor Atoms

The [Ir(bt)₂(S^S)], [Ir(bt)₂(S^N)], and [Ir(bt)₂(CH₃CN)₂]PF₆ complexes, where (bt)^? is a deprotonated form of 2-phenylbenzothiazole and (S^S)^? and (S^N)^? are diethyldithiocarbamate, O-ethyldithiocarbonate, 2-mercaptobenzothiazolate, 2-mercaptobenzoxazolate, and 2-mercaptopyridinate ions, and the effect of Hg(II), Cu(II), Cd(II), and Zn(II) cations on the optical characteristics of these complexes are studied by electron absorption spectroscopy and emission spectroscopy. A hypsochromic shift of the absorption and phosphorescence bands of complexes in substituting the (S^S)^? and (S^N)^? chelating ligands with acetonitrile ligands is attributed to a lower energy of d_Ir orbitals compared with the mixed d_Ir/p(S) orbitals. It is shown that the presence of Hg(II) cations results in a hypsochromic shift of the absorption and phosphorescence bands of complexes [Ir(bt)₂(S^S)] and [Ir(bt)₂(S^N)] because of an effective reaction of substitution of chelating ligands to acetonitrile ligands.     

Azobenzene Pd(II) complexes with N^N- and N^O-type ligands

Methods of synthesis of cyclometalated azobenzene palladium(II) complexes of [Pd(N^N)Azb]ClO₄ and [Pd(N^O)Azb]ClO₄ types (where Azb^– is the deprotonated form of azobenzene; N^N is 2NH₃, ethylenediamine, or 2,2′-bipyridine; and (N^O)^– is the deprotonated form of amino acid (glycine, α-alanine, β-alanine, tyrosine, or tryptophan)) are developed. The electronic absorption and the electrochemical properties of these complexes are studied.     

Optical and electrochemical properties of cyclometalated Pd(II) and Pt(II) complexes with a metal-metal chemical bond

Cyclometalated [M(C^N)(μ-(N-S))]₂ complexes ((M = Pd(II), Pt(II)), (C^N)^? are the deprotonated forms of 2-tolylpyridine and benzo[h]quinoline, and (N-S)^? are pyridine-2-thiolate and benzothiazole-2-thiolate ions) are studied by ¹H NMR, IR, electronic-absorption, and emission spectroscopy, as well as by voltammetry. It is shown that the formation of the metal-metal chemical bond and the σ _dz2 ^* orbital as a HOMO of complexes leads to the long-wavelength spin-allowed (410–512 nm) and spin-forbidden (595–673 nm) optical transitions σ _dz2 ^* ?π _(C^N) ^* in the absorption and phosphorescence spectra, as well as to the two-electron and successive one-electron oxidation with the formation of binuclear Pt(III) and Pd(III) complexes. The substitution of Pt(II) by Pd(II) is characterized by hypso- and bathochromic shifts of the spin-allowed and forbidden σ _dz2 ^* ?π _(C^N) ^* optical transitions in the absorption and phosphorescence spectra of complexes, by phosphorescence quenching of Pd(II) complexes in liquid solutions, and by an anodic shift of the oxidation potential of Pd(II) complexes compared with Pt(II) complexes.     

Mononuclear Co(III) and Ni(II) Complexes with Polypyridyl Ligands, [Co(phen)2(taptp)]3+ and [Ni(phen)2(taptp)]2+: Synthesis, Photocleavage and DNA-binding

Two novel, mixed ligand complexes of cobalt(III) and nickel(II), [Co(phen)₂(taptp)]³⁺ (1) and [Ni(phen)₂(taptp)]²⁺ (2) (phen = 1,10-phenanthroline and taptp = 4,5,9,18-tetraazaphenanthreno [9,10-b]triphenylene), were synthesized and characterized by elemental analyses, UV-visible and NMR spectroscopies. The binding interactions of the two complexes with DNA have been investigated using absorption and emission spectroscopy methods and electrophoresis measurement mode. The intrinsic binding constants for these complexes to DNA are in the order of 10⁵. In Tris buffer, the Co(III) complex shows a moderate luminescence which was enhanced after binding to DNA. However for complex Ni(II), no emission was observed in Tris buffer. The [Co(phen)₂(taptp)]³⁺ and [Ni(phen)₂(taptp)]²⁺ can cause the photocleavage of DNA supercoiled pBR322 upon irradiation by 360 nm light. Based on the data, an intercalative mode of DNA binding is suggested for the two complexes.     

Infrared and Raman Spectra of Sulfur-Nitride Complexes of Nickel(II) and Palladium(II)

Abstract

The infrared and Raman spectra of trans-Ni(S₂N₂CH₃)₂ and Pd(S₃N)₂ were measured from 4000-200 cm^?1. The absorption bands were assigned by comparison to the sulfur nitride complexes of nickel(II), palladium(II) and platinum(II). Normal coordinate analyses on these complexes were carried on these data using molecular parameters taken from X-ray data. To aid in band assignments, isotope shift data on trans-⁶²Ni(S₂N₂CH₃)₂ have also been carried out.     

XAFS investigations of copper(II) complexes with tetradentate Schiff base ligands

X‐ray absorption fine structure spectra have been investigated at the K‐edge of copper in copper(II) salen/salophen complexes: [Cu(salen)] (1), [Cu(salen)CuCl₂].H₂O (2), [Cu(salophen)] (3) and [Cu(salophen) CuCl₂].H₂O (4), where salen^2? = N,N′‐ethylenebis (salicylidenaminato); salophen^2? = o‐phenylenediaminebis(salicylidenaminato). Complexes 1 and 3 are supposed to have one type of copper centers (called (Cu1)) and complexes 2 and 4 two types of copper centers (called (Cu1) and (Cu2)) having different coordination environments and geometries. A theoretical model has been generated using the available crystallographic data of complex 1 and it has been used for analysis of the extended X‐ray absorption fine structure (EXAFS) data of the four complexes to obtain the structural parameters for (Cu1) center. For this center, the obtained Cu–Cu distance (3.2 Å) verifies the binuclear nature of all the complexes. For determining the coordination geometry around (Cu2) center in 2 and 4, a theoretical model has been generated using the crystal structure of a Cu(II) complex, [Cu(C₁₆H₁₂N₂O₂Cl₂)]. This theoretical model has been fitted to the EXAFS data of 2 and 4 to obtain the structural parameters for (Cu2) center. The present analysis shows that (Cu1) center has square pyramidal geometry involving 2N and 3O donor atoms, whereas (Cu2) center has distorted tetrahedral geometry with 2O and 2Cl donor atoms. The values of the chemical shifts and presence of typical Cu(II) X‐ray absorption near‐edge spectroscopy features suggest that copper is in the +2 oxidation state in all these complexes. The intensity of ls → 3d pre‐edge feature has been used to investigate the geometry and binuclear nature of the complexes. Copyright © 2012 John Wiley & Sons, Ltd.     

Calix Receptor Edifice; Scrupulous Turn Off Fluorescent Sensor for Fe(III), Co(II) and Cu(II)

Novel Supramolecular fluorescence receptor derived from calix-system i.e. calix[4]resorcinarene bearing dansylchloride as fluorophore was designed and synthesized. The compound was purified by column chromatography and characterized by elemental analysis, NMR and Mass spectroscopy. Tetradansylated calix[4] resorcinarene (TDCR) shows a boat conformation with C₂v symmetry. The complexation behaviour of metal cations [Ag(I), Cd(II), Co(II), Fe(III), Hg(II), Cu(II), Pb(II), Zn(II), U(VI) (1?×?10^-4?M)] with tetra dansylated calix[4]resorcinarene (1?×?10^-6?M) was studied by spectophotometry and spectrofluorometry. Red shift in the absorption spectra led us to conclude that there is strong complexation Fe(III), Co(II) and Cu(II) with TDCR. These metal cations also produce quenching with red shifts in the emission spectra. The maximum quenching in emission intensity was observed in the case of Fe(III) and its binding constant was also found to be significantly higher than that of Co(II) and Cu(II). Quantum yield of metal complexes of Fe(III) was found to be lower in comparison with Co(II) and Cu(II) complexes. Stern Volmer analysis indicates that the mechanism of fluorescence quenching is either purely dynamic, or purely static.     

Spectroscopic and electrochemical properties of dichlorobenzoquinoline complexes of Au(III), Pt(II), and Pd(II)

The dichloride complexes of Au(III), Pt(II), and Pd(II) with 2,2′-biquinoline are obtained and characterized by ¹H NMR spectroscopy, electronic spectroscopy, and cyclic voltammetry. It is shown that the low efficiency of the metal-ligand (2,2′-biquinoline) interaction leads to almost the same positions of the intraligand bands in the absorption and fluorescence spectra of the complexes and to the closeness of their reduction potentials.     

DNA Binding,Cleavage and Antibacterial Activity of Mononuclear Cu(II), Ni(II) and Co(II) Complexes Derived from Novel Benzothiazole Schiff Bases

A series of novel bivalent metal complexes M(L₁)₂ and M(L₂)₂ where M = Cu(II), Ni(II), Co(II) and L₁ = 2-((benzo [d] thiazol-6-ylimino)methyl)-4-bromophenol [BTEMBP], L₂ = 1-((benzo [d] thiazol-6-ylimino)methyl) naphthalen-2-ol [BTEMNAPP] were synthesized. All the compounds have been characterized by elemental analysis, SEM, Mass, ¹H NMR, ¹³C NMR, UV–Vis, IR, ESR, spectral data and magnetic susceptibility measurements. Based on the analytical and spectral data four-coordinated square planar geometry is assigned to all the complexes. DNA binding properties of these complexes have been investigated by electronic absorption spectroscopy, fluorescence and viscosity measurements. It is observed that these binary complexes strongly bind to calf thymus DNA by an intercalation mode. DNA cleavage efficacy of these complexes was tested in presence of H₂O₂ and UV light by gel electrophoresis and found that all the complexes showed better nuclease activity. Finally the compounds were screened for antibacterial activity against few pathogens and found that the complexes have potent biocidal activity than their free ligands.     

New luminescing complexes of Pd(II) with 2-(phenyl)benzothiazolate

The luminescent properties of the complexes [PdBt(μ-Cl)]₂, [PdEnBt]ClO₄, and [PdBryBt]PF₆ (where Bt is 2-(phenyl)benzothiazolate-N,C²′-ion, En is 1,2-(diamine)ethane, and Bpy is 2,2′-bipyridyl) are studied and a qualitative diagram of their electronically excited states is presented.     

Infrared Spectra of the Copper(II), Nickel(II) and Palladium(II) Complexes of 4-amino-3-pentene-2-one

Abstract

The infrared spectra of the metal complexes of 4-amino-3-pentene-2-one were measured from 4000 - 20 cm^?1. The absorption bands were assigned by comparison to other similar molecules: The Cu(II) complex of 4-methylamino-3-pentene-2-one, and complexes of acetylacetone. Force constants for the molecules were calculated using the A_xsm matrix method. The spectra were measured at 298^oK and 77^oK.     

Absorption spectra and the nature of complexes in the polyvinyl Alcohol-Nickel (II) chloride system

We have used electronic spectroscopy in the 160–1100 nm range to study the polyvinyl alcohol-nickel(II) chloride system. Based on the results obtained, we hypothesize formation of mixed-ligand complexes of the type [Ni(H₂O)_6-nCl_n]^2-n (n = 0, 1,..., 5) in the polyvinyl alcohol matrix. Transformation of the coordination sphere as the NiCl₂ concentration changes is apparent both in the region of the d-d transition bands (350–1100 nm) and in the region of the charge transfer bands (160–250 nm). We propose assigning the absorption bands separated by mathematical treatment to complexes of specific compositions. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 1, pp. 136–138, January–February, 2006.