Mixed-ligand complexes of Pt(II) and Pd(II) with 2-phenylbenzothiazole

The mixed-ligand cyclometalated [M(Bt)(μ-Cl)]₂ and [(M(N∧N))(Bt)]⁺ complexes (M = Pd(II), Pt(II); Bt^? is the deprotonated form of 2-phenylbenzothiazole; and ( N∧N) is ethylenediamine (En) and orthophenanthroline (Phen)) are studied and described by ¹H NMR spectroscopy, electronic absorption and emission spectroscopy, and voltammetry. The one-electron reduction of complexes is attributed to the electron transfer to the π * orbitals of both diimine and cyclometalated ligands. The long-wavelength absorption bands and vibrationally structured luminescence bands are assigned to optical transitions that are localized mainly on the M(Bt) metal-complex fragment.     

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.     

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 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.     

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.     

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 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.     

Spectral and luminescent properties of ammonia cyclopalladated complexes

The synthesis of ammonia cyclometalated palladium(II) complexes [Pd(NH₃)₂C^N]ClO₄ (C^N is the deprotonated form of 2-phenylpyridine, 2-(para-tolyl)pyridine, 7,8-benzo(h)quinoline, 2,6-diphenylpyridine, and 4-phenylpyrimidine) is developed. The IR and electronic absorption and emission spectra of these complexes are studied. It is found that the ammine and analogous ethylenediamine cyclometalated Pd(II) complexes have similar spectral and luminescent properties and the same nature of the electronically excited ³(π-π*)-type state responsible for the long-lived luminescence, the π and π* orbitals being localized on the corresponding cyclometalating ligand. The efficient temperature quenching of the luminescence of Pd(II) complexes at room temperature is assigned to the thermally activated population of metal-centered electronically excited states with subsequent nonradiative deactivation.     

Effect of acidification on spectral parameters of solutions of mixed-ligand cyclometalated Pt(II) and Pd(II) complexes

The effect of acidification of water-ethanol solutions of cyclometalated Pt(II) and Pd(II) complexes with ethylenediamine and cyanide ligands is studied. It is found that, unlike the ethylenediamine complexes, the cyclometalated complexes with cyanide ligands are unstable and undergo irreversible decyclometalation.     

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.     

Luminescence quenching of cyclometalated Pt(II) complexes by halogenide ions

The luminescence quenching of [Pt(CΛN)En]ClO₄ complexes ((CΛN)^? = ppy^?, tpy^?, and bt^? are deprotonated forms of 2-phenylpyridine, 2(2′-thienyl(pyridine), and 2-phenylbenzothiazole, respectively; En is ethylenediamine) by halogenide ions (Hal^? = Cl^?, Br^?, I^?) in ethanol solutions is studied. It is shown that the quenching has a dynamic character and its bimolecular rate constants are consistent with the enhancement of nonradiative deactivation of the excited state of {[Pt(CΛN)En]*...Hal} collision complexes with increasing spin-orbit interaction constant of the halogen.     

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.     

The effect of the nature of peripheral platinated and bridging mercapto ligands on the optical and electrochemical properties of binuclear Pt(II) complexes with a metal-metal chemical bond

The effect of heterocyclic metalated and bridging ligands on the optical and electrochemical properties of [Pt(C^N)(μ-N^S)]₂ complexes ((C^N)^? and (N^S)^? are the deprotonated forms of 1-phenylpyrazole, 2-tolylpyridine, benzo[h]quinoline, 2-phenylbenzothiazole and 2-mercaptobenzothiazole, 2-mercaptobenzoxazole, 2-mercaptopyridine) is studied by ¹H NMR, electronic absorption, and emission spectroscopy, as well as by voltammetry. The long-wavelength spin-allowed (415–540 nm) absorption bands of the complexes are attributed to the metal-metal-to-ligand charge transfer (MMLCT) optical transitions. It is shown that the interaction of the d _Z2 and π _(C^N ^*) orbitals of two {Pt(C^N)} fragments of binuclear complexes leads to a cathodic shift (0.5–1.0 V) of their metal-centered oxidation potential and to an anodic shift (0.1–0.2 V) of their ligand-centered reduction potential with respect to [Pt(C^N)En]⁺ complexes. The luminescence of binuclear complexes in solutions at room temperature is assigned to the spin-forbidden MMLCT transition. It is shown that, in frozen (77 K) solutions, in addition to the MMLCT optical transitions, spin-forbidden radiative processes occur from the intraligand (π_(C^N)?π _(C^N) ^* ) and metal-to-ligand charge transfer (d_Pt?π _(C^N) ^* ) excited states.     

Specific features of spectra of cyclometalated Pt(II) and Pd(II) complexes in polyvinyl alcohol

The absorption spectra and luminescent properties of ethylenediamine complexes of Pt(II) and Pd(II) with cyclometalating ligands (2-phenylpyridinate and 2-2’-thienyl)pyridinate) in polyvinyl alcohol are studied. It is ascertained that, upon an increase in temperature, the nonradiative degradation of energy in palladium complexes occurs according to the mechanism of strong vibronic coupling, whereas platinum complexes show weak vibronic coupling.     

Spectroscopic properties of 2-phenylbenzothiazole and 1-phenylpyrazole luminophores metalated with platinum metals

The effect of metalation of 2-phenylbenzothiazole and 1-phenylpyrazole with Pd(II), Pt(II), and Rh(III) on the structure and optical properties of luminophore complexes is studied by ¹H NMR spectroscopy, IR spectroscopy, and electronic absorption and emission spectroscopy. It is shown that metalation of luminophores leads to the formation of five-membered {M(C??N)} fragments in the composition of square planar and octahedral complexes, which exhibit a long-wavelength charge-transfer band. The luminescence properties of the complexes are characterized by quenching of the fluorescence and by enhancement of the phosphorescence from the mainly intraligand excited state. Fluorescence quenching of complexes is attributed to the thermally activated energy transfer to metal-centered states and their efficient nonradiative decay.     

Structural Investigations of Pd(II) and Pt(II) Complexes with O-Vanillin Thiosemicarbazone and 4-Phenylthiosemicarbazone and their Mixed Ligand Complexes

The Pd(II) and Pt(II) complexes with two dibasic tridentate ligands viz. o-vanillin thiosemicarbazone and o-vanillin-4-phenylthiosemicarbazone, have been synthesized and characterized on the basis of their elemental analysis, magnetic susceptibility, conductance, ir and electronic spectral and thermogravimetric data. The presence of chlorine atom in the coordination sphere imparts a square planar geometry to these complexes having the general formula [M (L) Cl]. The mixed ligand complexes of the type [M (L) py. H₂O] have also been prepared employing pyridine as an additional heterocyclic base. The complexes are square pyramidal and the presence of chlorine, water molecules is revealed by the study of their thermograms supported by the presence of relevant bands in their ir spectra. Suitable structures have been assigned to these binary and ternary complexes.     

Local31P and distant31P and195Pt ENDOR studies of powdered samples of Bis(O,O′-disubstituted-dithiophosphato)copper(II) complexes magnetically diluted in the corresponding Pd(II) and Pt(II) host lattices

ENDOR studies on bis(dithiophosphato)copper(II) complexes magnetically diluted in the corresponding Pd(II) and Pt(II) host lattices performed with the use of the method of “polycrystalline ENDOR crystallography” are reported. In these samples well resolved local³¹P (A_iso ca. 29 MHz and A_aniso ca. 0.9 MHz) as wel1 as distant³¹P (A _iso ca. 1.3 and 5.5 MHz and A_aniso ca. 0.2 and 0.4 MHz) and¹⁹⁵Pt (A_iso ca. 3.1 MHz and A_aniso ca. 0.2 MHz) ENDOR transitions are recorded. It is shown that the directions of the main values of A_aniso for all local³¹P and distant³¹P and¹⁹⁵Pt ENDOR transitions are parallel. Comparison of these results with those reported about the same complexes but diluted in other host lattices shows that there is no difference in the EPR and local³¹P ENDOR parameters thus suggesting that the structure of the paramagnetic complex remains unchanged. It is found that distant ENDOR transitions appear only in the case when the host lattice contains one molecule in the unit cell, i.e., when all molecules are parallel to each other. Using the obtained data from local and distant³¹P ENDOR transitions some structural features of Cu(dtp)₂ as well as Pd(dtp)₂ and Pt(dtp)₂ complexes are found for the first time.     

Infrared Spectra of Some Metal (II) Complexes of 2-Aminomethylpyridine

Abstract

Band assignments in the IR spectra (700–150 cm^?1) of [M(amp)₃] (ClO₄)₂ (amp = 2-aminomethylpyridine; M = Mn(II), Fe(II), Co(II), Ni(II), Zn(II), [Zn(amp)₂Cl₂] and [Pt(amp)Cl₂] derived from amp-ND₂, their unlabelled analogues, [Zn(amp)₂X₂] (X = Br, I) and [Pt(amp)Br₂] are discussed.     

The key Cl− ligand for metal‐to‐ligand charge transfer in mononuclear terpyridine ruthenium(II) and binuclear ruthenium(II) tetrapyridylpyrazine complexes

Electronic structures of binuclear ruthenium complexes [Ru₂(terpy)₂(tppz)]⁴⁺ ( 1A ) and [Ru₂Cl₂(L)₂(tppz)]²⁺ {L = bpy ( 2A ), phen ( 3A ), and dpphen ( 4A )} were studied by density functional theory calculations. Abbreviations of the ligands (Ls) are bpy = 2,2′‐bipyridine, phen = 1,10‐phenanthroline, dpphen = 4,7‐diphenyl‐1,10‐phenanthroline, terpy = 2,2′:6′,2″‐terpyridine, and tppz = tetrakis(2‐pyridyl)pyrazine. Their mononuclear reference complexes [Ru(terpy)₂]²⁺ ( 1B ) and [RuClL(terpy)]⁺ {L = bpy ( 2B ), phen ( 3B ), and dpphen ( 4B )} were also examined. Geometries of these mononuclear and binuclear Ru(II) complexes were fully optimized. Their geometric parameters are in good agreement with the experimental data. The binuclear complexes were characterized by electrospray ionization mass spectrometry, UV–Vis spectroscopy, and cyclic voltammograms. Hexafluorophosphate salts of binuclear ruthenium complexes of 3A and 4A were newly prepared. The crystal structure of binuclear complex 1A (PF₆)₄ was also determined. Orbital interactions were analyzed to characterize the metal‐to‐ligand charge‐transfer (MLCT) states in these complexes. The Cl^? ligand works to raise the orbital energy of the metal lone pair, which leads to the low MLCT state. Copyright © 2011 John Wiley & Sons, Ltd.