Room temperature phosphorescence from a platinum(II) diimine bis(pyrenylacetylide) complex

Room temperature phosphorescence has been observed in a synthetically facile Pt(II) complex, Pt(dbbpy)(CtriplebondC-pyrene)(2) (dbbpy = 4,4'-di(tert-butyl)-2,2'-bipyridine; CtriplebondC-pyrene = 1-ethynylpyrene), in fluid solution. The static and time-resolved absorption and luminescence data are consistent with phosphorescence emerging from the appended CtriplebondC-pyrenyl units following excitation into the low energy dpi Pt --> pi* dbbpy metal-to-ligand charge transfer absorption bands.     

Synthesis and spectroscopic studies of cyclometalated Pt(II) complexes containing a functionalized cyclometalating ligand, 2-phenyl-6-(1H-pyrazol-3-yl)-pyridine

Three new luminescent cyclometalated Pt(II) complexes, [Pt(L)Cl] (1), [Pt2(L-)2] (2), and [Pt(L)(PPh3)]ClO4 (3.ClO4) (where HL=2-phenyl-6-(1H-pyrazol-3-yl)-pyridine), were synthesized and characterized by X-ray crystallography. HL represents a new class of C,N,Npyrazolyl cyclometalating ligands containing a Cphenyl, a Npyridyl, and a Npyrazolyl donor moiety, as well as a 1-pyrazolyl-NH, that can also be available for metal coordination and other chemical interactions. Complex 1 possesses intense intraligand transitions at 275-375 nm and moderately intense metal-to-ligand charge transfer (1MLCT) (dpi(Pt)-->pi*(L)) transition at 380-410 nm. The room temperature solid-state emission lambdamax of 1 occurs at 580 nm and is attributable to the 3MMLCT (dsigma*(Pt)-->pi*(L)) transition. It also displays strong phosphorescence in acetonitrile solutions at room temperature with an emission lambdamax at 514 nm, which can be tentatively assigned to the 3MLCT (pi*(L)-->dpi(Pt)) transition. Complex 1 can be deprotonated in organic solvents to yield a cycloplatinated dimer 2, which shows a relatively high room-temperature luminescent quantum yield of 0.59 in DMF (lambdamax=509 nm). Substitution of the ancillary chloro-ligand in 1 by triphenylphosphine yields 3, which also possesses a good room-temperature luminescent quantum yield of 0.52 in DMF (lambdamax=504 nm) and a better solubility in water. Complex 3 is synthesized to demonstrate the pH dependence of luminescent properties of this C,N,Npyrazolyl cyclometalated Pt(II) system. Such a pH response is ascribable to the protonation/deprotonation of the 1-pyrazolyl-NH on the C,N,Npyrazolyl cyclometalating ligand. The pKa of the 1-pyrazolyl-NH in 3, measured in 1:2 (v/v) aqueous DMF solutions, is approximately 4.0.     

Luminescence Properties of Platinum(II) Dithiooxamide Compounds

Tight contact ion pairs of general formula {Pt(H(2)-R(2)-dto)(2)(2+),(X(-))(2)} have been prepared, and their absorption spectra and luminescence properties (at room temperature in dichloromethane fluid solution and at 77 K in butyronitrile rigid matrix) have been studied (dto = dithiooxamide; R = methyl, X = Cl (1); R = butyl, X = Cl (2); R = benzyl, X = Cl (3); R = cyclohexyl, X = Cl (4); R = cyclohexyl, X = Br (5); R = cyclohexyl, X = I (6)). The absorption spectra of all the compounds are dominated by moderately strong Pt(dpi)/S(p) to dithiooxamide (pi) charge transfer (Pt/S --> dto CT) bands in the visible region (epsilon in the 10(4)-10(5) M(-)(1) cm(-)(1) range). Absorption features are also present at higher energies, due to pi-pi transitions centered in the dto ligands (ligand centered, LC). All the compounds exhibit a unstructured luminescence band in fluid solution at room temperature, with the maximum centered in the 700-730 nm range. The luminescence bands are blue-shifted about 4000 cm(-)(1) on passing to the rigid matrix at 77 K. Luminescence lifetimes are on the 10(-)(8)-10(-)(7) s time scale at room temperature and 1 order of magnitude longer at 77 K. Luminescence is assigned to triplet Pt/S --> dto CT excited states in all cases. Compounds 3-6 also exhibit a second higher-energy luminescence band at room temperature, centered at about 610 nm, attributed to a LC excited state. Charge transfer interactions between halides and dto ligands destabilize dto-centered orbitals, affecting the energy of Pt/S --> dto CT transitions and states. The X counterions and X --> dto CT levels are proposed to play a role in promoting excited state conversion between LC and Pt/S --> dto CT levels. The R substituents on the nitrogen atoms of the dto ligands influence the absorption and photophysical properties of the compounds, by affecting proximity of the ion pairs. The possibility to functionalize the R substituents may open the way to interface these luminescent compounds with desired substrates and to construct supramolecular assemblies.     

Platinum(II) 1,10-phenanthroline complexes of acetylides containing redox-active groups

The new diimine ligand 3,8-di-n-pentyl-4,7-di(phenylethynyl)-1,10-phenanthroline (1) was used for the synthesis of a range of Pt(II) complexes, viz.[Pt(1)Cl2], [Pt(1)(C triple bond C-Ph)2], [Pt(1)(C triple bond C-Fc)2] and [Pt(1)(C triple bond C-p-C6H4-C triple bond C-Fc)2](Fc = ferrocenyl). Crystal structure analyses were performed for [Pt(1)Cl2] and [Pt(1)(C triple bond C-Ph)2] and revealed that the di(acetylide)pi-tweezer of the latter binds a molecule of chloroform through C-H...pi hydrogen bonds. The redox and optical properties of 1 and its complexes were investigated by (spectro-)electrochemistry, UV-Vis and luminescence spectroscopy, and an energy level diagram was derived for [Pt(1)(C triple bond C-Fc)2] and related compounds on the basis of the data collected. The ferrocenyl-substituted Pt(II) complexes are donor-sensitiser assemblies. Intramolecular quenching of the photoexcited Pt(II) diimine unit leads to very short luminescence lifetimes for [Pt(1)(C triple bond C-p-C(6)H(4)-C triple bond C-Fc)2](2 ns) and [Pt(1)(C triple bond C-Fc)2](0.3 ns), as opposed to [Pt(1)(C triple bond C-Ph)2](0.7 micros). Excimer formation has been observed for [Pt(1)(C triple bond C-Ph)(2)] at room temperature in dichloromethane and at low temperatures in frozen glassy dichloromethane and 2-methyltetrahydrofuran solution, but not in the solid state.     

Blue luminescent 2-(2'-pyridyl)benzimidazole derivative ligands and their orange luminescent mononuclear and polynuclear organoplatinum(II) complexes

Five new 2-(2'-pyridyl)benzimidazole derivative ligands, 1,4-bis[2-(2'-pyridyl)benzimidazolyl]benzene (1,4-bmb), 4,4'-bis[2-(2'-pyridyl)benzimidazolyl]biphenyl (bmbp), 1-bromo-4-[2-(2'-pyridyl)benzimidazolyl]benzene (Brmb), 1,3-bis[2-(2'-pyridyl)benzimidazolyl]benzene (1,3-bmb), and 1,3,5-tris[2-(2'-pyridyl)benzimidazolyl]benzene (tmb), have been synthesized by Ullmann condensation methods. The corresponding mononuclear and polynuclear PtII complexes, Pt2(1,4-bmb)Ph4 (1), Pt2(bmbp)Ph4 (2), Pt(Brmb)Ph2 (3), Pt2(1,3-bmb)Ph4 (4), and Pt3(tmb)Ph6 (5), have been obtained by the reaction of the appropriate ligand with [PtPh2(SMe2)]n. The structures of the free ligands 1,4-bmb, bmbp, and tmb, as well as the complexes 1-3, were determined by single-crystal X-ray diffraction. All ligands display fluorescent emissions in the purple/blue region of the spectrum at ambient temperature and phosphorescent emissions in the blue/green region at 77 K, which are attributable to ligand-centered pi --> pi* transition. No ligand-based emission was observed for the PtII complexes 1-5. All PtII complexes display orange/red emissions at 77 K in a frozen solution or in the solid state, attributable to metal-to-ligand charge transfers (MLCT). Variable-temperature 1H NMR experiments establish that complexes 1, 4, and 5 exist in isomeric forms in solution at ambient temperature due to the hindered rotation of the square PtC2N2 planes in the complexes.     

Solid-state and solution-state coordination chemistry of the zinc triad with the mixed N,S donor ligand bis(2-methylpyridyl) sulfide

The binding of group 12 metal ions to bis(2-methylpyridyl) sulfide (1) was investigated by X-ray crystallography and NMR. Seven structures of the chloride and perchlorate salts of Hg(II), Cd(II), and Zn(II) with 1 are reported. Hg(1)(2)(ClO(4))(2), Cd(1)(2)(ClO(4))(2), and Zn(1)(2)(ClO(4))(2).CH(3)CN form mononuclear, six-coordinate species in the solid state with 1 binding in a tridentate coordination mode. Hg(1)(2)(ClO(4))(2) has a distorted trigonal prismatic coordination geometry while Cd(1)(2)(ClO(4))(2) and Zn(1)(2)(ClO(4))(2).CH(3)CN have distorted octahedral geometries. With chloride anions, the 1:1 metal to ligand complexes Hg(1)Cl(2), [Cd(1)Cl(2)](2), and Zn(1)Cl(2) are formed. A bidentate binding mode that lacks thioether coordination is observed for 1 in the four-coordinate, distorted tetrahedral complexes Zn(1)Cl(2) and Hg(1)Cl(2). [Cd(1)Cl(2)](2) is dimeric with a distorted octahedral coordination geometry and a tridentate 1. Hg(1)Cl(2) is comprised of pairs of loosely associated monomers and Zn(1)Cl(2) is monomeric. In addition, Hg(2)(1)Cl(4) is formed with alternating chloride and thioether bridges. The distorted square pyramidal Hg(II) centers result in a supramolecular zigzagging chain in the solid state. The solution (1)H NMR spectra of [Hg(1)(2)](2+) and [Hg(1)(NCCH(3))(x)()](2+) reveal (3)(-)(5)J((199)Hg(1)H) due to slow ligand exchange found in these thioether complexes. Implications for use of Hg(II) as a metallobioprobe are discussed.     

Blue-emitting platinum(II) complexes bearing both pyridylpyrazolate chelate and bridging pyrazolate ligands: synthesis, structures, and photophysical properties

A new Pt(II) dichloride complex [Pt(fppzH)Cl2] (1), in which fppzH = 3-(trifluoromethyl)-5-(2-pyridyl)pyrazole, was prepared by the treatment of a pyridylpyrazole chelate fppzH with K2PtCl4 in aqueous HCl solution. Complex 1 could further react with its parent pyrazole (pzH), 3,5-dimethylpyrazole (dmpzH), or 3,5-di-tert-butylpyrazole (dbpzH) to afford the monometallic [Pt(fppz)(pzH)Cl] (2), [Pt(fppz)(dmpzH)Cl] (3), [Pt(fppz)(dmpzH)2]Cl (4), or two structural isomers with formula [Pt(fppz)(dbpzH)Cl] (5a,b). Single-crystal X-ray diffraction studies of 2, 4, and 5a,b revealed a square planar Pt(II) framework, among which a strong interligand hydrogen bonding occurred between fppz and pzH ligands in 2. This interligand H-bonding is replaced by dual N-H...Cl interaction in 4 and both intermolecular N-H...O (with THF solvate) and N-H...Cl interaction in 5a,b, respectively; the latter are attributed to the bulky tert-butyl substituents that force the dbpzH ligand to adopt the perpendicular arrangement. Furthermore, complex 2 underwent rapid deprotonation in basic media to afford two isomeric complexes with formula [Pt(fppz)(mu-pz)]2 (6a,b), which are related to each other according to the spatial orientation of the fppz chelates, i.e., trans- and cis-isomerism. Similar reaction exerted on 3 afforded isomers 7a,b. Both 6a,b (7a,b) are essentially nonemissive in room-temperature fluid state but afford strong blue phosphorescence in solid state prepared via either vacuum-deposited thin film or 77 K CH2Cl2 matrix. As also supported by the computational approaches, the nature of emission has been assigned to be ligand-centered triplet pipi* mixed with certain metal-to-ligand charge-transfer character.     

Syntheses,structures, and fluxionality of blue luminescent zinc(II) complexes: Zn(2,2',2"-tpa)Cl2, Zn(2,2',2"-tpa)2(O2CCF3)2, and Zn(2,2',3"-tpa)4(O2CCF3)2 (tpa = tripyridylamine)

Three novel Zn(II) complexes containing either 2,2',2"-tripyridylamine (2,2',2"-tpa) or 2,2',3"-tripyridylamine (2,2',3"-tpa) have been synthesized and structurally characterized. Compound 1, Zn(2,2',2"-tpa)Cl2, has a tetrahedral geometry while compounds 2, Zn(2,2',2"-tpa)2(O2CCF3)2, and 3, Zn(2,2',3"-tpa)4(O2CCF3)2, have an octahedral geometry. The 2,2',2"-tpa ligand in 1 and 2 functions as a bidentate ligand, chelating to the zinc center, while the 2,2",3"-tpa ligand in 3 functions as a terminal ligand, binding to the zinc center through the 3-pyridyl nitrogen atom. All three compounds emit a blue color in solution and in the solid state. The emission maxima for the three compounds in solution are at lambda = 422, 426, and 432 nm, respectively. The blue luminescence of the complexes is due to a pi *-->pi transition of the tpa ligand as established by an ab initio calculation on the free ligand 2,2',2"-tpa and complex 1. Compounds 1 and 2 are fluxional in solution owing to an exchange process between the coordinate and noncoordinate 2-pyridyl rings of the 2,2',2"-tpa ligand. Compound 2 is also fluxional owing to a cis-trans isomerization process, as determined by variable-temperature 1H NMR spectroscopic analysis.     

Room-temperature emission from platinum(II) complexes intercalated into zirconium phosphate-layered materials

The direct ion exchange of chloro(2,6-bis(N-methylbenzimidazol-2-yl)pyridine)platinum(II) ([Pt(Me(2)bzimpy)Cl]+) and chloro(2,2':6',2' '-terpyridine)platinum(II) ([Pt(tpy)Cl]+) complexes within a zirconium phosphate (ZrP) framework has been accomplished. The physical and spectroscopic properties of [Pt(Me(2)bzimpy)Cl]+ and [Pt(tpy)Cl]+ intercalated in ZrP were investigated by X-ray powder diffraction and X-ray photoelectron, infrared, absorption, and luminescence spectroscopies. In contrast to unintercalated complexes in fluid solution, which do not emit at room temperature, both intercalated materials in the solid state and in colloidal suspensions exhibit intense emissions at room temperature. A [Pt(Me(2)bzimpy)Cl]+-exchanged ZrP colloidal methanol suspension gives rise to an emission at 612 nm that originates from a lowest (3)MMLCT[dsigma*(Pt) --> pi*(tpy)] state (MMLCT = metal-metal-to-ligand charge transfer) characteristic of strong Pt...Pt interactions. A [Pt(tpy)Cl]+-exchanged ZrP colloidal aqueous suspension exhibits a strong emission band at 600 nm. The accumulated data demonstrate that at high concentrations, [Pt(Me(2)bzimpy)Cl]+ and [Pt(tpy)Cl]+ ions can serve as luminescent pillars inside the ZrP framework.     

Syntheses, characterization, and luminescence of Pt II-M I (M = Cu, Ag, Au) heterometallic complexes by incorporating Pt(diimine)(dithiolate) with [M2(dppm)2]2+ (dppm = Bis(diphenylphosphino)methane)

Reaction of Pt(diimine)(edt) (edt = 1,2-ethanedithiolate) with M(2)(dppm)(2)(MeCN)(2)(2+) (dppm = bis(diphenylphosphino)methane) gave heterotrinuclear complexes [PtCu(2)(edt)(mu-SH)(dppm)(3)](ClO(4)) (11) and [PtCu(2)(diimine)(2)(edt)(dppm)(2)](ClO(4))(2) (diimine = 2,2'-bpyridine (bpy), 12; 4,4'-dibutyl-2,2'-bipyridine (dbbpy), 13; phenanthroline (phen), 14; 5-bromophenanthroline (brphen), 15) when M = Cu(I). The reaction, however, afforded tetra- and trinuclear complexes [Pt(2)Ag(2)(edt)(2)(dppm)(2)](SbF(6))(2) (17) and [PtAu(2)(edt)(dppm)(2)](SbF(6))(2) (21) when M = Ag(I) and Au(I), respectively. The complexes were characterized by elemental analyses, electrospray mass spectroscopy, (1)H and (31)P NMR, IR, and UV-vis spectrometry, and X-ray crystallography for 14, 17, and 18. The Pt(II)Cu(I)(2) heterotrinuclear complexes 11-15 exhibit photoluminescence in the solid states at 298 K and in the frozen acetonitrile glasses at 77 K. It is likely that the emission originates from a ligand-to-metal charge transfer (dithiolate-to-Pt) (3)[p(S) --> d(Pt)] transition for 11 and from an admixture of (3)[d(Cu)/p(S)-pi(diimine)] transitions for 12-16. The Pt(II)(2)Ag(I)(2) heterotetranuclear complexes 17 and 18 are nonemissive in the solid states and in solutions at 298 K but show photoluminescence at 77 K. The Pt(II)Au(I)(2) heterotrinuclear complexes 19-21, however, are luminescent at room temperature in the solid state and in solution. Compounds 19 and 20 afford negative solvatochromism associated with a charge transfer from an orbital of a mixed metal/dithiolate character to a diimine pi orbital.     

Synthesis, structural characterization, and photophysical properties of palladium and platinum(II) complexes containing 7,8-benzoquinolinate and various phosphine ligands

A series of mononuclear cyclometalated benzo[h]quinolinate platinum and palladium(II) complexes with phosphine ligands, namely, [M(bzq)ClL] (L=PPh2H, Pt 1, Pd 2; PPh2CCPh, Pt 3, Pd 4), [Pt(bzq)(PPh2H)(PPh2CCPh)]ClO4 5, [Pt(bzq)(PPh2C(Ph)=C(H)PPh2)]ClO4 6, and [Pt(bzq)(CCPh)(PPh2CCPh)] (7a, 7b), were synthesized. The X-ray crystal structures of 1, 6.CH3COCH3.1/2CH3(CH2)4CH3, and 7b.CH3COCH3 have been determined. In 1, the metalated carbon atom and the P atom are mutually cis, whereas in 7b they are trans located. For complex 6, C and N are crystallographically indistinguishable. Reaction of [Pt(bzq)(mu-Cl)]2 with PPh2H and excess of NEt3 leads to the phosphide-bridge platinum dimer [Pt(bzq)(mu-PPh2)]2 8 (X-ray). Moderate pi-pi intermolecular interactions and no evident Pt-Pt interactions are found in 1, 7b, and in 8. All of the complexes exhibit absorption bands at high energy due to the intraligand transitions (1IL pi --> pi) and absorptions at lower energy which are attributed to MLCT (5d) pi --> pi (CLambdaN) transition. Platinum complexes show strong luminescence in both solid state and frozen solutions. The influence of the coligands on the photophysics of the platinum complexes has been examined by absorption and emission spectroscopy.     

Luminescent amidate-bridged one-dimensional platinum(II)-thallium(I) coordination polymers assembled via metallophilic attraction

The neutral square-planar complexes [Pt(RNH2)2(NHCO(t)Bu)2] (R = H, 1; Et, 2) and [Pt(DACH)(NHCO(t)Bu)2] (DACH = 1,2-diaminocyclohexane, 3) act as metalloligands and make bonds to closed-shell Tl(I) ions to afford one- and two-dimensional platinum-thallium oligomers or polymers based on heterobimetallic backbones. A series of heteronuclear platinum(II)-thallium(I) complexes have been synthesized and structurally characterized. The structures of the Pt-Tl compounds resulted from [Pt(RNH2)2(NHCO(t)Bu)2] and TlX [X = NO3(-), ClO4(-), PF6(-), and Cp2Fe(CO2)2(2-)] are dependent on both counteranions and the amine substituents. The compounds [Pt(NH3)2(NHCO(t)Bu)2Tl]X (X = NO3(-), 8; ClO4(-), 9) adopt one-dimensional zigzag chain structures consisting of repeatedly stacked [Pt(NH3)2(NHCO(t)Bu)2Tl]+ units, whereas [{Pt(NH3)2(NHCO(t)Bu)2}2Tl2]X2 (X = PF6(-), 10) consists of a helical chain. Compound 3 reacts with Tl+ to give [{Pt(DACH)(NHCO(t)Bu)2}2Tl](NO3) x [Pt(DACH)(NHCO(t)Bu)2] x 3 H2O (14) and one-dimensional polymeric [{Pt(DACH)(NHCO(t)Bu)2}2Tl2]X2 (X = ClO4(-), 15; PF6(-), 16). Reactions of [Pt(DACH)(NHCOCH3)2] with Tl+ ions afford one-dimensional coordination polymers [{Pt(DACH)(NHCOCH3)2}2Tl2]X2 (X = NO3(-), 17; ClO4(-), 18; PF6(-), 19). The polymeric [{Pt(DACH)(NHCOR')2}2Tl2]2+ (R = CH3, (t)Bu) complexes adopt helical structures, which are generated around the crystallographic 2(1) screw axis. The distance between the coils corresponds to the unit cell length, which ranges from 22.58 to 22.68 A. The platinum-thallium bond distances fall in a narrow range around 3.0 A. The complexes derived from [Pt(NH3)2(NHCO(t)Bu)2] are luminescent at 77 K. The trinuclear complexes [{Pt(RNH2)(NHCO(t)Bu)2}2Tl]+ do not emit at room temperature but are emissive at 77 K, whereas the polymeric platinum-thallium complexes containing 1,2-diaminocyclohexane are intensively luminescent at both room temperature and 77 K. The color variations are interesting; 15 exhibits intense yellow-green, 16 exhibits green, and 17-19 exhibit blue luminescence. The presence of bonding between platinum and thallium is supported by the short metal-metal separations and the strong low-energy luminescence of these compounds in their solid states.     

Importance of platinum(II)-assisted platinum(IV) substitution for the oxidation of guanosine derivatives by platinum(IV) complexes

Guanosine derivatives with a nucleophilic group at the 5' position (G-5') are oxidized by the Pt (IV) complex Pt( d, l)(1,2-(NH 2) 2C 6H 10)Cl 4 ([Pt (IV)(dach)Cl 4]). The overall redox reaction is autocatalytic, consisting of the Pt (II)-catalyzed Pt (IV) substitution and two-electron transfer between Pt (IV) and the bound G-5'. In this paper, we extend the study to improve understanding of the redox reaction, particularly the substitution step. The [Pt (II)(NH 3) 2(CBDCA-O,O')] (CBDCA = cyclobutane-1,1-dicarboxylate) complex effectively accelerates the reactions of [Pt (IV)(dach)Cl 4] with 5'-dGMP and with cGMP, indicating that the Pt (II) complex does not need to be a Pt (IV) analogue to accelerate the substitution. Liquid chromatography/mass spectroscopy (LC/MS) analysis showed that the [Pt (IV)(dach)Cl 4]/[Pt (II)(NH 3) 2(CBDCA-O,O')]/cGMP reaction mixture contained two Pt (IV)cGMP adducts, [Pt (IV)(NH 3) 2(cGMP)(Cl)(CBDCA-O,O')] and [Pt (IV)(dach)(cGMP)Cl 3]. The LC/MS studies also indicated that the trans, cis-[Pt (IV)(dach)( (37)Cl) 2( (35)Cl) 2]/[Pt (II)(en)( (35)Cl) 2]/9-EtG mixture contained two Pt (IV)-9-EtG adducts, [Pt (IV)(en)(9-EtG)( (37)Cl)( (35)Cl) 2] and [Pt (IV)(dach)(9-EtG)( (37)Cl)( (35)Cl) 2]. These Pt (IV)G products are predicted by the Basolo-Pearson (BP) Pt (II)-catalyzed Pt (IV)-substitution scheme. The substitution can be envisioned as an oxidative addition reaction of the planar Pt (II) complex where the entering ligand G and the chloro ligand from the axial position of the Pt (IV) complex are added to Pt (II) in the axial positions. From the point of view of reactant Pt (IV), an axial chloro ligand is thought to be substituted by the entering ligand G. The Pt (IV) complexes without halo axial ligands such as trans, cis-[Pt(en)(OH) 2Cl 2], trans, cis-[Pt(en)(OCOCF 3) 2Cl 2], and cis, trans, cis-[Pt(NH 3)(C 6H 11NH 2)(OCOCH 3) 2Cl 2] ([Pt (IV)(a,cha)(OCOCH 3) 2Cl 2], satraplatin) did not react with 5'-dGMP. The bromo complex, [Pt (IV)(en)Br 4], showed a significantly faster substitution rate than the chloro complexes, [Pt (IV)(en)Cl 4] and [Pt (IV)(dach)Cl 4]. The results indicate that the axial halo ligands are essential for substitution and the Pt (IV) complexes with larger axial halo ligands have faster rates. When the Pt (IV) complexes with different carrier ligands were compared, the substitution rates increased in the order [Pt (IV)(dach)Cl 4] < [Pt (IV)(en)Cl 4] < [Pt (IV)(NH 3) 2Cl 4], which is in reverse order to the carrier ligand size. These axial and carrier ligand effects on the substitution rates are consistent with the BP mechanism. Larger axial halo ligands can form a better bridging ligand, which facilitates the electron-transfer process from the Pt (II) to Pt (IV) center. Smaller carrier ligands exert less steric hindrance for the bridge formation.     

Probing the electronic communication of the isocyanide bridge through the luminescence properties of the d9-d9 [ClPt(mu-dppm)2Pt(C triple bond N-PCP)]+ and A-Frame [ClPd(mu-dppm)2(mu-C=N-PCP)PdCl] complexes

The homodinuclear d9-d9 ClM(mu-dppm)2MCl2 complexes, 1 (M ) Pt) and 2 (M ) Pd) react with the conjugated and luminescent PCP-NC ligand (3, PCP ) [2.2]paracyclophane) to provide the corresponding d9-d9 terminal[ClPt(mu-dppm)2Pt(CNsPCP)]Cl (4) and d8-d8 A-frame [ClPd(mu-dppm)2(mu-CdNsPCP)PdCl] (5) isocyanide complexes, respectively. These two bimetallic complexes were characterized by IR, 1H, and 31P{1H} NMR and bychemical analysis. IR data (nu(CN) bridging vs terminal) reveal a terminal isocyanide bonding mode for 4 (2147cm(-1)) and an A-frame structure for 5 (1616 cm(-1)). The optical and emission properties of the free isocyanide 3as well as those of the homodinuclear complexes 4 and 5 were studied by UV-visible and luminescence spectroscopy and by photophysical measurements. The unexpected presence of simultaneous intraligand pipi* fluorescence and phosphorescence attributable to the organic PCP-NC ligand, as well as luminescence from the inorganic M2-bonded Pt2(mu-dppm)2 center arising from a lower energy excited LMCT state (ligand-to-metal-charge-transfer) for4 at 77 K, indicates a weak conjugation between the two chromophores and an absence of efficient singlet andtriplet energy transfers. For 5, only the fluorescence and phosphorescence bands of the PCP-NC ligand are observed [since the A-frame XPd(mu-dppm)2(mu-L)PdX (L ) isocyanide, X ) halide) is not luminescent], stressing that the NtC bridge exhibits modest electronic communication properties.     

Sensitised near-infrared luminescence from lanthanide(III) centres using Re(I) and Pt(II) diimine complexes as energy donors in d-f dinuclear complexes based on 2,3-bis(2-pyridyl)pyrazine

The luminescent transition metal complexes [Re(CO)(3)Cl(bppz)] and [Pt(CC-C(6)H(4)CF(3))(2)(bppz)] [bppz = 2,3-bis(2-pyridyl)pyrazine], in which one of the diimine binding sites of the potentially bridging ligand bppz is vacant, have been used as 'complex ligands' to make heterodinuclear d-f complexes by attachment of a {Ln(dik)(3)} fragment (dik = a 1,3-diketonate) at the vacant site. When Ln = Pr, Nd, Er or Yb the lanthanide centre has low-energy f-f excited states capable of accepting energy from the (3)MLCT excited state of the Pt(II) or Re(I) centre, quenching the (3)MLCT luminescence and affording sensitised lanthanide(III)-based luminescence in the near-IR region. UV/Vis and luminescence spectroscopic titrations allowed measurement of (i) the association constants for binding of the {Ln(dik)(3)} fragment at the vacant diimine site of [Re(CO)(3)Cl(bppz)] or [Pt(CC-C(6)H(4)CF(3))(2)(bppz)], and (ii) the degree of quenching of the (3)MLCT luminescence according to the nature of the Ln(III) centre. In all cases Nd(III) was found to be the most effective of the series at quenching the (3)MLCT luminescence of the d-block component because the high density of f-f excited states of the appropriate energy make it a particularly effective energy-acceptor.     

Luminescent alkynylplatinum(II) complexes of 2,6-bis(N-alkylbenzimidazol-2'-yl)pyridine-type ligands with ready tunability of the nature of the emissive states by solvent and electronic property modulation

A new class of luminescent alkynylplatinum(II) complexes of tridentate bis(N-alkylbenzimidazol-2'-yl)pyridines (bzimpy), [Pt(R,R'-bzimpy)(C[triple chemical bond]C-R')]X (X=PF(6), OTf), and one of their chloro precursor complexes, [Pt(R,R'-bzimpy)Cl]PF(6), have been synthesized and characterized; one of the alkynyl complexes has also been structurally characterized by X-ray crystallography. Electrochemical studies showed that the oxidation wave is alkynyl ligand-based in nature with some mixing of the metal center-based contribution, whereas the two quasi-reversible reduction couples are mainly bzimpy-based reductions. The electronic absorption and luminescence properties of the complexes have also been investigated. In solution, the high-energy and intense absorption bands are assigned as the pi-pi* intraligand (IL) transitions of the bzimpy and alkynyl ligands, whereas the low-energy and moderately intense absorptions are assigned to an admixture of metal-to-ligand charge-transfer (MLCT) (dpi(Pt)-->pi*(R,R'-bzimpy)) and ligand-to-ligand charge-transfer (LLCT) (pi(C[triple chemical bond]C-R')-->pi*(R,R'-bzimpy)) transitions. Upon variation of the electronic effects of the arylalkynyl ligands, vibronic-structured or structureless emission bands, originating from triplet metal-perturbed intraligand (IL) or an admixture of triplet metal-to-ligand charge-transfer (MLCT) and ligand-to-ligand charge-transfer (LLCT) excited states respectively, were observed in solution. Interestingly, two of the complexes showed a dual luminescence that was sensitive to the polarity of the solvents. Upon cooling from 298 K to 155 K, drastic color, UV/Vis, and luminescence changes were observed in a butyronitrile solution of 1, and were ascribed to the formation of aggregate species through PtPt and pi-pi stacking interactions. DFT and time-dependent DFT (TD-DFT) calculations have been performed to verify and elucidate the results of the electrochemical and photophysical properties.     

Synthesis, structure, and photophysical properties of luminescent platinum(II) complexes containing cyclometalated 4-styryl-functionalized 2-phenylpyridine ligands

A series of new luminescent cyclometalated platinum(II) complexes functionalized with various substituted styryl groups on the cyclometallating ligand [Pt(C/\N-ppy-4-styryl-R)(O/\O-(O)CCR'CHCR'C(O))] (ppy-4-styryl-R = E-4(4-(R)styryl-2-phenylpyridine) (3, R' = Me (acac); 4, R' = (t)Bu (dpm); R = H, OMe, NEt2, NO2) have been prepared. All complexes undergo an E-Z photoisomerization process in CH2Cl2 solution under sunlight, as monitored by 1H NMR. The solid-state structures of 3-OMe, 3-NEt2, 3-NO2, and 4-OMe have been determined by X-ray diffraction studies and compare well with optimized geometries obtained by density functional theory (DFT) calculations. The orbital pictures of 3-H, 3-OMe, and 3-NO 2 are very similar, the highest occupied molecular orbital (HOMO) being highly Pt(5d) metal-based. For 3-NMe2, an additional contribution from the amino-styryl fragment leads to a decreased metal parentage of the HOMO, suggesting a predominantly ILCT character transition. Complexes 3-H, 3-OMe, and 3-NO2 show a low-energy band (350-400 nm) assigned to predominantly charge-transfer transitions. The amino derivative 3-NEt2 displays a very strong absorption band at 432 nm, tentatively assigned to a mixture of ILCT (Et2N --> CH=CH) and metal-to-ligand charge-transfer (MLCT) (dpi(Pt) --> pi) transitions. Complexes 3 are weakly luminescent in CH2Cl2 solution at room temperature; the low intensity may be due to a competitive quenching through the E-Z photoisomerization process. All complexes exhibit similar structured emission bands under these conditions (around 520 nm), independent of the nature of the styryl-R group. In a frozen EPA glass (77 K), the spectrum of the representative complex 3-H exhibits two sets of vibronically structured bands (460-560, 570-800 nm; lambda(max) = 596 nm), due to the presence of two emitting species, the E and Z isomers, which have significantly different triplet excited-state energies. The other three complexes show similar behavior to 3-H at 77 K, but the lower-energy emission bands are progressively red-shifted in the order H < OMe < NO2 < NEt2 (e.g., for 3-NEt2, lambda(max)(em) = 658 nm; tau = 26 micros). The very large red-shift compared to related unsubstituted complexes (e.g., to [Pt(C/\N-ppy)(O/\O-acac)]) is the result of the extension of the pi-conjugated system and the electronic effects of substituent R.     

Structural, spectroscopic and thermal characterization of 2-tert-butylaminomethylpyridine-6-carboxylic acid methylester and its Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and UO(2)(II) complexes

Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and UO(2)(II) complexes with the ligand 2-tert-butylaminomethylpyridine-6-carboxylic acid methylester (HL(2)) have been prepared and characterized by elemental analyses, molar conductance, magnetic moment, thermal analysis and spectral data. 1:1 M:HL(2) complexes, with the general formula [M(HL(2))X(2)].nH(2)O (where M = Co(II) (X = Cl, n = 0), Ni(II) (X = Cl, n = 3), Cu(II) (grey colour, X = AcO, n = 1), Cu(II) (yellow colour, X = Cl, n = 0) and Zn(II) (X = Br, n = 0). In addition, the Fe(III) and UO(2)(II) complexes of the type 1:2 M:HL(2) and with the formulae [Fe(L(2))(2)]Cl and [UO(2)(HL(2))(2)](NO(3))(2) are prepared. From the IR data, it is seen that HL(2) ligand behaves as a terdentate ligand coordinated to the metal ions via the pyridyl N, carboxylate O and protonated NH group; except the Fe(III) complex, it coordinates via the deprotonated NH group. This is supported by the molar conductance data, which show that all the complexes are non-electrolytes, while the Fe(III) and UO(2)(II) complexes are 1:1 electrolytes. IR and H1-NMR spectral studies suggest a similar behaviour of the Zn(II) complex in solid and solution states. From the solid reflectance spectral data and magnetic moment measurements, the complexes have a trigonal bipyramidal (Co(II), Ni(II), Cu(II) and Zn(II) complexes) and octahedral (Fe(III), UO(2)(II) complexes) geometrical structures. The thermal behaviour of the complexes is studied and the different dynamic parameters are calculated applying Coats-Redfern equation.     

Crystal structures and solution behaviors of dinuclear d(10)-metal complexes containing anions of N,N'-bis(pyrimidine-2-yl)formamidine

The salts of Zn(II), Cd(ii) and Hg(II) react instantaneously with Kpmf (pmf(-) = anion of N,N'-bis(pyrimidine-2-yl)formamidine, Hpmf) in THF, producing bimetallic complexes of the types [M(2)(pmf)(3)](X) (M = Zn(II), X = I(3)(-), ; M = Zn(II), X = NO(3)(-), ; M = Zn(II), X = ClO(4)(-), ; M = Cd(II), X = NO(3)(-), ; M = Cd(II), X = ClO(4)(-), ) and Hg(2)(pmf)(2)X(2) (X = Cl, ; Br, ; I, ). New tridentate and tetradentate coordination modes were observed for the pmf(-) ligands and their fluxional behaviors investigated by measuring variable-temperature (1)H NMR spectra. Complexes and , which possess only tetradentate coordination modes for the pmf(-) ligands in the solid state show larger free energy of activation (DeltaG(c)( not equal)) for the exchange than complexes and with tetradentate and/or tridentate coordination modes. Complexes and are the first dinuclear Zn(II) and Hg(II) complexes containing formamidinate ligands. Moreover, the separation between the two Hg(II) atoms are 3.4689(9), 3.4933(13) and 3.5320(10) A for complexes , respectively, similar to the sum of van der Waals radii of two Hg(II) atoms which is 3.50(7) A. All the complexes exhibit emissions and the nature of the anions hardly change the emission wavelengths of the complexes with the same metal centers. The emission bands may be tentatively assigned as intraligand (IL) pi-->pi* transitions.     

Luminescent charge-transfer platinum(II) metallacycle

The photophysical and electrochemical properties of a platinum(II) diimine complex bearing the bidentate diacetylide ligand tolan-2,2'-diacetylide (tda), Pt(dbbpy)(tda) [dbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine] (1), are compared with two reference compounds, Pt(dbbpy)(C[triple bond]CPh)(2) (2) and Pt(dppp)tda [dppp = 1,3-bis(diphenylphosphino)propane] (3), respectively. The X-ray crystal structure of 1 is reported, which illustrates the nearly perfect square planarity exhibited by this metallacycle. Chromophore 2 possesses low-lying charge-transfer excited states analogous to 1, whereas structure 3 lacks such excited states but features a low-lying platinum-perturbed tda intraligand triplet manifold. In CH(2)Cl(2), 1 exhibits a broad emission centered at 562 nm at ambient temperature, similar to 2, but with a higher photoluminescence quantum yield and longer excited-state lifetime. In both instances, the photoluminescence is consistent with triplet-charge-transfer excited-state parentage. The rigidity imposed by the cyclic diacetylide ligand in 1 leads to a reduction in nonradiative decay, which enhances its room-temperature photophysical properties. By comparison, 3 radiates highly structured tda-localized triplet-state phosphorescence at room temperature. The 77 K emission spectrum of 1 in 4:1 EtOH/MeOH becomes structured and is quantitatively similar to that measured for 3 under the same conditions. Because the 77 K spectra are nearly identical, the emissions are assigned as (3)tda in nature, implying that the charge-transfer states are raised in energy, relative to the (3)tda levels in 1 in the low-temperature glass. Nanosecond transient absorption spectrometry and ultrafast difference spectra were determined for 1-3 in CH(2)Cl(2) and DMF at ambient temperature. In 1 and 2, the major absorption transients are consistent with the one-electron reduced complexes, corroborated by reductive spectroelectrochemical measurements performed at room temperature. As 3 does not possess any charge-transfer character, excitation into the pipi* transitions of the tda ligand generated transient absorptions in the relaxed excited state assigned to the ligand-localized triplet state. In all three cases, the excited-state lifetimes measured by transient absorption are similar to those measured by time-resolved photoluminescence, suggesting that the same excited states giving rise to the photoluminescence are responsible for the absorption transients. ESR spectroscopy of the anions 1- and 2- and reductive spectroelectrochemistry of 1 and 2 revealed a LUMO based largely on the pi* orbital of the dbbpy ligand. Time-dependent density functional theory calculations performed on 1-3 both in vacuum and in a CH(2)Cl(2) continuum revealed the molecular orbitals, energies, dipole moments, and oscillator strengths for the various electronic transitions in these molecules. A DeltaSCF-method-derived shift applied to the calculated transition energies in the solvent continuum yielded good agreement between theory and experiment for each molecule in this study.