Showing papers in "Inorganic Chemistry in 1995"

Electronic Spectroscopy of Chloro(terpyridine)platinum(II)

Abstract: The electronic spectrum of [Pt(tpy)Cl]^+ (tpy = 2,2':6',2"-terpyridine) is influenced dramatically by intermolecular stacking interactions in solution and in the solid state. The crystal structure of [Pt(tpy)Cl]ClO_4 (monoclinic, P2_1/c (No. 14); a = 7.085(2), b = 17.064(5), c = 26.905(8) A; β = 90.0(1) °; Z = 8) consists of discrete Pt_2 units (Pt-Pt = 3.269(1) A) arranged along an infinite tpy-π stack (spacing ~ 3.35 A). Variable-temperature and concentration studies of the absorption and emission spectra of [Pt(tpy)Cl]^+ suggest that similar metal-metal and ligand-ligand interactions persist in the solution phase. The high concentration, low-temperature emission spectrum (5:5:1 ethanol:methanol:DMF) reveals a 740-nm band indicative of M-M oligomerization, a 650-nm band attributable to tpy π-π interactions, and a 470-nm band characteristic of mononuclear [Pt(tpy)Cl]^+ π-π* emission. Concentration-dependent absorption spectra were fit to a "two-dimer" model, yielding equilibrium constants for the formation of Pt-Pt-, and tpy-tpy-bound dimers of 1.3(1) x 10^3 and 1.0(1) x 10^3 M^(-1), respectively, in 0.1 M aqueous NaCl. The low temperature solid-state luminescence of [Pt(tpy)Cl]^+ is assigned to a ^3(MMLCT) (MMLCT = metal-metal-to-ligand charge transfer) transition. The energy of this band is highly dependent on the counterion (PF_6^-, ClO_4^- , C1^-, CF_3SO_3^-), in line with the different colors of these various salts. In contrast, the room-temperature solid-state emission spectra are more difficult to interpret. While the red perchlorate salt exhibits a relatively narrow emission band at 725 nm (red-shifted from the 77-K maximum at 695 nm), consistent with a 3(MMLCT) transition, the orange (Cl^-, ClO_4^-, CF_3SO_3^-) and yellow (PF6^-) salts have extremely broad room-temperature emission bands that all appear at nearly the same energy (λ_(max) ~ 640 nm). We assign this luminescence to an eximeric intraligand transition resulting from π- π interactions and propose that the temperature dependent emissions from the orange and yellow solid materials originate from multiple electronic states.

Carboxylation of Kinetically Inert Platinum(IV) Hydroxy Complexes. An Entr.acte.ee into Orally Active Platinum(IV) Antitumor Agents.

Abstract: Carboxylation of hydroxide coordinated to Pt(1V) by anhydrides, pyrocarbonates, and isocyanates to form the corresponding Pt(1V) carboxylates, carbonates, and carbamates is described. For example, the acylation with acetic anhydride of (OC-6-33)-amminedichloro(cyclohexanamine)dihydroxyplatinum(IV) leads to formation of (OC-6-43)-bis(acetato-O)amminedichloro(cyclohexanamine)platinum(IV) (JM-216) in 60% yield. This compound is currently in worldwide clinical trials as an orally active antitumor agent. Pt(1V) dicarbonates and dicarbamates are prepared similarly by reaction of a Pt(1V) hydroxide with a pyrocarbonate or isocyanate. The carboxylation reaction can be used to prepare molecules containing ligands with pendant functional groups that would be difficult to introduce by substitution reactions. Thus (OC-6-43)-amminedic~oro(cyclohexanamine)bis((methylthio)acetatoO)platinum(IV) was prepared, which was oxidized to the corresponding sulfoxide (OC-6-43)-amminedichloro(cyclohexanamine)bis( methylsulfiiy1)acetato-O)platinum(IV). Finally, unsymmetrical carboxylate complexes may be obtained by reaction of a binary mixture of two electrophiles with a Pt(IV) hydroxide followed by chromatographic separation of the carboxylation products. A simplified synthesis of the K[PtnC13NH3] in 55% yield from cisplatin is also reported. This improves tHe availability of molecules of the general formula cis-PtnC12AA’ (A, A’ = ammine, amine) which are critical intermediates in the multistep synthesis of the Pt(IV) carboxylates having antitumor activity.

Designed Synthesis of Mononuclear Tris(heteroleptic) Ruthenium Complexes Containing Bidentate Polypyridyl Ligands

Abstract: A general synthetic methodology is reported for tris(bidentate)ruthenium(II) complexes containing three different polypyridyl ligands, based on the sequential addition of the ligands to the oligomer [Ru(CO)₂Cl₂](subscript n). The tris(heteroleptic) complexes were characterized by FAB mass spectrometry and NMR spectroscopy. An X-ray crystal structure determination was made for the complex, [Ru(Me₂bpy)(phen)(bpa)](PF₆)₂. C₆H₁₄·[C₄ₒH₄₃F₁₂N₇P₂Ru, M = 1062.8; Me(2)bpy = 4,4'-dimethyl-2,2'-bipyridine, phen = 1,10-phenanthroline, bpa = bis(2-pyridyl)amine]: triclinic, space group

Influence of electronic delocalization in metal-to-ligand charge transfer excited states

Abstract: In the metal-to-ligand-charge transfer (MLCT) excited states of the ligand-bridged complexes [(dmb){sub 2}Ru({mu}-bbpe)-Ru(dmb){sub 2}](PF{sub 6}){sub 4} and [(bpy){sub 2}Os({mu}-bbpe)Os(bpy){sub 2}](PF{sub 6}){sub 4} (bpy is 2,2{prime}-bipyridine, dmb is 4,4{prime}-dimethyl-2,2{prime}-bipyridine, bbpe is trans-1,2-bis-(4-(4{prime}-methyl)-2,2{prime}bipyridyl)ethene) bbpe acts as the acceptor ligand. This conclusion is based on transient UV-visible and resonance Raman measurements, which also reveal that the excited electron in the Ru complex is localized over the bbpe ligand. Compared to related complexes having comparable energy gaps, the lifetimes of [(dmb){sub 2}Ru({mu}-bbpe)Ru(dmb){sub 2}]{sup 4+*} ({tau} = 1.31 {mu}s in CH{sub 3}CN at 298 K) and [(dmb){sub 2}Ru(bbpe)]{sup 2+*} ({tau} = 1.15 {mu}s in CH{sub 3}CN at 298 K) are unusually long. The extended lifetimes are a delocalization effect caused by decreased bond displacement changes in the excited state. This decreases vibrational overlap between states, and the rate constant for nonradiative decay. Delocalization disperses the excited electron over the molecular framework of the acceptor ligand, decreasing changes in local bond displacements compared to bpy. These results have important implications for the design of complexes which are broad visible light absorbers and yet retain accessible excited state lifetimes.

Molecular structure and magnetic properties of acetato-bridged lanthanide(iii) dimers

Abstract: Structural, magnetic, and EPR studies of diaquatetrakis({mu}-acetato)dicopper(II) have provided important insight into the magnetic interaction phenomenon in polynuclear species involving 3d ions. This compound may be considered at the archetype of the exchange-coupled copper(II) dimers. Until now, no compound of the same nature involving lanthanide(III) ions had been reported, and the factors determining the sign and the magnitude of the magnetic interaction between lanthanide(III) ions are far from being well understood. Herein the authors report on the synthesis, the structure and the magnetic properties of two lanthanide(III) dimers, namely [Ln{sub 2}(CH{sub 3}CO{sub 2}){sub 6-} (phen){sub 2}] with phen = o-phenanthroline and Ln = Ce (1) and Gd (2).

Multinuclear nmr, raman, exafs, and x-ray-diffraction studies of uranyl carbonate complexes in near-neutral aqueous-solution - x-ray structure of c(nh2)(3) (6) (uo2)(3)(co3)(6) center-dot-6.5h(2)o

Abstract: C-13 and O-17 NMR and Raman spectroscopies were used to monitor the fractions of UO2(CO3)(3)(4-) (1) and (UO2)(3)(CO3)(6)(6-) (2) in aqueous carbonate solutions as a function of pH, ionic strength, carbonate concentration, uranium concentration, and temperature. The multinuclear NMR and Raman data are consistent with the formation of (UO2)(3)(CO3)(6)(6-). The pH dependence of the C-13 NMR spectra was used to determine the equilibrium constant for the reaction 3UO(2)(CO3)(3)(4-) + 3H(+) reversible arrow (UO2)(3)(CO3)(6)(6-) + 3HCO(3)(-), log K = 18.1(+/- 0.5) at I-m = 2.5 m and 25 degrees C, and corresponds to log beta(36) = 55.6(+/- 0.5) for the reaction 3UO(2)(2+) + 6CO(3)(2-) reversible arrow (UO2)(3)(CO3)(6)(6-) under the same conditions. Raman spectra showed the uranyl nu(1) stretching band at 831.6 cm(-1) for monomeric 1 and at 812.5 cm(-1) for trimeric (UO2)(3)(CO3)(6)(6-) (2). EXAFS data from solid [C(NH2)(3)](6)[(UO2)(3)(CO3)(6)] and a solution of (UO2)(3)(CO3)(6)(6-) suggest that the same uranium species is present in both the solid and solution states. Fourier transforms of the EXAFS spectra of both solid and solution samples revealed five well-resolved peaks corresponding to nearly identical near-neighbor distances for solid and solution- samples of 2. Fitting of these peaks yields U-O(uranyl) = 1.79, U-O(carbonate) = 2.45, U- -C = 2.90, U- -O(terminal carbonate) = 4.16, and U- -U = 4.91 Angstrom for the solid and similar distances for the solution sample. A peak at 4.75 Angstrom in both Fourier transforms (uncorrected for phase shift) corresponds to a U- -U interaction at 4.91 Angstrom, a conclusion which is supported by the absence of this peak in the Fourier transform of the crystalline monomeric K-4[UO2(CO3)(3)] Multiple scattering along the uranyl vector is believed to play a significant role in the EXAFS of all three systems. The EXAFS data are consistent with the trimeric uranyl carbonate species indicated by NMR spectroscopy. Single crystals of [C(NH2)(3)](6)[(UO2)(3)(CO3)(6)]. 6.5H(2)O were obtained from a solution that contained stoichiometric amounts of uranyl nitrate and guanidinium carbonate and an excess of guanidinium nitrate at pH 6.5 under a CO2 atmosphere. The solid state molecular structure of [C(NH2)(3)](6)[(UO2)(3)(CO3)6]. 6.5H(2)O contains a planar D-3h trimetallic (UO2)(3)(CO3)(6)(6-) anion, the structure that Aberg and co-workers originally proposed for the trimeric solution species. The trimetallic anion contains three uranium atoms and all six carbonate ligands in the molecular plane with three uranyl oxygen atoms above and three below the plane. Uranyl U=O distances average 1.78(1) Angstrom, while U-O distances to the carbonate oxygen atoms average 2.41(1) Angstrom for terminal and 2.48(1) Angstrom for bridging ligands. Particularly significant is the average nonbonding U- -U distance of 4.97 Angstrom which compares favorably to the 4.91 Angstrom distance seen in the EXAFS analysis. The molecule crystallizes in the triclinic space group P ($) over bar 1, with a = 6.941(2) Angstrom, b = 14.488(2) Angstrom, c = 22.374(2) Angstrom, alpha = 95.63(2)degrees, beta = 98.47(2)degrees, gamma = 101.88(2)degrees, R = 0.0555, R(w), = 0.0607, V = 2158.5 Angstrom(3),d(cal), = 2.551 g cm(-3), and Z = 2.

Novel Contrast Agents for Magnetic Resonance Imaging. Synthesis and Characterization of the Ligand BOPTA and Its Ln(III) Complexes (Ln = Gd, La, Lu). X-ray Structure of Disodium (TPS-9-145337286-C-S)-[4-Carboxy-5,8,11-tris(carboxymethyl)-1-phenyl-2-oxa- 5,8,11-triazatridecan-13-oato(5-)]gadolinate(2-) in a Mixture with Its Enantiomer

Abstract: The syntheses of the ligand BOPTA, (4-carboxy-5,8,1 l-tris(carboxymethyl)-l-pheny1-2-oxa-5,8,1 l-triazatridecan13-oic acid; benic acid) and its Gd(III), La(III), and Lu(1U) complexes are reported. Protonation constants for BOPTA have been determined by potentiometry, and the microscopic protonation sequence has been investigated by 'H NMR. The results obtained together with the value of the Gd-BOPTA2- stability constant (log KML = 22.59) show that the complexing properties of the ligand, in comparison with DTPA, are little affected by the presence of the benzyloxymethyl residue in the structure. The solid state structure of Gd-BOPTA disodium salt [C22H2&01 I (H~O)Gd]Na2~/2H20 was determined in a single-crystal X-ray diffraction study. The structure consists of [C22H2a3011(H20)Gdl2- anions, sodium cations, and water molecules; the space group is Pi (Z = 2), with a = 9.083(6) A, b = 9.469(2) A, c = 16.698(6) A, a = 102.22(3)", = 92.48(4)', y = 102.26(3)", V = 1366(1) A3, and d = 1.84 g/mL. The gadolinium ion adopts a nine-coordinate geometry, which is best described as a distorted tricapped trigonal prism. Eight coordinating sites are occupied by the ligand (three nitrogen atoms and five carboxylate oxygens), and the ninth site is occupied by the oxygen atom of a water molecule. Relaxation studies have shown that in solution also Gd-BOPTA2- has one water molecule directly coordinated to the metal ion. 139La NMR studies on the La-BOPTA2- complex have further supported the view that such complexes maintain in solution the same kind of coordination as found in the solid state for Gd-BOPTA disodium salt. I3C NMR spectra of the diamagnetic La- and Lu-BOPTA2- complexes at various temperatures are consistent with the presence of two couples of isomers interconverting through a dynamic process. Such a process has previously been reported for the parent Ln-DTPA2- complexes.

Synthetic, Structural, and Spectroscopic Studies on Solids Containing Tris(dipicolinato) Rare Earth Anions and Transition or Main Group Metal Cations

Abstract: The synthesis and basic characterisation are reported for 85 new solids of the general formula [ML{sub x}][Ln(dipic){sub 3}]{center_dot}nH{sub 2}O (M = Cr or Co; L = urea, ammonia, and various amines; Ln = La-Lu, plus Y; dipic = pyridine-2,6-dicarboxylate). Syntheses of some seven Cs{sub 3}[Ln(dipic){sub 3}] and [N(C{sub 2}H{sub 5}){sub 4}]{sub 3}[Ln(dipic){sub 3}] species are also given. Low-temperature luminescence measurements on a variety of these compounds and full X-ray crystallographic structure determinations for Cs{sub 3}[Eu(dipic){sub 3}]{center_dot}9H{sub 2}O (orthorhombic, space group C222{sub 1}; a = 10.165(2), b = 18.164(4), c = 18.724(4) {angstrom}; Z = 4; R{sub 1} = 0.041 for 1573 {open_quotes}observed{close_quotes} reflections) and [Co(sar)][Eu(dipic){sub 3}]{center_dot}13H{sub 2}O (monoclinic, space group P2{sub 1}/n; a = 10.611(4), b = 26.500(10), c = 17.583(7) {angstrom}; {beta} = 91.97(3){degrees}; Z = 4; R{sub 1} = 0.037 for 7695 {open_quotes}observed{close_quotes} reflections) are described to illustrate the range and complexity of the physical properties of these new materials. Both Cr(III) and Co(III) act as very efficient quenchers of the normally strong [Eu/Tb(dipic){sub 3}]{sup 3{minus}} luminescence, though in at least one system it appears that Cr(III) may act to transfer excitation energy to Ln excited states from its own higher levels while simultaneously deactivating the Ln ionmore » through its lower (doublet) states.« less

Facile Electrophilic Iodination of Icosahedral Carboranes. Synthesis of Carborane Derivatives with Boron-Carbon Bonds via the Palladium-Catalyzed Reaction of Diiodocarboranes with Grignard Reagents

Abstract: Electrophilic diiodination reactions of icosahedral closo1,2-C2B IOHI 2 and closo1,7-C2B IOHI 2 using 2 molar equiv of iodine monochloride in the presence of catalytic amounts of aluminum chloride yielded the corresponding clos0-9,12-12-1,2-C2B10H10 and closo-9,10-I2-1,7-C2B10H10 complexes in excellent yields. Palladium-mediated cross-coupling reactions of these diiodocarboranes with a variety of alkyl, aralkyl, and aryl Grignard reagents were reinvestigated, and it was demonstrated that the addition of copper(1) iodide as a cocatalyst is crucial to the success of this reaction. A reaction mechanism involving the initial formation of binary organocopper species (RCu; R = alkyl, aralkyl, aryl) followed by the reaction of (a-carborany1)palladium iodides (LzPd(Cb1)I and L2Pd(CbR)I; L = PPh3, Cb = c~oso-~ ,~ -C~BIOHIO, closo-1 7-C2BloHlo) via a four-centered transition state is proposed. The molecular structures of closo-9,10-12-1,7-C2B10H10, 1, and C~O~O-~,~~-(C~H~)~-~,~-C~BIOHIO, 10, have been determined. Crystallographic data are as follows: for 1, monoclinic, space group P21lc, a = 13.2719-

A simple method for preparing magnesium porphyrins

Abstract: The authors present a method for the preparation of magnesium tetraarylporphyrins. A field of solvents, metal halides, and prophyrins was considered for reactions near room temperature. It was found that a noncoordinating reaction scheme and a delicate balance of solubilities directed the reaction toward the Mg-porphorinato complexes.

Synthesis, structure, and spectroscopic properties of ortho-metalated platinum(II) complexes

Abstract: The ortho-metalated Pt(II) complexes Pt(ppy)(CO)Cl (1), Pt(ptpy)(CO)Cl (2), and Pt(ppy)(Hppy)Cl (3) (where ppy and ptpy are respectively the ortho-C-deprotonated forms of 2-phenylpyridine and 2-p-tolylpyridine and Hppy is 2-phenylpyridine) have been prepared. The CO ligand is coordinated trans to the nitrogen atom of the ortho-metalated ligand and exerts a strong trans effect resulting in a relatively long Pt-N bond [2.114(19) {angstrom}]. This structure shows both the bidentate ppy ligand and the monodentate Hppy with the nitrogens of these ligands trans to each other. The UV/vis electronic absorption spectra of 1-3 have intense bands in the near-UV region ({approximately}375 nm) which have been assigned as metal to ligand charge transfer (MLCT) transitions, and higher energy bands were assigned as ligand-centered transitions. Each complex exhibits relatively long-lived structured emissions in the solid state at ambient temperature and at 77 K and 77 K glassy toluene solutions. These emissions are proposed to originate from triplet MLCT states. Notably, in solution both the lifetime and spectrum of 2 proved to be a function of the concentration, a phenomenon interpreted in terms of the propensity of square planar d{sup 8} complexes to oligomerize. In contrast, the more sterically hindered complex 3 displayed no such tendency towardmore » oligomerization.« less

When Is an Odd-Electron Dinuclear Complex a Mixed-Valent Species? Tuning of Ligand-to-Metal Spin Shifts in Diruthenium(III,II) Complexes of Noninnocent Bridging Ligands OC(R)NNC(R)O

Abstract: The complexes { (adc-R)[Ru(bpy)z]z}" with bpy = 2,2'-bipyridine and adc-R = azodicarbonyl ligands O=C(R)-N=N-C(R)=O, R = NR'2 (piperidyl), OC~HS, OCH2C&, CH3, C~5,4-C6C however, the EPR spectra observable only below 50 K reveal a strongly substituent(R-) dependent degree of metal contribution to the singly occupied MO. X P S measurements of two 3+ ions which show Ru(I1) and Ru(1II) signals also exhibit a marked substituent effect on the electronic structure. Whereas the 4 f ions formed at rather positive potentials also seem to possess strongly mixed frontier orbitals, the stable 2+ ions clearly contain two Ru(I1) centers and fully reduced, i.e. 1,2-dicarbonylhydrazid0(2-) bridging ligands, [O=C(R)-N-N-C(R)=O]2-. The results are interpreted within a hole vs electron transfer scheme, based on a three-site MO model for the mewmetal communication in ligand-bridged mixed-valent dimers according to which the intermediates { (ad~-R)[Ru(bpy)2]2}~+ are best described as delocalized systems with varying contributions from Ru"/(adc-R)'-/Ru" and Run/(adc-R)2-/Run1 resonance forms.

Solid State EXAFS and Luminescence Studies of Neutral, Dinuclear Gold(I) Complexes. Gold(I)-Gold(I) Interactions in the Solid State

Abstract: A series of neutral, dinuclear gold(I) complexes, containing phosphine and thiolate ligands, have been studied by EXAFS and luminescence spectroscopy. Gold(I)-gold(I) interactions are detected for the first time by EXAFS studies on solid samples at liquid helium temperature. A strong, distinct peak at 1.90 {+-} 0.02 {angstrom}, assigned to Au-P and Au-S bonds, appears in the Fourier transform for complexes 1-8. A less intense peak appears for complexes 2-6 at 2.8 {angstrom} with the amplitude maximizing toward high k characteristic of a gold backscattering atom. The calculated EXAFS results indicate gold(I)-gold(I) distances ranging from 3.0 to 3.2 {angstrom} for complexes 2-6. In contrast, no gold(I)-gold(I) interactions are detected for complexes 1, 7, and 8. The Au-Au and Au-P(S) distances calculated by EXAFS are similar to those measured by X-ray diffraction. All of the neutral, dinuclear gold(I) complexes luminescence at room temperature in the solid state. The Stokes shifts average 6 x 10{sup 3} cm{sup {minus}1} and are indicative of a large distortion in the excited state compared to the ground state. Spectral acquisition using time delays of 10-50 {mu}s confirms the phosphorescent nature of the emission. The origin of the luminescence of complexes 1-8 is consistent with a S {yields}more » Au CT excited state that is perturbed by substituent electronic effects leading to the red shift in emission for 5-8 relative to 1-4. There is no correlation between gold(I)-gold(I) bonding and the energy or band shape of the excitation and emission of 1-8. The luminescence and EXAFS results taken together demonstrate that a gold(I)-gold(I) interaction is not a necessary condition for luminescence. Further, the presence of a gold(I)-gold(I) interaction does not significantly perturb the luminescence in this series of gold(I) complexes.« less