Pt-Pt Distance Research Articles

Theoretical investigation of the apparently irregular behavior of pt-pt nuclear spin-spin coupling constants.

One-bond Pt-Pt nuclear spin-spin coupling constants J(Pt-Pt) for closely related dinuclear Pt complexes can differ by an order of magnitude without any obvious correlation with Pt-Pt distances. As representative examples, the spin-spin couplings of the dinuclear Pt(I) complexes [Pt(2)(CO)(6)](2+) (1) and [Pt(2)(CO)(2)Cl(4)](2-) (2) have been computationally studied with a recently developed relativistic density functional method. The experimental values are (1)J((195)Pt-(195)Pt) = 5250 Hz for 2 but 551 Hz for 1. Many other examples are known in the literature. The experimental trends are well reproduced by the computations and can be explained based on the nature of the ligands that are coordinated to the Pt-Pt fragment. The difference for J(Pt-Pt) of an order of magnitude is caused by a sensitive interplay between the influence of different ligands on the Pt-Pt bond, and relativistic effects on metal-metal and metal-ligand bonds as well as on "atomic orbital contributions" to the nuclear spin-spin coupling constants. The results can be intuitively rationalized with the help of a simple qualitative molecular orbital diagram.

Synthesis and characterization of Pt(CN-p-(C(2)H(5))C(6)H(4))(2)(CN)(2), a crystalline vapoluminescent compound that detects vapor-phase aromatic hydrocarbons.

The vapochromic and vapoluminescent compound Pt(CN-p-(C(2)H(5))C(6)H(4))(2)(CN)(2) (abbreviated PtC(2)) is conveniently synthesized by the thermal rearrangement of [Pt(CN-p-(C(2)H(5))C(6)H(4))(4)][Pt(CN)(4)]. Recrystallization of PtC(2) gives a crystalline orange morph (O-PtC(2)) and an amorphous purple morph (P-PtC(2)) that both contain the cis isomer and differ only in their solid-state packing arrangements. Both compounds were fully characterized by elemental analysis, X-ray powder diffraction, NMR, IR, and TGA. O-PtC(2) is vapochromic and vapoluminescent: it reversibly sorbs aromatic hydrocarbons and ethanol from air or nitrogen with resulting color changes and shifts in the emission spectrum. The lambda(max) values (nm) for emission from O-PtC(2) x (guest) are as follows: no guest, 611; toluene, 565; benzene, 586; chlorobenzene, 592; p-xylene, 585; mesitylene, 565; ethanol, 587. In the case of toluene and mesitylene, intermediate emitting phases are observed. Recrystallization of O-PtC(2) from dichloromethane/toluene gave single crystals of PtC(2) x 0.5(toluene). The single-crystal X-ray structure of PtC(2) x 0.5(toluene) contains infinite stacks of cis geometry and planar molecules with chains of platinum atoms parallel to the c axis of the monoclinic unit cell. The average Pt-Pt separation in PtC(2) x 0.5(toluene) is c/4 = 3.288(2) A. There are solvent channels parallel with the c axis that contain the toluene molecule guests. Thin films of O-PtC(2) rapidly sorb toluene from the gas phase to form PtC(2) x 0.25(toluene) and PtC(2) x 0.5(toluene). Long-term exposure gives PtC(2) x 1.0(toluene). Removal of the toluene source causes rapid desorption to PtC(2) x 0.5(toluene) and then to PtC(2) x 0.25(toluene). The remaining 0.25(toluene) lattice guests require heating for rapid removal. X-ray powder diffraction identified the PtC(2),PtC(2) x .25(toluene), and PtC(2) x 0.5(toluene) phases and showed that the sorption of toluene is accompanied by small changes in the unit cell dimensions that include lengthening the Pt-Pt distances in the structure. The sorption process improves the packing in the structure by utilizing some of the free volume for the toluene lattice guests.

Vapochromism and Crystal Structures of Luminescent Dicyano(2,2′-Bipyridine)Platinum(II)

Vapochromic behavior of the crystal of dicyano(2,2'-bipyridine)platinum(II), [Pt(CN) 2 (bpy)], has been investigated structurally and emission spectroscopically. Red Form with an infinite PtPt chain transforms to Yellow Form reversibly by taking up water vapor. The crystal structure of Yellow Form ([Pt(CN) 2 (bpy)]H 2 O) was determined by X-ray analysis: the square-planar complexes form the inclined stack with short and long PtPt distances (3.3279(3) and 4.6814(3) Å). The crystal water makes hydrogen bonds with CN m ligands connecting the stacks. The transformation is accompanied by the sensitive luminescence change as well as the color change, which reflects the change of the Pt > Pt electronic interactions. The sensitive vapochromism for this system is attributable to the slight deformation of the stacking structure induced by water molecules. platinum complex luminescence spectrum vapochromism metal-metal interaction crystal structure

Structural and Optical Properties of Pt 2 ( dtp ) 4 Br 2 ( dtp =dithiopropionato) and its Halogen-Replacement Effect

A novel binuclear Pt(III) complex, Pt 2 ( dtp ) 4 Br 2 ( dtp =CH 3 CH 2 CS 2 m , dithiopropionato), was synthesized by a reaction of Pt 2 ( dtp ) 4 and Br 2 in refluxing toluene, which could be used as starting material for a new MMX-chain system such as a possible mixed-valence Pt 2 ( dtp ) 4 Br. The title complex has been characterized by X-ray single-crystal structure analysis, UV-Visible-NearIR, IR, and polarized Raman spectroscopies. The Pt 2 ( dtp ) 4 Br 2 crystallized in monoclinic P 2 1 / a and this structure is almost same as Pt 2 ( dtp ) 4 I 2 . Halogen-replacement effect from X=I to Br on Pt 2 ( dtp ) 4 X 2 has been examined. The Pt-Pt distance in X=Br is slightly shorter than that in X=I. Raman peak of the x (Pt-Pt)mode is slightly shifted to higher wavenumber from X=I to Br. These changes are considered to be mainly caused by the difference of electron densities of antibonding d * orbitals. MMX chain mixed valence diplatinum(III) complex binuclear complex

Metallic behavior and periodical valence ordering in a MMX chain compound, Pt(2)(EtCS(2))(4)I.

A new one-dimensional (1-D) halogen-bridged mixed-valence diplatinum(II,III) compound, Pt(2)(EtCS(2))(4)I (3), has been successfully synthesized from [Pt(2)(EtCS(2))(4)] (1) and [Pt(2)(EtCS(2))(4)I(2)] (2). These three compounds have been examined using UV-visible-near-IR, IR, polarized Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray crystal structure analyses (except for 1). Compound 3 was further characterized through electrical transport measurements, determination of the temperature dependence of lattice parameters, X-ray diffuse scattering, and SQUID magnetometry. 3 crystallizes in the monoclinic space group C2/c and exhibits a crystal structure consisting of neutral 1-D chains with a repeating -Pt-Pt-I- unit lying on the crystallographic 2-fold axis parallel to the b axis. The Pt-Pt distance at 293 K is 2.684 (1) A in the dinuclear unit, while the Pt-I distances are essentially equal (2.982 (1) and 2.978 (1) A). 3 shows relatively high electrical conductivity (5-30 S cm(-1)) at room temperature and undergoes a metal-semiconductor transition at T(M-S) = 205 K. The XPS spectrum in the metallic state reveals a Pt(2+) and Pt(3+) mixed-valence state on the time scale of XPS spectroscopy ( approximately 10(-17) s). In accordance with the metal-semiconductor transition, anomalies are observed in the temperature dependence of the crystal structure, lattice parameters, X-ray diffuse scattering, and polarized Raman spectra near T(M-S). In variable-temperature crystal structure analyses, a sudden and drastic increase in the Pt-I distance near the transition temperature is observed. Furthermore, a steep increase in U(22) of iodine atoms in the 1-D chain direction has been observed. The lattice parameters exhibit significant temperature dependence with drastic change in slope at about 205-240 K. This was especially evident in the unit cell parameter b (1-D chain direction) as it was found to lengthen rapidly with increasing temperature. X-ray diffraction photographs taken utilizing the fixed-film and fixed-crystal method for the metallic state revealed the presence of diffuse scattering with line shapes parallel to the a* axis indexed as (-, n + 0.5, l) (n; integer). Diffuse scattering with k = n + 0.5 is considered to originate from the 2-fold periodical ordering corresponding to -Pt(2+)-Pt(2+)-I-Pt(3+)-Pt(3+)-I- or -Pt(2+)-Pt(3+)-I-Pt(3+)-Pt(2+)-I- in an extremely short time scale. Diffuse lines corresponding to 2-D ordering progressively decrease in intensity below 252 K and are converted to the diffuse planes corresponding to 1-D ordering near T(M-S). Furthermore, diffuse planes condensed into superlattice reflections below T(M-S). Polarized Raman spectra show temperature dependence through a drastic low-energy shift of the Pt-I stretching mode and also through broadening of bands above T(M-S).

Completion of the series of M2(hpp)4Cl2 compounds from W to Pt: the W, Os, and Pt compounds.

The series of M2(hpp)4Cl2 complexes (hpp is the anion of 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine) from M = W to M = Pt has been completed by the preparation and characterization of those with M = W, Os, and Pt. W(hpp)4Cl2 (1) has a W-W distance of 2.250(2) A, is diamagnetic, and can be assigned a W-W triple bond based on a sigma 2 pi 4 electron configuration. Os2(hpp)4Cl2 (2) has an Os-Os distance of 2.379(2) A and displays a temperature-independent paramagnetism. It can be assigned a sigma 2 pi 4 delta 2 delta*2 configuration. Pt2(hpp)4Cl2 has a Pt-Pt distance of 2.440(1) A and is diamagnetic. A bond order of 1, based on a configuration in which only the sigma* orbital is empty, is consistent with these data.

Crystal structure and optical spectroscopy of Er2[Pt(CN)4]3.21H2O and Er2[Pt(CN)4]2.SO4.11.5H2O.

We have synthesized two forms of erbium tetracyanoplatinates, Er2[Pt(CN)4]3.21H2O (red form) and Er2[Pt(CN)4]2.SO4.11.5H2O (yellow form), and determined their crystal structures by X-ray diffraction. While the red form crystallizes in the orthorhombic space group Pbcn, with a = 15.4848(3) A, b = 13.8186(2) A, c = 19.07820(10) A, alpha = beta = gamma = 90 degrees, and Z = 4, the yellow form precipitates in the tetragonal space group I4cm, with a = b = 14.321(2) A, c = 13.338(3) A, alpha = beta = gamma = 90 degrees, and Z = 4. Both forms show [Pt(CN)4]2- chains but differ markedly in color and morphology. This is due to the incorporation of sulfate ions in the latter modification, leading to an increased Pt-Pt distance. The observed optical absorption and emission behavior of the title compounds is correlated with the Pt-Pt distances.

Synthesis and Synchrotron Radiation Structure Analysis of Tetra-Dithiopropanato-Diplatinum(II) with Infinite Linear Chain Structure

Diplatinum(II) complex, Pt2(EtCS2)4, is synthesized and characterized by X-ray crystal structure analysis using a synchrotron radiation at SPring-8. The crystal structure consists of diplatinum units stacking in columns along the four-fold axis, with intra and interdimer Pt-Pt distances of 2.764(1) and 3.428 (1) Å, respectively.

Synthesis and Crystal and Electronic Structures of the Dinuclear Platinum Compounds [PEtPh(3)](2)[Pt(2)(&mgr;-PPh(2))(2)(C(6)F(5))(4)] and [Pt(2)(&mgr;-PPh(2))(2)(C(6)F(5))(4)]: A Computational Study by Density Functional Theory.

The electrolytic behavior of the dinuclear complexes [NBu(4)](2)[MM'(&mgr;-PPh(2))(2)(C(6)F(5))(4)] (M = M' = Pt (1), Pd (1a); M = Pt, M' = Pd (1b)) has been studied, showing electrochemically irreversible oxidation and related reduction processes. The chemical oxidation of the binuclear compound for M = M' = Pt, results in the formation of the binuclear Pt(III) compound [Pt(2)(&mgr;-PPh(2))(2)(C(6)F(5))(4)]. The crystal structure analysis of both complexes has been carried out, showing very similar structures with similar Pt-C and Pt-P distances and analogous skeletons. However the Pt-Pt distances are very different, 3.621(1) Å for the Pt(II) compound and 2.7245(7) Å for the Pt(III) derivative (as are the parameters geometrically related to this Pt-Pt distance), suggesting that, in the Pt(III) compound, there is a strong Pt-Pt bond. Results of DFT calculations on [Pt(2)(&mgr;-PH(2))(2)(C(6)F(5))(4)](n)()(-) (n = 2, 0) agree very well with the crystallographic data and indicate that, in the Pt(III) compound, there is approximately a single sigma bond between the metal atoms.

Synthesis and crystal structure of a dinuclear platinum(II) bis( N,N-diethylamino)carbeniumdithiocarboxylate complex Pt 2μ-(Et 2N) 2C 2S 22Cl 4·0.5CH 2Cl 2: structural study of the coordinated inner salt

The bis(diethylamino)carbeniumdithiocarboxylate-bridged Pt(II) dinuclear complex, Pt 2(Et 2N) 2C 2S 2 2Cl 4·0.5CH 2Cl 2, was synthesized and its X-ray crystal structure was solved. The two dithiocarboxylate ligands bridge the two Pt atoms in cis position. Although two possible inner-salt electronic structures, one with a C-C bond and the other with a C-C bond, had been postulated for the ligand, the actual C-C distances in the X-ray structure of the carbonium-carboxylate part of the ligand are 1.50(4) and 1.50(3) Å, suggesting that the bridging ligands are an inner-salt structure with a C-C single bond. The Pt-Pt distance is 3.094(2) Å and is not bonding.

Structure of Green-Phase of Bis(diphenylglyoximato)Pt(II) with High χ(3)

Structure of the green-phase of bis(diphenylglyoximato)Pt(II) formed by epitaxial growth with slow deposition rate was analyzed by electron microscopy. The phase is a tetragonal structure with the short Pt-Pt distance of about 0.33nm, which leads to an enhancement in χ(3).

The bicluster oxidative addition as a route to bicapped hexaplatinum clusters

The reaction of either the 84-electron cluster [Pt6(μ-CO)6(μ-dppm)3] (1) or the 82-electron cluster [Pt6(CO)6(μ-dppm)3]2+ (2), dppm = Ph2PCH2PPh2, with SnX3− or Hg2X2 gave the corresponding bicapped trigonal prismatic 86-electron clusters [Pt6(μ3-SnX3)2(μ-CO)6(μ-dppm)3] (3: X = F(3a, Cl(3b), Br(3e) or [Pt6(μ3-HgX)2(μ-CO)6(μ-dppm)3] 4: X = Cl (4a), Br (4b), l (4c), respectively. The new clusters 3 and 4 have been characterized spectroscopically and 4c has also been characterized by X-ray diffraction. Crystals of 4c·CH2Cl2·2Et2O are monoclinic, space group P21c, a=20.092(9), b=18.718(7), c=26.258(7) Å, β=108.09(3)°V=9387(6) Å3, Z=4. The molecular core in 4c is a Pt6 trigonal prism with each triangular Pt3 face capped by an Hgl fragment. The intertriangle Pt-Pt bond distances (2.910(1)–2.948(1) Å) are longer than the intratriangle Pt-Pt distances (2.634(1)–2.687(1) Å) and this is consistent with EHMO calculations. The reaction of 1 with Hg2X2 to give 4 is termed a bicluster oxidative addition; according to predictions from EHMO calculations it should lead to stronger intertriangle Pt-Pt bonding in 3 and 4 than in the precursor cluster 1, but this is not suppored by structural data observed in 3c and 4c.

The structure of amorphous Pt-uridine blue nitrate by WAXS and SAXS

Amorphous Pt-uridine blue nitrate was studied in the solid state by the wide angle X-ray scattering method and in aqueous solution by the small angle X-ray scattering method. The radial distribution function (RDF) closely resembled that of Pt-uridine blue sulfate. It is proposed that both are mixtures of Pt(II) 2 and Pt(III) 2 units with Pt-Pt distance of 3.0 and 2.6 Å, respectively. However, the RDF for Pt-uridine blue nitrate could also be reproduced quite well with a mononuclear model, where the Pt-ONO 2 distance is about 2.6 Å. In aqueous solution Pt-uridine blue nitrate forms aggregates whose radius of gyration in low concentrations is about 8.4 ± 0.7 Å.

XAFS Characterization of Platinum Clusters Synthesized in the Channel of a Mesoporous Zeolite

[Pt 15 (CO) 30 ] 2- was synthesized by reductive carbonylation of H 2 PtCl 6 in the channels of FSM-16 modified with NEt 4 Cl. The platinum clusters in the channels whose diameter was 28 A were characterized by Pt L III edge EXAFS as well as FT-IR, UV-vis spectroscopy, and TEM measurements. After exposure of H 2 PtCl 6 /Cl/FSM-16 to CO + H 2 O at 323 K. Pt carbonyl clusters were selectively produced. The Pt L III edge EXAFS spectrum of this sample was exactly the same as that of [NEt 4 ] 2 [Ptj 5 (CO) 30 ], and gave Pt-Pt distances typical of these types of platinum clusters at 2.68 and 3.08 A. Uniform platinum particles (15 A diameter) were observed in the channels of FSM-16 by a TEM measurement; this suggests that [Pt 15 (CO) 30 ] 2- was synthesised in the channel of FSM-16. The platinum clusters in the channel were converted to platinum metal particles by evacuation above 363 K.Pt L III EXAFS spectra of these samples revealed that the bridge CO of the clusters were desorbed by the evacuation at 343 K while retaining their cluster framework; the clusters were converted to Pt 50-60 particles by evacuation above 363 K.

Pt LIII-Edge EXAFS Studies on Pt-Cu-Fe Alloy Electrocatalysts Supported on Carbon

Carbon supported Pt-Cu-Fe alloys with compositions of Pt:Cu:Fe=6:1:1 and 2:1:1 have been prepared. Both catalysts exhibit higher specific activities for oxygen reduction than Pt alone. In order to reveal the local structure around Pt, we have performed X-ray absorption experiment at the Pt L III -edge. The local structure around Pt has been analyzed by fitting the first shell including the Pt-Pt, Pt-Cu, and Pt-Fe contributions to EXAFS spectra. The fitted C.N. for both alloys are similar to that for bulk Pt, indicating that the particle size is not small. The Pt-Pt distances for both alloys are found to be slightly shorter than that of bulk Pt, and the Pt-Cu and Pt-Fe distances decrease as the amounts of Cu and Fe increase. It is therefore concluded that the catalytic activity is strongly influenced by the bonding character.

Synthetic, Structural, Spectroscopic, and Theoretical Studies of Structural Isomers of the Cluster Pt(3)(&mgr;-PPh(2))(3)Ph(PPh(3))(2). A Unique Example of Core Isomerism in Phosphine Phosphido-Rich Clusters.

Two isomers of the phosphido-bridged platinum cluster Pt(3)(&mgr;-PPh(2))(3)Ph(PPh(3))(2) (2 and 3) have been isolated, and their structures have been solved by single-crystal X-ray diffraction. Compound 2 crystallizes in the orthorhombic space group Cmc2(1) with a = 22.192(10) Å, b = 17.650(9) Å, c = 18.182(8) Å, and Z = 4. Compound 3 crystallizes with 2 molecules of dichloromethane in the monoclinic space group C2/c with a = 21.390(10) Å, b = 18.471(9) Å, c = 19.021(11) Å, beta = 105.27(5) degrees, and Z = 4. The two isomers differ essentially in their metal-metal distances and Pt-(&mgr;-PPh(2))-Pt angles. Thus 2, having an imposed C(s) symmetry, contains a bent chain of metal atoms with two short Pt-Pt distances of 2.758(3) Å and a long separation of 3.586(2) Å. In 3, which has an imposed C(2) symmetry, the metal atoms form an isosceles triangle with two Pt-Pt distances of 2.956(3) Å and one of 3.074(4) Å. These isomers can be smoothly interconverted by changing the crystallization solvents. Solution and solid-state (31)P NMR studies have been performed in order to assign the resonances of the different P nuclei and relate their chemical shifts with their structural environments. Raman spectroscopy was used to assign the nu(Pt-Pt) modes of the two structural isomers. Theoretical studies based on extended Hückel calculations and using the fragment molecular orbital approach show that the isomer with the three medium Pt-Pt distances is slightly more stable, in agreement with earlier theoretical predictions. Cluster core isomerism remains a rare phenomenon, and the present example emphasizes the role and the importance of flexible phosphido bridges in stabilizing clusters as well as the unprecedented features which can be observed in phosphine phosphido-rich metal clusters.

Synthesis and Structural Studies of Platinum Complexes Containing Monodentate, Bridging, and Chelating Formamidine Ligands.

The reactions of K(2)PtCl(4) with N,N'-diphenylformamidine (HDPhF) and N,N'-di-p-tolylformamidine (HDTolF) produce the trans square-planar compounds PtCl(2)(HDPhF)(2), 1a, and PtCl(2)(HDTolF)(2), 1b. Compound 1a crystallizes as yellow parallelepipeds in the space group P2(1)/c with two independent molecules in the asymmetric unit and unit cell dimensions a = 23.427(7) Å, b = 16.677(6) Å, c = 12.980(4) Å, and beta = 96.10(2) degrees. These compounds are soluble in common organic solvents and have been used as starting materials for the preparation of diplatinum compounds. Treatment of 1a and 1b with NaOMe and the halide abstraction reagent TlPF(6) produces the compounds Pt(2)(&mgr;-DArF)(2)(eta(2)-DArF)(2), Ar = Ph (2a) and Tol (2b), respectively. Compound 2a crystallizes as yellow rods in the space group P&onemacr; with unit cell dimensions a = 12.296(3) Å, b = 12.310(4) Å, c = 15.374(4) Å, alpha = 90.75(2) degrees, beta = 91.02(2) degrees, and gamma = 110.20(2) degrees. Compound 2b crystallizes with a molecule of THF, as yellow rods in the space group P2(1)/c with a = 17.883(3) Å, b = 14.517(3) Å, c = 22.581(3) Å, and beta = 98.17(1) degrees. These compounds contain two cis bridging formamidinato ligands and two formamidinato ligands that are chelated to separate Pt centers. Upon heating, they further react to give the tetrabridged compounds Pt(2)(&mgr;-DArF)(4), Ar = Ph (3a), Tol (3b). Compound 3a crystallizes as orange cubes in the cubic space group I432 with a = 19.671(1) Å. On going from the bis-bridged, bis-chelate structure in 2a to the tetrabridged structure in 3a, the metal-metal separation decreases from 2.910(1) to 2.649(1) Å. Both 2band 3b have been oxidized to give the Pt(II)-Pt(III) compound Pt(2)(&mgr;-DTolF)(4)(PF(6)), 4. Compound 4 crystallizes as cubes in the tetragonal space group P4/ncc with a = 14.392(1) Å and c = 14.436(1) Å. The Pt-Pt distance in 4 is 2.5304(6) Å.

Crystal Structures and Luminescence Properties of Platinum(II) Complexes Containing 3,3'-Biisoquinoline.

Three new platinum complexes containing 3,3'-biisoquinoline (i-biq), [Pt(CN)(2)(i-biq)] (1), [PtCl(2)(i-biq)] (2), and [Pt(i-biq)(2)](PF(6))(2) (3), have been synthesized as orange-red, yellow, and colorless crystals, respectively. Their crystal structures and luminescence properties are reported. Crystal data: for 1.0.5H(2)O, PtO(0.5)N(4)C(20)H(13), orthorhombic, Pbcm, a = 13.989(2) Å, b = 18.304(1) Å, c = 6.682(3) Å, V = 1710.9(6) Å(3), Z = 4, and final R = 0.039 (R(w) = 0.033) for 970 independent reflections; for 2.DMF.H(2)O, PtCl(2)O(2)N(3)C(21)H(21), triclinic, P&onemacr;, a = 11.047(1) Å, b = 12.397(3) Å, c = 8.000(2) Å, alpha = 106.56(1) degrees, beta = 100.15(1) degrees, gamma = 76.15(1) degrees, V = 1012.8(3) Å(3), Z = 2, and final R = 0.058 (R(w) = 0.077) for 4219 independent reflections; for 3.2DMF, PtP(2)F(12)O(2)N(6)C(42)H(38), triclinic, P&onemacr;, a = 10.795(2) Å, b = 13.511(2) Å, c = 8.281(1) Å, alpha = 105.22(1) degrees, beta = 112.17(1) degrees, gamma = 85.02(1) degrees, V = 1079.2(3) Å(3), Z = 1, and final R = 0.038 (R(w) = 0.042) for 3606 independent reflections. Square-planar complexes of 1 are stacked in the crystal to form a columnar structure with the Pt-Pt distance of 3.34 Å. The crystal emits strongly, even at room temperature, and the emission spectrum is similar to that for the [Pt(CN)(2)(bpy)] crystal (bpy = 2,2'-bipyridine), which is due to a (3)dpi[dsigma(Pt) --> pi(i-biq)] transition. The single crystal emission spectrum at 77 K is, however, observed as a superposition of broad (3)dpi and sharp (3)pipi(i-biq) emissions. The crystal structure of 2 has a completely different stacking structure from that of 1. The stacking occurs on the i-biq ligands, and the Pt atoms are separated more than 6 Å. The complex exhibits only a structured emission component assigned to the (3)pipi(i-biq) transition in the crystal at 77 K, in agreement with the crystal structure with no Pt-Pt interaction. In the crystal of 3, the [Pt(i-biq)(2)](2+) complexes are stacked but offset, being in close contact between parts of adjacent i-biq ligands. There is no Pt-Pt interaction also in this case. Two i-biq ligands in the complex are distorted to adopt the bowed conformation due to the steric crowding of the alpha-hydrogens on opposite ligands. Nevertheless, 3 provides almost the same (3)pipi emission spectrum as 1 and 2 in dilute glassy solution at 77 K. The (3)pipi emission spectra observed in the crystals of these Pt(II) complexes are red-shifted compared with those in dilute glassy solution. The fact is attributable to the pi-pi intermolecular interactions between the ligands in the crystals. The factors controlling the crystal structures for these complexes are also discussed.

Synthesis and Reactivity of (Pentafluorophenyl)platinate(II) Complexes with Bridging 1,8-Naphthyridine (napy) and X Ligands (X = C(6)F(5), OH, Cl, Br, I, SPh). Crystal Structure of [NBu(4)][Pt(2)(&mgr;-napy)(&mgr;-OH)(C(6)F(5))(4)].CHCl(3).

By reaction of [NBu(4)](2)[Pt(2)(&mgr;-C(6)F(5))(2)(C(6)F(5))(4)] with 1,8-naphthyridine (napy), [NBu(4)][Pt(C(6)F(5))(3)(napy)] (1) is obtained. This compound reacts with cis-[Pt(C(6)F(5))(2)(THF)(2)] to give the dinuclear derivative [NBu(4)][Pt(2)(&mgr;-napy)(&mgr;-C(6)F(5))(C(6)F(5))(4)] (2). The reaction of several HX species with 2 results in the substitution of the bridging C(6)F(5) by other ligands (X) such as OH (3), Cl (4), Br (5), I (6), and SPh (7), maintaining in all cases the naphthyridine bridging ligand. The structure of 3 was determined by single-crystal X-ray diffraction. The compound crystallizes in the monoclinic system, space group P2(1)/n, with a = 12.022(2) Å, b = 16.677(3) Å, c = 27.154(5) Å, beta = 98.58(3) degrees, V = 5383.2(16) Å(3), and Z = 4. The structure was refined to residuals of R = 0.0488 and R(w) = 0.0547. The complex consists of two square-planar platinum(II) fragments sharing a naphthyridine and OH bridging ligands, which are in cis positions. The short Pt-Pt distance [3.008(1) Å] seems to be a consequence of the bridging ligands.

Reactions of Nitroplatinum Complexes. 2. Reactions of K2[Pt(NO2)4] and Related Complexes with Aqueous Acids (CH3CO2H, HClO4, CF3SO3H, HNO3, and H2SO4): Pathways to Platinum(III) Complexes with Acetate Bridges. Crystal Structure of K2[{Pt(NO2)2(.mu.-CH3CO2)}2].cntdot.H2O

Full title: Reactions of nitroplatinum complexes. 2. Reactions of K2[Pt(NO2)4] and related complexes with aqueous acids (CH3CO2H, HClO4, CF3SO3H, HNO3, and H2SO4): Pathways to platinum(III) complexes with acetate bridges. Crystal structure of K2[{Pt(NO2)22(μ-CH 3CO2)}2]·H2O. Reaction of K2[Pt(15NO2)4] under argon with 1 M HClO4 or CF3SO3H gave an initial blue solution (λmax = 627 nm), due to nitrosyl complexes of platinum(IV). With heating, the color faded, and 195Pt and 15N NMR peaks were observed from cis-[Pt(15NO2)2(H2O)2], [Pt(15NO2)(H2O)3]+, and fac-[Pt(15NO2)3(H2O) 3]+. In air or oxygen, reaction was faster, giving [Pt(H2O)4]2+ as well as mixed nitrito-N/aqua platinum(II) complexes, and larger proportions of platinum(IV) complexes, including [Pt(OH)6]2- in solution, and solid H2[Pt(OH)6]. With 0.5 M H2SO4, reactions were similar, but a greater variety of platinum(IV) complexes were formed, some probably containing coordinated sulfate. With 1 M HNO3, K2[Pt(NO2)6] formed. Reactions of K2[Pt(NO2]4] with aqueous acetic acid gave mixtures of Pt(II) and Pt(IV) mononuclear complexes and dinuclear Pt(III) complexes containing acetate bridges. The composition of the solution depended on the reaction conditions (heated for various times with argon, air, or oxygen above the solution or bubbled through). Crystals of K2[{PtII(NO2)2(μ-CH 3CO2)}2]·H2O were obtained from a reaction under argon, and the crystal structure was determined by X-ray diffraction: space group P1 (no. 2); a = 7.202(2) A; b = 8.987(2) A; c = 13.592(2) A; α = 94.01(2)°; β = 90.68(2)°; γ = 111.04(2)°; Z = 2; R = 0.0371, for 2875 reflections. The structure showed two acetate ligands bridging between cis-Pt(NO2)2 units, with the Pt-Pt distance 2.986(1) A. Reactions of cis-[Pt(NO2)2(H2O)2] with various oxidants in the presence of acetic acid were studied. [{(CH3CO2)PtIII(NO2) 2(μ-CH3CO2)}2]2- is formed by the oxidation of preformed [{PtII(NO2)2(μ-CH3CO 2)}2]2-. Under anaerobic conditions, the major oxidant is HNO3 formed in the reaction mixture. Oxidation of [{PtII(NO2)2(μ-CH3CO 2)}2]2- with NO2 formed in the reaction mixture in the presence of oxygen provides one route to [(O2N)PtIII(NO2)2(μ-CH 3CO2)2PtIII(NO2) 2(O2CCH3)]2-. Continued heating of solutions containing these Pt(III) complexes eventually gave solutions containing [{(CH3CO2)PtIII(NO2)} 2(μ-CH3CO2)3]-.