Tuning the electronic structures of platinum(II) complexes with a cyclometalating aryldiamine ligand

Triflate salts of four platinum(II) pyridyl complexes with a mer-coordinating tridentate pincer ligand, pip(2)NCN(-) (pip(2)NCNH = 1,3-bis(piperidylmethyl)benzene), are reported: Pt(pip(2)NCN)(L)(+) (2, L = pyridine; 3, L = 4-phenylpyridine; 5, L = 2,6-pyridinedimethanol) and [(Pt(pip(2)NCN))(2)(micro-4,4'-bipyridine)](2+) (4). The complexes have been fully characterized by (1)H NMR spectroscopy, elemental analysis, and X-ray crystallography. Compound 2(CF(3)SO(3)(-)): triclinic, P1, a = 9.7518(6) A, b = 12.0132(8) A, c = 12.6718(9) A, alpha = 114.190(2) degrees, beta = 100.745(3) degrees, gamma = 103.545(2) degrees, V = 1247.95(14) A(3), Z = 2. Compound 3(CF(3)SO(3)(-)): monoclinic, P2(1)/c, a = 15.550(2) A, b = 9.7386(11) A, c = 18.965(3) A, beta = 92.559(7) degrees, V = 2869.1(6) A(3), Z = 4. Compound 4(CF(3)SO(3)(-))(2).1/2(CH(3))(2)CO: monoclinic, I2/a, a = 21.3316(5) A, b = 9.6526(2) A, c = 26.1800(6) A, beta = 96.4930(10) degrees, V = 5356.0(2) A(3), Z = 4. Compound 5(CF(3)SO(3)(-)).3/2CHCl(3): monoclinic, P2(1)/n, a = 17.1236(10) A, b = 9.3591(5) A, c = 21.3189(11) A, beta = 96.11(3) degrees, V = 3397.2(3) A(3), Z = 4. The accumulated data indicate that the phenyl group of pip(2)NCN(-) labilizes the trans pyridyl ligand. The electronic structures were investigated using cyclic voltammetry, as well as UV-visible absorption and emission spectroscopies. Red emission from 2 in rigid media originates from a lowest triplet ligand field excited state, whereas yellow-green emissions from 3 and 4 originate from a lowest pyridyl ligand-centered triplet pi-pi state, indicating that substitution of the pyridyl ligand results in a dramatic change in the orbital character of the emissive state.     

Dissociative photoionization of methyl chloride studied with threshold photoelectron-photoion coincidence velocity imaging

Utilizing threshold photoelectron-photoion coincidence (TPEPICO) velocity imaging, dissociation of state-selected CH(3)Cl(+) ions was investigated in the excitation energy range of 11.0-18.5 eV. TPEPICO time-of-flight mass spectra and three-dimensional time-sliced velocity images of CH(3)(+) dissociated from CH(3)Cl(+)(A(2)A(1) and B(2)E) ions were recorded. CH(3)(+) was kept as the most dominant fragment ion in the present energy range, while the branching ratio of CH(2)Cl(+) fragment was very low. For dissociation of CH(3)Cl(+)(A(2)A(1)) ions, a series of homocentric rings was clearly observed in the CH(3)(+) image, which was assigned as the excitation of umbrella vibration of CH(3)(+) ions. Moreover, a dependence of anisotropic parameters on the vibrational states of CH(3)(+)(1(1)A') provided a direct experimental evidence of a shallow potential well along the C-Cl bond rupture. For CH(3)Cl(+)(B(2)E) ions, total kinetic energy released distribution for CH(3)(+) fragmentation showed a near Maxwell-Boltzmann profile, indicating that the Cl-loss pathway from the B(2)E state was statistical predissociation. With the aid of calculated Cl-loss potential energy curves of CH(3)Cl(+), CH(3)(+) formation from CH(3)Cl(+)(A(2)A(1)) ions was a rapid direct fragmentation, while CH(3)Cl(+)(B(2)E) ions statistically dissociated to CH(3)(+) + Cl via internal conversion to the high vibrational states of X(2)E.     

Self-assembly of coordination polymers from AgX (X = SbF(6)(-), PF(6)(-), and CF(3)SO(3)(-)) and oxadiazole-containing ligands

The coordination chemistry of the oxadiazole-containing rigid bidentate ligands 2,5-bis(4-pyridyl)-1,3,4-oxadiazole (L1), 2,5-bis(3-pyridyl)-1,3,4-oxadiazole (L2), and 2,5-bis(3-aminophenyl)-1,3,4-oxadiazole (L3) with inorganic Ag(I) salts has been investigated. Four new coordination polymers (1, 2, 3, and 5) and one new bimetallic macrocyclic supramolecular complex (4) were synthesized from solution reactions of L1-L3 with inorganic Ag(I) salts, respectively. Compounds [[Ag(L1)]SbF(6)](n) (1) (1, monoclinic, P2(1)/c, a = 6.6846(4) A, b = 27.1113(15) A, c = 8.6802(5) A, beta = 94.1080(10) degrees, Z = 4) and [[Ag(L1)]PF(6)](n) (2) (2, monoclinic, P2(1)/c, a = 6.6753(3) A, b = 27.2824(14) A, c = 8.2932(4) A, beta = 94.6030(10) degrees, Z = 4) were obtained from the reactions of L1 with AgSbF(6) and AgPF(6) in a CH(2)Cl(2)/CH(3)OH mixed solvent system, respectively. Compounds 1 and 2 are isostructural and feature a novel two-dimensional zeolite-like net with two different individual rings. [[Ag(L2)]SbF(6)](n) (3) (3, monoclinic, P2(1)/c, a = 5.5677(3) A, b = 17.3378(9) A, c = 15.6640(8) A, beta = 94.4100(10) degrees, Z = 2) and [Ag(2)(L2)(2)](SbF(6))(2) (4) (4, triclinic, P1, a = 8.7221(5) A, b = 9.2008(6) A, c = 10.7686(7) A, alpha = 70.6270(10) degrees, beta = 75.7670(10) degrees, gamma = 73.7560(10) degrees, Z = 1) were obtained from one-pot reaction of L2 with AgSbF(6) in a CH(2)Cl(2)/CH(3)OH mixed solvent system. Compound 3 features a one-dimensional chain pattern, while compound 4 adopts a novel bimetallic macrocyclic structural motif which consists of Ag(2)(L2)(2) ringlike units (crystallographic dimensions, 8.06 x 7.42 A(2)). [[Ag(L3)]SO(3)CF(3)](n) (5) is generated from L3 and AgSO(3)CF(3) in a CH(2)Cl(2)/CH(3)OH mixed solvent system and crystallizes in the unusual space group Pbcn, with a = 9.8861(5) A, b = 20.2580(10) A, c = 17.5517(8) A, Z = 8. It adopts novel two-dimensional sheets that are cross-linked to each other by strong interlayer N-H...O hydrogen bonding interactions into a novel H-bonded three-dimensional network.     

One-dimensional coordination polymers incorporating silver(I) perfluorocarboxylate cuboctahedral clusters and the bis(methylthio)methane ligand

Two topologically comparable complexes, [Ag6(CF3CO2)3(L1-Me)3(SCH3)3]infinity (1) and [Ag6(CF3CF2CO2)3(L1-Me)2(SCH3)3(H2O)]infinity (2), were prepared and characterized by single-crystal diffractometry. The structures consist of Ag12S6 clusters linked by bis(methylthio)methane ligands, L1-Me, thus forming 1D coordination polymers. The 12 Ag atoms of the cluster are situated at the corners of a distorted cuboctahedron. The sulfur atoms of the six mu4-SCH3 entities occupy a position approximately 0.8 A above the center of each of the square faces of the polyhedron. The cleavage of the C-S bond of some of the ligands occurs during the syntheses, producing the -SCH3 anions. The coordination of the silver atoms varies from 5 to 7. The Ag...Ag contacts range from 2.9250(5) to 3.3615(6) A and from 2.961(1) to 3.380(1) A for 1 and 2, respectively. A polymeric ribbon is obtained when four ligands link a given cluster to two others. The chains of 1, held only by van der Waals forces, pack in a hexagonal manner. The two water molecules in 2 (Ag-OH2 = 2.385(7) A) are coordinated to silver atoms of the cluster. They are also strongly hydrogen bonded to the oxygen atoms of two pentafluoropropionate groups, one within the cluster (O...O = 2.741(1) A), the other in an adjacent chain (O...O = 2.818(1) A). The chains, thus H bonded to one another, generate a 2D coordination network.     

Synthesis and optical properties of asymmetric polyamides derived from cyclopropyl diacids and diamines

The polyamides were prepared from the dicarbonyl chloride of (+) (S)- or (?)(R)-trans-1,2-cyclopropanedicarboxylic acid (C3A) with either the dihydrochloride salt of (+)(S)- or (?)(R)-trans-1,2-diaminocyclopropane (C3B) or the dihydrobromide salt of (+)(S)- or (?)(R)-trans-1,2-bis(methylamino)cyclopropane (C3MB) by interfacial polycondensation. Several diamide model compounds composed of these monomers were also synthesized. The polyamides [poly(C3A-C3B)] derived from C3A and C3B have the capability of hydrogen bonding, while the polyamides [poly-(C3A-C3MB)] derived from C3A and C3MB do not. Poly(C3A-C3B) were insoluble in common organic solvents except strong acids. Poly(C3A-C3MB) were soluble in common organic solvents. Poly(C3A-C3B) had melting points higher than 300°C. Poly(C3A-C3MB) melted at 180–235°C. The ORD and CD study has shown that poly(+)C3A(+)C3B in methane sulfonic acid (MSA), 2,2,2-trifluoroethanol (TFE) (5 v % MSA), and tetramethylenesulfone (TMS) (5 v % MSA) exhibits a very strong Cotton effect or CD peak at 212–218 mμ, attributable to a component of the split π–π^* transition of the amide chromophores. Poly(+)C3A(+)C3MB in MSA and TFE (5 v % MSA) shows a strong Cotton effect or CD peak at 217–223 mμ and an intermediate Cotton effect or CD trough at 202–204 mμ as well as an intermediate Cotton effect or CD trough at 220–222 mμ and an intermediate Cotton effect or CD peak at 202–204 mμ in TFE and TMS. These peaks and troughs may be assigned to splitting of the π–π^* transition. The CD spectra of poly(+)C3A(+)C3MB in nonacidic media are quite different from those in acidic media: they are almost mirror images. The CD spectra in this transition induced by MSA suggests that a transition from a compact helix to another more extended helix with opposite handedness occurs similar to poly-L-proline I ? II. This transition may be explained by electrostatic repulsion between protonated amide groups. Viscosity data have shown that the conformation is changed to a highly extended from in acidic media. The polyamides and diamides derived from enantiomers exhibit mirror image spectra. Poly(+)C3A(+)C3B and poly(+)C3A(+)C3MB in every solvent studied exhibit a marked enhancement of the rotatory strength of ORD and CD with respect to the corresponding diamide models.     

Tetrahedranyllithium: synthesis, characterization, and reactivity

The first representative of stable tetrahedranyl anion, tris(trimethylsilyl)tetrahedranyllithium (3), has been synthesized by the reaction of tetrakis(trimethylsilyl)tetrahedrane (2) with methyllithium in tetrahydrofuran. The structural characterization of the tetrahedranyllithium has been achieved by X-ray crystallography, showing that the structure of 3.(TMEDA)1.5 represents a stretched tetrahedron. The endocyclic C(Li)-C(SiMe3) bond lengths range from 1.5408(15) to 1.5441(15) A (av 1.5425(15) A), and are longer than the endocyclic C(SiMe3)-C(SiMe3) bond lengths, which range from 1.4961(15) to 1.5009(15) A (av 1.4986(15) A). Methyl- and hydrogen-substituted tetrahedranes have also been prepared by the reaction of 3 with dimethyl sulfate and cyclopentadiene, respectively.     

Synthesis and anti-tumor activity of new steroidal nuclear analogues of aragusterol A

3alpha,7alpha-Dihydroxy-5-epiaragusterol A (3) was synthesized from bile acid (cholic acid) as a new steroidal nuclear analogue of antitumor marine steroid aragusterol A. 7alpha-Hydroxyaragusterol A (4) was also derived from xestokerol B. The in vitro anti-proliferative activity of each of these analogues toward KB cells as well as in vivo anti-tumor activity of 5-epiaragusterol A (2) previously synthesized by the authors and 3 were assessed.     

Building unit and topological evolution in the hydrothermal DABCO-U-F system

Compounds NDUF-1 ([C(6)H(14)N(2)](UO(2))(2)F(6); P2(1)/c, a = 6.9797(15) A, b = 8.3767(15) A, c = 23.760(5) A, beta = 91.068(4) degrees, V = 1388.9(5) A(3), Z = 4), NDUF-2 ([C(6)H(14)N(2)](2)(UO(2))(2)F(5)UF(7).H(2)O), NDUF-3 ((NH(4))(7)U(6)F(31); R3, a = 15.4106(8) A, c = 10.8142(8) A, V = 2224.1(2) A(3), Z = 3), and NDUF-4 ([NH(4)]U(3)F(13)) have been synthesized hydrothermally from fixed composition reactant mixtures over variable time periods [DABCO (C(6)H(12)N(2)), UO(2)(NO(3))(2).6H(2)O, HF, and H(2)O; 2-14 days]. Observed is a systematic evolution of the structural building units within these materials from the UO(2)F(5) pentagonal bipyramid in NDUF-1 and -2 to the UF(8) trigonal prism in NDUF-2 and finally to the UF(9) polyhedron in NDUF-3 and -4 as a function of reaction time. Coupled to this coordination change is a reduction of U(VI) to U(IV) as well as a breakdown of the organic structure-directing agent from DABCO to NH(4)(+). These processes contribute to a structural transition from layered topologies (NDUF-1) to chain (NDUF-2), back to layered (NDUF-3), and ultimately to framework (NDUF-4) connectivities. The synthesis conditions, crystal structures, and possible transformation mechanisms within this system are presented.     

三氮唑配合物[Cu2(CH3COO)4(C4H8N4)2]·2CH3CN的合成及晶体结构

Cu(CH3COO)2 和4 氨基 3,5 二甲基 1,2,4 三氮唑反应制得标题化合物的单晶[Cu2(CH3COO)4(C4H8N4)2]·2CH3CN。晶体属三斜晶系 ,空间群 ,a=8.266(2),b=8.585(2),c=10.741(2) ,α=75.58(3),β=88.46(3),γ=86.35(3)°,V=736.7(3) 3 ,Z=1,Dc=1.509g·cm 3,F(000)=346,μ=1.502mm 1 。X 射线衍射结构分析表明 ,Cu2(CH3COO)4(C4H8N4)2 单元是中心对称的双核配合物 ,两个铜原子间距为2.698 。每个金属原子被围成四方锥的配位结构 ,四个乙酸根配体中最近的四个氧原子处在底面上[Cu O=1.965(3)～1.986(3) ] ,一个4 氨基 3,5 二甲基 1,2,4 三氮唑配体位于顶点位置Cu N=2.172 。     

Na3PbII[B(O3POH)4]: an alkali-metal lead borophosphate with heterocubane-like units Na3PbO4

Na 3Pb (II)[B(O 3POH) 4] was synthesized under hydrothermal conditions. The crystal structure determination from single-crystal X-ray diffraction data ( I4 1/ a, Z = 4, a = 6.9182(8) A, c = 27.309 (3) A, V = 1307.0(3) A (3)) revealed the presence of [B(O 3POH) 4] (5-) oligomers and heterocubane-like units Na 3PbO 4 with mixed-occupied metal cation sites.     

Metal-oxygen-metal arrays in lamellar hybrid materials: cobalt and manganese 4-cyclohexene-1,2-dicarboxylates

We have obtained three layered hybrid materials from the hydrothermal reaction of 4-cyclohexene-1,2-dicarboxylic acid with Co and Mn salts: Co(C(8)H(8)O(4))[1], Mn(H(2)O)(C(8)H(8)O(4))[2], and Mn(4)(H(2)O)(C(8)H(8)O(4))(4).0.3(H(2)O)[3]. The structures for all materials were solved by single-crystal XRD ([1]P1, a=4.805(2) A, b=6.650(3) A, c=12.960(6) A, alpha=98.285(7) degrees, beta=98.986(7) degrees, gamma=95.689(7) degrees, V= 401.6(3) A(3), R(1)= 0.0438; [2] P2(1)/c, a=11.151(2) A, b=11.330(2) A, c=7.6560(15) A, beta=108.813(3) degrees , V=915.6(3) A(3), R(1)=0.0412; [3] P1, a= 11.412(3) A, b=12.136(4) A, c=13.809(4) A, alpha=104.703(6) degrees, beta=103.207(6) degrees, gamma=92.468(5) degrees, V=1790.6(9) A(3), R(1)=0.1056). While all three structures are two-dimensional overall, the metal-oxygen-metal dimensionality within the layers varies from isolated metal atoms in the case of [1] to 1D ribbons of vertex sharing MnO(6) octahedra [2] and 2D arrays of edge- and vertex-sharing polyhedra in [3].     

Visible-light Photochemistry and Phototoxicity of Thiarubrines

Abstract. Thiarubrines, a group of intensely red, sulfur-containing pigments produced by asteraceous plants, are photola-bile, yielding thiophenes and elemental sulfur upon exposure to UV or visible light. The mechanism of this light-induced conversion for thiarubrines A (la), B (lb) and D (lc), isolated from the roots of Ambrosia chamis-sonis (Asteraceae), was investigated. Visible-light irradiation of thiarubrines resulted in the formation of novel 2,6-dithiabicyclo[3.1.0]hex-3-ene polyyne photointerme-diates (photosulfides) that rapidly undergo desulfuriza-tion to yield thiophenes. Six photosulfides, photosulfides 3a and 3a' from thiarubrine A (la), photosulfides 3b and 3b' from thiarubrine B (lb) and photosulfides 3c and 3c' from thiarubrine D (lc) were characterized. Thiarubrine photointermediates are short-lived and unstable, with the photosulfides formed from thiarubrine A having a half-life of 12.3 min at room temperature. While the immediate fate of the extruded sulfur is unknown, we identified cyclooctasulfur (S₈) in photolysis solutions of thiarubrine A using electron impact mass spectrometry. Visible-light irradiation of Candida albicans cell suspensions treated with thiarubrine A led to a 99% decrease in cell viability, suggesting that the photosulfides, or other molecules generated by the exposure of thiarubrines to light, have significant toxicity.     

Deuterium isotope effects on (13)C NMR chemical shifts reflect the smaller steric size of CD(3) compared to CH(3) groups

A CD(3) group close in space to (but many bonds distant from) a carbon atom A causes a substituent effect on the chemical shift of C(A) that is algebraically smaller than the effect of a CH(3) group, in agreement with the notion of shorter C-D relative to C-H bonds. Hence, the deuterium isotope effect of CD(3) upon delta(C(A)) is shielding when the substituent effect is deshielding, and vice versa.     

Generation of mono- and bis-dioxiranes from 2,3-butanedione

Biacetyl reacts with oxone to give bis-dioxirane [3,3'-dimethyl-3,3'-bidioxirane, 3B] and mono-dioxirane [1-(3-methyl-dioxiran-3-yl)ethanone, 3A)]. Bis-dioxirane 3B is formed when two oxygens are incorporated into biacetyl, while mono-dioxirane 3A incorporated only one. A greater stability is observed in 3B compared to 3A, which is attributed to an alpha-dioxiranyl (anomeric) effect in the former. In contrast, 3A suffers from a destabilizing pi-electron withdrawing effect from the adjacent carbonyl group.     

Synthesis and characterization of a porous magnetic diamond framework, Co3(HCOO)6, and its N2 sorption characteristic

[Co3(HCOO)6](CH3OH)(H2O) (1), the isostructural analogue of the porous magnet of coordination framework [Mn3(HCOO)6](CH3OH)(H2O), and its desolvated form [Co3(HCOO)6] (2) were prepared and characterized by X-ray and neutron diffraction methods, IR, thermal analyses, and BET, and their magnetic properties were measured. The parent compound, 1, crystallizes in the monoclinic system, space group P21/c, a = 11.254(2) A, b = 9.832(1) A, c = 18.108(3) A, beta = 127.222(2) degrees , V = 1595.5(4) A3, Z = 4, R1 = 0.0329 at 180 K. It possesses a unit cell volume that is 9% smaller than [Mn3(HCOO)6](CH3OH)(H2O) due to the smaller radius of Co2+ ion. Compared with the parent compound 1, the desolvated compound 2 has slightly larger lattice with cell parameters of a = 11.2858(4) A, b = 9.8690(4) A, c = 18.1797(6) A, beta = 127.193(2) degrees , V = 1613.0(1) A3, R1 = 0.0356 at 180 K. The cell parameters of 2, obtained from neutron powder data at 2 K, are a = 11.309(2) A, b = 9.869(1) A, c = 18.201(3) A, beta = 127.244(8) degrees , V = 1617.3(5) A3. The pore volume reduces from 33% to 30% by replacing Mn by Co. The material exhibits a diamond framework based on Co-centered CoCo4 tetrahedral nodes, in which all metal ions have octahedral coordination geometry and all HCOO groups link the metal ions in syn-syn/anti modes. It displays thermal stability up to 270 degrees C. The compound easily loses guest molecules without loss of crystallinity, and it partly reabsorbs water from the atmosphere. Significant N2 sorption was observed for the desolvated framework suggesting that the material possesses permanent porosity. The magnetic properties show a tendency to a 3D long-range magnetic ordering, probably antiferromagnetic with a spin canting arrangement below 2 K.     

Structure determination and relative properties of novel noncentrosymmetric borates MM'4(BO3)3 (M = Na, M' = Ca and M = K, M' = Ca, Sr)

A series of novel noncentrosymmetric borates, MM'4(BO3)3 (M = Na, M' = Ca; M = K, M' = Ca, Sr), have been successfully synthesized via a standard solid-state reaction. The crystal structures have been determined by the SDPD (structure determination from powder diffraction) method. They crystallize in the noncentrosymmetric space group Ama2 with the following lattice parameters: a = 10.68004(11) A, b = 11.28574(11) A, c = 6.48521(6) A for NaCa4(BO3)3; a = 10.63455(10) A, b = 11.51705(11) A, c = 6.51942(6) A for KCa4(BO3)3; and a = 11.03843(8) A, b = 11.98974(9) A, c = 6.88446(5) A for KSr4(BO3)3. The fundamental building units are isolated BO3 anionic groups. Their second harmonic generation (SHG) coefficients were one-half (NaCa4(BO3)3), one-third (KCa4(BO3)3), and two-thirds (KSr4(BO3)3) as large as that of KH2PO4 (KDP). The infrared and UV-vis spectra of the three compounds are discussed. Moreover, a comparison of the structures of these novel compounds and three other novel cubic compounds with the same formula, MM'4(BO3)3 (M = Li, M' = Sr; M = Na, M' = Sr, Ba), is presented here.     

STRUCTURE OF（C6H5COCHCOC6H5）SmI2（THF）3

<正> (C6H5COCHCOC6H5)SmI2(THF)3,Mr= 843. 75,triclinic space group P1,a=13. 274(3),b=9. 886(3),c= 12. 526(4)A,a= 110. 89(3),B=93. 98(2),y=85. 16(2) ,V=1528. 9(8)A3,Z=2,Dc=1. 83g/cm3, (MoKa) = 0. 71069A,u= 40. 3cm-1,F(000) - 810. The structure was solved by Patterson and Fourier techniques and refined by least-squares method to a final conventional R value of 0.082(Rw= 0. 083). The central Sm(III) ion is coordinated by two iodine ions, two oxygen atoms from C6H5COCHCOC6H5 and three oxygen atoms from three THF molecules to form a distorted pentagonal bipyramid. The Sm-I distances are 3. 103 and 3. 092 A ,The Sm-O (O atom from C6H5COCHCOC6H5) distances are 2. 273 and 2. 307 A and the average Sm -O(THF) distance is 2. 500A.     

束-气条件下He(23S)与CH3Cl及CH3I的传能研究

在束-气条件下，通过检测产物的化学发光，研究了亚稳电子激发态He（23S）原子与CH3Cl、CH3I传能反应.采用参比反应的方法，测得了由上述反应产生的主要碎片CH（A2△）、CH（B2∑-）、CH（C2∑+）和H*形成速率常数．通过对测得的CH（A2△－X2∏r）和CH（B2∑-－X2∏r）色散谱进行计算机模拟，获得了初生态的CH（A2△，v＝0－2）和CH（B2∑-，v＝0态）的振动-转动布居，实验结果表明，CH（A2△，v＝0）态的转动布居是呈双Boltzman分布的，并且反应的可资用能大部分将转变成产物的平动能．根据实验结果和反应阈能的分析，本文对He（23S）与CH3Cl／CH3I传能反应机理进行了探讨。     

Ground and low-lying excited states of propadienylidene (H2C=C=C:) obtained by negative ion photoelectron spectroscopy

A joint experimental-theoretical study has been carried out on electronic states of propadienylidene (H(2)CCC), using results from negative-ion photoelectron spectroscopy. In addition to the previously characterized X(1)A(1) electronic state, spectroscopic features are observed that belong to five additional states: the low-lying ?(3)B(1) and b(3)A(2) states, as well as two excited singlets, ?(1)A(2) and B(1)B(1), and a higher-lying triplet, c(3)A(1). Term energies (T(0), in cm(-1)) for the excited states obtained from the data are: 10,354±11 (?(3)B(1)); 11,950±30 (b(3)A(2)); 20,943±11 (c(3)A(1)); and 13,677±11 (?(1)A(2)). Strong vibronic coupling affects the ?(1)A(2) and B(1)B(1) states as well as ?(3)B(1) and b(3)A(2) and has profound effects on the spectrum. As a result, only a weak, broadened band is observed in the energy region where the origin of the B(1)B(1) state is expected. The assignments here are supported by high-level coupled-cluster calculations and spectral simulations based on a vibronic coupling Hamiltonian. A result of astrophysical interest is that the present study supports the idea that a broad absorption band found at 5450 ? by cavity ringdown spectroscopy (and coincident with a diffuse interstellar band) is carried by the B(1)B(1) state of H(2)CCC.     

Synthesis, spectroscopic, and structural studies on transition metal complexes involving homoleptic tripodal selenoether and telluroether coordination

The reaction of [MCl2(NCMe)2] (M = Pd or Pt) with 2 molar equiv of MeC(CH2ER)3 (E = Se, R = Me; E = Te, R = Me or Ph) and 2 molar equiv of TlPF6 affords the bis ligand complexes [M(MeC(CH2ER)3)2][PF6]2. The crystal structure of [Pt(MeC(CH2SeMe)3)2][PF6]2 (C16H36F12P2PtSe6, a = 12.272(10) A, b = 18.563(9) A, c = 15.285(7) A, beta = 113.18(3) degrees, monoclinic, P2(1)/n, Z = 4) confirms distorted square planar Se4 coordination at Pt(II), derived from two bidentate tripod selenoethers with the remaining arm not coordinated and directed away from the metal center. Solution NMR studies indicate that these species are fluxional and that the telluroether complexes are rather unstable in solution. The octahedral bis tripod complexes [Ru(MeC(CH2SMe)3)2][CF3-SO3]2 and [Ru(MeC(CH2TePh)3)2][CF3SO3]2 are obtained from [Ru(dmf)6][CF3SO3]3 and tripod ligand in EtOH solution. The thioether complex (C18H36F6O6RuS8, a = 8.658(3) A, b = 11.533(3) A, c = 8.659(2) A, alpha = 108.33(2) degrees, beta = 91.53(3) degrees, gamma = 106.01(2) degrees, triclinic, P1, Z = 1) is isostructural with its selenoether analogue, involving two facially coordinated trithioether ligands in the syn configuration. NMR spectroscopy confirms that this configuration is retained in solution for all of the bis tripod Ru(II) complexes. These low-spin d6 complexes show unusually high ligand field splittings. The hexaselenoether Rh(III) complex [Rh(MeC(CH2SeMe)3)2][PF6]3 was obtained by treatment of [Rh(H2O)6]3+ with 2 molar equiv of MeC(CH2SeMe)3 in aqueous MeOH in the presence of excess PF6- anion, while the iridium(III) analogue [Ir(MeC(CH2SeMe)3)2][PF6]3 was obtained via the reaction of the Ir(I) precursor [IrCl(C8H14)2]2 with the selenoether tripod in MeOH/aqueous HBF4. NMR studies reveal different invertomers in solution for both the Rh and Ir species. The Cu(I) complexes [Cu(MeC(CH2ER)3)2]PF6 were obtained from [Cu(NCMe)4]PF6 and tripod ligand in CH2Cl2 solution. The corresponding Ag(I) species [Ag(MeC(CH2TeR)3)2]CF3SO3 (R = Me or Ph) were obtained from Ag[CF3SO3] and tripod telluroether. In contrast, a similar reaction with 2 molar equiv of MeC(CH2SeMe)3 afforded only the 1:1 complex [Ag(MeC(CH2SeMe)3)]CF3SO3. The structure of this species (C9H18AgF3O3SSe3, a = 8.120(3) A, b = 15.374(3) A, c = 14.071(2) A, beta = 93.86(2) degrees, monoclinic, P2(1)/n, Z = 4) reveals a distorted trigonal planar geometry at Ag(I) derived from one bidentate selenoether and one monodentate selenoether. These units are then linked to adjacent Ag(I) ions to give a one-dimensional linear chain cation.