Phosphine coordination complexes of the diphenylphosphenium cation: a versatile synthetic methodology for P-P bond formation

A series of phosphine-diphenylphosphenium donor-acceptor cationic complexes have been synthesized and comprehensively characterized (phosphine = diphenylchlorophosphine, triphenylphosphine, trimethylphosphine, and tricyclohexylphosphine). The complexes involve homoatomic P-P coordinate bonds that are susceptible to ligand exchange reactions highlighting a versatile new synthetic method for P-P bond formation. Phosphenium complexes of 1,2-bis(diphenylphosphino)benzene and 1,2-bis(tert-butylphosphino)benzene undergo unusual rearrangements to give a "segregated" diphosphine-phosphonium cation and a cyclic di(phosphino)phosphonium cation, respectively. The rearrangement products reveal the kinetic stability of the phosphine-phosphenium bonding arrangement.     

Resonance effect in the allyl cation and anion: a revisit

The interest over the magnitude of the conjugation effect in the allyl cation (1) and anion (2) has been revived recently by Barbour and Karty (J. Org. Chem. 2004, 69, 648-654), who derived the resonance energies of 20-22 and 17-18 kcal/mol for 1 and 2, respectively, using an empirical extrapolation approximation. This paper revisits the case by explicitly calculating the Pauling-Wheland resonance energy, which measures the stabilization from the most stable resonance structure to the delocalized energy-minimum state of a conjugated system, using our newly developed block-localized wave function (BLW) method. This BLW method has the geometrical optimization capability. The computations result in adiabatic resonance energies of 37 kcal/mol for 1 and 38 kcal/mol for 2. The significant disagreement between these values and Barbour and Karty's results originates from the neglect of structural and electronic variations in their derivation which are energy costing.     

Magnetic anisotropy and molecular assembling in d complex cation–f complex anion type coordination compounds

The system [Fe(bpca)₂][Er(NO₃)₄(H₂O)₂] (1) (Hbpca = bis(2-pyridil-carbonyl) amine) is a complex cation–complex anion type coordination compound consisting of distinct d and f units, interlinked by hydrogen bonds. Particularly, the association of f-type complex anions in dimers is remarked and discussed. The energy decomposition analyses based on DFT calculations offered supplementary insight into the coordination effects at the lanthanide ions and the hydrogen bond driven supramolecular association of the complex units. Special ab initio procedures and subsequent modeling afforded the computation of anisotropic magnetization tensors of the [Er(NO₃)₄(H₂O)₂]^? f-type units. The computed results are in line with the experimental data for compound 1.     

Platinum coordination compounds of thiosemicarbazide derivatives: a new class of platinum blues

Platinum(II) forms blue 1?:?2 coordination compounds with 1-phenylthiosemicarbazide [H(1-PTSC)], 4-phenylthiosemicarbazide [H(4-PTSC)], 1,4-diphenylthiosemicarbazide [H(1,4-DPTSC)] and 4-(2-pyridyl)-thiosemicarbazide [H(4-(2py)-TSC)]. Electronic spectra of these compounds have been studied in different solvents. In all compounds, a band is observed in the 650–750?nm region that appears to be a metal-to-ligand charge transfer band. Infrared and proton NMR studies have been carried out to determine possible coordination sites and the nature of the complexes. IR spectra indicate bonding through sulfur and nitrogen and proton NMR spectra indicate bonding through the N¹nitrogen.     

Coumarin-strapped calix[4]pyrrole: a fluorogenic anion receptor modulated by cation and anion binding

A new strapped calix[4]pyrrole containing a fluorophore as part of the strap has been synthesized and characterized. Association constants with various anions have been determined using both fluorescence titration and isothermal titrations calorimetry (ITC). The two sets of association constants were found to be in good agreement with one another. The fluorescence emission properties of this new receptor could be controlled by addition of Na+ (or H2O) and anions. However, the fluorescence quenching by anions is only observed in the presence of Na+ (or H2O). All the experimental evidence is consistent with the notion that independent PET processes are modulated by separate cation and anion recognition events. As such, this system operates as an elementary logic gate wherein anion and cation concentrations serve as the input and fluorescence intensity changes provide the output.     

Supramolecular assemblies based on organometallic quinonoid linkers: a new class of coordination networks

Self-assembly of coordination frameworks exhibiting original architectures is an active area of research. Generally, such assemblies are constructed from organic spacers and transition metals of different geometrical structures. Herein, we report a novel class of supramolecular coordination assemblies with organometallic linkers based on metalated quinonoid and thioquinonoid complexes that serve as spacers. The organometallic ligands are stable and have the general formula [Cp*M(eta(4)-benzoquinone)] (o- and p-benzoquinone, Cp*=C(5)Me(5), M=Rh, Ir) and [Cp*Ir(eta(4)-thiobenzoquinone)] (o- and p-thiobenzoquinone). These units bind through both oxygen or sulfur atoms to metal ions of different coordination geometry, such as Cu(I), Ag(I), and Pt(II), to generate supramolecular coordination networks, with the metalated quinonoid or thioquinonoid linkers acting as backbones and the metal centers as nodes. This novel family of supramolecular assemblies exhibits short pi-pi and MM interactions. These results illustrate successfully the role of the organometallic linkers to produce an impressive range of novel supramolecular architectures that hold promise for the development of functional materials.     

Spectroscopic studies of anion complexes and clusters: a microscopic approach to understanding anion solvation

Recent infrared spectroscopic studies of negatively charged clusters in the gas phase have furnished new information on non-covalent bonds between anions and neutral molecules, and provided fresh perspectives on the microscopic details of anion solvation. We describe the central spectroscopic techniques employed for obtaining infrared spectra of mass-selected solvated anions in the gas phase, and illustrate recent progress by describing studies of simple halide-H2 dimers, and larger clusters in which up to 9 C2H2 molecules are attached to a Cl- anion.     

Anion coordination and cation packing in oxides

It is shown by considering a few examples that oxide structures are usefully described in terms of their cation packings and the coordination of the anions by these cations. This, together with a consideration of nonbonded repulsions between the atoms, leads simply to a rationalization of some crystal structures and coordination numbers, and to an understanding of the volume changes in certain phase transitions.     

Bisxantphos: Stereoselective synthesis and coordination behaviour of a new class of cyclic double bridged diphosphines

A new class of cyclic double bridged diphosphine ligands was developed and the coordination properties are described. The reaction of 4,5-dilithioxanthene with dichlorophenylphosphine gave a cyclic double bridged diphosphine ligand based on two xanthene backbones (4) as a single stereoisomer. X-ray crystal structure determination revealed that the groups bridging the two phosphorus atoms are arranged in a syn-disposition. This new cyclic bisxantphos structure was modified with bulky residues at the third substituent of the phosphorus atoms, thus forming cavity-shaped ligands.     

Novel CuIII bis-1,2-dichalcogenene complexes with tunable 3D framework through alkaline cation coordination: a structural and theoretical study

The deprotonated form of the ligands pyrazine-2,3-diselenol (pds) and pyrazine-2,3-dithiol (pdt) react with Cu(ClO(4))(2).6 H(2)O to form different Cu(III) complexes Na[Cu(III)(pds)(2)].2 H(2)O (1), Li[Cu(III)(pds)(2)].3 H(2)O (2), and Na[Cu(III)(pdt)(2)].2 H(2)O (4) depending on the countercation compound used as deprotonating agent (NaOH, LiOH). Two other Cu(III) complexes were obtained by replacement of the alkali metal cations with tetrabutylammonium (TBA(+)), namely, TBA[Cu(III)(pds)(2)] (3), and TBA[Cu(III)(pdt)(2)] (5). All complexes were characterized by (1)H and (13)C NMR and IR spectroscopy, electronic absorption, elemental analysis, cyclic voltammetry (CV), and X-ray crystallography. Electrical conductivity measurements on single crystals show that these salts exhibit insulating behavior. The crystal structure of these species revealed a lateral coordination capability of the N atoms of the pyrazine ring of both pds and pdt ligands towards the alkali metal ions, which leads to the build up of a net of coordinative bonds, hydrogen bonds, and contacts that result in the final 3D structure. Two parameters control the crystal engineering of the final 3D structures: the nature of the alkali metal countercation and the nature of the chalcogen atom (Se/S), which allow fine-tuning of complex 3D crystal lattice. Density functional calculations were performed on the [Cu(pds)(2)] and [Cu(pdt)(2)] systems to investigate the electronic structure of the complexes and understand their electronic and electrochemical behavior by studying the frontier molecular orbitals. This study also reveals whether the redox processes take place on the ligands or on the metal center, a question under continuous discussion in the literature.     

Polynuclear lanthanide hydroxo complexes: new chemical precursors for coordination polymers

The synthesis of hexanuclear lanthanide hydroxo complexes by controlled hydrolysis led to polymorphic compounds. The hexanuclear entities crystallize in four different ways that depend on the extent of their hydration. The four structures can be described as hexanuclear lanthanide entities with formula [Ln(6)(mu(6)-O)(mu(3)-OH)(8)(NO(3))(6)(H(2)O)(12)](2+). Two additional NO(3)(-) ions intercalate between the hexanuclear entities in order to ensure the electroneutrality of the crystal structure. Some crystallization water molecules fill the intermolecular space. The three first families of compounds (1-3) exhibit crystal structures that have previously been reported. The fourth family of compounds (4) is described here for the first time. Its chemical formula is [Ln(6)(mu(6)-O)(mu(3)-OH)(8)(NO(3))(6)(H(2)O)(12)](NO(3))(2).2H(2)O (Ln = Gd, Er, and Y). In this paper, the chemical and thermal stabilities of the hexanuclear lanthanide compounds are reported together with the magnetic properties of the Gd(III)-containing species. To use these entities as precursors for new materials, the substitution of the nitrato groups by chloride ions has been studied. Two byproduct compounds have so been obtained: The first (compound 5) is a nitrato/chloride hexanuclear compound of chemical formula [Er(6)(mu(6)-O)(mu(3)-OH)(8)(NO(3))(6)(H(2)O)(12)](NO(3))Cl.2H(2)O. The second one (compound 6) is a polymeric compound in which the hexanuclear entities are linked by an unexpected and original N(2)O(4) bridge. Its chemical formula is [Er(6)(mu(6)-O)(mu(3)-OH)(8)(NO(3))(4)(H(2)O)(11)(OH)(ONONO(2))]Cl(3).2H(2)O. Its crystal structure can be described as the juxtaposition of chainlike molecular motifs. To the best of our knowledge, this is the first example of a coordination polymer synthesized from an isolated polylanthanide hydroxo complex.     

Cobalt coordination in cation exchange resins

Cobaltous ions were sorbed from chloride and nitrate solutions on a sulfonic cation exchange resin of various crosslinkings. The spectral characteristics of the dried resins showed that in all cases tetrahedral species have been preferentially sorbed. The composotion of the species sorbed depends on the crosslinking of the resin and is essentially a function of hydration, electrolyte uptake and interaction with the sulfonic group.     

A one-pot pseudo nine-component isocyanide-based reaction: synthesis of a new class of zinc 1,5-disubstituted 1H-tetrazol-5-yl coordination complexes

A novel one-pot pseudo nine-component synthesis of zinc 1,5-disubstituted 1H-tetrazol-5-yl coordination complexes in good yields starting from simple and readily available substrates, including a 1,3-dicarbonyl compound, an isocyanide, N,N-dimethylformamide dimethyl acetal, sodium azide, and zinc chloride in methanol at ambient temperature, is described.     

Surface-attached sensors for cation and anion recognition

The development of surface-attached sensors for cationic and anionic guests is of intense current research interest. In addition to the environmental flexibility, robustness and reusability of such devices, surface-confined sensors typically exhibit an amplified response to target analytes owing to preorganization of the receptor. Whereas redox-active cations may be sensed by studying the cyclic voltammetry of host–guest systems containing ion-selective receptors attached to an appropriate electrode, redox-inactive ionic species require the use of electrochemical impedance spectroscopy, with appropriately functionalized electrodes and redox probes. Alternatively, receptors may be constructed that incorporate an electrochemical or optical reporter group within their structure to provide a macroscopic response to the presence of an ionic guest. This critical review seeks to present an up-to-date, although necessarily selective, account of the progress in the field, and provides insights into possible future developments, including the utilization of receptor–nanoparticle conjugates and mechanically interlocked receptors.     

A unique coordination environment for an ion: EXAFS studies and bond valence model approach of the encapsulated cation in the Preyssler anion

X-Ray absorption spectroscopy was used to probe the coordination of different encrypted cations in the Preyssler anions [M(n+)P5W(30)O(110)]((15-n)-)(M(n+)= Sr2+, Am3+, Eu3+, Sm3+, Y3+, Th4+, U4+ in decreasing order of ionic radius, IR), hereafter abbreviated [M(n+)PA](15-n)-. The increase of the M-W distance and the decrease of the M-P distance with increasing M ionic radius reveal that the M cation is displaced along the C5 axis within the Preyssler cavity. The slight change (0.07 A) of the M-O distance that does not correspond to the IR difference of 0.27 A confirms that the cavity retains its rigidity upon cation substitution. Geometric modeling of the encapsulated cation in the channel was performed for comparison to the EXAFS results. The position of the cation in the cavity was calculated as well as the M-O10, -W5 and -P5 distances. This modeling confirms the cation displacement toward the center of the Preyssler anion as the cation size increases, which is understood in terms of the non-homogenous electrostatic potential present within the cavity. The bond valence model approach was applied to obtain experimental bond valences. Only the bond valence sum (BVS) of Am3+ is close to its actual charge. Sums smaller than the actual valences of the +3 and +4 ions (2.39-2.63 for +3 cations, Y, Sm, Eu; 3.17 and 3.38 for +4 cations, U and Th, respectively) were obtained, and a larger sum (2.89) was obtained for Sr2+. The deviations from the formal M sums of the encapsulated ions are attributed to the rigidity of the Preyssler framework. The tendency toward coordinative unsaturation for electroactive cations, such as Eu3+, is thought to be the driving force for facile reduction. Unlike other inorganic chelating ligands, the Preyssler anion provides a unique redox system to stabilize an electroactive cation in a low oxidation state.