Photophysical, electrochemical and anion sensing properties of Ru(II) bipyridine complexes with 2,2'-biimidazole-like ligand

A new anion sensor [Ru(bpy)(2)(DMBbimH(2))](PF(6))(2) (3) (bpy is 2, 2'-bipyridine and DMBbimH(2) is 7,7'-dimethyl-2,2'-bibenzimidazole) has been developed. Its photophysical, electrochemical and anion sensing properties are compared with two previously investigated systems, [Ru(bpy)(2)(BiimH(2))](PF(6))(2) (1) and [Ru(bpy)(2)(BbimH(2))](PF(6))(2) (2) (BiimH(2) is 2,2'-biimidazole and BbimH(2) is 2,2'-bibenzimidazole). The high acidity of the N-H fragments in these complexes make them easy to be deprotonated by strong basic anions such as F(-) and OAc(-), and they form N-H···X hydrogen bonds with weak basic anions like Cl(-), Br(-), I(-), NO(3)(-), and HSO(4)(-). Complex 3 displays strong hydrogen bonding with these 5 weak basic anions, with binding constants between 17,000 and 21,000, which are larger than those observed in complex 1, with binding constants between 3300 and 5700, and in complex 2, which shows no hydrogen bonding toward Cl(-), Br(-), I(-), and NO(3)(-), and forms considerable hydrogen bonds with HSO(4)(-) with a binding constant of 11,209. These hydrogen bonding behaviours give different NMR, emission and electrochemical responses. The different anion binding affinity of these complexes may be mainly attributed to their different pK(a1) values, 7.2 for 1, 5.7 for 2, and 6.2 for 3. The additional methyl groups at the 7 and 7' positions of complex 3 may also play an important role in the enhancement of anion binding strength.     

Metal complexes of tetrapodal ligands: synthesis, spectroscopic and thermal studies, and X-ray crystal structure studies of Na(I), Ca(II), Sr(II), and Ba(II) complexes of tetrapodal ligands N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine and N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine

Twelve complexes 1-12 of general category [M(ligand)(anion)(x)(water)(y)], where ligand = N,N,N',N'-tetrakis(2-hydroxypropyl/ethyl)ethylenediamine (HPEN/HEEN), anion = anions of picric acid (PIC), 3,5-dinitrobenzoic acid (DNB), 2,4-dinitrophenol (DNP), and o-nitrobenzoic acid (ONB), M = Ca(2+), Sr(2+), Ba(2+), or Na(+), x = 1 and 2, and y = 0-4, were synthesized. All of these complexes were characterized by elemental analysis, IR, (1)H and (13)C NMR, and thermal studies. X-ray crystal studies of these complexes 1-12, [Ca(HPEN)(H(2)O)(2)](PIC)(2).H(2)O (1), [Ca(HEEN)(PIC)](PIC) (2), Ba(HPEN)(PIC)(2) (3), [Na(HPEN)(PIC)](2) (4), Ca(HPEN)(H(2)O)(2)](DNB)(2).H(2)O (5),Ca(HEEN)(H(2)O)](DNB)(2).H(2)O (6), [Sr(HPEN)(H(2)O)(3)](DNB)(2) (7), [Ba(HPEN)(H(2)O)(2)](DNB)(2).H(2)O](2) (8), [[Ba(HEEN)(H(2)O)(2)](ONB)(2)](2) (9), [[Sr(HPEN)(H(2)O)(2)](DNP)(2)](2) (10), [[Ba(HPEN)(H(2)O)(2)](DNP)(2)](2) (11), and [Ca(HEEN)(DNP)](DNP) (H(2)O) (12), have been carried out at room temperature. Factors which influence the stability and the type of complex formed have been recognized as H-bonding interactions, presence/absence of solvent, nature of the anion, and nature of the cation. Both the ligands coordinate the metal ion through all the six available donor atoms. The complexes 1 and 5-11 have water molecules in the coordination sphere, and their crystal structures show that water is playing a dual character. It coordinates to the metal ion on one hand and strongly hydrogen bonds to the anion on the other. These strong hydrogen bonds stabilize the anion and decrease the cation-anion interactions by many times to an extent that the anions are completely excluded out of the coordination sphere and produce totally charge-separated complexes. In the absence of water molecules as in 2 and 3 the number of hydrogen bonds is reduced considerably. In both the complexes the anions case interact more strongly with the metal ion to give rise to a partially charge-separated 2 or tightly ion-paired 3 complex. High charge density Ca(2+) forms only monomeric complexes. It has more affinity toward stronger nucleophiles such as DNP and PIC with which it gives partially charge-separated eight-coordinated complexes. But with relatively weaker nucleophile like DNB, water replaces the anion and produces a seven coordinated totally charge-separated complex. Sr(2+) with lesser charge/radius ratio forms only charge-separated monomeric as well as dimeric complexes. Higher coordination number of Sr(2+) is achieved with coordinated water molecules which may be bridging or nonbridging in nature. All charge-separated complexes of the largest Ba(2+) are dimeric with bridging water molecules. Only one monomeric ion-paired complex was obtained with Ba(PIC)(2). Na(+) forms a unique dinuclear cryptand-like complex with HPEN behaving as a heptadentate chelating-cum-bridging ligand.     

Ruthenium(II) 2,2'-bibenzimidazole complex as a second-sphere receptor for anions interaction and colorimeter

A ruthenium(II) complex [Ru(bpy) 2(H 2bbim)](PF 6) 2 ( 1) as anions receptor has been exploited, where Ru(II)-bpy moiety acts as a chromophore and the H 2bbim ligand as an anion binding site. A systematic study suggests that 1 interacts with the Cl (-), Br (-), I (-), NO 3 (-), HSO 4 (-), and H 2PO 4 (-) anions via the formation of hydrogen bonds. Whereas 1 undergoes a stepwise process with the addition of F (-) and OAc (-) anions: formation of the monodeprotonated complex [Ru(bpy) 2(Hbbim)] with a low anion concentration, followed by the double-deprotonated complex [Ru(bpy) 2(bbim)], in the presence of a high anion concentration. These stepwise processes concomitant with the changes of vivid colors from yellow to orange brown and then to violet can be used for probing the F (-) and OAc (-) anions by naked eye. The deprotonation processes are not only determined by the basicity of the anion but also related to the strength of hydrogen bonding, as well as the stability of the formed compounds. Moreover, a double-deprotonated complex [Ru(bpy) 2(bbim)].CH 3OH.H 2O ( 3) has been synthesized, and the structural changes induced by the deprotonation has also been investigated. In addition, complexes [Ru(bpy) 2(Hbbim)] 2(HOAc) 3Cl 2.12H 2O ( 2), [Ru(bpy) 2(Hbbim)](HCCl 3CO 2)(CCl 3CO 2).2H 2O ( 4), and [Ru(bpy) 2(H 2bbim)](CF 3CO 2) 2.4H 2O ( 5) have been synthesized to observe the second sphere coordination between the Ru(II)-H 2bbim moiety and carboxylate groups via hydrogen bonds in the solid state.     

Contribution of the intramolecular hydrogen bond to the shift of the pKa value and the oxidation potential of phenols and phenolate anions

Intramolecularly OHO[double bond, length as m-dash]C hydrogen bonded phenols, 2-HO-C6H2-3,5-(t-Bu)2-CONH-t-Bu (1-OH), 2-HO-C6H2-5-t-Bu-1,3-(CONH-t-Bu)2 (2-OH) and 2-HO-C6H2-3,5-(t-Bu)2-NHCO-t-Bu (4-OH), were synthesized and their phenolate anions were prepared as tetraethylammonium salts (-1O-(NEt4+), 2-O-(NEt4+) and 4-O-(NEt4+)) with intramolecular NHO(oxyanion) hydrogen bonds. 4-HO-C(6)H(2)-3,5-t-Bu(2)-CONH-t-Bu (3-OH) and its phenolate anion, 3-O-(NEt4+), were synthesized as non-hydrogen bonded references. The presence of intramolecular hydrogen bonds was established through the crystallographic analysis and/or (1)H NMR spectroscopic results. Intramolecular NHO(phenol) hydrogen bonds shift the pK(a) of the phenol to a more acidic value. The results of cyclic voltammetry show that the intramolecular OH...O=C hydrogen bond negatively shifts the oxidation potential of the phenol. In contrast, the intramolecular NHO(oxyanion) hydrogen bond positively shifts the oxidation potential of the phenolate anion, preventing oxidation. These contributions of the hydrogen bond to the pKa value and the oxidation potentials probably play an important role in the formation of a tyrosyl radical in photosystem II.     

Imidazolium-based macrocycles as multisignaling chemosensors for anions

A series of structurally novel anion receptors , , and in which a ferrocene unit and a fluorescent moiety are linked to two imidazolium rings have been designed and prepared from 1,1'-bis(imidazolylmethyl)ferrocene. Their crystal structures revealed that these receptors are capable of incorporating anions such as PF(6)(-) and Br(-). Consequently, the anion binding studies were carried out using various techniques including electrochemistry (CV and OSWV), fluorescence, UV-vis, and (1)H NMR spectroscopy. All the receptors showed a special electrochemical response to the F(-) anion with a remarkable cathodic shift of more than 260 mV and displayed a unique selectivity for F(-) and AcO(-) anions with fluorescence enhancement over various other anions of present interest (Cl(-), Br(-), I(-), HSO(4)(-), H(2)PO(4)(-)). In addition, for receptor , obvious absorption changes were observed when the H(2)PO(4)(-) anion was added while other anions (F(-), Cl(-), Br(-), I(-), AcO(-), HSO(4)(-)) showed only a minor influence on the UV-vis spectra. (1)H NMR titrations demonstrated that receptors and can bind anions through (C-H)(+)X(-) hydrogen bonds and showed strong affinity and high selectivity for the AcO(-) anion in acetonitrile.     

Fluoride-selective colorimetric sensor based on thiourea binding site and anthraquinone reporter

A structurally simple colorimetric sensor, N-4-nitrobenzene-N'-1'-anthraquinone-thiourea (1), for anions was synthesized and characterized by (1)H NMR, ESI mass and IR methods. In acetonitrile, the addition of F(-) changed 1 solution from colorless to yellow. In the presence of other anions such as CH(3)CO(2)(-), H(2)PO(4)(-), HSO(4)(-) and Cl(-), however, the absorption spectrum of 1 was slightly red shifted with no obvious color changes observed. The association constants of anionic complexes followed the order of F(-)>CH(3)CO(2)(-)>H(2)PO(4)(-)>HSO(4)(-)>Cl(-)>Br(-), which was different from the order of anion basicity. AM1 calculation results indicated that the most stable configuration of 1 existed in the Z-E-conformation with a six-membered ring via intramolecular hydrogen bond. This made thiourea moiety of 1 in an unfavorable conformation to bond with oxygen-anionic substrates such as CH(3)CO(2)(-) and H(2)PO(4)(-), thus leading to a high selectivity and sensitivity for the detection of F(-).     

Activation of C--H... Halogen (Cl, Br, and I) hydrogen bonds at the organic/inorganic interface in fluorinated tetrathiafulvalenes salts

The electrocrystallization of fluorinated bis(2,2'-difluoropropylenedithio)tetrathiafulvalene (1) in the presence of linear (ICl2-, IBr2-, I2Br-) or cluster ([Mo6Cl14]2-) anions affords 1:1 and 2:1 cation radical salts such as [1][ICl2] and [1]2[Mo6Cl14].(CH3CN)2. In both salts, the 1*+ radical ion adopts a boat conformation and envelops the anion through C-H...Hal(anion) (Hal(anion) = Cl, Br, I) hydrogen bonds. This demonstrates the activating role of the neighboring electron-withdrawing CF2 moieties in the stabilization of bi- or trimolecular neutral entities. With smaller linear anions, fluorine segregation controls the solid-state associations of the bimolecular [1]*+[X] entities, and gives rise to layered materials with a limited overlap interaction between the open-shell organic cations and magnetic spin chain behavior. With the larger [Mo6Cl14]2 ions, a strong overlap interaction between radical cations gives rise to diamagnetic [1]2(2+) dimers, which alternate with the cluster anions to form hybrid organic/inorganic ...[1]2(2+)[Mo6Cl14]2... chains. This behavior is also observed in [2]2(2+)[Mo6Cl14]2-.(CH2Cl2)2, in which compound 2 is the unsymmetrically substituted (ethylenedithio)(2,2'-difluoropropylenedithio)tetrathiafulvalene. On the other hand, the unsymmetrically substituted 2,2'-difluoropropylenedithiotetrathiafulvalene (3) affords a mixed-valence 4:1 salt with [Mo6Cl14]2, which is formulated as [3]4[Mo6Cl14].(CH3CN)2. This semiconducting salt is characterized by the coexistence of both the fluorine/fluorine segregation (with solvent inclusion) and the organic/inorganic segregation (with delocalized overlap interactions). Both Csp2-H...Cl and Csp3-H...Cl hydrogen bonds facilitate the stabilization of the organic/inorganic interface and the presence of conducting organic slabs.     

Ab initio electronic structure study of one-electron reduction of polychlorinated ethylenes

Polychlorethylene radicals, anions, and radical anions are potential intermediates in the reduction of polychlorinated ethylenes (C(2)Cl(4), C(2)HCl(3), trans-C(2)H(2)Cl(2), cis-C(2)H(2)Cl(2), 1,1-C(2)H(2)Cl(2), C(2)H(3)Cl). Ab initio electronic structure methods were used to calculate the thermochemical properties, (298.15 K), S degrees (298.15 K,1 bar), and DeltaG(S)(298.15 K, 1 bar) of 37 different polychloroethylenyl radicals, anions, and radical anion complexes, C(2)H(y)Cl(3)(-)(y)(*), C(2)H(y)Cl(3)(-)(y)(-), and C(2)H(y))Cl(4)(-)(y)(*)(-) for y = 0-3, for the purpose of characterizing reduction mechanisms of polychlorinated ethylenes. In this study, 8 radicals, 7 anions, and 22 radical anions were found to have stable structures, i.e., minima on the potential energy surfaces. This multitude of isomers for C(2)H(y)Cl(4)(-)(y)(*)(-) radical anion complexes are pi*, sigma*, and -H...Cl(-) structures. Several stable pi* radical anionic structures were obtained for the first time through the use of restricted open-shell theories. On the basis of the calculated thermochemical estimates, the overall reaction energetics (in the gas phase and aqueous phase) for several mechanisms of the first electron reduction of the polychlorinated ethylenes were determined. In almost all of the gas-phase reactions, the thermodynamically most favorable pathways involve -H...Cl(-) complexes of the C(2)H(y)Cl(4)(-)(y)(*)(-) radical anion, in which a chloride ion is loosely bound to a hydrogen of a C(2)H(x)Cl(2)(-)(x))(*) radical. The exception is for C(2)Cl(4), in which the most favorable anionic structure is a loose sigma* radical anion complex, with a nearly iso-energetic pi* radical anion. Solvation significantly changes the product energetics with the thermodynamically most favorable pathway leading to C(2)H(y)Cl(3)(-)(y)(*) + Cl(-). The results suggest that a higher degree of chlorination favors reduction, and that reduction pathways involving the C(2)H(y)Cl(3)(-)(y)(-) anions are high energy pathways.     

Anion binding to a ferric porphyrin complexed with per-O-methylated beta-cyclodextrin in aqueous solution

5,10,15,20-Tetrakis(4-sulfonatophenyl)porphinato iron(III) (Fe(III)TPPS) forms a very stable 1:2 complex with heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin (TMe-beta-CD), whose iron(III) center is located at a hydrophobic cleft formed by two face-to-face TMe-beta-CD molecules. Various inorganic anions (X(-)) such as F(-), Cl(-), Br(-), I(-), N(3)(-), and SCN(-) coordinate to Fe(III)TPPS(TMe-beta-CD)(2) to form five-coordinate high-spin Fe(III)TPPS(X)(TMe-beta-CD)(2), while no coordination occurs with ClO(4)(-), H(2)PO(4)(-), NO(3)(-), and HSO(4)(-). Except for F(-), none of the anions investigated coordinate to Fe(III)TPPS in the absence of TMe-beta-CD due to extensive hydration to the anions as well as to Fe(III)TPPS. The present system shows a high selectivity toward the N(3)(-) anion. The thermodynamics suggests that Lewis basicity, hydrophilicity, and shape of an X(-) anion are the main factors to determine the stability of the Fe(III)TPPS(X)(TMe-beta-CD)(2) complex.     

Influence of anionic sulfonate-containing co-ligands on the solid structures of silver complexes supported by 4,4'-bipyridine bridges

In this paper, ten new silver compounds, namely [Ag(bipy)](L1).H2O (1), [Ag(bipy)](L2).2H2O (2), [Ag2(bipy)2(H2O)2](L3).H2O (3), [Ag(L4)(bipy)].H2O (4), [Ag(L5)(bipy)] (5), [Ag(L6)(bipy)].0.5CH3CN (6), [Ag3(L7)2(bipy)2].2(H2O) (7), [Ag2(L8)(bipy)1.5(H2O)].H2O (8), [Ag2(L9)(bipy)2(H2O)2] (9) and [Ag3(L10)(bipy)2][(bipy)(H2O)2].(H2O)3.5 (10) (where bipy = 4,4'-bipyridine, L1 = 6-amino-1-naphthalenesulfonate anion, L2 = 2-naphthalenesulfonate anion, L3 = sulfosalicylate anion, L4 = p-aminobenzenesulfonate anion, L5 = 4-dimethyaminoazobenzenen-4'-sulfonate anion, L6 = 2,5-dichloro-4-amino-benzenesulfonate anion, L7 = 8-hydroxyquinoline-5-sulfonate anion, L8 = 2-nitroso-1-naphthol-4-sulfonate anion, L9 = 2,6-naphthalenedisulfonate anion and L10 = 1,3,5-naphthalenetrisulfonate anion), have been synthesized and characterized by elemental analyses, IR spectroscopy and X-ray crystallography. In compounds 1-6, Ag(I) centers are linked by bipy ligands to form 1D Ag-bipy chain structures, in which the sulfonate anions of compounds 1-3 act as counter ions. The sulfonate anions of compounds 4 and 5 connect Ag-bipy chains to form 1D double chain structures, respectively. The sulfonate anions of compound 6 connect Ag-bipy chains to form a 2D layer structure. Unexpectedly, compound 7 shows a hinged chain structure, and these chains interlace with each other through hydrogen bonds and pi-pi interactions to generate a 3D structure with channels along the c axis. Compounds 8 and 9 show 1D ladder-like structures. In compound 10, the Ag-bipy chains are connected by sulfonate anions to generate a 3D poly-threaded network, in which an isolated Ag-bipy chain is inserted. The results indicate that the anionic sulfonate-containing co-ligands play an important role in the final structures of the Ag(I) complexes. Additionally, the luminescent properties of these compounds were also studied.     

Conversion of a Re(IV) tetrahedral cluster to a Re(III) octahedral cluster: synthesis of [(CH3)C(NH2)(2)](4)[Re(6)Se(8)(CN)(6)] by a solvothermal route

The compound [(CH(3))C(NH(2))(2)](4)[Re(6)Se(8)(CN)(6)] has been synthesized by the reaction at 200 degrees C for 3 days of Re(4)Te(4)(TeCl(2))(4)Cl(8), KSeCN, and NH(4)Cl in superheated acetonitrile. This compound crystallizes in the space group C2/c of the monoclinic system with four formula units in a cell of dimensions a = 20.3113(14) A, b = 10.1332(7) A, c = 19.9981(14) A, beta = 106.754(1) degrees, V = 3941.3(5) A(3) (T = 153 K). The [Re(6)Se(8)(CN)(6)](4-) anion comprises an Re(6) octahedron face capped by mu(3)-Se atoms, with each Re atom liganded by a CN group. The anions and cations are connected by an extensive network of hydrogen bonds. The conversion of a Re(IV) tetrahedral cluster to a Re(III) octahedral cluster appears to be unprecedented.     

Dimerization and anion binding of a fluorescent phospholipid analogue

A diarylacetylene fluorophore featuring spatially separated urea and phosphocholine (PC) groups forms a macrocyclic "head-to-tail" dimer stabilized by NH(urea)···OP(PC) hydrogen bonds. At concentrations above ～2 × 10(-5) M in CH(2)Cl(2), the emission intensity of the dimer is quenched by HCO(3)(-) and H(2)PO(4)(-) but not by Cl(-) and NO(3)(-). Under more dilute conditions, all four anions are bound unselectively with association constants on the order of 10(5) M(-1).     

Metallosupramolecular chemistry with bis(benzene-o-dithiolato) ligands

The bis(benzene-o-dithiol) ligands H(4)-1, H(4)-2, and H(4)-3 react with [Ti(OC(2)H(5))(4)] to give dinuclear triple-stranded helicates [Ti(2)L(3)](4)(-) (L = 1(4)(-), 2(4)(-), 3(4)(-)). NMR spectroscopic investigations revealed that the complex anions possess C(3) symmetry in solution. A crystal structure analysis for (PNP)(4)[Ti(2)(2)(3)] ((PNP)(4)[14]) confirmed the C(3) symmetry for the complex anion in the solid state. The complex anion in Li(PNP)(3)[Ti(2)(1)(3)] (Li(PNP)(3)[13]) does not exhibit C(3) symmetry in the solid state due to the formation of polymeric chains of lithium bridged complex anions. Complexes [13](4)(-) and [14](4)(-) were obtained as racemic mixtures of the Delta,Delta and Lambda,Lambda isomers. In contrast to that, complex (PNP)(4)[Ti(2)(3)(3)] ((PNP)(4)[15]) with the enantiomerically pure chiral ligand 3(4)(-) shows a strong Cotton effect in the CD spectrum, indicating that the chirality of the ligands leads to the formation of chiral metal centers. The o-phenylene diamine bridged bis(benzene-o-dithiol) ligand H(4)-4 reacts with Ti(4+) to give the dinuclear double-stranded complex Li(2)[Ti(2)(4)(2)(mu-OCH(3))(2)] containing two bridging methoxy ligands between the metal centers. The crystal structure analysis and the (1)H NMR spectrum of (Ph(4)As)(2)[Ti(2)(4)(2)(mu-OCH(3))(2)] ((Ph(4)As)(2)[(16]) reveal C(2) symmetry for the anion [Ti(2)(4)(2)(mu-OCH(3))(2)](2)(-). For a comparative study the dicatechol ligand H(4)-5, containing the same o-phenylene diamine bridging group as the bis(benzene-o-dithiol) ligands H(4)-4, was prepared and reacted with [TiO(acac)(2)] to give the dinuclear complex anion [Ti(2)(5)(2)(mu-OCH(3))(2)](2)(-). The molecular structure of (PNP)(2)[Ti(2)(5)(2)(mu-OCH(3))(2)] ((PNP)(2)[17]) contains a complex anion which is similar to [16](2)(-), with the exception that strong N-H...O hydrogen bonds are formed in complex anion [17](2)(-), while N-H...S hydrogen bonds are absent in complex anion [16](2)(-).     

{AsW9O33}-{Mo3S4} based polyoxometalates including a metal-metal bond with Pd or Ni. Synthesis, structure and studies in solution

Heterometallic cuboidal clusters [Mo(3)S(4)M(H(2)O)(9)Cl](3+) M = Pd or Ni react with the trivacant [AsW(9)O(33)](9-) anion to give tetramodular complexes [(H(2)AsW(9)O(33))(4){Mo(3)S(4)M(H(2)O)(5)}(2)](20-) (M = Pd for anion 2 and M = Ni for anion 3) in good yield. Both anions crystallized as single crystals of potassium salts to give K-2 and K-3 salts which have been characterized structurally by X-ray diffraction. Both compounds are isomorphous and the anions 2 and 3 are described as two dimeric moeties, associated by internal hydrogen bonds, electrostatic interactions involving four outer potassium ion and coordination bonds within a central {M(2)S(2)} unit containing a M-M metallic bond. Studies in solution reveal that the dimeric association is maintained in solution in the 2 × 10(-4)-2 × 10(-3) mol L(-1) range. Conversely, in the presence of exogeneous ligands, such as iodide or pyridine the UV-vis data are consistent with the dissociation of the anion 2 into monomer through a Pd-L coordination bond (L = I(-) or Py). Furthermore, (183)W NMR spectrum of 2 shows that molecular structure of 2 is retained in solution. Elemental analysis and IR are also supplied. Electrochemical behavior of 2 and 3 are given and compared with the Pd or Ni free parent anion. The CVs are dominated mainly by irreversible reduction or oxidation processes, where the peak potentials appear dependent upon the ionic charge of the complex. However, the CV of the Pd-containing anion (2) is consistent with the deposition of Pd metal at the electrode, which gives rise to an oxidation process into palladium oxide.     

Tricopper(II) complexes of unsymmetrical macrocycles incorporating phenol and pyridine moieties: the development of two stepwise routes

Two stepwise approaches to preparing large unsymmetrical macrocycles incorporating diethylenetriamine lateral units are described: the first utilises protecting group chemistry, whereas the second exploits irreversible amide bond formation in the presence of an excess of the amine. In the first approach condensation of two equivalents of N-acetyldiethylenetriamine 1 with 2,6-diformyl-4-methylphenol, followed by a sodium borohydride reduction of the newly formed imine bonds and acidic removal of the protecting groups, yields a phenol-containing "two-armed" precursor as an HCl salt 2. Using the second approach the new pyridine-containing "two-armed" precursor , is prepared from 2,6-dimethylpyridinedicarboxylate and an excess of diethylenetriamine. These two "two-armed" di-primary amine precursors, 2 (after reaction with KOH) and 3, can be condensed with the dicarbonyl head units of choice. The lead templated condensation of 2 with 2,6-diacetylpyridine results in the formation of the macrocyclic dilead(II) complex {[Pb(II)(2)(L1)(Cl)](ClO(4))(2)}(infinity) 4. Transmetallation of 4 with three equivalents of copper(II) perchlorate produces Cu(II)(3)(L1)(OH)(ClO(4))(4) 5. Condensation of 3 with 2,6-diacetylpyridine or 2,6-diformylpyridine in the presence of barium(ii) ions results in the macrocyclic complexes [Ba(II)(H(2)L2)](ClO(4))(2) 6 and [Ba(II)(H(2)L3)](ClO(4))(2) 7, respectively. Copper(II) acetate templates the formation of the crystallographically characterised unsymmetrical macrocyclic complex [Cu(II)(3)(L4)(OH)(NCS)(2)].EtOH, 8.EtOH, from 3, 2,6-diformyl-4-methylphenol and NaNCS.     

Two new "onium" fluorosilicates, the products of interaction of fluorosilicic acid with 12-membered macrocycles: structures and spectroscopic properties

Two novel compounds, (L(1)H)(2)[SiF(6)] x 2H(2)O (1) and (L(2)H)(2)[SiF(5)(H(2)O)](2) x 3H(2)O (2), resulting from the reactions of H(2)SiF(6) with 4'-aminobenzo-12-crown-4 (L(1)) and monoaza-12-crown-4 (L(2)), respectively, were studied by X-ray diffraction and characterised by IR and (19)F NMR spectroscopic methods. Both complexes have ionic structures due to the proton transfer from the fluorosilicic acid to the primary amine group in L(1) and secondary amine group incorporated into the macrocycle L(2). The structure of 1 is composed of [SiF(6)](2-) centrosymmetric anions, N-protonated cations (L(1)H)(+), and two water molecules, all components being bound in the layer through a system of NH[...]F, NH[...]O and OH[...]F hydrogen bonds. The [SiF(6)](2-) anions and water molecules are assembled into inorganic negatively-charged layers via OH[dot dot dot]F hydrogen bonds. The structure of 2 is a rare example of stabilisation of the complex anion [SiF(5)(H(2)O)](-), the labile product of hydrolytic transformations of the [SiF(6)](2-) anion in an aqueous solution. The components of 2, i.e., [SiF(5)(H(2)O)](-), (L(2)H)(+), and water molecules, are linked by a system of NH[...]F, NH[...]O, OH[...]F, OH[dot dot dot]O hydrogen bonds. In a way similar to 1, the [SiF(5)(H(2)O)](-) anions and water molecules in 2 are combined into an inorganic negatively-charged layer through OH[...]F and OH[...]O interactions.     

Factors affecting the solid-state structure and dimensionality of mercury cyanide/chloride double salts, and NMR characterization of coordination geometries

In the reaction of organic monocationic chlorides or coordinatively saturated metal-ligand complex chlorides with linear, neutral Hg(CN)(2) building blocks, the Lewis-acidic Hg(CN)(2) moieties accept the chloride ligands to form mercury cyanide/chloride double salt anions that in several cases form infinite 1-D and 2-D arrays. Thus, [PPN][Hg(CN)(2)Cl].H(2)O (1), [(n)Bu(4)N][Hg(CN)(2)Cl].0.5 H(2)O (2), and [Ni(terpy)(2)][Hg(CN)(2)Cl](2) (4) contain [Hg(CN)(2)Cl](2)(2-) anionic dimers ([PPN]Cl = bis(triphenylphosphoranylidene)ammonium chloride, [(n)Bu(4)N]Cl = tetrabutylammonium chloride, terpy = 2,2':6',6' '-terpyridine). [Cu(en)(2)][Hg(CN)(2)Cl](2) (5) is composed of alternating 1-D chloride-bridged [Hg(CN)(2)Cl](n)(n-) ladders and cationic columns of [Cu(en)(2)](2+) (en = ethylenediamine). When [Co(en)(3)]Cl(3) is reacted with 3 equiv of Hg(CN)(2), 1-D [[Hg(CN)(2)](2)Cl](n)(n-) ribbons and [Hg(CN)(2)Cl(2)](2-) moieties are formed; both form hydrogen bonds to [Co(en)(3)](3+) cations, yielding [Co(en)(3)][Hg(CN)(2)Cl(2)][[Hg(CN)(2)](2)Cl] (6). In [Co(NH(3))(6)](2)[Hg(CN)(2)](5)Cl(6).2H(2)O (7), [Co(NH(3))(6)](3+) cations and water molecules are sandwiched between chloride-bridged 2-D anionic [[Hg(CN)(2)](5)Cl(6)](n)(6n-) layers, which contain square cavities. The presence (or absence), number, and profile of hydrogen bond donor sites of the transition metal amine ligands were observed to strongly influence the structural motif and dimensionality adopted by the anionic double salt complex anions, while cation shape and cation charge had little effect. (199)Hg chemical shift tensors and (1)J((13)C,(199)Hg) values measured in selected compounds reveal that the NMR properties are dominated by the Hg(CN)(2) moiety, with little influence from the chloride bonding characteristics. delta(iso)((13)CN) values in the isolated dimers are remarkably sensitive to the local geometry.     

The nature of the H3O+ hydronium ion in benzene and chlorinated hydrocarbon solvents. Conditions of existence and reinterpretation of infrared data

Salts of the C(3v) symmetric hydronium ion, H(3)O(+), have been obtained in the weakly basic solvents benzene, dichloromethane, and 1,2-dichloroethane. This is made possible by using carborane counterions of the type CHB(11)R(5)X(6)(-) (R = H, Me, Cl; X = Cl, Br, I) because they combine the three required properties of a suitable counterion: very low basicity, low polarizability, and high chemical stability. The existence of the H(3)O(+) ion requires the formation of three more-or-less equivalent, medium-to-strong H-bonds with solvent or anion bases. With the least basic anions such as CHB(11)Cl(11)(-), IR spectroscopy indicates that C(3v) symmetric trisolvates of formulation [H(3)O(+) .3Solv] are formed with chlorocarbon solvents and benzene, the latter with the formation of pi bonds. When the solvents and anions have comparable basicity, contact ion pairs of the type [H(3)O(+).nSolv.Carborane] are formed and close to C(3v) symmetry is retained. The conditions for the existence of the H(3)O(+) ion are much more exacting than previously appreciated. Outside of the range of solvent basicity bounded at the lower end by dichloromethane and the upper end by tributyl phosphate, and with anions that do not meet the stringent requirements of weak basicity, low polarizability of high chemical stability, lower symmetry species are formed. One H-bond from H(3)O(+) to the surrounding bases becomes stronger than the other two. The distortion from C(3v) symmetry is minor for bases weaker than dichloromethane. For bases stronger than tributyl phosphate, H(2)O-H(+)-B type species are formed that are more closely related to the H(5)O(2)(+) ion than to H(3)O(+). IR data allow criteria to be defined for the existence of the symmetric H(3)O(+) ion. This includes a linear dependence between the frequencies of nu(max)(OH) and delta(OH(3)) within the ranges 3010-2536 cm(-1) for nu(max)(OH) and 1597-1710 cm(-1) for delta(OH(3)). This provides a simple way to assess the correctness of the formulation of the proton state in monohydrated acids. In particular, the 30-year-old citation classic of the IR spectrum believed to arise from H(3)O(+) SbCl(6)(-) is re-interpreted in terms of (H(2)O)(x)().HSbCl(6) hydrates. The correctness of the hydronium ion formulation in crystalline H(3)O(+)A(-) salts (A(-) = Cl(-), NO(3)(-)) is confirmed, although, when A(-) is a fluoroanion, distortions from C(3)(v)() symmetry are suggested.     

Homochiral column structure of rac- and lambda-tris(ethylenediamine)cobalt(III) cyclotriphosphate dihydrate in crystal structures and cation-anion association in aqueous solution

rac- and Lambda-tris(ethylenediamine)cobalt(III) cyclotriphosphate dihydrate with the chemical formulas rac-[Co(en)(3)]P(3)O(9).2H(2)O (1) and Lambda-[Co(en)(3)]P(3)O(9).2H(2)O (2) were synthesized, and their crystal structures were determined by single-crystal X-ray analyses. In 1, the cationic complex molecule [Co(en)(3)](3+) with the Delta or Lambda enantiomer and cyclotriphosphate anion are alternately arrayed and connected by multiple hydrogen bonds to form a homochiral column structure. Adjacent homochiral columns with different chirality for 1 are connected by intercolumn hydrogen bonds through P(3)O(9)(3)(-) anions, as the bridging groups, to form a tetrameric cyclic cylindrical structure, while the adjacent columns with the same chirality are connected for 2 to form the cyclic cylindrical structure. All 6 amino groups per [Co(en)(3)](3+) participate in the formation of 12 hydrogen bonds, in which 8 hydrogen bonds contribute to the construction of a homochiral column and the remaining 4 hydrogen bonds contribute to the intercolumn interactions. The circular dichroism spectrum of the aqueous solution of Lambda-[Co(en)(3)](3+) changes drastically when excess P(3)O(9)(3)(-) is added, and this change is explained by ion-pair formation. The thermodynamic association constant of [Co(en)(3)](3+) with P(3)O(9)(3)(-), calculated from the conductivity data, was log K = 4.26 at 25 degrees C.     

Aqueous reactions of U(VI) at high chloride concentrations: syntheses and structures of new uranyl chloride polymers

The reactions of UO(3) with acidic aqueous chloride solutions resulted in the formation of two new polymeric U(VI) compounds. Single crystals of Cs(2)[(UO(2))(3)Cl(2)(IO(3))(OH)O(2)].2H(2)O (1) were formed under hydrothermal conditions with HIO(3) and CsCl, and Li(H(2)O)(2)[(UO(2))(2)Cl(3)(O)(H(2)O)] (2) was obtained from acidic LiCl solutions under ambient temperature and pressure. Both compounds contain pentagonal bipyramidal coordination of the uranyl dication, UO(2)(2+). The structure of 1 consists of infinite [(UO(2))(3)Cl(2)(IO(3))(mu(3)-OH)(mu(3)-O)(2)](2-) ribbons that run down the b axis that are formed from edge-sharing pentagonal bipyramidal [UO(6)Cl] and [UO(5)Cl(2)] units. The Cs(+) cations separate the chains from one another and form long ionic contacts with terminal oxygen atoms from iodate ligands, uranyl oxygen atoms, water molecules, and chloride anions. In 2, edge-sharing [UO(3)Cl(4)] and [UO(5)Cl(2)] units build up tetranuclear [(UO(2))(4)(mu-Cl)(6)(mu(3)-O)(2)(H(2)O)(2)](2-) anions that are bridged by chloride to form one-dimensional chains. These chains are connected in a complex network of hydrogen bonds and interactions of uranyl oxygen atoms with Li(+) cations. Crystal data: 1, orthorhombic, space group Pnma, a = 8.2762(4) A, b = 12.4809(6) A, c = 17.1297(8) A, Z = 4; 2, triclinic, space group P1, a = 8.110(1) A, b = 8.621(1) A, c = 8.740(1) A, Z = 2.