Synthesis and crystal structure of a molybdovanadate with a Keggin-type anion

Institute of Inorganic Chemistry, Academy of Sciences of the USSR, Siberian Branch. Institute of Chemical Sciences, Academy of Sciences of the Kazakh SSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 31, No. 6, pp. 97–103, November–December, 1990.     

A discrete conglomerate of a distorted Mo(v)-porphyrin with a directly coordinated Keggin-type polyoxometalate

The reaction of a saddle-distorted Mo(v)-dodecaphenylporphyrin complex and a Keggin-type polyoxometalate gives a discrete and nanosized molecule, [{Mo(DPP)(O)}(2)(H(2)SiW(12)O(40))], which involves direct coordination between the Mo(v) centers and terminal oxo groups of the polyoxometalate and exhibits excellent stability in solution to show reversible multi-redox processes.     

A rare earth metallocene containing a 2,2′-azopyridyl radical anion

Introducing spin onto organic ligands that are coordinated to rare earth metal ions allows direct exchange with metal spin centres. This is particularly relevant for the deeply buried 4f-orbitals of the lanthanide ions that can give rise to unparalleled magnetic properties. For efficacy of exchange coupling, the donor atoms of the radical ligand require high-spin density. Such molecules are extremely rare owing to their reactive nature that renders isolation and purification difficult. Here, we demonstrate that a 2,2′-azopyridyl (abpy) radical (S = 1/2) bound to the rare earth metal yttrium can be realized. This molecule represents the first rare earth metal complex containing an abpy radical and is unambigously characterized by X-ray crystallography, NMR, UV-Vis-NIR, and IR spectroscopy. In addition, the most stable isotope ⁸⁹Y with a natural abundance of 100% and a nuclear spin of ½ allows an in-depth analysis of the yttrium–radical complex via EPR and HYSCORE spectroscopy. Further insight into the electronic ground state of the radical azobispyridine-coordinated metal complex was realized through unrestricted DFT calculations, which suggests that the unpaired spin density of the SOMO is heavily localized on the azo and pyridyl nitrogen atoms. The experimental results are supported by NBO calculations and give a comprehensive picture of the spin density of the azopyridyl ancillary ligand. This unexplored azopyridyl radical anion in heavy element chemistry bears crucial implications for the design of molecule-based magnets particularly comprising anisotropic lanthanide ions.

Unambiguous characterization of the first 2,2′-azobispyridine radical-containing rare earth metal complex through X-ray crystallography, DFT computations, EPR and HYSCORE spectroscopy.     

A unique 2D framework containing linear trimeric cobalt(II) of mixed Td-Oh-Td geometries linked by two different single-carboxylate-aromatic amine ligands: structure and magnetic properties

A new 2D coordination polymer Co3(OH)2(pa)2(ina)2 (1, pa = 3-(1H-benzimidazol-2-yl) propanoic carboxylate, ina = isonicotinate) contained uncommon, linear Co(ii) trimers of mixed Td-Oh-Td geometries, exhibits spin canting below 20 K. Such magnetic behavior mainly arises from the Dzyaloshinski-Moriya interaction from the anisotropic, mixed geometries trimeric Co(II) ions to the crimpled 2D network based on the nature of the binding modes of Co(II)-carboxylate trimer and the effect of the intertrimers arrangement of 1. The mixed single-carboxylate-aromatic amine ligands bridged metal systems display a new structurally authenticated example of a thick 2D layer, and also indicate homometallic Co(II) clusters with Td-Oh-Td mixed-geometries can result in relatively obvious noncompensation moments, according to different efficient spins of Co(II) at very low temperature, in spite of antiferromagnetic intracluster interactions.     

Cobaloxime complexes containing imidazole and perchlorate or tetrafluoroborate anion

Summary Cobaloxime complexes containing the biologically active ligand imidazole and poorly coordinating anions, such as ClO ₄ ^– or BF ₄ ^– , have been synthesised. The perchlorate anion is not involved in coordination and there is evidence that [Co(DH)₂(L)₂]ClO₄ complexes are formed, whereas the tetrafluoroborate anion is involved in weak coordination giving complexes of the type [Co(DH)₂(L)(BF₄)] in the solid state. However, solvolysis of these latter complexes in solution yields 11 electrolytic species. The i.r. and electronic spectra, magnetic and conductivity measurements in nonaqueous media have been employed to characterise the complexes.Ligand abbreviations Py pyridine - Im imidazole - Me methyl - Al allyl - Vi vinyl     

A hybrid macrocycle containing benzene and pyridine subunits is a better anion receptor than both its homoaromatic congeners

The hybrid tetraamide receptor 3 containing both 2,5-diamidopyridine and 1,3-diamidobenzene anion binding units has been synthesized. NOESY spectroscopy revealed that the new receptor is well preorganized for anion complexation, presumably owing to the macrocyclic topology and the rigidity of the 2,5-diamidopyridine unit. Association constants of 3 with several anions are higher than those determined earlier for its homoaromatic congeners 1 and 2. X-ray crystallographic analysis of the chloride complex of hybrid macrocycle 3 enabled direct comparison of structural aspects of anion recognition by the 2,5-diamidopyridine and 1,3-diamidobenzene moieties.     

A selective colorimetric anion sensor based on an amide group containing macrocycle

A new colorimetric anion sensor 4 allows for selective 'naked-eye' differentiation of F-, AcO- and H2PO4- with similar basicity.     

A novel benzimidazole‐containing phthalonitrile monomer with unique polymerization behavior

A novel benzimidazole‐containing phthalonitrile monomer (BIPN) was synthesized. The chemical structure of BIPN was confirmed by various spectroscopic techniques. Differential scanning calorimetry measurement revealed that the self‐promoted polymerization reaction of the BIPN proceeds extremely sluggish and showed low polymerization exothermic effect. Subsequent rheological measurement displayed that the BIPN was able to keep a stable and low melt viscosity for 4 h at 300 °C, 2 h at 310 °C, and 50 min at 330 °C. The derived BIPN polymers showed excellent thermal properties revealed by thermogravimetric analysis, which were better than those of the corresponding polymer derived from phthalonitrile monomer without benzimidazole moiety. IR analysis confirmed the occurrence of the triazine ring within the polymer crosslinking sites. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Ionic liquids containing the triply negatively charged tricyanomelaminate anion and a B(C6F5)3 adduct anion

Room‐temperature ionic liquids containing the triply charged tricyanomelaminate (tcmel) ion [C₃N₆(CN)₃]^3? were synthesized. The 1‐methyl‐3‐methylimidazolium (MMIm), 1‐ethyl‐3‐methylimidazolium (EMIm), and 1‐butyl‐3‐methylimidazolium (BMIm) salts of the tricyanomelaminate ion have glass transition temperatures (?6, ?20, and ?30 °C) similar to those found for the analogous monomeric dicyanoamide salts. They are thermally stable up to over 200 °C and dissolve in polar organic solvents. Addition of B(C₆F₅)₃ to M₃[tcmel] (M=Na, MMIm, EMIm, BMIm) yields salts containing the very voluminous adduct ion [C₃N₆{CN ? B(C₆F₅)₃}₃]^3? (tcmel_3B). The solid‐state structure of [MMIm]₃[tcmel] shows only long cation ??? anion contacts but in large number, while the solid‐state structure of [Na(THF)₃]₃[tcmel_3B] ? 1.76 THF displays strong interactions of the sodium cation with the amido nitrogen atoms of the anion. Hence this adduct anion cannot be regarded as a weakly coordinating anion. A similar situation is found for the MMIm salt, [MMIm]₃[tcmel_3B] ? 2.66 CH₂Cl₂, in which weak hydrogen bonds with the acidic proton of the MMIm ion are observed. On the basis of computations the energetics, structural trends, and charge transfer of adduct anion formation were studied.     

Hexagonal columnar porphyrin assembly by unique trimeric complexation of a porphyrin dimer with pi-pi stacking: remarkable thermal behavior in a solid

On heating, syn-diporphyrin zinc complexes fused with bis(ethano)dimethoxyanthracene, the crystal structure of which showed a unique trimeric assembly, extruded one ethylene molecule at 240-310 degrees C to give a porphyrin-naphthoporphyrin diad, and the second retro-Diels-Alder reaction and concomitant decomposition of the methoxy groups occurred at 280-350 degrees C to give the anthraquinone-fused diporphyrin, while the first thermal conversion of the anti-diporphyrin zinc complex occurred in a much lower temperature range (180-230 degrees C).     

Physicochemical characterization of a novel surfactant peptide containing an arginine cation and laurate anion

 A novel surfactant peptide consisting of an arginine cation with laurate anion has been synthesized, purified and characterized. The critical micellar concentration (cmc) of peptide in aqueous solutions has been determined using spectroscopic techniques and is found to increase from 0.06 to 0.11 mM with increasing temperature (15–45 °C). Cmc is also determined in the presence of salts like NaCl, KCl and sodium acetate and it is found that these electrolytes hinder aggregation with a significant increase in the case of sodium acetate. The aggregation number of the surfactant peptide has been determined using fluorescence quenching measurements and is observed to decrease from 14 to 6 with increasing temperature (15–45 °C). The standard free energy change (ΔG ⁰ _m) and standard enthalpy change (ΔH ⁰ _m) of the peptide aggregate are found to be negative with a small positive value for standard entropy change (ΔS ⁰ _m). The peptide aggregate seems to undergo phase transition above 50 °C as observed from UV–vis and fluorescence spectroscopy. From pyrene binding studies, it is shown that the interior dielectric constant increases from 5.08 at 34 °C to 8.77 at 50 °C and further decreases with increase in temperature indicating a phase change at 50 °C. Also, the ratio of excimer intensity to monomer intensity, which is a measure of microviscosity of the aggregate, decreases with increase in temperature with a change at 50 °C indicating a phase change. Received: 14 February 1997 Accepted: 13 August 1997     

A unique NH-spacer for N-benzamidothiourea based anion sensors. Substituent effect on anion sensing of the ICT dual fluorescent N-(p-dimethylaminobenzamido)-N'-arylthioureas

A series of N-(p-dimethylaminobenzamido)-N'-(substituted-phenyl)thioureas (substituent = p-CH3, H, p-Cl, p-Br, m-Br, m-NO2, and p-NO2) were designed as anion sensors in order to better understand the -NH-spacer via a substituent effect investigation. In these molecules the dual fluorescent intramolecular charge transfer (ICT) fluorophore p-dimethylaminobenzamide as the signal reporter was linked to the anion-binding site, the thiourea moiety, via an N-N single bond. Correlation of the NMR signals of the aromatic and -NH protons with substituents in these molecules indicated that the N-N single bond stopped the ground-state electronic communication between the signal reporter and the anion-binding site. Dual fluorescence was observed in highly polar solvents such as acetonitrile with the former five derivatives. The fact that the CT emission wavelength and the CT to LE emission intensity ratio of the sensors were independent of the substituent existing in the anion-binding moiety suggested that the substituent electronic effect could not be communicated to the CT fluorophore in the excited-state either. Yet in acetonitrile both the CT dual fluorescence and the absorption of the sensors were found to be highly sensitive toward anions. A conformation change around the N-N bond in the sensor molecules was suggested to occur upon anion binding that established the electronic communication between the signal reporter and the anion-binding site. The anion binding constants of the N-(p-dimethylaminobenzamido)thiourea sensors were found higher than those of the corresponding traditional N-phenylthiourea counterparts and the substituent effect on the anion binding constant was much higher than that in the latter. "-NH-" was shown to be a unique spacer that affords N-benzamidothiourea allosteric anion sensors.     

Nitrovinyl substituted calix[4]pyrrole as a unique,reaction-based chemosensor for cyanide anion

A new calix[4]pyrrole bearing a nitrovinyl group at β-pyrrolic position was synthesized and studied as a cyanide selective chemodosimetric sensor. Selective Michael-type nucleophilic addition of cyanide to the α-position of the nitrovinyl group followed by β-elimination resulted in the unique product 3.     

Synthesis and anion binding studies of a new crown ether containing 2,2′-biimidazole

A novel crown ether which incorporates the 2,2′-biimidazole moiety was prepared by cyclization of 1,1′-dibenzyl-1H,1′H-[2,2′]biimidazolyl-4,4′-dicarboxylic acid and 4,7,10-trioxa-1,13-tridecanediamine followed by removal of the benzyl groups. The diacid has been obtained by hydrolysis of the diester previously prepared by alcoholysis of the corresponding dicyano biimidazole. The cyano group is introduced by a palladium-catalyzed procedure starting from the corresponding dibromo biimidazole. The macrocyclic structure of the N-dibenzylated derivative of the receptor has been studied by X-ray diffraction. Binding constants for 1:1 biimidazole–anion complexation (K_assoc) are on the order of 10⁵ M⁻¹ for H₂PO₄⁻ and Cl⁻.     

Cobalt phosphonates: an unusual polymeric cobalt phosphonate containing a clathrated phosphonate anion and a layered bisphosphonate

Novel cobalt phosphonates [Co(H(2)O)(4)(H(4)L)][H(2)L].2H(2)O, 1, and Co(2)(H(2)O)(2)(L), 2, have been synthesized from 1,8-octylenediphosphonic acid (H(4)L). 1 has been fully characterized by X-ray single-crystal data, TGA, IR spectroscopy, and chemical analysis. The compound crystallizes in the triclinic space group P1 with a = 5.5415(8) A, b = 8.6382(8) A, c = 16.794 (2) A, alpha = 87.694(2) degrees, beta = 80.859(2) degrees, gamma = 76.005(2) degrees, V = 770.11(19) A(3), and Z = 1. A cobalt atom lies in the center of symmetry and is octahedrally coordinated by two oxygen atoms from two undissociated diphosphonic ligands H(4)L and four molecules of water. The cobalt atom and undissociated ligand H(4)L are combined to form polymeric chains along the c-axis, resulting in the formation of a one-dimensional framework. The positive charge on the cobalt atom remains upon coordination and is balanced by a negatively charged uncoordinated ligand (H(2)L) found as a clathrate in the lattice. Two lattice water molecules, hydrogen-bonded with the coordinated and uncoordinated ligands, complete the structure. The metal phosphonate chains are held together and bridge the uncoordinated anionic ligands by a number of strong hydrogen bonds, which make the structure possible. Cobalt phosphonate 2 has been characterized by TGA measurements, IR spectroscopy, and chemical analysis. The compound has a layered structure with an interlayer spacing of 14.26 A. Metal phosphonate layers are cross-linked by hydrocarbon chains. The water molecules are coordinated to the metal atom. According to IR data, compound 2 contains two equivalent PO bonds and one different PO bond, which may be a result of the different types of Co-O-P connectivity within one phosphonic group.     

A molecular oyster: a neutral anion receptor containing two cyclopeptide subunits with a remarkable sulfate affinity in aqueous solution

An artificial anion receptor is presented, in which two cyclohexapeptide subunits containing l-proline and 6-aminopicolinic acid subunits in an alternating sequence are connected via an adipinic acid spacer. This compound was devised to stabilize the 2:1 sandwich-type anion complexes that are observed when the two cyclopeptide moieties are not covalently connected and to obtain a 1:1 stoichiometry for these aggregates. Electrospray ionization mass spectrometry and NMR spectroscopic investigations showed that the bridged bis(cyclopeptide) does indeed form defined 1:1 complexes with halides, sulfate, and nitrate. ROESY NMR spectroscopy and molecular modeling allowed a structural assignment of the sulfate complex in solution. The stabilities of various anion complexes were determined by means of NMR titrations and isothermal titration microcalorimetry in 50% water/methanol. Both methods gave essentially the same quantitative results, namely stability constants that varied in the range 105-102 M-1 and decreased in the order SO42- > I- > Br- > Cl- > NO3-. This order was rationalized in terms of the size of the anions with the larger anions forming the more stable complexes because they better fit into the cavity of the host. The ability of sulfate to form stronger hydrogen bonds to the NH groups of the receptor, in addition to its slightly larger ionic radius with respect to iodide, causes the higher stability of the sulfate complex. No significant effect of the countercation on complex stability was observed. Furthermore, complex stability is enthalpically as well as entropically favored. A comparison of the iodide and sulfate complex stabilities of the ditopic receptor with those of a cyclopeptide that forms 1:1 anion complexes in solution showed that the presence of a second binding site increases complex stability by a factor of 100-350.     

A catenane host system containing integrated triazole C-H hydrogen bond donors for anion recognition

A 3,5-bis(triazole)-pyridinium motif is integrated into a catenane structural framework via chloride anion templation. The catenane host system displays a high degree of selectivity for halide anions over dihydrogen phosphate.     

A novel zirconium polyoxometalate complex that contains both a coordinated saturated anion, [PMo12O40]3-, and a coordinated unsaturated anion, [PMo11O39]7-

The novel 8-coordinate zirconium compound (NH(4))(6)[Zr(PMo(12)O(40))(PMo(11)O(39))].26H(2)O (1) has been synthesized and characterized by single-crystal X-ray diffraction, elemental analysis, and vibrational and (31)P NMR spectroscopy. It is the first example of a metal complex containing both parent, [PMo(12)O(40)](3)(-), and monovacant lacunary, [PMo(11)O(39)](7)(-), anions. Furthermore, this is the first crystallographic determination of the [PMo(11)O(39)](7)(-) anion.