Cyanate Complexes Research Articles

Taming Copper(I) Cyanate and Selenocyanate with N‐Heterocyclic Carbenes

The synthesis of N‐heterocyclic carbene (NHC) adducts of copper(I) cyanate and copper(I) selenocyanate has been successfully achieved via the reaction of [Cu(NHC)Cl] with silver(I) cyanate and potassium selenocyanate respectively. Three copper(I) cyanate complexes [Cu(IXy)(NCO)] (1), [Cu(IPr)(NCO)] (2) and [Cu(SIPr)(NCO)] (3) [IXy = 1,3‐bis(2,6‐dimethylphenyl)imidazol‐2‐ylidene, IPr = 1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene, SIPr = 1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene] have been prepared and fully characterised. The X‐ray crystal structures reveal the three complexes to be monomeric species in which the cyanate ligand is end‐on, N‐bound. These complexes, represent the first examples of monomeric copper(I) cyanate complexes. In addition, the copper(I) selenocyanate species [Cu(IPr)(NCSe)]2 (4) was prepared and fully characterised. The X‐ray crystal structure reveals that a centrosymmetric dimer is formed with bridging selenocyanate ligands bound through both N and Se. This is in contrast to the monomeric structure observed in the previously reported and related complex [Cu(IPr)(NCS)]. Complex 4 represents a rare example of a stable dimeric adduct of copper(I) selenocyanate.

Synthesis, characterization and properties of oxo-bridged diruthenium(III) complexes with thiocyanato and cyanato ligands

The oxo-bridged diruthenium(III) complexes with thiocyanato and cyanato ligands, trans(μ-O,L)-[Ru2(μ-O)(μ-CH3COO)2(bpy)2(L)2] (bpy=2,2′-bipyridine; L=SCN− (1); OCN− (2)), have been synthesized, characterized, and their properties studied. X-ray single crystallography revealed that the thiocyanato ligands of 1 are N-bonded to the Ru centers at the trans sites to the oxo-bridge. The OCN− ligand in 2 is also N-bonded based on the infrared spectroscopy. The cyclic voltammograms of 1 and 2 in dimethyl sulfoxide (DMSO) solutions of 0.1M (n-Bu)4NPF6 showed two redox couples at around −0.5V and +0.5Vvs Ag/AgCl, which were assigned to the processes Ru2III,III/Ru2III,II and Ru2IV,III/Ru2III,III, respectively. The electronic absorption spectra of 1 and 2 in CH3CN solutions showed strong absorption bands at 625 and 637nm, respectively. The bands showed a remarkable blueshift in H2O to 578 and 581nm as a consequence of the solvent interactions at the free end of the thiocyanato and cyanato ligands, respectively. The theoretical calculations of both 1 and 2 and also their coordination isomers (N-bonded and S-bonded for the thiocyanate complex, and N-bonded and O-bonded for the cyanate complex) revealed that the N-bonded isomers are energetically more stable. Both the SCN− and OCN− ligands are primarily good σ donors to the Ru2O core. The contributions of SCN− to the dπ(Ru)–pπ(μ-O) conjugated system are particularly significant (>20%). The strong visible absorption bands of both 1 and 2 were attributed to mainly the metal-to-metal charge transfer (MMCT) transitions with some contributions from the ligand (SCN−, OCN−)-to-ligand (μ-O) charge transfer (LLCT).

Determination of cyanide, thiocyanate, cyanate, hexavalent chromium, and metal cyanide complexes in various mixtures by ion chromatography with conductivity detection

ABSTRACTThe first aim of this study was to develop a selective, sensitive, and reliable method for direct simultaneous determination of cyanate, thiocyanate, and hexavalent chromium by ion chromatography (IC) with conductivity detection. The other target was to successfully determine cyanides by utilizing same chromatographic system. Yet, since cyanides can not be detected by the direct method, free cyanide ions were converted into cyanate with chloramine-T at alkaline pH. In addition, strongly complexed metal cyanides were converted into cyanate by using photo-oxidation following chloramine-T. Total cyanate ion obtained from developed methods were analyzed with IC. The chromatographic separations on anion exchange column were accomplished by optimized multistep gradient eluent program using NaOH as the eluent. Proposed method was applied for the simultaneous determination of cyanide and hexavalent chromium in electroplating bath solutions and in industrial wastewater. Cyanide and hexavalent chromium could be measured in the linear dynamic ranges of 0.6–961.5 and 0.9–118.5 µmol L−1, respectively. The limit of detection and limit of quantification of cyanide were 0.18 and 0.61 µmol L−1, and these values for chromium(VI) were 0.26 and 0.86 µmol L−1, respectively.

Nitrogen atom transfer from a dinitrogen-derived vanadium nitride complex to carbon monoxide and isocyanide.

Reduction of [(ONO)V(THF)] with KH under an N2 atmosphere cleaves the N≡N bond to afford a bis(μ-nitride) V(IV) dimer. This complex is oxidized to generate a V(V) nitride. The reactions of the V(V) nitride with carbon monoxide and isocyanide led to formation of cyanate and carbodiimide complexes. Following treatment of the cyanate complex with alkyne produces an alkyne adduct along with the release of potassium cyanate. Dissolution of the alkyne adduct in THF regenerates the starting complex [(ONO)V(THF)], thereby closing a synthetic cycle for conversion of N2 and CO into [NCO](-).

Human carbonic anhydrase II-cyanate inhibitor complex: putting the debate to rest.

The binding of anions to carbonic anhydrase II (CA II) has been attributed to high affinity for the active-site zinc. An anion of interest is cyanate, for which contrasting binding modes have been reported in the literature. Previous spectroscopic data have shown cyanate behaving as an inhibitor, directly binding to the zinc, in contrast to previous crystallographic data that implied that cyanate acts as a substrate mimic that is not directly bound to the zinc but overlaps with the binding site of the substrate CO2. Wild-type and the V207I variant of CA II have been expressed and X-ray crystal structures of their cyanate complexes have been determined to 1.7 and 1.5 Å resolution, respectively. The rationale for the V207I CA II variant was its close proximity to the CO2-binding site. Both structures clearly show that the cyanate binds directly to the zinc. In addition, inhibition constants (∼40 µM) were measured using (18)O-exchange mass spectrometry for wild-type and V207I CA II and were similar to those determined previously (Supuran et al., 1997). Hence, it is concluded that under the conditions of these experiments the binding of cyanate to CA II is directly to the zinc, displacing the zinc-bound solvent molecule, and not in a site that overlaps with the CO2 substrate-binding site.

μ-Phenoxo-μ-pseudohalide and μ-pseudohalide dinuclear, tetranuclear and one-dimensional complexes: magneto-structural correlation and interesting type of solid state isomerism

Five Schiff base ligands have been utilized to explore metallo-pseudohalide (azide or cyanate) systems. These ligands are the 1:1 condensation products of 3-methoxysalicylaldehyde with ethanolamine (H2L1)/1-(2-aminoethyl)-piperidine (HL2)/ 4-(2-aminoethyl)-morpholine (HL3) or salicylaldehyde with 1-(2-aminoethyl)-piperidine (HL4)/4-(2-aminoethyl)-morpholine (HL5). The derived complexes are as follows: Four heterobridged μ-phenoxo-μ1,1-azide/cyanate dinickel(II) compounds of composition [Ni\(^{\rm II}_{2}\)(HL\(^{1})_{3}(\mu_{1,1}\)-N3)]·3H2O (1), [Ni\(^{\rm II}_{2}\)(L\(^{2})_{2}(\mu _{1,1}\)-N3)(N3)(H2O)]·CH3CH2OH (2), [Ni\(^{\rm II}_{2}\)(L\(^{3})_{2}\) (μ1,1-N3)(CH3CN)(H2O)](ClO4)·H2O·CH3CN (3) and [Ni\(^{\rm II}_{2}\)(HL\(^{1})_{3}(\mu _{1,1}\)-NCO)]·2H2O (4); Two μ1,3-azide bridged tetranickel(II) compounds [{NiII(L\(^{4})(\mu _{1,3}\)-N3)(H2O)}4] (5) and [{NiII(L\(^{5})(\mu _{1,3}\)-N3)(H2O)}4] (6); Two μ1,3-azide/cyanate one-dimensional compounds [CuIIL\(^{5}(\mu _{1,3}\)-NCO)] n ·2nH2O (7) and [CuIIL\(^{5}(\mu _{1,3}\)-N3)] n · 2nH2O (8). Except compound 5 which shows overall antiferromagnetic coupling, other compounds exhibit overall ferromagnetic interaction. Syntheses, crystal structures, magnetic properties, density functional theoretical (DFT) calculations and experimental/theoretical magneto-structural correlations have been carried out which have revealed some interesting observations on composition/topology, magneto-structural correlations and solid state isomerism. The results have been already published. The present report deals with a review of the salient and interesting features of these works. This article reviews some recent studies on metallo-pseudohalide compounds, only pseudohalide bridged or heterobridged µ-phenoxo-µ1,1-azide/cyanate complexes, and focuses on the following features: (i) unprecedented type of structures; (ii) unique bridge distance dependency of exchange integral; (iii) experimental and density functional theoretical magneto-structural correlations; (iv) interesting magnetic, crystallographic and supramolecular isomerisms.

Electronic and molecular structure of [Cr(N)(NCO)4]2−, the first example of a mixed nitride–cyanate complex

Metathesis of [Cr(N)Cl 4 ] 2− with excess cyanate affords the title complex which is the first example of a nitride complex with only cyanate auxiliary ligands. The electronic spectrum allows assignment of the ligand field transitions: B 1 (C 4v ) ← B 2 (C 4v ) and E(C 4v ) ← B 2 (C 4v ). From these data, cyanate can be deduced to be intermediate between azide and thiocyanate with respect to σ-donation and comparable to thiocyanate, but weaker than azide with respect to π-donation. Solution EPR demonstrates the cyanate ligands to be N-bonded with similar super-hyperfine couplings to all nitrogen ligators, and the X-ray crystal structure of (Ph 3 PNPPh 3 ) 2 [Cr(N)( N CO) 4 ] ( 1 ) establishes the expected 5-coordinate square pyramidal structure with a short Cr–N(nitride) bond, 1.520(5) Å and chromium–cyanate bond lengths in the range 1.948(12)–2.05(2) Å. As the first example of a complex with only nitride and cyanate ligands, [Cr(N)(NCO) 4 ] 2− was prepared by metathesis from the chloro complex. The cyanate ligands are N-bonded and intermediate between azide and thiocyanate in ligand field strength. ► Metathesis reactions of Cr(V) nitride complexes. ► Structural comparison of pseudo halide complexes. ► d–d transitions in UV–vis spectroscopy. ► Cyanate ligand-field strength. ► Fitting of EPR spectral traces.

UIII‐Induced Reductive Co‐Coupling of NO and CO to Form UIV Cyanate and Oxo Derivates

CO and NO give NCO and O! Sequential treatment of [U(?-C8H6{SiiPr3-1,4}2)(?-Cp*)] with CO followed by NO (or vice versa) affords a mixture of the bridging cyanate complex [{U(?-C8H6{SiiPr3-1,4}2)(?-Cp*)}2(µ-OCN)2] and the bridging oxo complex [{U(?-C8H6{SiiPr3-1,4}2)(?-Cp*)}2(µ-O)], both of which have been structurally characterised (see scheme).

Rhenium(IV) cyanate complexes: Synthesis, crystal structures and magnetic properties of NBu 4[ReBr 4(OCN)(DMF)] and (NBu 4) 2[ReBr(OCN) 2(NCO) 3

Two new rhenium(IV) mononuclear compounds of formula NBu 4[ReBr 4(OCN)(DMF)] ( 1) and (NBu 4) 2[ReBr(OCN) 2(NCO) 3] ( 2) (NBu 4 = tetrabutylammonium cation, OCN = O-bonded cyanate anion, NCO = N-bonded cyanate anion and DMF = N, N-dimethylformamide) have been synthesized and their crystal structures determined by single-crystal X-ray diffraction. 1 crystallizes in the monoclinic system with the space group P2 1/ n, whereas 2 crystallizes in the triclinic one with P 1 ¯ as space group. In both complexes the rhenium atom is six-coordinated, in 1 by four Br atoms in the equatorial plane, and two trans-oxygen atoms, one of a DMF molecule and another one from a cyanato group, while in 2 by one bromide anion and five cyanate ligands, two of which are O-bonded and three N-bonded, forming a somewhat distorted octahedral surrounding. Magnetic susceptibility measurements on polycrystalline samples of 1 and 2 in the temperature range 1.9–300 K are interpreted in terms of magnetically isolated spin quartets with large values of the zero-field splitting (|2 D| is ca. 41.6 and 39.2 cm −1 for 1 and 2, respectively).

Facile and stereoselective condensation of acetone with ammonia ligands on cobalt(III): structure of a N-bonded cyanate complex containing the 2-methyl-2-amino-4-imino-pentane ligand

The complex [(NH 3) 5CoO 3SCF 3](CF 3SO 3) 2 reacts with excess NaNCO in warm acetone solution to give, stereoselectively, a Schiff base complex (40%) which has been characterized by standard NMR techniques as one of the six isomers of [Co{NH 2C(CH 3) 2CH 2C(CH 3)NH} 2(NH 3)NCO](ClO 4) 2 · H 2O, confirmed by a single crystal X-ray structural analysis. Schiff base formation in non-basic conditions for kinetically inert Co(III) complexes is unprecedented. Also, this is only the second cyanate complex of pentaaminecobalt(III) to be structurally characterized (CoNCO: Co–N, 1.908 Å; N–C, 1.152 Å; C–O, 1.206 Å; Co–N–C, 170°; N–C–O, 177°).

Removal of Selenocyanate in Water by Precipitation: Characterization of Copper−Selenium Precipitate by X-ray Diffraction, Infrared, and X-ray Absorption Spectroscopy

During refining of sour crude oils produced from reservoirs containing seleniferous marine shales, selenium is concentrated into process waters and wastewaters. Selenium, present in the waters as selenocyanate, must be removed to meet regulatory discharge limits. Treatment of wastewaters with copper(II) salts effectively precipitates selenium. An objective of the present study was to determine whether selenium was precipitated as elemental Se or immobilized in the form of cyanate complexes or any other form that remains to be identified. The precipitate had a Se/(Se+S) mole ratio of 0.09. The incorporation of selenium in the copper thiocyanate lattice was proven by X-ray diffraction. The presence of native selenium was disallowed by Se K-edge X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy. Selenium was shown by EXAFS to be present as selenide and surrounded by one nearest C atom and three next-nearest Cu atoms. This local environment is typic...

A MOLECULAR ORBITAL APPROACH TO COLIGAND ISOMER FORMATION

Abstract Coligand isomerism is exemplified by a pair of [Cu(dmpz)2(NCO)2] and [Cu(dmpz.NCO)2] complexes (dmpz = 3,5-dimethylpyrazole). The former isomer (I) contains dmpz and NCO− ligands whereas the latter (II) consists of 1-carbamoyl-3,5-dimethylpyrazolate anions chelated to the copper(II) central atom. This new ligand is formed by nucleophilic addition of the dmpz ligand to the cyanate group in the Cu(II) coordination sphere. The cyanate complex transforms under heating to the more stable isomer II. On the contrary, isomer II disolves in DMSO and DMF and its counterpart I is formed. A molecular-orbital study (quasirelativistic INDO/1 method) rationalizes this behaviour and maps the reaction path of the hydrogen transfer over the molecular skeleton.

Molecular orbital study of coordinated dioxygen VII. Dioxygen activation on cyanate complexes of Mn, Fe, Co, Ni and Cu

Dioxygen complexes of the type κ[M(CN) 5(O 2)] q were investigated by the CNDO/3-UHF method of MO/3-LCAO/3-SCF calculations. Five central atoms M, three oxidation states q, and two spin states κ, yield 30 combinations under study. The dioxygen activation is described in terms of the local electron configuration of the dioxygen π antibonding orbitals. The Wiberg indices, charge distributions and energy partitioning complete this description. The complexes studied were classified into three groups depending on the degree of dioxygen activation. A limited geometry variation for the 2[Co(CN) 5(O 2)] 3− complex was also performed.

Study of the co-ordination behaviour of the thiocyanate and cyanate ions in some platinum(II) complexes by heteronuclear resonance spectroscopy

The isomers present in solutions of [Pt(CNS)2L2](L = NMe3, PMe3, PMe2Et, PMeEt2, PEt3, AsMe3, AsMe2Et, AsMeEt2, AsEt3, SbMe3, SMe2, and SeMe2) have been identified by 1H-{195Pt} INDOR and 31P n.m.r. measurements. The mode of co-ordination of the thiocyanate ion is shown to be sensitive to the size of the cis ligands. Some related cyanate complexes have been prepared and are shown to be entirely N-bonded. Some representative infrared and Raman spectra are reported and the shortcomings of such measurements as a means of establishing stereochemistry are discussed.

Complexes of esters of pyridine carboxylic acids. Part I. complexes with Ni(II) and Co(II) thiocyanates

The syntheses of Nickel(II) and Cobalt(II) thio- cyanate complexes of type ML n(NCS) 2 where M = Co or Ni and n = 2 for L = methyl picolinate (MP), ethyl picolinate (EP), isopropyl picolinate (IP) and n = 4 for L = ethyl nicotinate (EN) and ethyl isonicotinate (EIN), are described. The complexes have been characterised by elemental analyses, molar conductance, magnetic susceptibility, thermogravimetric, electronic and infrared spectral data. The complexes are non-electrolytes in nitrobenzene and have high spin distorted octahedral structure with N-bonded thiocyanate groups in trans-position. MP, EP and IP act as bidentate ligands coordinating through pyridine ring nitrogen and carbonyl oxygen while EN and EIN act as unidentate ligands and coordinate through ring nitrogen only. The values of splitting energy (10 Dq), Racah parameter (B) and nephelauxetic ratio (β) have been evaluated for the nickel complexes.

σ-Bonded organotransition-metal ions. Part XIV. Characterisation of monomeric and bridged anionic complexes of organocobaloximes

A number of alkyl-, alkenyl-, and alkynyl-bis(dioximato)cyanocobaltate(III) ions have been prepared and characterised as tetraphenylarsonium and tetra-alkylammonium salts. Corresponding dimeric bridged anionic complexes, in which two organocobalt groups are bonded to the same cyanide ligand, have been isolated and/or characterised in solution. The cyanide stretching frequency of the dimeric complexes is ca. 30–40 cm–1 greater than that of the monomeric complexes, and both increase with the electronegativity of the α-carbon of the organic group(s). Bridged cyanide complexes in which the two organocobalt components differ have been shown to rearrange and disproportionate by an intermolecular mechanism. A trimeric compound containing two cyanide bridges has also been isolated. Similar monomeric and dimeric azido- and thiocyanato-complexes have been isolated. Both Sand N-bonded thiocyanate complexes are believed to coexist and to exchange in solution, the latter being slightly favoured. Only monomeric cyanate complexes have been prepared, and may involve a rapidly established equilibrium between the O- and the N-bonded species in solution.

Formation and oxidation-reduction changes of the cyanate complexes of iron in methanol

Formation and oxidation-reduction changes of the cyanate complexes of iron in methanol

Magnetic Susceptibility Measurements of Cytochrome c Peroxidase and Its Complexes

Abstract A highly purified preparation of cytochrome c peroxidase was prepared by reconstituting the enzyme from the apoprotein and protohemin. Paramagnetic susceptibilities of the enzyme and of its complexes with cyanide, azide, cyanate, and fluoride were measured at temperatures from 77° K to 273° K. The susceptibilities of the cyanide and fluoride complexes obeyed Curie's law over the entire temperature range and it was confirmed that these complexes are in purely low spin and high spin states. All of the other complexes, in addition to the free enzyme, were found to deviate from Curie's law above certain temperatures. The effective Bohr magneton numbers (neff) of the enzyme at different pH values were explained by assuming that cytochrome c peroxidase is a mixture of acidic and alkaline forms and that both forms have low spin and high spin states in thermal equilibria. The temperature dependence of the equilibria was also characterized spectrophotometrically for the enzyme at pH 7 and its cyanate complex. The optical measurements were in good agreement with the susceptibility measurements of the corresponding samples. The temperature-dependent changes of n2eff were analyzed on the basis of a thermal equilibrium between high spin and low spin states. Several thermodynamic parameters such as the energy difference (e), the enthalpy difference (ΔH°), and the entropy difference (ΔS°) between the two spin states, the entropy factor (γ), and the compensation temperature (Tc) were estimated from the temperature dependence of the equilibrium constants of the mixed spin states. The relation between ΔH° and ΔS° is discussed and compared with myoglobin and hemoglobin.

Rare earth selecnocyanate complexes

The synthesis and characterization of selenocyanate complexes of the type [(n−C4H9)4N]3 [M(NCSe)6] for the rare earth ions PrIII, NdIII, SmIII DyIII, HoIII, and ErIII is described. Infrared spectra measurements indicate theat the selecocyanate groups are bonded through the nitrogen atom. The tendency of the complexes to dissociate in nitrobenxene decreases as the atomic number of the rare earth ion increases, the complexes being slightly less stable in this respect than the corresponding thiocyanate complexes. The complexes are reasonably stable when dry, but tend to decompose in moist air or in solution at room temperature. The magnitude o fhte molar absorptivities of the absorption maxima in hte visible spectra of the complexes indicates pronounced deviations from Oh symmetry, possibly due to non-linear MNCSe linkages. The wavelengths of the absorption maxima of the corresponding selenocyanate, thiocyanate and chloride complexes generally increase in the order NCSe− < NCS− < Clt̄. Attempts to prepare the analogous cyanate complexes by comparable synthetic procedures were unsuccessful.

Complex hexacyanates of rhenium and molybdenum

The complex hexacyanates of Re(IV), Re(V), and Mo(III) have been prepared using molten dimethylsulfone as the reaction medium. These were isolated and characterized as the cesium or tetraphenylarsonium salts. Infrared spectra indicate these to be the first examples of oxygen-bonded cyanate complexes.