Cyano Ligands Research Articles

Photochemical reactivity of a binuclear Fe(I)–Fe(I) hydrogenase model compound with cyano ligands

Iron–iron hydrogenase model compounds have potential as hydrogen producing catalysts that are inexpensive and environmentally friendly. Many of these model compounds are dependent on light for activity but little is know about the photochemical intermediates or products that are formed and catalytically important. The photochemistry of μ-pdt-[Fe(CO)2CN]22− (2) is explored in acetonitrile and spectral changes in the IR support lost of CN−. UV–Vis spectroscopy was used to determine quantum yields for the disappearance of 2, which was found to be 0.38±0.04 in acetonitrile when irradiated with 365nm light under nitrogen.

The stacking interactions of bipyridine complexes: the influence of the metal ion type on the strength of interactions.

The strength of the stacking interactions in the bipy complexes of nickel, palladium, and platinum, [M(CN)2 bipy]2 (M = Ni, Pd, Pt), was calculated using the ωB97xD/def2-TZVP method. The results show that for all considered geometries, interactions are the strongest for platinum, and weakest for nickel complexes, as a result of higher dispersion contributions of platinum over the palladium and nickel complexes. It was also shown that strength of interactions considerably rises with an increase of the stacking overlap area. As a consequence of the favorable electrostatic term, the strength of interactions also rises when metal atom and cyano ligands are involved in the overlap with bipy ligand. The strongest interaction was calculated in the platinum complex, for the geometry that has overlap of metal and cyano ligands with bipy ligand with an energy of -39.80 kcal mol(-1). The energies for similar geometries of palladium and nickel complexes are -34.60 and -32.45 kcal mol(-1). These energies, remarkably, exceed the strength of the stacking interactions between organic aromatic molecules. These results can be of importance in all systems with stacking interactions, from materials to biomolecules.

Pathogenic Mutations Differentially Affect the Catalytic Activities of the Human B12-processing Chaperone CblC and Increase Futile Redox Cycling

Human CblC catalyzes the elimination of the upper axial ligand in cobalamin or B12 derivatives entering the cell from circulation. This processing step is critical for assimilation of dietary cobalamin into the active cofactor forms that support the B12-dependent enzymes, methionine synthase and methylmalonyl-CoA mutase. Using a modified nitroreductase scaffold tailored to bind cobalamin and glutathione, CblC exhibits versatility in the mechanism by which it removes cyano versus alkyl ligands in cobalamin. In this study, we have characterized the effects of two pathogenic missense mutations at the same residue, R161G and R161Q, which are associated with early and late onset of the CblC disorder, respectively. We find that the R161Q and R161G CblC mutants display lower protein stability and decreased dealkylation but not decyanation activity, suggesting that cyanocobalamin might be therapeutically useful for patients carrying mutations at Arg-161. The mutant proteins also exhibit impaired glutathione binding. In the presence of physiologically relevant glutathione concentrations, stabilization of the cob(II)alamin derivative is observed, which occurs at the expense of increased oxidation of glutathione. Futile redox cycling, which is suppressed in wild-type human CblC, explains the reported increase in oxidative stress levels associated with the CblC disorder.

Synthesis and Crystal Structure of the Electron‐Rich Cyano‐Rhodate Ba3[Rh(CN)3

AbstractBrownish gray microcrystalline powders of Ba3[Rh(CN)3] were synthesized from pellets of mixtures of Ba2N, rhodium, NaCN, and graphite at 1070 K in an argon atmosphere. Synchrotron powder diffraction data at 293(1) K revealed the crystal structure of the compound [P63/m, a = 9.23266(7) Å, c = 5.81612(6) Å] is isostructural to Ba3[Co(CN)3] and Ba3[Ir(CN)3]. The trigonal‐planar complex [Rh(CN)3]6– is surrounded by nine Ba2+ cations forming a tri‐capped trigonal prism. Compared to typical cyano ligands, the C–N bond is long [1.21(5) Å] and the vibrational frequencies are low (IR 1674 cm–1, Raman 1728 cm–1).

Structural differences between the active sites of the Ni-A and Ni-B states of the [NiFe] hydrogenase: an approach by quantum chemistry and single crystal ENDOR spectroscopy.

The two resting forms of the active site of [NiFe] hydrogenase, Ni-A and Ni-B, have significantly different activation kinetics, but reveal nearly identical spectroscopic features which suggest the two states exhibit subtle structural differences. Previous studies have indicated that the states differ by the identity of the bridging ligand between Ni and Fe; proposals include OH(-), OOH(-), H2O, O(2-), accompanied by modified cysteine residues. In this study, we use single crystal ENDOR spectroscopy and quantum chemical calculations within the framework of density functional theory (DFT) to calculate vibrational frequencies, (1)H and (17)O hyperfine coupling constants and g values with the aim to compare these data to experimental results obtained by crystallography, FTIR and EPR/ENDOR spectroscopy. We find that the Ni-A and Ni-B states are constitutional isomers that differ in their fine structural details. Calculated vibrational frequencies for the cyano and carbonyl ligands and (1)H and (17)O hyperfine coupling constants indicate that the bridging ligand in both Ni-A and Ni-B is indeed an OH(-) ligand. The difference in the isotropic hyperfine coupling constants of the β-CH2 protons of Cys-549 is sensitive to the orientation of Cys-549; a difference of 0.5 MHz is observed experimentally for Ni-A and 1.9 MHz for Ni-B, which results from a rotation of 7 degrees about the Cα-Cβ-Sγ-Ni dihedral angle. Likewise, the difference of the intermediate g value is correlated with a rotation of Cys-546 of about 10 degrees.

Investigating retention characteristics of a mixed-mode stationary phase and the enhancement of monolith selectivity for high-performance liquid chromatography.

The synthesis and chromatographic behavior of an analytical size mixed-mode bonded silica monolith was investigated. The monolith was functionalized by an in situ modification process of a bare silica rod with chloro(3-cyanopropyl)dimethyl silane and chlorodimethyl propyl phenyl silane solutions. These ligands were selected in order to combine both resonance and nonresonance π-type bonding within a single separation environment. Selectivity studies were undertaken using n-alkyl benzenes and polycyclic aromatic hydrocarbons in aqueous methanol and acetonitrile mobile phases to assess the methylene and aromatic selectivities of the column. The results fit with the linear solvent strength theory suggesting excellent selectivity of the column was achieved. Comparison studies were performed on monolithic columns that were functionalized separately with cyano and phenyl ligands, suggesting highly conjugated molecules were able to successfully exploit both of the π-type selectivities afforded by the two different ligands on the mixed-mode column.

New cyano bridged heteropolynuclear Cu(II) and Cd(II)-tetracyanopalladate(II) polymeric complexes with 2-methylimidazole ligand

New cyano-bridged heteronuclear polymeric complexes, [M(mim)2Pd(CN)4]n (M=Cu(II) (1) or Cd(II) (2); mim=2-methylmidazole), have been synthesized and characterized by elemental, thermal, FT-IR and Raman spectral analyses. The crystal structure of complex 1 has been determined by single crystal X-ray diffraction technique. The crystallographic analysis reveals that it crystallizes in the monoclinic system, space group P21/c. The Pd(II) atom is coordinated by four cyano ligands, while Cu(II) atom is also surrounded by the two mim and two cyano ligands. The structure of 1 is formed by infinite 2,2-TT type chains of the [–Cu(mim)2–NC–Pd(CN)2–CN–]n composition; these are interlinked by hydrogen bonds (HBs) leading to two-dimensional patterns. FT-IR and Raman spectral data indicate the presence of bridging cyano ligands in the structures of the complexes.

Cyano‐Functionalized Triarylamines on Au(111): Competing Intermolecular versus Molecule/Substrate Interactions

The self‐assembly of cyano‐substituted triarylamine derivatives on Au(111) is studied with scanning tunneling microscopy and density functional theory calculations. Two different phases, each stabilized by at least two different cyano bonding motifs are observed. In the first phase, each molecule is involved in dipolar coupling and hydrogen bonding, while in the second phase, dipolar coupling, hydrogen bonding and metal‐ligand interactions are present. Interestingly, the metal–ligand bond is already observed for deposition of the molecules with the sample kept at room temperature leaving the herringbone reconstruction unaffected. It is proposed that for establishing this bond, the Au atoms are slightly displaced out of the surface to bind to the cyano ligands. Despite the intact herringbone reconstruction, the Au substrate is found to considerably interact with the cyano ligands affecting the conformation and adsorption geometry, as well as leading to correlation effects on the molecular orientation.

Two dimensional cyano-bridged hetero-metallic coordination polymers containing metal⋅⋅⋅π interactions

Three cyano bridged hetero-metallic complexes of general formula, [Cu(NH3)2(μ-ampy)M(μ-CN)2(CN)2]n [ampy=4-aminomethylpyridine, M=Ni(II) (1), Pd(II) (2) and Pt(II) (3)] have been synthesized and characterized by vibrational (FT-IR and Raman) spectroscopy, single crystal X-ray diffraction, thermal analyses and elemental analyses. The complexes crystallize in triclinic system with space group P-1. In all complexes, M(II) ions are coordinated by four cyano ligands, and four N atoms in the equatorial plane around the Cu atom form a slightly distorted square-planar arrangement, while the slightly distorted octahedral coordination is completed by the cyanide N atoms in the axial positions. In one-dimensional structures of all the complexes, [Cu(ampy)]2+ cations and [M(CN)4]2− anions are linked via bridging cyano ligands. The adjacent one-dimensional structures form a 2D network to connect by the μ-ampy bridging ligands. The 2D layers are further linked by metal⋯π and hydrogen bonding interactions to generate a three dimensional network.

Reprint of “EPR studies of a cyano-bridged {Fe2IIINiII} coordination complex and its corresponding FeIII mononuclear building-block”

High-field/frequency electron paramagnetic resonance measurements have been performed on a cyano-bridged trinuclear Fe2IIINiII complex and an analogous mononuclear FeIII building block. The mononuclear FeIII complex exhibits a low-spin configuration resulting from a strong-field coordination environment and can be modeled as an effective s=1/2 Kramers ion that exhibits significant g-anisotropy: gz=3.7, gy=2.2 and gx=1.92. The corresponding Fe2IIINiII complex possesses an S=2 spin ground state as a result of ferromagnetic exchange that is mediated by the bridging cyano ligands. Simulations of frequency dependent EPR data establish that the Fe2IIINiII complex exhibits easy-axis type magnetoanisotropy, with best-fit simulation parameters of: S=2, D=−2.09cm−1, E=0.08cm−1, B40=2.3×10−3cm−1, gz=2.4, gy=gx=1.95.

Syntheses, crystal structures, spectroscopic and thermal analyses of 3- and 4-aminomethylpyridinium tetracyanometallate(II) complexes

In this study, six new complexes (3ampyH)2[Ni(CN)4] (1), (3ampyH)2[Pd(CN)4] (2), (3ampyH)2[Pt(CN)4] (3), (4ampyH)2[Ni(CN)4] (4), (4ampyH)2[Pd(CN)4] (5) and (4ampyH)2[Pt(CN)4] (6) (3ampy=3-aminomethylpyridine and 4ampy=4-aminomethylpyridine) have been synthesized and characterized by spectroscopic, elemental and thermal analyses, and single crystal X-ray diffraction techniques. Complexes 1, 2 and 3 crystallize in the monoclinic system, space groups P21/c, C2 and C2, respectively, whereas complexes 4, 5 and 6 crystallize in the triclinic system, space groups P1¯. The asymmetric units contain one halves of the [M(CN)4]2− anions and the 3ampyH or the 4ampyH cations, where M is Ni(II), Pd(II) or Pt(II), respectively. The metal atoms are located on inversion centres and each metal atom is coordinated in a distorted square planar geometry by the four symmetry related C atoms from four cyano ligands.

Syntheses, thermal analyses, crystal structures, FT-IR and Raman spectra of 2D [Zn(NH3)2(μ–ampy)M′(μ–CN)2(CN)2]n (M′ = Ni(II), Pd(II) or Pt(II)) complexes

Three new cyano-bridged heteronuclear polymeric complexes, [Zn(NH3)2(μ–ampy)Ni(μ–CN)2(CN)2]n (1), [Zn(NH3)2(μ–ampy)Pd(μ–CN)2(CN)2]n (2) and [Zn(NH3)2(μ–ampy)Pt(μ–CN)2(CN)2]n (3) (ampy=4-aminomethylpyridine) have been synthesized and characterized by vibrational spectroscopy (FT-IR and Raman), thermal (TG, DTG and DTA) and elemental analyses. The crystal structures of complexes 1 and 2 have been determined by the X-ray single crystal diffraction technique. Complexes 1 and 2 crystallize in the triclinic system with the space group P1¯. Structural studies reveal that the Ni(II) or Pd(II) ions are four coordinate with four cyanide–carbon atoms in a square planar geometry and the Zn(II) ion exhibits a distorted octahedral coordination geometry completed by the six N atoms from two ammine, one ampy and two cyano ligands. The adjacent metal centers are bridged by bis-monodentate cyano ligands to form a one-dimensional linear chain. These chains are linked by ampy ligands into a 2D sheet structure. The 2D units are connected together via intramolecular C–H⋯N and intermolecular N–H⋯N hydrogen bonding to form 3D supramolecular networks. In additional, there are also interactions between the Ni(II) or Pd(II) ion and the aromatic π-system. Vibrational spectral data indicate the presence of two ν(CN) bands for the complexes, which can be assigned to the terminal and bridging cyanide ligands. Decomposition reactions take place in the temperature range 40–900°C in a static air atmosphere.

Syntheses, crystal structures and spectral properties of 1D tetracyanonickelate(II) complexes with 1-ethylimidazole

Three new cyano-bridged tetracyanonickelate(II) complexes with 1-ethylimidazole (etim) ligand, [Ni(etim)4Ni(μ-CN)2(CN)2]n (1), [Zn(etim)4Ni(μ-CN)2(CN)2]n (2) and {[Cd(etim)4Ni(μ-CN)2(CN)2]2·2H2O}n (3) have been synthesized and characterized by spectroscopic (IR and Raman) and X-ray diffraction techniques. According to the crystallographic data, it was understood that the complexes with the chain 2,2-TT structures belong to P−1 space group of triclinic crystal system. In the complexes, it was observed that Ni(II), Zn(II) and Cd(II) ions have distorted octahedral geometries. In the [Ni(μ-CN)2(CN)2]2− anion, the Ni(II) ion is coordinated by the four carbon atoms of the four cyano ligands, and exhibits square-planar coordination geometry. The crystallographic analyses reveal that the crystal structures of complexes 1–3 are one dimensional linear chain polymers and these chains are held together by the CH⋯π, CH⋯Ni and hydrogen bonding interactions, forming three-dimensional networks.

EPR studies of a cyano-bridged {Fe2IIINiII} coordination complex and its corresponding FeIII mononuclear building-block

High-field/frequency electron paramagnetic resonance measurements have been performed on a cyano-bridged trinuclear Fe2IIINiII complex and an analogous mononuclear FeIII building block. The mononuclear FeIII complex exhibits a low-spin configuration resulting from a strong-field coordination environment and can be modeled as an effective s=1/2 Kramers ion that exhibits significant g-anisotropy: gz=3.7, gy=2.2 and gx=1.92. The corresponding Fe2IIINiII complex possesses an S=2 spin ground state as a result of ferromagnetic exchange that is mediated by the bridging cyano ligands. Simulations of frequency dependent EPR data establish that the Fe2IIINiII complex exhibits easy-axis type magnetoanisotropy, with best-fit simulation parameters of: S=2, D=−2.09cm−1, E=0.08cm−1, B40=2.3×10−3cm−1, gz=2.4, gy=gx=1.95.

Synthesis and Structural Studies of PdII/ZnII Architecture with N,N′-Bis(2-hydroxyethyl)ethylenediamine as Capping Ligand

A new compound of the composition [-{Zn-di-μ-bishydeten(O)-Zn}-μ-(CN)2Pd(CN)2] (1) was obtained from the reaction of PdCl2, bishydeten [N,N′-bis(2-hydroxyethyl)ethylenediamine], KCN and ZnCl2 in water/ethanol mixture. This dimeric polymer was characterized by IR spectroscopy and elemental analysis, and its thermal properties were studied by TG and DTG. In addition, the crystal structure was determined by single-crystal X-ray analysis. IR spectroscopy pointed out the existence of both terminal and bridged cyano ligands in the complex structure. When it comes to thermal analysis, the complex followed usual decomposition mechanism in which neutral ligands are decomposed first and then anionic ligands left the structure. Single crystal X-ray analysis revealed that 1 exhibited polymeric structure. An interesting feature of this complex is that ancillary bishydeten ligand acted as a bridge just like cyano groups did. In the complex structure, dimeric Zn units, which were gathered by –O atoms of bishydeten ligands in an asymmetric fashion, were bridged by tetracyanopalladateII anions. 1D chain turned into 3D chains by means of intermolecular hydrogen bonds.

Two dimensional heteropolynuclear Zn(II) and Cd(II)-tetracyanopalladate(II) complexes with the 1-ethylimidazole ligand exhibiting C–H⋯Pd interactions

The cyano-bridged heteronuclear complexes [Zn(etim)2Pd(μ-CN)4]n (1) and [Cd(etim)2Pd(μ-CN)4]n (2) (etim=1-ethylimidazole), have been synthesized and characterized by FT-IR, Raman spectroscopy, thermal and elemental analyses. The crystal structures of the complexes have been determined by X-ray single crystal diffraction. In the complexes, the Pd(II) ion is coordinated by four cyano ligands, forming a square-planar geometry, and the Zn(II) or Cd(II) ions are coordinated by six N atoms from four bridging cyano ligands and two etim ligands in a distorted octahedral geometry. The most important features of the complexes are the presence of C–H···Pd hydrogen-bonding interactions between the Pd(II) ion and the hydrogen atoms of the etim ligand.

Two dimensional cyano-bridged heteropolynuclear complex containing Pd ···π interactions

Abstract The heteronuclear complex, [Cd(NH3)2(μ-ampy)Pd(μ-CN)2(CN)2] n (1) (ampy = 4-aminomethylpyridine), was synthesized and characterized by vibrational (FT-IR and Raman) spectroscopy, elemental and thermal analyses and single crystal X-ray diffraction techniques. The complex crystallizes in the triclinic system, space group P-1. The Cd(II) ion exhibits a distorted octahedral coordination by two different N-atoms from two symmetrically equivalent ampy ligands, two ammine ligands and two bridging cyano groups, whereas the Pd(II) ion has square planar coordination and is coordinated by four cyano ligands. The tetracyanopalladate(II) anion is coordinated to the adjacent two Cd(II) ions to generate a one-dimensional chain. The adjacent 1D chains are connected by the μ-ampy bridging ligands to form a 2D network. The 2D layers are further linked by Pd···π and hydrogen bonding interactions to generate a 3D supramolecular network. The decomposition reaction takes places in the temperature range of 40–900 °C in the static air atmosphere.

Development of a surface plasmon assisted label-free calorimetric method for sensitive detection of mercury based on functionalized gold nanorods

In this investigation, we established a new sensitive, selective and label free optical method for the detection of mercury ions (Hg2+) by utilizing cyano (–CN) ligand functionalized gold nanorods (GNRs) based on the surface plasmon resonance (SPR) of the GNRs. The functionalization of the GNRs was specifically done with a –CN group containing polymer, poly(2-aminobenzonitrile) (P2ABN), to preconcentrate the Hg2+ ions on the surface of the GNRs prior to detection. The functionalization of the GNRs was carried out by two approaches. In the first approach, the GNR surface was modified with a porous silica network containing P2ABN (designated as GNR@silica-CN). In the second approach, GNR was modified with P2ABN (designated as GNR@P2ABN). The Hg2+ ion detection strategy involves the preconcentration of Hg ions on the surface of GNR@silica-CN or GNR@P2ABN through the interaction of the –CN groups in P2ABN with Hg2+ ions, reduction to Hg0 atoms by ascorbic acid (AA), and monitoring the SPR of GNRs. The porous network in GNR@silica-CN allows efficient migration of Hg0 to reach the GNR surface and causes effective amalgamation compared to GNR@P2ABN. As a result, GNR@silica-CN exhibits a significant change in the SPR of GNRs over a wide dynamic concentration range (from 50 nM to 5 μM) for Hg2+ ions. The very low detection limit of 1 ppb with GNR@silica-CN for Hg2+ ions suggests its excellent potential for the monitoring and detection of ultra low levels of Hg. In addition, the GNR@silica-CN shows no sensitivity for other environmentally relevant metal ions which confirms the high specificity for Hg2+ ion detection in practical samples. We demonstrated the effectiveness of the present method by detecting Hg2+ ions in spiked water (pond and water) samples. We envisage that this simple, fast and sensitive method will be suitable for environmental monitoring in the future.

Trifluoropropynyl as a Surrogate for the Cyano Ligand and Intense, Room-Temperature, Metal-Centered Emission from Its Rh(III) Complex

The trifluoropropynyl ligand -C≡CCF(3) was studied as a possible surrogate for the cyano ligand. Complexes of the type trans-[M(cyclam)(C≡CCF(3))(2)]OTf (where M = Cr(3+), Co(3+), and Rh(3+); OTf = trifluoromethanesulfonate) were prepared and then characterized by electronic spectroscopy and by cyclic voltammetry for the Co(3+) complex. The UV-vis spectra for all three bear a remarkable similarity to that of the trans-M(cyclam)(CN)(2)(+) cations. The trifluoropropynyl complex of Co(3+) shows electrochemical behavior nearly identical with that of its dicyano analogue. Metal-centered phosphorescence from the Rh(III) complex in room-temperature aqueous solution has a quantum yield of 0.12 and a lifetime of 73 μs, nearly 10 times higher than those of its dicyano analogue.

Structural Basis for the Reaction Mechanism of S-Carbamoylation of HypE by HypF in the Maturation of [NiFe]-Hydrogenases

As a remarkable structural feature of hydrogenase active sites, [NiFe]-hydrogenases harbor one carbonyl and two cyano ligands, where HypE and HypF are involved in the biosynthesis of the nitrile group as a precursor of the cyano groups. HypF catalyzes S-carbamoylation of the C-terminal cysteine of HypE via three steps using carbamoylphosphate and ATP, producing two unstable intermediates: carbamate and carbamoyladenylate. Although the crystal structures of intact HypE homodimers and partial HypF have been reported, it remains unclear how the consecutive reactions occur without the loss of unstable intermediates during the proposed reaction scheme. Here we report the crystal structures of full-length HypF both alone and in complex with HypE at resolutions of 2.0 and 2.6 Å, respectively. Three catalytic sites of the structures of the HypF nucleotide- and phosphate-bound forms have been identified, with each site connected via channels inside the protein. This finding suggests that the first two consecutive reactions occur without the release of carbamate or carbamoyladenylate from the enzyme. The structure of HypF in complex with HypE revealed that HypF can associate with HypE without disturbing its homodimeric interaction and that the binding manner allows the C-terminal Cys-351 of HypE to access the S-carbamoylation active site in HypF, suggesting that the third step can also proceed without the release of carbamoyladenylate. A comparison of the structure of HypF with the recently reported structures of O-carbamoyltransferase revealed different reaction mechanisms for carbamoyladenylate synthesis and a similar reaction mechanism for carbamoyltransfer to produce the carbamoyl-HypE molecule.