Cyanide Ligands Research Articles

Synthesis, spectroscopic, thermal and structural properties of 4-(2-aminoethyl)pyridinium tetracyanometallate(II) complexes

In this study, three new complexes (4aepyH)2[Ni(CN)4] (1), (4aepyH)2[Pd(CN)4] (2) and (4aepyH)2[Pt(CN)4] (3) [4aepy = 4-(2-aminoethyl)pyridine] have been synthesized and characterized by elemental, thermal, vibrational (FT-IR and Raman) and single-crystal X-ray diffraction techniques. The crystallographic analyses reveal that the complexes crystallize in the monoclinic system, space group C2/c. The asymmetric units of the complexes contain one M(II) ion, two cyanide ligands and one non-coordinated the 4aepy ligand. Each M(II) ion is four coordinated with four cyanide-carbon atoms in a square planar geometry and the [M(CN)4]2- anions act as a counter ion. The 4aepyH cations in the complexes compose of the protonation of the 4aepy. The vibrational spectral data also supported to the crystal structures of the complexes. Thermal stabilities and decomposition products of the complexes were investigated in the temperature range 40–700 °C in the static air atmosphere.

Crystal structure of bis-(1-ethyl-pyridinium) dioxonium hexa-cyanidoferrate(II).

The title compound, (C7H10N)2(H3O)2[Fe(CN)6] or (Etpy)2(H3O)2[Fe(CN)6] (Etpy+ is 1-ethyl-pyridinium), crystallizes in the space group Pnnm. The FeII atom of the [Fe(CN)6]4- anion lies on a site with site symmetry ..2/m, and has an octa-hedral coordination sphere defined by six cyanido ligands. Both the Etpy+ and the oxonium cations are located on a mirror plane. In the crystal, electron-donor anions of [Fe(CN)6]4- and electron-acceptor cations of Etpy+ are each stacked parallel to the b axis, resulting in a columnar structure with segregated moieties. The crystal packing is stabilized by a three-dimensional O-H⋯N hydrogen-bonding network between the oxonium ions and the cyanide ligands of [Fe(CN)6]4-.

Titanium(III) Member of the Family of Trigonal Building Blocks with Scorpionate and Cyanide Ligands.

The titanium(III) cyanide compound [Et4N][Tp*Ti(CN)3] ([Et4N] = tetraethylamonium; Tp* = 3,5-dimethyltrispyrazolylhydroborate) is reported, which exhibits a trigonally distorted geometry. Magnetic data and ab initio calculations verified that the molecule is an S = 1/2 paramagnet and that it exhibits significant temperature-independent paramagnetism.

Inhibition of the Cysteine Protease Human Cathepsin L by Triazine Nitriles: Amide⋅⋅⋅Heteroarene π-Stacking Interactions and Chalcogen Bonding in the S3 Pocket.

We report an extensive "heteroarene scan" of triazine nitrile ligands of the cysteine protease human cathepsin L (hCatL) to investigate π-stacking on the peptide amide bond Gly67-Gly68 at the entrance of the S3 pocket. This heteroarene⋅⋅⋅peptide bond stacking was supported by a co-crystal structure of an imidazopyridine ligand with hCatL. Inhibitory constants (Ki ) are strongly influenced by the diverse nature of the heterocycles and specific interactions with the local environment of the S3 pocket. Binding affinities vary by three orders of magnitude. All heteroaromatic ligands feature enhanced binding by comparison with hydrocarbon analogues. Predicted energetic contributions from the orientation of the local dipole moments of heteroarene and peptide bond could not be confirmed. Binding of benzothienyl (Ki =4 nm) and benzothiazolyl (Ki =17 nm) ligands was enhanced by intermolecular C-S⋅⋅⋅O=C interactions (chalcogen bonding) with the backbone C=O of Asn66 in the S3 pocket. The ligands were also tested for the related enzyme rhodesain.

Diiodomethane as a halogen bond donor toward metal-bound halides

A 1,3,5,7,9-pentaazanona-1,3,6,8-tetraenate (PANT) chloride platinum(II) complex (1) was obtained via the metal-mediated double coupling of 2,3-diphenylmaleimidine with both nitrile ligands in trans-[PtCl2(NCtBu)2]. Compound 1 was then co-crystallized with diiodomethane forming solvate 1·½CH2I2. The XRD experiment reveals that this solvate displays the halogen bonds H2C(I)–I⋯Cl–Pt and hydrogen bonds I2C(H)–H⋯Cl–Pt, which join two complex and one CH2I2 molecules in a heterotrimeric supramolecular cluster. Inspection of the CCDC database reveals only one example of the halogen bond H2C(I)–I⋯I–Pt between the CH2I2 molecule and metal-coordinated halide in the structure of VEMWOA. In VEMWOA, CH2I2 serves solely as a halogen bond donor with no hydrogen bond contribution. Results of the Hirshfeld surface analysis and DFT calculations (M06/DZP-DKH level of theory) followed by topological analysis of the electron density distribution within the formalism of Bader's theory (QTAIM method) for both 1·½CH2I2 and VEMWOA confirmed the formation of these weak interactions. The evaluated energies of halogen bonds involving CH2I2 are in the 2.2–2.8 kcal mol−1 range.

One-dimensional coordination polymers with 4-(2-aminoethyl)pyridine: Synthesis, crystal structures and spectroscopic properties

Two new one-dimensional polymeric metal complexes, namely [Zn(NH3)(μ-4aepy)Ni(μ-CN)(CN)3]n (1) and [Cu(H2O)(μ-4aepy)Pd(μ-CN)(CN)3]n (2) [4aepy=4-(2-aminoethyl)pyridine], were synthesized and characterized by vibrational (FT-IR and Raman) spectroscopy, single crystal X-ray diffraction, thermal and elemental analyses techniques. The complexes crystallize in the monoclinic system, P21/n space group. The asymmetric units of 1 and 2 contain two M(II) ions [M=Zn(II) and Ni(II) in 1 and Cu(II) and Pd(II) in 2], four cyanide ligands, one 4aepy ligand and one coordinated ligand (ammine in 1 and aqua in 2) in a distorted tetragonal coordination geometry. The crystal structures of the complexes revealed that three cyanide groups are terminal whereas one different cyanide group behaves as bridging ligand. The most important features of the complexes are the presence of obvious M⋯π [M(II)=Ni(II) or Pd(II)] interactions. The spectral and thermal analysis results also support the crystal structures of the complexes.

Ruthenium-Catalyzed Selective Hydroboration of Nitriles and Imines.

Ruthenium-catalyzed hydroboration of nitriles and imines is attained using pinacolborane with unprecedented catalytic efficiency. Chemoselective hydroboration of nitriles over esters is also demonstrated. A simple [Ru(p-cymene)Cl2]2 complex (1) is used as a catalyst precursor, which upon reaction with pinacolborane in situ generates the monohydrido-bridged complex [{(η6-p-cymene)RuCl}2(μ-H-μ-Cl)] 2. Further oxidative addition of pinacolborane to intermediate 2 leading to the formation of mononuclear ruthenium hydride species is suggested. Mass spectral analysis of the reaction mixture and independent experiments with phosphine-ligated ruthenium complexes indicated the involvement of mononuclear ruthenium intermediates in the catalytic cycle. Consecutive intramolecular 1,3-hydride transfers from the ruthenium center to coordinated nitrile and boronate imine ligands, leading to the reduction and resulting in the formation of diboronate amines, are proposed as a plausible reaction mechanism.

Comment on "Are polynuclear superhalogens without halogen atoms probable? A high-level ab initio case study on triple-bridged binuclear anions with cyanide ligands" [J. Chem. Phys. 140, 094301 (2014)

For the vertical electron detachment energies of triply-bridged Mg2(CN)5- superhalides, the Outer Valence Green Function (OVGF) yields results similar to those of the coupled-cluster singles and doubles plus approximate triples, or CCSD(T), method. Invalid comparisons between states with different symmetry or localization properties underlie the assertion of Yin et al that OVGF produces large discrepancies with respect to CCSD(T) for several isomers of Mg2(CN)5-.

Thermal Dehydrogenation of Methane by [ReN]+

The thermal reaction of the diatomic rhenium nitride cation [ReN]+ with methane has been explored using FT-ICR mass spectrometry complemented by high-level quantum chemical calculations. Mechanistic aspects of the reaction have been addressed to uncover scenarios for the competitive generation of a methylene and a hydrogen cyanide ligand attached to the rhenium center. The role the nitrogen atom plays in the reactive [ReN]+ /CH4 couple is elucidated, and the cause of the rather different reactivities of [ReN]+ and its lighter congener [MnN]+ is revealed.

Binuclear trivalent and tetravalent uranium halides and cyanides supported by cyclooctatetraene ligands

AbstractAlthough the first organoactinide chloride Cp3UCl (Cp=η5-C5H5) was synthesized more than 50 years ago, binuclear uranium halides remain very rare in organoactinide chemistry. Herein, a series of binuclear trivalent and tetravalent uranium halides and cyanides with cyclooctatetraene ligands, (COT)2U2Xn(COT=η8-C8H8; X=F, Cl, CN;n=2, 4), have been systematically studied using scalar-relativistic density functional theory (DFT). The structures with bridging halide or cyanide ligands were predicted to be the most stable complexes of (COT)2U2Xn, and all the complexes show weak antiferromagnetic interactions between the uranium centers. However, for each species, there is no significant uranium-uranium bonding interaction. The bonding between the metal and the ligands shows some degree of covalent character, especially between the metal and terminal halide or cyanide ligands. The U-5f and 6d orbitals are predominantly involved in the metal-ligand bonding. All the (COT)2U2Xnspecies were predicted to be more stable compared to the mononuclear half-sandwich complexes at room temperature in the gas phase such that (COT)2U2X4might be accessible through the known (COT)2U complex. The tetravalent derivatives (COT)2U2X4are more energetically favorable than the trivalent (COT)2U2X2analogs, which may be attributed to the greater number of strong metal-ligand bonds in the former complexes.

Synthesis and characterization of dinuclear silver(I) complexes with exchangeable nitrile ligands

We have prepared three silver(I) complexes of the type [Ag2(P∩N)3(NCR)](BF4)2 with (R=Me, Et, Ph). The crystal structures of the complexes were determined. The nitrile ligands can be easily exchanged by re-crystallisation in the respective nitrile. The luminescence properties were also investigated.

Pt(II) nitrile complexes: New insights on old complexes from a combined experimental and theoretical study

The spectroscopic characterization of cis- and trans-[PtCl2(NCR)2] (R=CH3, Ph, CH2Ph) was reported in solid state and solution phase. Moreover, the X-ray structures of cis-[PtCl2(NCCH3)2], cis- and trans-[PtCl2(NCPh)2] were redetermined at low temperature. FT-IR and NMR showed a blue-shift and a slight shielding of the νCN and δ(13CCN) values, respectively, in a counterintuitive way with respect to the well known improved reactivity towards nucleophiles of nitriles ligands coordinated to platinum(II), when compared to their free forms. These spectroscopic behaviors were also confirmed by theoretical experiments at DFT level. Moreover, DFT approach showed that the increased reactivity of the nitrile ligands, after coordination to Pt(II), can be explained by the energy decreasing of the ligands’ LUMOs, instead of an increased polarization of the CN bond, accordingly with the orbital control model previously proposed for trans-[PtCl2(MeCN)2]. Finally, bond analysis also discarded the occurrence of Pt→N back-donation.The combined experimental and theoretical study herein reported, provides a rationale of the chemical and physical behavior for Pt(II)-acetonitrile and -benzonitrile complexes, proving to be a potential tool to set suitable based-nitrile intermediates for the synthesis of new organometallic derivatives.

The Heptacyanotungstate(IV) Anion: A New 5 d Transition-Metal Member of the Rare Heptacyanometallate Family of Anions.

The heptacyanotungstate(IV) anion was isolated in the salt (n-Bu4 N)3 [W(IV) (CN)7 ] (1) from the reduction of (n-Bu4 N)3 [W(V) (CN)8 ] with concomitant loss of one cyanide ligand. The anion in 1 adopts a slightly distorted pentagonal bipyramidal geometry with an average W-C distance of 2.169 Å. The spectroscopic and magnetic properties are described.

The Heptacyanotungstate(IV) Anion: A New 5 d Transition‐Metal Member of the Rare Heptacyanometallate Family of Anions

AbstractThe heptacyanotungstate(IV) anion was isolated in the salt (n‐Bu4N)3[WIV(CN)7] (1) from the reduction of (n‐Bu4N)3[WV(CN)8] with concomitant loss of one cyanide ligand. The anion in 1 adopts a slightly distorted pentagonal bipyramidal geometry with an average W−C distance of 2.169 Å. The spectroscopic and magnetic properties are described.

A cyanide-bridged heterometallic coordination polymer constructed from square-planar [Ni(CN)4](2-): synthesis, crystal structure, thermal decomposition, electron paramagnetic resonance (EPR) spectrum and magnetic properties.

Square-planar complexes are commonly formed by transition metal ions having a d(8) electron configuration. Planar cyanometallate anions have been used extensively as design elements in supramolecular coordination systems. In particular, square-planar tetracyanometallate(II) ions, i.e. [M(CN)4](2-) (M(II) = Ni, Pd or Pt), are used as good building blocks for bimetallic Hofmann-type assemblies and their analogues. Square-planar tetracyanonickellate(II) complexes have been extensively developed with N-donor groups as additional co-ligands, but studies of these systems using O-donor ligands are scarce. A new cyanide-bridged Cu(II)-Ni(II) heterometallic compound, poly[[diaquatetra-μ2-cyanido-κ(8)C:N-nickel(II)copper(II)] monohydrate], {[Cu(II)Ni(II)(CN)4(H2O)2]·H2O}n, has been synthesized and characterized by X-ray single-crystal diffraction analyses, vibrational spectroscopy (FT-IR), thermal analysis, electron paramagnetic resonance (EPR) and magnetic moment measurements. The structural analysis revealed that it has a two-dimensional grid-like structure built up of cationic [Cu(H2O)2](2+) and anionic [Ni(CN)4](2-) units connected through bridging cyanide ligands. The overall three-dimensional supramolecular network is expanded by a combination of interlayer O-H...N and intralayer O-H...O hydrogen-bond interactions. The first decomposition reactions take place at 335 K under a static air atmosphere, which illustrates the existence of guest water molecules in the interlayer spaces. The electron paramagnetic resonance (EPR) spectrum confirms that the Cu(II) cation has an axial coordination symmetry and that the unpaired electrons occupy the d(x(2)-y(2)) orbital. In addition, magnetic investigations showed that antiferromagnetic interactions exist in the Cu(II) atoms through the diamagnetic [Ni(CN)4](2-) ion.

A Redox Active [2Fe-2S] Cluster on the Hydrogenase Maturase HydF.

[FeFe]-hydrogenases are nature's most prolific hydrogen catalysts, excelling at facilely interconverting H2 and protons. The catalytic core common to all [FeFe]-hydrogenases is a complex metallocofactor, referred to as the H-cluster, which is composed of a standard [4Fe-4S] cluster linked through a bridging thiolate to a 2Fe subcluster harboring dithiomethylamine, carbon monoxide, and cyanide ligands. This 2Fe subcluster is synthesized and inserted into [FeFe]-hydrogenase by three maturase enzymes denoted HydE, HydF, and HydG. HydE and HydG are radical S-adenosylmethionine enzymes and synthesize the nonprotein ligands of the H-cluster. HydF is a GTPase that functions as a scaffold or carrier for 2Fe subcluster production. Herein, we utilize UV-visible, circular dichroism, and electron paramagnetic resonance spectroscopic studies to establish the existence of redox active [4Fe-4S] and [2Fe-2S] clusters bound to HydF. We have used spectroelectrochemical titrations to assign iron-sulfur cluster midpoint potentials, have shown that HydF purifies with a reduced [2Fe-2S] cluster in the absence of exogenous reducing agents, and have tracked iron-sulfur cluster spectroscopic changes with quaternary structural perturbations. Our results provide an important foundation for understanding the maturation process by defining the iron-sulfur cluster content of HydF prior to its interaction with HydE and HydG. We speculate that the [2Fe-2S] cluster of HydF either acts as a placeholder for HydG-derived Fe(CO)2CN species or serves as a scaffold for 2Fe subcluster assembly.

Two Cyanide-Bridged Mn(II)-Nb(IV) Coordination Chain Ferrimagnets Promoted by Interchain Ferromagnetic Interactions.

Two new coordination chain compounds based on octacyanoniobate(IV) are reported: {[Mn(II)(bpy)(H2O)2]2[Nb(IV)(CN)8]·5H2O}n (1) and {[Mn(II)(bpy)(H2O)2][Mn(II)(bpy)2][Nb(IV)(CN)8]·5H2O}n (2) (bpy = 2,2'-bipyridine). Both have the topology of vertex-sharing CN-bridged squares. The Mn2Nb2 units are mutually parallel in 1 and perpendicular in 2. The antiferromagnetic intrachain interactions between the Mn(II) and Nb(IV) centers in 1 and 2, typical for Mn(II)-[Nb(IV)(CN)8] family of compounds, lead to ferrimagnetic ground state of each single chain. Both compounds show bulk ferrimagnetic ordering below their critical temperatures (Tc) of 6.4 K in 1 and 4.7 K in 2. Such a behavior is due to the ferromagnetic interchain interactions, assured by the π-π contacts between the 2,2'-bipyridine rings and by the hydrogen bonds between the terminal cyanide ligands of the [Nb(IV)(CN)8]-building blocks and coordination/crystallization water molecules. 1 and 2 are rare examples of ferrimagnets promoted by interchain ferromagnetic exchange, and the Tc of 1 is one of the highest among similar 1-D coordination polymers.

Exchange Interactions on the Highest-Spin Reported Molecule: the Mixed-Valence Fe42 Complex.

The finding of high-spin molecules that could behave as conventional magnets has been one of the main challenges in Molecular Magnetism. Here, the exchange interactions, present in the highest-spin molecule published in the literature, Fe42, have been analysed using theoretical methods based on Density Functional Theory. The system with a total spin value S = 45 is formed by 42 iron centres containing 18 high-spin FeIII ferromagnetically coupled and 24 diamagnetic low-spin FeII ions. The bridging ligands between the two paramagnetic centres are two cyanide ligands coordinated to the diamagnetic FeII cations. Calculations were performed using either small Fe4 or Fe3 models or the whole Fe42 complex, showing the presence of two different ferromagnetic couplings between the paramagnetic FeIII centres. Finally, Quantum Monte Carlo simulations for the whole system were carried out in order to compare the experimental and simulated magnetic susceptibility curves from the calculated exchange coupling constants with the experimental one. This comparison allows for the evaluation of the accuracy of different exchange-correlation functionals to reproduce such magnetic properties.

NiFe]-Hydrogenase Maturation.

[NiFe]-hydrogenases catalyze the reversible conversion of hydrogen gas into protons and electrons and are vital metabolic components of many species of bacteria and archaea. At the core of this enzyme is a sophisticated catalytic center comprising nickel and iron, as well as cyanide and carbon monoxide ligands, which is anchored to the large hydrogenase subunit through cysteine residues. The production of this multicomponent active site is accomplished by a collection of accessory proteins and can be divided into discrete stages. The iron component is fashioned by the proteins HypC, HypD, HypE, and HypF, which functionalize iron with cyanide and carbon monoxide. Insertion of the iron center signals to the metallochaperones HypA, HypB, and SlyD to selectively deliver the nickel to the active site. A specific protease recognizes the completed metal cluster and then cleaves the C-terminus of the large subunit, resulting in a conformational change that locks the active site in place. Finally, the large subunit associates with the small subunit, and the complete holoenzyme translocates to its final cellular position. Beyond this broad overview of the [NiFe]-hydrogenase maturation process, biochemical and structural studies are revealing the fundamental underlying molecular mechanisms. Here, we review recent work illuminating how the accessory proteins contribute to the maturation of [NiFe]-hydrogenase and discuss some of the outstanding questions that remain to be resolved.

Platinum(II)‐Mediated Double Coupling of 2,3‐Diphenylmaleimidine with Nitrile Functionalities To Give Annulated Pentaazanonatetraenate (PANT) Systems

Treatment of trans-[PtCl2(NCR)2] [R = Et 1, nPr 2, tBu 3, CH2Ph 4, Ph 5, p-CF3C6H4 6, NMe2 7, NEt2 8, N(CH2)5 9] with 2.5 equiv. of 2,3-diphenylmaleimidine in CH2Cl2 at room temperature for 5 min [for R = p-CF3C6H4 6, NMe2 7, NEt2 8, N(CH2)5 9] or 14 h (for R = Et 1, nPr 2, tBu 3, CH2Ph 4, Ph 5) furnishes (1,3,5,7,9-pentaazanona-1,3,6,8-tetraenato)platinum(II) [(PANT)PtII; PtCl{HN=C(R)N=CN[C(Ph)=C(Ph)]C=NC(R)=NH}] complexes 10–18. These species are formed by platinum(II)-mediated double coupling of 2,3-diphenylmaleimidine with both nitrile ligands. The formulation of the complexes was supported by satisfactory C, H, and N elemental analyses, which were in agreement with HRESI-MS, IR, and 1H and 13C{1H} NMR spectra. The structures of 10, 11·1/8nC6H14, 15, 16·CCl4, and 17·CHCl3 were determined by single-crystal X-ray diffraction. Absorption and emission studies were performed on representative complexes 10, 15, and 18, and the results show weak phosphorescence maxima at around 730–750 and 770–820 nm in CH2Cl2 and in the solid state, respectively. Further insight into the photophysical properties was gained by time-dependent density functional theory (TD–DFT) with detailed analysis of the corresponding frontier molecular orbitals for the lower-lying transition. The calculated energies of the T1 state (in terms of wavelength) are 715.8 nm for 10, 764.6 nm for 15, and 697.7 nm for 18, and these values are in good agreement with the trend of the first vibronic peaks of their phosphorescence spectra.