NCS Bond Research Articles

Synthesis and Electrochemical Studies of Novel Isothiocyanato Macrocyclic Mn(III) Complexes: Experimental and Theoretical Studies

The coordination chemistry of macrocyclic complexes are of considerable interest because of their various applications in bioinorganic systems, catalysis and analytical practices. Herein, we synthesized Mn(III) macrocyclic complex, MnN4-complex, and its isothiocyanato derivative MnN5-complex. These complexes were characterized by elemental, FT-IR, UV-Vis and Mass spectroscopic techniques and also by magnetic susceptibility measurements. The results of UV-vis spectral studies suggested that the intense absorption band in the 520–570 nm range is due to the intermolecular charge transfer transition which is associated with Mn–NCS bond in MnN5-complex. The electrochemical investigation indicated the stabilization of unusual oxidation state and modification of electronic structure of Mn central atom through SCN− coordination at fifth position of MnN4-complex. Further, geometric optimization of two complexes was also carried out by DFT calculations using B3LYP/6-31G* basis set. It was suggested that axial coordination of Cl is in interior of N4 cavity whereas NCS is at exterior.

Structural Variability of 4f and 5f Thiocyanate Complexes and Dissociation of Uranium(III)-Thiocyanate Bonds with Increased Ionicity.

A series of complexes [Et4N][Ln(NCS)4(H2O)4] (Ln = Pr, Tb, Dy, Ho, Yb) have been structurally characterized, all showing the same structure, namely a distorted square antiprismatic coordination geometry, and the Ln-O and Ln-N bond lengths following the expected lanthanide contraction. When the counterion is Cs+, a different structural motif is observed and the eight-coordinate complex Cs5[Nd(NCS)8] isolated. The thorium compounds [Me4N]4[Th(NCS)7(NO3)] and [Me4N]4[Th(NCS)6(NO3)2] have been characterized, and high coordination numbers are also observed. Finally, attempts to synthesize a U(III) thiocyanate compound has been unsuccessful; from the reaction mixture, a heterocycle formed by condensation of five MeCN solvent molecules, possibly promoted by U(III), was isolated and structurally characterized. To rationalize the inability to isolate U(III) thiocyanate compounds, thin-layer cyclic voltammetry and IR spectroelectrochemistry have been utilized to explore the cathodic behavior of [Et4N]4[U(NCS)8] and [Et4N][U(NCS)5(bipy)2] along with a related uranyl compound [Et4N]3[UO2(NCS)5]. In all examples, the reduction triggers a rapid dissociation of [NCS]- ions and decomposition. Interestingly, the oxidation chemistry of [Et4N]3[UO2(NCS)5] in the presence of bipy gives the U(IV) compound [Et4N]4[U(NCS)8], an unusual example of a ligand-based oxidation triggering a metal-based reduction. The experimental results have been augmented by a computational investigation, concluding that the U(III)-NCS bond is more ionic than the U(IV)-NCS bond.

Crystal structure and spectroscopic properties of isothiocyanato[(3,14-dimethyl-2,6,13,17-tetraazatricyclo(16.4.0.07,12)docosane)]copper(II) thiocyanate

A new complex [Cu(L1)(NCS)]SCN, where L1 = 3,14-dimethyl-2,6,13,17-tetraazatricyclo( 16.4.0.07,12)docosane is prepared and characterized by single crystal X-ray crystallographic analysis. The complex crystallizes in the triclinic space group P1 with two mononuclear formula units in a cell of dimensions a = 7.9681(2) A, b = 8.8644(2) A, c = 18.8165(5) A, α = 76.758(70)°, β = 78.490(2)° and γ = 77.679(2)°. The Cu(II) ion is five-coordinate in an axially elongated square pyramidal environment, with the four amine N atoms at the equatorial positions and the N atom of one thiocyanate at an apical site. The macrocyclic cyclam moiety adopts a stable trans-III configuration. The Cu–N basal plane bond length has a mean value of 2.037(2) A. The coordinated Cu–NCS bond length is 2.322(3) A. The N atom of the thiocyanate anion is connected to the macrocyclic ligand of the cation via an NH…N(CS) hydrogen bond. The UV-visible absorption and IR spectral properties are also discussed.

Synthesis and conformational study of new S-polyfluoroalkyl dithiocarbamates

The synthesis of a series of new S-polyfluoroalkyl dithiocarbamates from isothiocyanates and polyfluoroalkyl thiols is reported. The reaction was carried out in the presence of triethylamine and the are produced in moderate to good yields. These compounds were characterized by NMR, FT-IR and MS techniques. In addition, the conformational s-cis/s-trans isomerisation in these dithiocarbamates was investigated using dynamic NMR experiments. The free energies of activation thus obtained were in the range 12–16kcal/mol. The effects of N- and S-substituents on the barrier to rotation around the NCS bond in these dithiocarbamates are discussed and compared with those in thiocarbamate analogs.

O-perfluoroalkyl thiocarbamates: Synthesis and perfluoroalkyl effects on the barrier to N[sbnd]CS rotation

A series of new O-perfluoroalkyl thiocarbamates were synthesized by the reaction of isothiocyanates with perfluoroalkyl alcohols. Substituent effects on the barrier to rotation around the NCS bond in these thiocarbamates were investigated using variable temperature 1H NMR spectroscopy. The free energies of activation were in the range 14–17kcal/mol and are attributed to the conformational S-cis and S-trans isomerization. The results obtained for different O-perfluoroalkyl thiocarbamates were discussed and compared with those of non-fluorinated analogs.

A Trisheteroleptic Cyclometalated RuII Sensitizer that Enables High Power Output in a Dye‐Sensitized Solar Cell

The low embodied energy and high power-conversion efficiency (h) over disparate light intensities renders the dyesensitized solar cell (DSSC) a promising alternative to conventional photovoltaic technologies. Significant penetration of the DSSC into the photovoltaic market, however, is hindered predominantly by the long-term stability of dyes and electrolytes under practical conditions. The instability of champion (i.e., h> 10%) dyes (which, until recently, all were derivatives of [Ru(dcbpy)2(NCS)2] (N3 ; dcbpy= 4,4’dicarboxy-2,2’-bipyridine)) in the DSSC is caused primarily by desorption of the dyes from the surface and/or liberation of the NCS ligands from the metal centre. While the rate of dye desorption from TiO2 can be manipulated by replacing the CO2H moiety with other anchoring groups, this strategy typically compromises electron injection into the TiO2. [8] An alternative approach is to replace the dcbpy ligands that comprise N3 with bidentate ligands bearing aliphatic substituents (e.g., Scheme 1a), which serve to hinder water from reaching the surface to hydrolytically cleave the TiO2–dye ester linkage. These groups provide the additional benefit of suppressing recombination between the electrolyte and the electrons in TiO2, thus leading to higher efficiencies (Scheme 1a). Chemical strategies for avoiding the labile Ru NCS bond have been realized recently; indeed, we and others have now documented remarkably high h values for DSSCs containing NCS -free Ru sensitizers. Cyclometalated Ru complexes such as [Ru(dcbpy)2(ppy)] 1+ (ppy= 2-phenylpyridine) provide a versatile platform in this respect because: 1) the highest occupied molecular orbital (HOMO) is extended over the metal and anionic ring thus enabling its modulation through judicious installation of substituents at the R2 site in Scheme 1b; and 2) the low-lying excited states, which contain orbital character that resides on the p* framework of the dcbpy ligand(s), are poised for electron injection into the TiO2. [10,11,15–18] This scenario leaves open the opportunity to replace one dcbpy with a bidentate ligand capable of suppressing recombination and enhancing the optical properties as per the aforementioned protocol (Scheme 1). While we recently demonstrated synthetic access to trisheteroleptic Ru sensitizers (e.g., 1 and 2 ; Scheme 2), we learned that removing the acid linkers

Spectroscopic and impedance studies of reverse biased degraded dye solar cells

The work that is presented here is focused on the results that were obtained during studies of the performance of dye solar cells under certain reverse bias conditions. This reverse voltage could permanently modify or damage a cell if it is not properly protected. Various techniques were employed to determine the physical changes in the cell. It was found that a cell that was subjected to a reverse bias of 2 V for 500 min showed a 58% recovery. The UV-vis spectra showed a blue shift (higher energy), the Raman showed no peak at 1,713 cm−1 and the FT-IR showed the disappearance of the S-C-N absorption band at 2,100 cm−1. The combined conclusion is that the NCS ligand has been depleted and replaced with I3− ions. Nyquist and Bode plots showed an increase in the charge transfer resistance at the counter electrode. This indicates a partial oxidation of the Pt catalyst on the counter electrode. The changes in the cell after being subjected to a reverse bias potential of 2 V for 500 min are changes on the NCS bonds on the Ru containing dye as well as the Pt on the counter electrode.

The syntheses, structures and reactivity of bis(tert-butylcyclopentadienyl)molybdenum derivatives: nitrogen alkylation of an η2-acetonitrile ligand and influence of the chalcogen on the barrier to inversion of chalcogenoether adducts

An investigation of the chemistry of the tert-butyl-substituted molybdenocene system, {(CpBut)2Mo} (CpBut = C5H4But), has demonstrated that the η2-acetonitrile ligand in (CpBut)2Mo(η2-MeCN) may be alkylated by RI (R = Me, Et) at nitrogen to give iminoacyl derivatives, [(CpBut)2Mo(η2-MeCNR)]+, which is a new type of reactivity for mononuclear acetonitrile complexes. A series of chalcogenolate–hydride complexes (CpBut)2Mo(EPh)H (E = S, Se, Te) have been obtained by reaction of (CpBut)2MoH2 with Ph2E2, and may be alkylated by MeI to give the chalcogenoether adducts [(CpBut)2Mo(PhEMe)H]I. Dynamic NMR studies on [(CpBut)2Mo(PhEMe)H]+ indicate that the barrier to inversion at the chalcogen increases in the sequence S < Se < Te. The oxo complex (CpBut)2MoO reacts with 2 equivalents of Me3SiX (X = Cl, Br, I, O2CMe, O3SMe) to yield (CpBut)2MoX2; for X = CN and NCS, (CpBut)2Mo(OSiMe3)X, the product of reaction with 1 equivalent may be isolated. (CpBut)2Mo(OSiMe3)X (X = CN, NCS) reacts with Me3SiNCS to give the thiocyanate complex (CpBut)2Mo(SCN)X, rather than the isocyanate isomer, (CpBut)2Mo(NCS)X, thereby indicating that the reactions do not involve a simple metathesis of the Si–NCS bond. Other complexes that are reported include: (CpBut)2MoX2 (X = H, Cl, Br, I, Me, CH2Ph, CH2SiMe3), (CpBut)2MoL (L = CO, C2H4, C2H2, MeCN, PMe3), [(CpBut)2Mo(μ-E)]2, (CpBut)2Mo(η2–E2) and (CpBut)2Mo(EPh)2 (E = S, Se, Te).

Structure and Reactivity of 1-Isothiocyanatosilatrane: The First Silatrane with a Direct Si-NCS Bond.

Some unique features of 1-isothiocyanatosilatrane, 1, include concomitant NMR couplings of quadrupolar 14N(NCS) nucleus with adjacent heteroatoms [J(13C−14N) = 26.17 Hz; J(29Si−14N) = 28.47 Hz] and the crystallographically determined shortest N→Si bond, 2.007(3) A, as well as a nearly linear structure of the heteroatoms N(1)−Si−N(2)−C(7)−S(1). Contrary to the known reactivity of tetracoordinate isothiocyanatosilanes, 1 invariably shows retention of the Si−N(CS) bond under normal nucleophilic/electrophilic reaction conditions. These novel features also get support from semiemperical MO calculations on the compound.

A structural study of (dibenzyldiaza-18-crown-6) lanthanum(III) thiocyanate

The structure of the complex La(NCS) 3C 26H 38N 2O 4 ( 1) was determined by single-crystal X-ray diffraction and the structure of the coordinating ligand, C 26H 38N 2O 4 ( 2), was studied by the semi-empirical PM3 method. The bonding around La consists of a primary coordination of three thiocyanate N atoms and a secondary coordination of two N atoms and four O atoms of the macrocycle. The primary coordination about La gives an almost planar trigonal configuration that bisects the plane of the macrocycle with La lying in the centre of the macrocycle cavity. The benzyl groups that are attached to the macrocycle are in syn conformation with respect to the macrocycle plane with one of the La–NCS bonds pointing above the plane and the other two La–NCS bonds pointing below the plane in the direction of the benzyl groups. The PM3 calculation shows that the optimised diazacrown has an open structure of a pseudo D 2d symmetry with the two benzyl side-arms positioned away from the cavity.

Structure and Reactivity of 1-Isothiocyanatosilatrane: The First Silatrane with a Direct Si-NCS Bond.

Some unique features of 1-isothiocyanatosilatrane, 1, include concomitant NMR couplings of quadrupolar 14N(NCS) nucleus with adjacent heteroatoms [J(13C−14N) = 26.17 Hz; J(29Si−14N) = 28.47 Hz] and the crystallographically determined shortest N→Si bond, 2.007(3) A, as well as a nearly linear structure of the heteroatoms N(1)−Si−N(2)−C(7)−S(1). Contrary to the known reactivity of tetracoordinate isothiocyanatosilanes, 1 invariably shows retention of the Si−N(CS) bond under normal nucleophilic/electrophilic reaction conditions. These novel features also get support from semiemperical MO calculations on the compound.

The H–NCS bond energy, ΔH○f (HNCS), ΔH○f (NCS), and IP(NCS) from photoionization mass spectrometric studies of HNCS, NCS, and (NCS)2

The species HNCS and NCS have been studied by photoionization mass spectroscopy. The adiabatic ionization potential (IP) of HNCS is ≤9.92 eV; the shape of the ion yield curve near threshold implies a large change in geometry, perhaps to linear HNCS+. Various appearance potentials (AP) from HNCS are determined by a more objective procedure, from which ΔH○f(HNCS)≳29.6 kcal/mol (and very likely ≥31.0±0.7 kcal/mol) is deduced. The adiabatic IP of NCS is 10.689±0.005 eV. This quantity, together with AP(NCS+/HNCS), yields D0(H–NCS)≤97.2±0.2 kcal/mol. However, a measurement of the appearance potential of NCS+ from (NCS)2 results in a still lower value, D0(H–NCS)≤93.3±1.1 kcal/mol, and ΔHf0○(NCS) ≤ 72.7 ± 0.8 kcal/mol. Approximate values are obtained for ΔHf0○(HNCS+) and for the proton affinity of NCS.

Synthesis and co-ordination chemistry of a new tripodal phosphine alcohol

The tripodal phosphine alcohol CH3C(CH2PPh2)2(CH2OH)(dpmp) was prepared and its co-ordination chemistry towards Group 6 metal carbonyls and a manganese(I) complex studied. In [M(CO)4(dpmp-P,P′)](M = Cr, Mo or W), the tripodal ligand behaves as a bidentate ligand with the hydroxyl site unco-ordinated. Reaction of dpmp with [Mn(CO)5Br] gave a stereoisomeric mixture of products, anti,fac-[Mn(CO)3Br(dpmp-P,P′)]4a and syn,fac-[Mn(CO)3Br(dpmp-P,P′)]4b Treatment of 4a or 4b with silver hexafluorophosphate yielded a facial complex fac-[Mn(CO)3(dpmp-P,P′,O)]PF66. Complex 6 reacted with the anions X (X = Br, I, N3 or SCN) stereospecifically to give syn,fac-[Mn(CO)3X(dpmp-P,P′)],(X = Br 4b, I 5b, N38b or NCS 9b). X-Ray crystal structures of complexes 4b, 6 and 9b were determined. The crystal structure of complex 9b is the first of a manganese thiocyanate complex containing carbonyl ligands. Both the bond angles [Mn–N–C 170.4(5), N–C–S 175.0(6)°] and the distances [C–N 1.143(8), S–C 1.637(7)A] of 9b clearly demonstrated the nature of the Mn–NCS bond, which is consistent with spectral data. Comparison of the co-ordination chemistry of dpmp with CH3C(CH2PPh2)2(CH2OCH3) is discussed.

The crystal and molecular structures of the N,N’-diisopropylbutyramide (DIPIBA) and N,N-dicyclohexylacetamide (DCA) complexes [Th(NCS) 4(DIPIBA) 3] and [Th(NCS) 2Cl 2(DCA) 3

The X-ray crystal structures of [Th(NCS) 4(DIPIBA) 3] ( 1) [DIPIBA Me 2CH CON(CHMe 2) 2] and [Th(NCS) 2Cl 2(DCA) 3]( 2) [DCA MeCON(cycloC 6H 11) 2] have been determined from three-dimensional X-ray diffraction data. The different steric constraints of the ligand are not sufficient for different coordination geometries. In 1 and 2 the coordination polyhedron about the seven-coordinate thorium atom is a pentagonal bipyramid geometry which is becoming rather common for thorium(IV) compounds. In these compounds two chlorine ( 2) and two thiocyanate ( 1) anions are in axial positions with a significant shortening of the axial Th—NCS bonds with respect to the equatorial ones, while in the equatorial plane a neutral ligand lies between two anionic ligands, the remaining coordination positions being occupied by two other neutral ligands. The average bonding distances are Th O = 2.34(1)Å, Th N ax = 2.42(1) and Th N eq = 2.46(1)Åin 1, and Th O = 2.357(5), Th N eq = 2.479(6) and Th Cl ax = 2.695(3)Åin 2.

Structure of 1-isothiocyanato-2,8,9-trioxa-5-aza-1-germabicyclo[3.3.3]undecane: the first metallatrane with a direct metal–NCS bond

A germatrane with a Ge–NCS bond has been isolated and characterised by X-ray crystallography and molecular spectroscopy; [graphic omitted] exhibits the shortest known Ge–N bond distance amongst germatranes and the first 13C–14N coupling [J(13C–14N)= 21.0 Hz] in a five-co-ordinate germanium compound.

THE PREPARATION AND CHARACTERIZATION OF Cd(XCN)4M TYPE COMPOUNDS

Abstract A series of compounds of the type Cd(XCN)4M (X=S and Se; M=Mn, Fe, Co and Zn) have been prepared and characterized. These compounds crystallize in the tetragonal system: space group I4[sbnd]S4 2. The bidentate thiocynate and selenocyanate ligands coordinate to the “hard” M(II) ions through the nitrogen atom and the “soft” Cd(II) ion through the sulfur or selenium atom. The Cd[sbnd]Se bond in Cd(XCN)4 M is slightly stronger than the Cd[sbnd]S bond while the M[sbnd]NCSe bond is slightly weaker than the M[sbnd]NCS bond. The M(II) ions tetrahedrally coordinated by the nitrogen end of XCN− are in the high spin state. The [sbnd]NCS and [sbnd]NCSe ligands are located at about the same place in the spectrochemical series.

IR Spectroscopic Characterization of 2‐Thiohydantoins and 2‐Thiobarbiturates

A characterization of 2‐thiohydantoins and 2‐thiobarbiturates by IR spectra is proposed, using three characteristic group frequencies: the “thioureide band” around 1500cm−1 and the antisymmetric‐symmetric stretching modes of NCS bonds around 1400 and 1200cm−1. The general characteristic absorption areas are found by comparison with N‐phenylthioureas and thioanilides.

An infrared study of organothallium thiocyanates

Some structural aspects of the organothallium(III) thiocyanates R 2 TlCNS (R = Me, Ph).[Ph 4 As][Me 2 Tl(CNS) 2 ] and Phtl(CNS) 2 have been studied by IR spectroscopy. From the frequencies of the NCS group vibrations in the solids, and the integrated intensity of the C≡N stretching absorption in solution, it was ascertained that the diorganothallium derivatives are isothiocyanates with a certain amount of ionic character in the TlNCS bonds, whereas PhTl(CNS), is essentially a TlSCN bonded compound. Apparently both solid Me 2 TlCNS and [Ph 4 As][Me 2 Tl(CNS) 2 ] do not show IR active ν s (TlC 2 )bands. The compound Me 2 TlCNS displays a double ν as (TlC 2 band, from which the presence in the solid of non-equivalent Me 2 Tl III moieties could be inferred. Possible configuration of the dimethylthallium derivatives are discussed.

Solvent control of the bonding mode of the co-ordinated thiocyanate ion

CoIII–SCN bonds can be formed in the presence of suitable ligands but, for some ligands, isomerisation occurs in solution to give a mixture of linkage isomers: in contrast to the behaviour observed for thiocyanatopalladium(II) complexes, M–NCS bond formation is promoted in solvents having high dielectric constants.