Five-coordinate Monomer Research Articles

Pentacoordinated isothiocyanate iron(III) complexes supported by asymmetric tetradentate donor and acceptor Schiff base ligands: Spectral, Structural and Hirshfeld Surface Analyses

The present study aims to synthesis and full characterization of two new pentacoordinated isothiocyanate iron(III) mixed ligand complexes featuring dianionic (N2O2)2− tetradentate Schiff-base ligands unsymmetrically substituted by either a pair of acceptor (4-fluorophenyl and nitro) or donor (ferrocenyl and methoxy) substituents. The two neutral complexes3 and 4 were prepared in very good yields (~90 %) upon reaction of their respective chloro-iron(III) precursors 1 and 2 with sodium thiocyanate in refluxing ethanol. The two paramagnetic compounds 3 and 4 were characterized by elemental analysis, FT-IR and UV-vis spectroscopy, and mass spectrometry. The stretching frequencies of the thiocyanate group observed at 2014 and 2062 cm−1, respectively, indicate a N-bonded NCS− moiety, in agreement with the HSAB principle. The crystal structure of 3 revealed that in the five-coordinate monomer, the iron atom adopts a slightly distorted square-pyramidal geometry, with the N and O atoms of the Schiff-base ligand occupying the basal sites and the nitrogen atom of the isothiocyanate co-ligand located at the apex of the pyramid. Intermolecular interactions in complex 3 have been addressed with the aid of Hirshfeld surface analysis as well as fingerprint plots. Magnetic susceptibility measurements (2-300 K) showed a high-spin configuration (S = 5/2) for thed5 Fe(III) ion in 3.

Pentacoordinated Chloro-Iron(III) Complexes with Unsymmetrically Substituted N2O2 Quadridentate Schiff-Base Ligands: Syntheses, Structures, Magnetic and Redox Properties

Since their development in the 1930s, Schiff-base complexes have played an important role in the field of coordination chemistry. Here, we report the synthetic, spectral, structural, magnetic and electrochemical studies of two new pentacoordinated neutral chloro-iron(III) complexes (3,5) supported by dianionic [N2O2]2− tetradentate Schiff-base ligands unsymmetrically substituted by either a pair of acceptor (F and NO2) or donor (ferrocenyl and OCH3) groups. The electron-withdrawing Schiff-base proligand 2 and the complexes 3 and 5 were prepared in good yields (79–86%). Complex 3 was readily obtained upon reaction of 2 with anhydrous iron chloride under basic conditions, while the bimetallic derivative 5 was synthesized by condensation of the free amino group of the ferrocenyl-containing O,N,N-tridentate half-unit 4 with 5-methoxysalicylaldehyde in the presence of FeCl3. The three new compounds were characterized by elemental analysis, FT-IR, UV–Vis, mass spectrometry and in the case of 2 by multinuclear NMR spectroscopy. The crystal structures of 3 and 5 revealed that in the two five-coordinate monomers, the iron atom showed distorted square-pyramidal geometry, with the N and O atoms of the Schiff-base ligand occupying the basal sites and the chlorine atom at the apex of the pyramid. Magnetic measurements showed a high-spin configuration (S = 5/2) for the Fe(III) ion in 3 and 5. Reduction associated with the Fe(III)/Fe(II) redox couple occurred at −0.464 and −0.764 V vs. Ag/Ag+, and oxidation taking place at the Schiff-base ligand was observed at 1.300 and 0.942 V vs. Ag/Ag+ for 3 and 5, respectively. A high-electronic delocalization of the Schiff-base ligand substituted by fluoro and nitro groups stabilizes the Fe(II) oxidation state and shifts the redox potential anodically.

Zinc triad metal ion complexes ofNN′S ligandN-(2-pyridylmethyl)-N-(2-(methylthio)ethyl)amine

The coordination chemistry of divalent zinc triad metal ions with N-(2-pyridylmethyl)-N-(2-(methylthio)ethyl)amine (L) was investigated by X-ray crystallography and proton NMR. Chloride salts yielded non-homologous M(L)Cl2 complexes. Hg(L)Cl2 and Zn(L)Cl2 were five-coordinate monomers with distorted square pyramidal and trigonal bipyramidal geometries, respectively. Cd(L)Cl2 formed a six-coordinate polymer with a distorted octahedral geometry. These complexes had similar nearly temperature independent proton NMR spectra suggesting structural differences between them were less extensive in solution due to fluxional processes. Although 1:1 metal to ligand complexes were most thermodynamically stable for the chloride salts at all [M2+]/[L], the thermodynamic stability of [M(L)(NCCH3) x ]2+ only exceeded that of [M(L)2]2+ when [M2+] ≥ [L] with perchlorate salts. Slow intramolecular and intermolecular exchange conditions for [M(L)2]2+ and slow intermolecular exchange conditions for [M(L)(NCCH3) x ]2+ were foun...

Why Is Re−Re Bond Formation/Cleavage in [Re(bpy)(CO)3]2 Different from That in [Re(CO)5]2? Experimental and Theoretical Studies on the Dimers and Fragments

The Re(NN)(CO)3(THF) (NN=bpy=2,2'-bipyridine or dmb=4,4'-dimethyl-2,2'-bipyridine) radical, produced by homolysis of [Re(NN)(CO)3]2 in THF solution by visible irradiation, dimerizes with rate constants kd=20 +/- 3 and 11 +/- 4 M(-1) s(-1) for NN=dmb and bpy, respectively. The dimerization processes are strikingly slow compared to those of typical metal radicals including Re(CO)5 (kd approximately 10(9) M(-1) s(-1)). In order to explain such slow reactions, we have performed B3LYP hybrid DFT and fully ab initio RHF and MP2 calculations on several conformations of [Re(bpy)(CO)3]2 (cis, trans, skewed cis, skewed trans) and [Re(CO)5]2 (staggered) and on their constituent monomer radicals and anions. The calculations show that the most stable geometry of [Re(bpy)(CO)3]2 is skewed cis, and the experimental infrared spectrum and photochemical properties of the [Re(bpy)(CO)3]2 dimer are best described by the calculated properties of the skewed cis conformer in which there is no low-lying unoccupied orbital that is predominantly sigma(MM) in character. The Re(bpy)(CO)3(THF) ligand radical is more stable than the 5-coordinate "17-electron" metal radical, Re(bpy)(CO)3, suggesting that the extremely slow dimerization rate most likely arises from the solvent blocking the binding site (i.e., the estimated fraction of the five-coordinate monomer is 1.6 x 10(-2)). Theoretical results are consistent with our experimental results that the dimerization process proceeds via the Re centered radical, which is involved in a pre-equilibrium favoring the ligand-centered radical. Furthermore, time-dependent DFT calculations on [Re(bpy)(CO)3]2 and [Re(bpy)(CO)3]- identify the origin of UV-vis absorption in THF.

A complex containing both five- and six-coordinate

The title compound, aquachloro4,4'-dibromo-2, 2'-[o-phenylenebis(nitrilomethylidyne)]diphenolato-O,N,N', O'iron(III)-chloro4,4'-dibromo-2, 2'-[o-phenylenebis(nitrilomethyli-dyne)]diphenolato-O,N,N', O'iron(III)-dimethylformamide (1/1/1), [FeCl(C(20)H(12)Br(2)N(2)O(2))][FeCl(C(20)H(12)Br(2)N(2)O(2))(H(2)O)] .C(3)H(7)NO, contains one independent five-coordinate [FeCl(C(20)H(12)Br(2)N(2)O(2))] monomer, one six-coordinate [FeCl(C(20)H(12)Br(2)N(2)O(2))(H(2)O)] monomer and a non-coordinating dimethylformamide solvent molecule in the asymmetric unit. In the five-coordinate monomer, the Fe atom shows distorted square-pyramidal geometry, with the N and O atoms of the ligand at the base and the Cl atom at the apex of the pyramid. In the six-coordinate monomer, the Fe atom is in a distorted octahedral geometry and coordinated by the donor atoms of the tetrafunctional ligand in the horizontal plane, and the coordination sphere is completed by the O atom of the water molecule and the Cl atom at the axial positions. The title compound contains intermolecular O-H.O hydrogen bonds. Apart from these hydrogen bonds, there are also intermolecular C-H.Cl and C-H.O contacts.

Structural chemistry of organotin ferrocenecarboxylic esters I. Synthesis and spectroscopic studies on dialkyltin esters of ferrocenecarboxylic acid FcCOOH and 1,1′-ferrocenedicarboxylic acid Fc(COOH) 2

Dibutyltin and dioctyltin esters of ferrocenecarboxylic acid and dibutyltin ester of 1,1′-ferrocenedicarboxylic acid have been synthesized and characterized by IR and NMR ( 1H, 13C, 119Sn) spectral data. Spectroscopic data suggest that the esters of ferrocenecarboxylic acid adopt an oxygen-bridge dimer structure mode. The structure features four anisobidentate bridging carboxylate ligands. The ester of 1,1′-ferrocenedicarboxylic acid is five-coordinate monomer in solution.

Structure of [N,N'-o-phenylenebis(salicylideneaminato)]iron(III) chloride as a five-coordinate monomer

The crystal contains three independent five-coordinate monomers of chloro{2,2'-[o-phenylenebis(nitrilomethylidyne)]diphenolato-N,N', O,O'}iron(III). The distances Fe(1)-Fe(1A), Fe(1)-Fe(1B) and Fe(1A)-Fe(1B) are 7.175 (1), 7.683 (1) and 7.207 (1) A, respectively. The planes of the ligand groups of the two neighbouring molecules bend away from each other

THE STEREOCHEMISTRY AND MASS SPECTRA OF OXOVANADIUM(IV) COMPLEXES OFN,N′-BIS(3-ETHOXYSALICYLIDENE) TRIMETHYLENEDIIMINE ANDN,N′-BIS(7-METHYLSALICYIDENE)TRIMETHYLENEDIIMINE

Abstract Oxovanadium(IV) complexes, VO[A[sbnd]C6H4ORC=N-(CH2)3-N=CROH4C6-A], (where A = 3-OC2H5, R=H and A=H, R=7-CH3) have been prepared and characterised. The studies showed that the complexes are polymeric in the solid state and exhibit distorted octahedral geometry, but break down to five-coordinate monomers in chloroform and in the gas phase.

Preparation, crystal and molecular structure of trichlorosulphido(triphenylphosphine sulphide)niobium(V)

The reaction between NbSCl 3 and triphenylphosphine sulphide leads to the formation of the 1:1 adduct, crystals which are triclinic, space group P 1 , with a = 12.524(5), b = 10.193(4), c = 17.823(6) Å, α = 103.80(3), β = 102.60(4), γ = 72.02(4)°, Z = 4. The structure was solved by Patterson and Fourier methods using diffractometer data and refined to R 0.058 for 2880 significant reflections. The unit cell contains two five-coordinate monomers and one centrosymmetric six co-ordinate dimer, the coexistence of which is a most unusual feature in the solid state. The niobium atom is displaced from the plane formed by the three chlorine atoms and the ligand sulphur atom towards the sulphido sulphur atom [0.553(2) Å, monomer, 0.397(2) Å, dimer]. This displacement is larger than any yet found in adducts of NbOCl 3.

ChemInform Abstract: EVIDENCE FOR FIVE‐COORDINATION IN TITANIUM(IV) COMPLEXES. A NUCLEAR MAGNETIC RESONANCE INVESTIGATION

Diketonato complexes of titanium(IV), (X3Ti(dik))2 (X = Cl, Br; dik = anions of dipivaloylmethane and benzoylacetone), of apparent five-coordinate stoichiometry have been prepared and investigated in nitrobenzene solutions using the variable temperature nuclear magnetic resonance technique. The nmr spectra reveal the existence of two equilibrium species; a five-coordinate X3Ti(dik) and a six-coordinate X2Ti(dik)2 complex. The data are interpreted in terms of a symmetric dissociation of the six-coordinate titanium(IV) dimer, (X3Ti(dik))2, into two five-coordinate monomers which then undergo a disproportionation reaction to the four-coordinate titanium tetrahalide and the six-coordinate X2Ti(dik)2 species.

Evidence for five-coordination in titanium(IV) complexes. A nuclear magnetic resonance investigation

Diketonato complexes of titanium(IV), (X3Ti(dik))2 (X = Cl, Br; dik = anions of dipivaloylmethane and benzoylacetone), of apparent five-coordinate stoichiometry have been prepared and investigated in nitrobenzene solutions using the variable temperature nuclear magnetic resonance technique. The nmr spectra reveal the existence of two equilibrium species; a five-coordinate X3Ti(dik) and a six-coordinate X2Ti(dik)2 complex. The data are interpreted in terms of a symmetric dissociation of the six-coordinate titanium(IV) dimer, (X3Ti(dik))2, into two five-coordinate monomers which then undergo a disproportionation reaction to the four-coordinate titanium tetrahalide and the six-coordinate X2Ti(dik)2 species.

Coordination Compounds of Indium. Part XXVII. Addition Compounds of Acetato(dimethyl)indium(III)

The compound Me2In(OAc), which is polymeric in the crystalline state, reacts with neutral donor ligands in organic solvents to yield three series of adducts. With monodentate donors, the product is Me2In(OAc)L (L = dimethylsulfoxide or pyridine), which is formulated as a five-coordinate monomer in solution. With bidentate donors, the product is either the monomeric six-coordinate Me2In(OAc)LII (LII = ethylenediamine or 1,2-bis(diphenylphosphino)ethane), or the complex [Me2In(OAc)]2LII (LII = 2,2′-bipyridyl or 1,10-phenanthroline). The n.m.r. and vibrational spectra of these compounds are discussed.