Octahedral Chromium Research Articles

Strong circularly polarized luminescence of an octahedral chromium(iii) complex.

The chiral spin-flip luminophore [Cr(ddpd)2]3+ can be resolved into enantiopure material by chiral HPLC. The corresponding enantiomers show very high luminescence dissymmetry factors of up to ∣glum ∣≈ 0.093 in circularly polarized luminescence (CPL) measurements for the "ruby-like" phosphorescence transition 2E/2T1 → 4A2 in the near-IR region around λ ≈ 775 nm.

Semiconducting, magnetic, luminescence properties and theoretical calculations of the tetra-azamacrocyclic compound: trans-Cr(cyclam)Cl2]TCNQ

We report the new macrocyclic compound: trans-[Cr(RSSR-cyclam)Cl2]TCNQ·H2O (1), (where cyclam: 1,4,8,11-tetraazacyclotetradecane and TCNQ: 7,7,8,8-tetracyanoquinodimethane). Its 3D structure showed π-π interactions between the TCNQ− moieties with alternating distances (3.24 and 3.87 Å). 1 exhibited an electric conductivity, σ = 1.94 × 10−5 Scm−1 at 300 K and a band-gap of 0.53 eV in the range of a semiconductor. Its magnetic behavior is of a typical Curie–Weiss paramagnet with an antiferromagnetic coupling (θ = −15 K). The measured magnetic moment, μexp = 3.84 B. M. at room temperature is lower than the expected, μcalc = 4.86 B. M. (only spin) for a d3 octahedral chromium (III) and an anionic radical TCNQ−; this is explained by the presence of diamagnetic dimers of TCNQ− in the crystal packing. 1 shows photoluminescence at low temperature from 80-17 K. Finally, by using DFT calculations, it was possible to assign van der Waals (CH–π, Cl–π) interactions and N–H hydrogen bonding, which are likely determining the observed antiferromagnetism. The calculations also allowed us to verify the presence of diamagnetic dimers in the crystal packing, formed by strong π–π interactions of TCNQ-entities.

Ligand-induced symmetry breaking and concomitant blueshift in the emission wavelength of an octahedral chromium complex.

The resulting distortion of the octahedral symmetry of the complex [CrIII(NH3)6]3+ upon replacing the axial ligands with halides (i.e., weaker ligands) affects the stability of the doublet state with respect to that of the quartet ground state. This substitution affects the doublet-to-quartet transition responsible for phosphorescence. The position of the halide with respect to ammonia in the spectrochemical series is a major influence on the emission wavelength of the complex. The close proximity of fluorine and ammonia in the spectrochemical series leads to a blueshift in the emission wavelength when fluoride ions are introduced into the complex, thus providing a rational approach to the design of blue-phosphorescent materials, which are desirable for OLEDs used in full-color displays. Graphical abstract Shifts in the phosphorescence emission wavelength of an octahedral Cr(III) complex caused by axial ligand substitution. Replacing the axial ligands leads to a change in the relative positions of the axial and equatorial ligands in the spectrochemical series, which in turn induces a redshift or a blueshift in the emission wavelength.

Coordination behavior of dimethyl pyridine-2,6-dicarboxylate towards mercury(II), cadmium(II) and chromium(III) in the solid- and gaseous state supported by CSD studies

In this work, three complexes, [Hg(MPC)Cl2] (1), [Cd(MPC)3][CdBr4] (2) and the coordination polymer, {K[Cr(PDC)2]}n (3) of dimethyl pyridine-2,6-dicarboxylate (MPC) and hydrolyzed MPC, pyridine-2,6-dicarboxylic acid (H2PDC), were prepared and identified by elemental analysis, FT-IR, Raman, 1H NMR spectroscopy and single-crystal X-ray diffraction. All coordination modes of dimethyl pyridine-2,6-dicarboxylate derivatives were studied by CSD to predict the behavior of MPC in reactions with metals. Subsequently, these coordination modes were optimized by DFT methods to determine of the most stable mode and charge distribution. In the crystal structure of 1, the mercury atom has a HgNO2Cl2 environment and inclines to a trigonal bipyramidal geometry. The molecule of 2 has two cadmium atoms with different geometries. One Cd atom has coordination number four and ideal tetrahedral geometry which is determined by using a new formula proposed in this paper. The crystal structure of 3 revealed a rare 2D s–d mixed-metal coordination polymer containing dodecahedrally coordinated potassium(I) and octahedral chromium(III). Common coordination number for mercury(II), cadmium(II) and chromium(III) is determined by studying of all complexes of them in CSD.

Dielectric dispersion and ac conduction phenomena of Li2O−Sb2O3−PbO−GeO2:Cr2O3 glass system

Lithium antimony lead germanate glasses doped with different concentrations of Cr2O3 (ranging from 0 to 0.5mol %) were synthesized. The optical absorption and ESR spectral studies have indicated that there is a gradual increase in presence of octahedral chromium ions with increase of Cr2O3 concentration in the glass network. These studies have also revealed that a fraction of chromium ions get oxidized into Cr5+ and Cr6+ states. IR and Raman spectroscopic studies have pointed out that there is an increasing degree of depolymerization of the titled glass network with increase of Cr2O3 content. The dielectric parameters (viz., dielectric constant, loss and electrical modulus coefficients measured over a wide range of frequency and temperature) and also ac conductivity were found to increase with increase of Cr2O3 content. The reasons for such increase were discussed quantitatively in terms of various polarization mechanisms coupled with structural variations of the glass network.

Derivation of a new set of force field parameters for ammine complexes of chromium(III) containing halogeno ligands: Modeling the trans-influence of halogenido ligands

An approach to model the trans-influence using partial atomic charges derived from the molecular electrostatic potential by means of the restrained electrostatic potential (RESP) fitting method is exemplified on a series of halogenido-ammine octahedral chromium(III) complexes. RESP charges incorporated in our vibrationally optimized consistent force field account for second-order phenomena, improve the modeling and assignment of skeletal vibrations, and reproduce the trends in frequency shifts along the (F, Cl, Br, I) series. In addition, a supplementary statistical analysis is given for Cr-halogen bonds in crystal structures from CSD.

An electron transfer series of octahedral chromium complexes containing a redox non-innocent α-diimine ligand.

An electron-transfer series of octahedral α-diimine complexes [((H)L(Cy))3Cr](n+)(BARF)n (n = 2, 1, 0) has been synthesized and crystallographically characterized. Cyclic voltammetry indicated additional formation of [((H)L(Cy))3Cr](3+). The molecular structures suggested that all redox processes were ligand-based. Magnetic moments were consistent with spin ground states of S = 0 for [(H)L(Cy)3Cr](0), S = 1/2 for [(H)L(Cy)3Cr](+1), and S = 1 for [(H)L(Cy)3Cr](+2). The experimental data is consistent with chromium maintaining the +III oxidation state throughout, while being coordinated by varying numbers of neutral diimines ((H)L(Cy)) and diimine radical anions ((H)L(Cy)˙(-)).

A paramagnetic octahedral trans-dihydroxy chromium(IV) complex with dianionic tetradentate Schiff base salophen and crystal structure of its trans-diisothiocyanato analog

A paramagnetic octahedral trans-dihydroxychromium(IV) complex, [Cr(OH)2(salophen)] (1) (H2salophen = N,N′-bis(salicylidene)-1,2-phenylenediamine), has been synthesized and characterized by elemental analysis, magnetic moment measurement, IR, UV-Vis, and EPR spectroscopic studies. Measured room temperature (RT) magnetic moment value is 2.79 BM for 1, indicating a d2 (S = 1) system with a triplet ground state. Compound 1 exhibits powder EPR spectra at RT and LNT, which show the allowed transition ΔM s = ±1 (g = 2.0038) as well as the “forbidden” half-field transition (ΔM s = ±2) at g = 4.2080. Two successive reduction waves are observed in the cyclic voltammogram of 1 in CH3CN at −0.84 and −1.63 V (vs. Ag/AgCl), respectively. Compound 1 readily reacts with Mn2+ ion, a Cr(IV)–specific reductant and also undergoes –OH substitution reactions in solution with NCS− and imidazole. The trans-diisothiocyanato analog, [Cr(NCS)2(salophen)] (2), with μ eff = 2.80 BM has been structurally characterized by X-ray crystallography and found to contain two N-bonded axial thiocyanato ligands with slightly different axial Cr–N bond lengths (N(3)–Cr(1), 2.032(2); N(4)–Cr(1), 2.015(2) Å). Compound 2 and the corresponding Cr(III) compound K[Cr(NCS)2(salophen)] · H2O (3) show significant difference in their electronic structures as revealed from their electronic spectra.

Synthesis, characterisation and magnetic properties of octahedral chromium(iii) compounds with six C-donor ligands

The homoleptic, square pyramidal organochromium(III) compound [NBu(4)](2)[Cr(C(6)F(5))(5)] (1) reacts with excess organic isocyanides, CNR [R = (t)Bu, 2,6-dimethylphenyl (Xy)], under dissociation of the apical C(6)F(5) ligand to give the more saturated, singly charged complexes [NBu(4)][trans-Cr(C(6)F(5))(4)(CNR)(2)] [R = (t)Bu (2), Xy (3)], containing six monodentate C-donor ligands. These compounds exhibit an axially distorted octahedral structure (single-crystal X-ray diffraction) with the four C(6)F(5) groups defining the equatorial positions and the CNR ligands occupying the axial ones. Compounds 2 and 3 both behave as spin quartet species (S = 3/2) at microscopic level (EPR spectroscopy), their macroscopic magnetic properties depending upon the nature of the terminal R group, as established by magnetisation measurements. When the R substituent is the saturated alkyl group (t)Bu, the compound (2) behaves as a simple paramagnet, with no magnetic interaction between individual Cr(III) centres along the whole temperature range measured (1.8-265 K). By contrast, a weak antiferromagnetic interaction is detected for compound 3 at low temperature with T(N) = 0.19(1) K. Since the closest intermetallic distances are similar in the crystals of 2·CH(2)Cl(2) and 3·1.75CH(2)Cl(2) (ca. 1.1 nm), we conclude that the insaturation of the aromatic Xy group together with the extended intermolecular π-π stacking interactions between Xy rings observed in the crystal lattice of 3·1.75CH(2)Cl(2) (centroid-to-centroid distance: 0.35 nm) favour magnetic interaction between the individual magnetic centres.

Computational Descriptors for Chelating P,P- and P,N-Donor Ligands1

The ligand knowledge base approach has been extended to capture the properties of 108 bidentate P,P- and P,N-donor ligands. This contribution describes the design of the ligand set and a range of DFT-calculated descriptors, capturing ligand properties in a variety of chemical environments. New challenges arising from ligand conformational flexibility and donor asymmetry are discussed, and descriptors are related to other parameters, such as the ligand bite angle. A novel map of bidentate ligand space, potentially useful in catalyst design and discovery, has been derived from principal component analysis of the resulting LKB-PP descriptors. In addition, a range of multiple linear regression models have been derived for both experimental and calculated data, considering ligand bite angles in square-planar palladium complexes and ligand dissociation energies from octahedral chromium complexes, respectively. These data sets were fitted with models based on LKB descriptors to explore the transferability of des...

Crystal field and covalency of octahedral chromium in natural [8](Mg1−x Ca x ) 3 [6] (Al0.67Cr0.33)2Si3O12 garnets from upper mantle rocks

In the course of a thorough study of the influences of the second coordination sphere on the crystal field parameters of the 3d N -ions and the character of 3d N –O bonds in oxygen based minerals, 19 natural Cr3+-bearing (Mg,Ca)-garnets from upper mantle rocks were analysed and studied by electronic absorption spectroscopy, EAS. The garnets had compositions with populations of the [8] X-sites by 0.881 ± 0.053 (Ca + Mg) and changing Ca-fractions in the range 0.020 ≤ w Ca[8] ≤ 0.745, while the [6] Y-site fraction was constant with x Cr 3+ [6] = 0.335 ± 0.023. The garnets had colours from deeply violet-red for low Ca-contents (up to x Ca = 0.28), grey with 0.28 ≤ x Ca ≤ 0.4 and green with 0.4 ≤ x Ca. The crystal field parameter of octahedral Cr3+ 10Dq decreases strongly on increasing Ca-fraction from 17,850 cm−1 at x Ca[8] = 0.020 to 16,580 cm−1 at x Ca[8] = 0.745. The data could be fit with two model which do statistically not differ: (1) two linear functions with a discontinuity close to x Ca[8] ≈ 0.3, $$ \begin{aligned}{} {\text{range }}0.0 & \le x_{{{\text{Ca}}[8]}} \le 0.3\quad 10{\text{Dq}} = ( - 2638.3x_{{{\text{Ca}}[8]}} ) + 17846.1\quad (r = 0.993) \\ {\text{range }}0.3 & \le x_{{{\text{Ca}}[8]}} \le 0.75\quad 10{\text{Dq}} = ( - 1417.8x_{{{\text{Ca}}[8]}} ) + 17616.5\quad (r = 0.997) \\ \end{aligned} ,$$ (2) one continuous second order function, $$ {\text{range }}0.0 \le x_{{{\text{Ca}}[8]}} \le 0.75\quad 10{\text{Dq}} = 1242.1x^{{\text{2}}}_{{{\text{Ca}}[8]}} - 2576.5x_{{{\text{Ca}}[8]}} + 17,836\quad (r = 0.996) $$ The behaviour of the crystal field parameter 10Dq and band widths on changing Ca-contents favour the first model, which is interpreted tentatively by different influences of Ca in the structure above and below x Ca[8] ≈ 0.3. The covalency of the Cr–O bond as reflected in the behaviour of the nephelauxetic ratio $$ \beta {\text{ = (}}B_{{{\text{crystal}}}} {\text{/}}B_{{{\text{free ion}}}} {\text{)}}_{{{\text{Cr}}^{{{\text{3+}}}} }} , $$ decreases on increasing Ca-contents.

ChemInform Abstract: Magnetic and Electronic Properties of CaCu3Cr4O12 and CaCu3Cr2Sb2O12 by First‐Principles Density Functional Calculation.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Magnetic and Electronic Properties of CaCu3Cr4O12 and CaCu3Cr2Sb2O12 by First-Principles Density Functional Calculation

The electronic and magnetic properties of CaCu3Cr4O12 and CaCu3Cr2Sb2O12 are investigated by the use of the full-potential linearized augumented plane wave (FPLAPW) method. The calculated results indicate that CaCu3Cr4O12 is a ferrimagnetic and half-metallic compound, in good agreement with previous theoretical studies. CaCu3Cr2Sb2O12 is a ferrimagnetic semiconductor with a small gap of 0.136 eV. In both compounds, because Cr4+ 3d (d2) and Cr3+ 3d (d3) orbitals are less than half filled, the coupling between Cr-Cu is antiferromagnetic, whereas that between Cu-Cu and Cr-Cr is ferromagnetic. The total net spin moment is 5.0 and 3.0 microB for CaCu3Cr4O12 and CaCu3Cr2Sb2O12, respectively. In CaCu3Cr4O12, the 3d electrons of Cr4+ are delocalized, which strengthens the Cr-Cr ferromagnetic coupling. For CaCu3Cr2Sb2O12, the doping of nonmagnetic ion Sb5+ reduces the Cr-Cr ferromagnetic coupling, and the half-filled Cr3+ t2g (t2g3) makes the chromium 3d electrons localized. In addition, the ordering arrangement of the octahedral chromium and antimony ions also prevents the delocalization of electrons. Hence, CaCu3Cr2Sb2O12 shows insulating behavior, in agreement with the experimental observation.

Synthesis and characterization of two stable paramagnetic octahedral chromium(IV) complexes with dianionic tridentate SNO donor ligands and of a chromium(III) complex with a ONO donor ligand

Two novel paramagnetic octahedral chromium(IV) complexes with dianionic tridentate SNO donor ligands containing extended π-system have been synthesized while only a paramagnetic octahedral chromium(III) complex is obtained when a related dianionic tridentate ONO donor ligand is used under similar conditions. These bischelate complexes [Cr(abtsal) 2] ( 1) (abtsalH 2 is the Schiff base of o-aminobenzenethiol and salicylaldehyde), [Cr(4-PhTSCsal) 2] · H 2O ( 2) (4-PhTSCsalH 2 is the Schiff base of 4-phenylthiosemicarbazide and salicylaldehyde) and K[Cr(sap) 2] · H 2O ( 3) (sapH 2 is the tridentate Schiff base of salicylaldehyde and o-aminophenol) are characterized by elemental analyses, magnetic moment measurements, IR, UV–Vis and EPR spectroscopic studies. Compound 3 has been structurally characterized by X-ray crystallography. Measured room temperature (RT) magnetic moment values are 2.98 BM for 1 and 2.83 BM for 2 indicating a d 2 system with a triplet ground state in both the cases. On the other hand, the magnetic moment value for 3 is found to be 3.74 BM at RT and is consistent with the presence of three unpaired electrons for a d 3 Cr(III) ion. The magnetic moment values rule out the large spin–orbit coupling which is substantiated by the presence of RT EPR signals. Compounds 1 and 2 exhibit very similar powder EPR spectra at RT and LNT, which show the allowed transition Δ M s = ±1 ( g = 2.004 for both 1 and 2) as well as the “forbidden” half-field transition (Δ M s = ±2) at g = 4.105 for 1 and g = 4.318 for 2, respectively. The X-band LNT frozen glass EPR spectrum of 1 in DMF shows the presence of zero-field split rhombic symmetry character, and results in the parameters g ≅ 2.0, D = 740 G, and E = 260 G. It suggests that the intensity of Δ M s = ±2 forbidden transition is large due to the large D value. The X-band frozen glass EPR spectrum of compound 3 in DMF is found to be very similar to that reported for trans-[Cr(py) 4F 2] + in DMF–H 2O–MeOH glass. The large difference (∼700 mV) in the reduction potential for the two octahedral complexes 1 (−1.40 V) and 3 (−0.70 V) is attributed to the difference in their metal ion oxidation states.

The crystal structure of a bis(2,6-pyridinedicarboxylato)chromate(III) anion with an elaborate network of hydrogen bonding and π stacking

The synthesis, X-ray crystallography, spectroscopic, and electrochemical properties of the title compound, [Hdpa][Cr(dipic)2]·3H2O, 1, are reported. Compound 1 crystallized in the triclinic space group P-1 with a = 7.1057(11) A, b = 12.965(2) A, c = 14.269(2) A, α = 80.306(3)°, β = 82.101(2)°, γ = 83.799(2)°, and V = 1278.6(4) A3 with Z = 2. The distorted octahedral chromium anions are part of an elaborate network of hydrogen bonding formed by the waters of solvation, the anion, and cation as well as π-stacking interactions.

Asymmetric Autocatalysis Induced by Octahedral Tris(acetylacetonato)chromium(III) Complex as a Homogeneous Chiral Initiator

Abstract Enantioselective addition of diisopropylzinc to 2-t-butylethynylpyrimidine-5-carbaldehyde in the presence of chiral Δ- and Λ-tris(acetylacetonato)chromium(III) complex [Cr(acac)3] affords highly enantiomerically enriched (S)- and (R)-5-pyrimidyl alkanols, respectively, in conjunction with asymmetric autocatalysis. The absolute configuration of the corresponding 2-t-butylethynyl-5-pyrimidyl alkanol is dependent upon the chirality of the octahedral chromium(III) complex.

Spectroscopy, crystal structure, valance molecular orbital energy level diagram and DFT study of cis-[Cr(2,2′-bipy)2Cl2](Cl)0.38(PF6)0.62

A new octahedral chromium(III) complex having 2,2′-bipyridine as ligand system was synthesized in methanol. Single crystal X-ray diffraction analysis shows that it possesses non-stoichiometry in its anionic primary covalency. It has also been studied by elemental analyses, optical spectroscopy (UV–vis, IR) and magnetic susceptibility data. DFT calculations (with B3LYP functional and double-ξ quality LANLDZ(D95V) basis set) were carried out to interpret the electronic and infrared spectra of the complex. The DFT optimized geometric structure for the complex is compared with the X-ray crystallographic data; the theory–experiment agreement is satisfactory.

Chromium(III) Octaethylporphyrinato Tetracarbonylcobaltate: A Highly Active, Selective, and Versatile Catalyst for Epoxide Carbonylation.

The development of a highly active and selective porphyrin-based epoxide carbonylation catalyst, [(OEP)Cr(THF)2][Co(CO)4] (1; OEP = octaethylporphyrinato; THF = tetrahydrofuran), is detailed. Complex 1 is a separated ion pair composed of a tetracarbonylcobaltate anion and an octahedral chromium porphyrin complex axially ligated by two THF ligands. Regarding the carbonylation of epoxides to β-lactones, catalyst 1 exhibits excellent turnover numbers (up to 10 000) and turnover frequencies (up to 1670 h-1), with regioselective carbonyl insertion occurring between the oxygen and the sterically less hindered carbon of the epoxide substrate. Complex 1 is highly tolerant of nonprotic functional groups, carbonylating an array of aliphatic and cycloaliphatic epoxides, as well as epoxides with pendant ethers, esters, and amides. With careful control of reaction conditions in the carbonylation of glycidyl esters, the exclusive production of either the β- or γ-lactone isomer was achieved. Through analysis of reaction...

Chromium(III) Octaethylporphyrinato Tetracarbonylcobaltate: A Highly Active, Selective, and Versatile Catalyst for Epoxide Carbonylation

The development of a highly active and selective porphyrin-based epoxide carbonylation catalyst, [(OEP)Cr(THF)2][Co(CO)4] (1; OEP = octaethylporphyrinato; THF = tetrahydrofuran), is detailed. Complex 1 is a separated ion pair composed of a tetracarbonylcobaltate anion and an octahedral chromium porphyrin complex axially ligated by two THF ligands. Regarding the carbonylation of epoxides to beta-lactones, catalyst 1 exhibits excellent turnover numbers (up to 10,000) and turnover frequencies (up to 1670 h(-1)), with regioselective carbonyl insertion occurring between the oxygen and the sterically less hindered carbon of the epoxide substrate. Complex 1 is highly tolerant of nonprotic functional groups, carbonylating an array of aliphatic and cycloaliphatic epoxides, as well as epoxides with pendant ethers, esters, and amides. With careful control of reaction conditions in the carbonylation of glycidyl esters, the exclusive production of either the beta- or gamma-lactone isomer was achieved. Through analysis of reaction stereochemistry, a mechanism for the formation of gamma-lactone products was proposed. Overall, a broad array of synthetically useful lactones has been synthesized in a rapid and selective fashion by catalytic carbonylation using [(OEP)Cr(THF)2][Co(CO)4].

The geometrical isomers of oxalato and malonato-(ethylenediamine-N,N’-di-S,S-2-propionato)-chromate(III) complexes

Three octahedral chromium(III) complexes of the general formula Na[Cr(S,S-eddp)L].2H2O, where eddp = the tetradentate O-N-N-O-type ligand ethylenediamine-N,N?-di-S,S-2-propionate and L = a bidentate O-O-type ligand, either oxalate or malonate, were prepared. The complexes were synthesized by the reaction of chromium(III) chloride, S,S-eddp and malonic acid or sodium oxalate, at 60?C. The complexes were isolated chromatographically and the geometric configuration of the complexes was proposed on the basis of their infrared and electronic absorption spectra.