Trinuclear Chromium Research Articles

Trinuclear salphen–chromium(III)chloride complexes as catalysts for the alternating copolymerization of epoxides and cyclic anhydrides

AbstractAlthough the alternating copolymerization of epoxides and cyclic anhydrides is a promising route to aliphatic polyesters, improved catalysts are required to realize commercialization of this process. Herein, trinuclear chromium complexes of salicylaldimine, in conjunction with a nucleophilic cocatalyst, are demonstrated as excellent catalysts for epoxide/cyclic anhydride copolymerization, selectively affording perfectly alternating polyesters. The effect of the distance between the chromium species is investigated by varying the bridging skeleton in a series of trinuclear salphen–Cr(III)Cl complexes for obtaining different Cr–Cr distances. Trinuclear salphenCr(III)–complexes with Cr–Cr distances of approximately 7.3 Å are found to be efficient copolymerization catalysts, even at high temperatures and extremely low catalyst loadings. In particular, a high activity of 10,620 h−1 is obtained for the copolymerization of cyclohexene oxide (CHO) and phthalic anhydride (PA) under a low catalyst loading (<0.01 mol%) at 100 °C. In situ infrared spectroscopy studies suggest that the activation energy of the trinuclear Cr(III)–salphen catalyst for CHO/PA copolymerization is 15 kJ mol−1 lower than that of the corresponding mononuclear catalyst owing to an intramolecular synergistic effect among the metal atoms.

A trinuclear chromium(iii) chlorocarbyne.

Reduction of CCl4 by CrCl2 in THF afforded a trinuclear chromium(iii) carbyne [CrCl(thf)2]3(μ3-CCl)(μ-Cl)3. The chlorocarbyne complex reacted with aldehydes to afford chloroallylic alcohols and terminal alkynes. The mechanistic study proposed two competitive pathways via an α-chlorovinyl intermediate.

Di- and Tri-nuclear VIII and CrIII Complexes of Dipyridyltriazoles: Ligand Rearrangements, Mixed Valency and Ferromagnetic Coupling.

The first dinuclear and trinuclear chromium(III) and dinuclear vanadium(III) complexes of N4-R-substituted-3,5-di(2-pyridyl)-1,2,4-triazole (Rdpt) ligands have been prepared by solvothermal complexations under inert atmospheres, and characterized. The reactions of CrIII and VIII with adpt (R = amino) resulted in deamination of the ligand and yielded the dinuclear doubly-triazolate bridged complexes [(dpt−)2Cl4] (1) and [(dpt−)2Cl4] (2). In the case of the CrIII complex 2 this bridging results in a rare example of ferromagnetic coupling for a dinuclear CrIII compound. DFT studies confirm that in 2 the ferromagnetic coupling pathways dominate over the antiferromagnetic pathways, whereas in 1 the reverse occurs, consistent with the observed overall antiferromagnetic coupling in that case. It was also found that the use of different additives in the reaction allows the nuclearity of the CrIII product to be manipulated, giving either the dinuclear system, or the first example of a trinuclear circular helicate for a Rdpt complex, [(dpt)3Cl6]·1¾MeCN·¼DCM (3). Reaction of N4-pydpt (R = 4-pyridyl) with VIII led to an unusual shift of the pyridyl substituent from N4 to N1 of the triazole, forming the ligand isomer N1-pydpt, and giving a dinuclear doubly-triazole bridged complex, [(N1-pydpt)2Cl6]·2MeCN (4). Reaction with CrIII results in loss of the 4-pyridyl ring and a mixture of the di- and trinuclear complexes, 2 and 3. Interestingly, partial oxidation of the VIII in dinuclear complex 4 to vanadyl VIV=O was identified by crystallographic analysis of partially oxidized single crystals, [(VIVO)0.84(VIII)1.16(N1-pydpt)2Cl5.16]·0.84H2O·1.16MeCN (5).

Dinitrogen Activation and Hydrogenation by C5Me4SiMe3-Ligated Di- and Trinuclear Chromium Hydride Complexes.

Activation of dinitrogen (N2) by well-defined metal hydrides is of much interest and importance, but studies in this area have remained limited to date. We report here N2 activation and hydrogenation by C5Me4SiMe3-ligated di- and trinuclear chromium polyhydride complexes. Hydrogenolysis of [Cp'Cr(μ-Me)2CrCp'] (Cp' = C5Me4SiMe3) (1) with H2 in a dilute hexane solution under N2-free conditions affords the dichromium dihydride complex [Cp'Cr(μ-H)2CrCp'] (2), while hydrogenolysis of 1 in a concentrated solution or without solvent provides the trinuclear chromium tetrahydride complex [(Cp'Cr)3(μ3-H)(μ-H)3] (3). When the reaction is carried out in the presence of N2 in a dilute hexane solution, the tetranuclear diimide/dihydride complex [(Cp'Cr)4(μ3-NH)2(μ3-H)2] (4) is formed via N-N bond cleavage and N-H bond formation. The reaction of 2 with N2 at room temperature gives the tetranuclear imide/nitride/dihydride complex [(Cp'Cr)3(C5Me3(CH2)SiMe3)Cr(μ3-NH)(μ3-N)(μ-H)2] (5) via N2 cleavage and hydrogenation and C-H bond activation of a Cp methyl group. At -30 °C, the reaction of 2 with N2 affords the dinitride intermediate [(Cp'Cr)4(μ3-N)2(μ3-H)2] (6), which is quantitatively transformed to 5 at room temperature. Complex 5 reversibly converts to the stereoisomer 5'. The hydrogenation of a mixture of 5 and 5' with H2 affords 4. The reaction of 3 with N2 proceeds at 100 °C to afford [(Cp'Cr)3(μ3-NH)2] (7). This transformation has also been investigated by DFT calculations. Both experimental and computational studies suggest that N2 incorporation into the chromium hydride cluster is involved in the rate-determining step. This work represents the first example of N2 cleavage and hydrogenation by well-defined chromium hydride complexes.

Spin induced inverter circuit with trinuclear chromium complexes

Density functional theory is used in conjunction with the non-equilibrium Green's functions approach to explore the spin polarized charge transport properties of homo-nuclear tri‑chromium and hetero-nuclear chromium‑ruthenium metal-string complexes. The metal strings comprise Cr-Cr-Cr, Cr-Cr-Ru, Cr-Ru-Cr, and Cr-Ru-Ru metal centers that are sandwiched between two Au (111) nano-electrodes. As deduced from the results, the Cr-Cr-Cr metal-string junctions could potentially be exploited in designing an inverter logic circuit to transfer the data at nanoscale. Considerably It also turns out that, among these single molecular junctions, Cr-Cr-Ru and Cr-Ru-Ru exhibit significant spin-up filtering with about 100% efficiency. More importantly, the Cr-Ru-Ru metal string complex demonstrates the negative differential resistance (NDR) effects in addition to its spin filtering properties. To analyze these phenomena, we examine the respective transmission spectra along with the potential drop across all the four metal-string junctions.

Metal-ligand coordination and antiradical activity of a trichromium(III) complex with the flavonoid naringenin

The trinuclear chromium(III) complex [Cr3O(CH3CO2)6(L)(H2O)2] (where L is the monoanion of the flavonoid naringenin) was synthesized and characterized. Density functional theory (DFT) calculations and quantum theory of atoms in molecules (QTAIM) analysis show that the flavonoid binds to CrIII as an O,O-bidentate ligand via the 5-hydroxy and 4-oxo groups. Reactions with 2,2-diphenyl-1-picrylhydrazyl (DPPH) indicate that the antiradical activity of this flavonoid-metal complex is enhanced in comparison with uncoordinated naringenin.

Crystal Structure and Spin Frustration Behavior of an Oxo‐centered Trinuclear Chromium(III) Complex

A trinuclear chromium(III) complex, [Cr3O(HCO2)6(CH3OH)3]NO3·H2O·CH3OH (1), is synthesized and structurally characterized by single‐crystal X‐ray diffraction. Three chromium(III) ions are bridged by one oxygen atom in the center, forming a triangular structure. The HCOO − anion acts as bidentate ligand and bridges couples of Cr(III) ions. Magnetic susceptibility measurement indicates that a strong antiferromagnetic interaction is operative between chromium(III) ions, and the S = 1/2 ground state reveals normal spin frustration behavior.

Synthesis, crystal structure and magnetic properties of trinuclear chromium(III) basic carboxylate assembly: [Cr3O(salH)7(H2O)2] (salH2=salicylic acid), a new member of [Cr3O] family

Synthesizing a novel trinuclear chromium(III) basic carboxylate complex could give rise to new materials with interesting properties. Complex [Cr3O(salH)7(H2O)2] is formed in a one-pot, self-assembly reaction when the inert reaction mixture is exposed to dioxygen. The structural property of the complex has been acquired by single-crystal X-ray crystallography and further characterized by elemental analysis (EA), infrared (IR), UV–Visible (UV–Vis), fluorescence spectroscopy and thermo gravimetric and differential thermal analysis (TG–DTA). X–ray structural analysis shows a slightly distorted equilateral of the Cr triangle. The most important feature of the title complex is the unusual framework of the [Cr3O] family due to a terminal Ph(OH)CO2- ion of Cr(2) center, which is unique among the structurally characterized (μ3-oxo)-trichromium(III) complexes. Variable-temperature magnetic susceptibility studies indicate that the total spin value of the ground state is 1/2.

Synthesis, crystal structure, and properties of a μ3-oxo-trichromium(III) propionate cluster with pyrazole

A new μ3-oxo trinuclear chromium(III) propionate cluster, [Cr3(μ3-O)(O2CCH2CH3)6(pyr)3]NO3·0.25(H2O) (1), has been synthesized by reaction of a μ3-oxo trinuclear chromium(III) propionate precursor [Cr3(μ3-O)(O2CCH2CH3)6(H2O)3]NO3 with a pyrazol ligand (pyr) and characterized by IR spectroscopy, single-crystal X-ray structure determination, and thermal analysis. Magnetic susceptibility and magnetization studies revealed antiferromagnetic exchange interactions within the trinuclear Cr(III) cluster (J = −11.9 cm−1) and determined the electronic ground state (S = ½) of the compound.

Organoselenium Small Molecules and Chromium(III) Complexes for Intervention in Chronic Low-grade Inflammation and Type 2 Diabetes.

There is growing evidence to suggest that chronic, low-grade inflammation occurs in abdominal obesity, insulin resistance, type 2 diabetes mellitus and related complications, and that proinflammatory cytokines play an important role in the onset and progression of type 2 diabetes. These findings consequently provide new opportunities for the use of anti-inflammatory strategies to correct the metabolic disorders. Discovery of new synthetic bioactive small molecules to interfere with chronic, low-grade inflammation and type 2 diabetes has attracted considerable attention in medicinal chemistry. To date, a number of organoselenium small molecules and chromium(III) complexes have been shown to have the potential to alleviate chronic low-grade inflammation and type 2 diabetes, including ebselen, selenomethionine, chromium picolinate, chromium dinicocysteinate, chromium phenylalaninate, trinuclear chromium propionate, chromium histidinate, chromium nicotinate, etc. Here, we review recent advances in development of organoselenium small molecules and chromium(III) complexes to intervene in chronic low-grade inflammation and type 2 diabetes, and discuss their mode of action, potential molecular mechanisms and toxicity.

Aminopyridine complexes of Cr(III) basic carboxylates as potential polymer precursors: Synthesis, characterization, and crystal structure of [Cr3O(propionate)6(X-aminopyridine)3]+ (X = 3 or 4)

Synthesizing one- and two-dimensional arrays of trinuclear chromium(III) basic carboxylate complexes could give rise to new materials with interesting magnetic properties. Trinuclear chromium(III) basic carboxylate complexes where a substituted pyridine ligand could be used to link the trinuclear complexes together could serve as avenue to the synthesis of such arrays. Toward this end, the syntheses, crystal structures, and properties of [Cr3O(propionate)6(4-aminopyridine)3]+ and [Cr3O(propionate)6(3-aminopyridine)3]+ are presented.

Synthesis and porous properties of chromium azolate porous coordination polymers.

We developed a new route for synthesis of Cr-based porous coordination polymers (PCPs) with azole ligands and characterized the unique open structures by single-crystal X-ray studies and other spectroscopy techniques. Chromium-based PCPs have been prepared from azolate ligands 3,5-dimethyl-1H-pyrazole-4-carboxylic acid (H2dmcpz) and 1,4-di(1H-tetrazole-5yl)benzene (H2BDT) by solvothermal reactions under an Ar atmosphere. [Cr3O(Hdmcpz)6(DMF)3]⊃DMF (1⊃DMF) is a coordination compound that forms a hydrogen-bonded porous network. [Cr3O(HBDT)2(BDT)Cl3)]⊃DMF (2⊃DMF) possesses a new type of trinuclear chromium μ3-O unit cluster and the novel topology of a Cr-based PCP with 700 m(2) g(-1) of Brunauer-Emmett-Teller surface area. [Cr(BDT)(DEF)]⊃DEF (3⊃DEF) is structurally flexible and reactive to O2 molecules because of the unsaturated Cr(2+) centers. This is the first report of a Cr-based PCP/metal-organic framework with noncarboxylate ligands and characterization by single-crystal X-ray diffraction.

Oxo-Centered Trinuclear Chromium(III) Complexes with Both Carboxylate and Amidoximate Ligands

Compounds [Cr 3 III (μ3-O)(O2CPh)5(H2N-sao)(EtOH)2]·EtOH (1·EtOH) and [Cr 3 III (μ3-O)(O2CPh)3(H2N-pao)3]NO3·H2N-paoH·EtOH (2·NO3·H2N-paoH·EtOH) have been obtained either in a sequential one-pot, two-step procedure in which Cr(NO3)3·9H2O is first reacted with sodium benzoate in ethanol under reflux, followed by the addition of salicylamidoxime (H2N-saoH2) or pyridine-2-amidoxime (H2N-paoH), or in a one-step protocol starting from [Cr 3 III (μ3-O)(O2CPh)6(EtOH)3]NO3. They were characterized by single-crystal X-ray diffraction, magnetometry and EPR spectroscopy. Complexes 1 and 2 are derived from the parent complex [Cr 3 III (μ3-O)(O2CPh)6(EtOH)3]+ by replacement of one and three benzoate ligands, respectively, by oximate ligands. The salicylamidoximate and pyridine-2-amidoximate ligands display a tridentate coordination mode with the N–O oximate group bridging a pair of Cr atoms and the additional ligating atom substituting for an ethanol ligand of the parent complex. In both cases susceptibility, magnetization and EPR data reveal a S T = 1/2 ground state with a nearly isotropic g-tensor.

Formation of oxo-centered trinuclear chromium carboxylate complexes and hydrolysis of Cr3 as established by paramagnetic 2H NMR spectroscopy

Paramagnetic 2H NMR techniques have been utilized to study the mechanism of formation of the oxo-bridged trinuclear Cr(III) carboxylate assembly [Cr3O(O2CCD3)6(H2O)3]+ from [Cr(H2O)6]3+ and d4-acetic acid. These studies reveal a complex mechanism dominated by the involvement of dinuclear intermediates. The oxo-bridged trinuclear Cr(III) carboxylate assembly [Cr3O(O2CCH2CH3)6(H2O)3]+ has been suggested for use as a chromium nutritional supplement and therapeutic agent as it is readily absorbed and has been proposed to enter cells intact. The paramagnetic 2 H NMR technique has been utilized to follow the stability of this Cr(III) carboxylate assembly in biologically relevant media; its stability is consistent with the assembly being able to enter cells intact.

Synthesis and Surface Photoelectric Properties of a Trinuclear Chromium(III) Complex

A trinuclear Chromium(III) complex [Cr3(μ3-O)(μ2-PCBA)6(CH3OH)3]NO3∙H2O∙CH3OH (HPCBA = 4-Chlorobenzoic acid) has been synthesized and characterized by single-crystal X-ray diffraction, IR spectra, UV-Vis absorption spectra and elemental analysis, which belongs to monoclinic, space group P21/c with a = 12.443 (3), b = 24.543 (5), c =22.094 (7)Å, α = 90°, β =115.76 (2) °, γ =90°, V = 6077 (3)Å3, Z = 4.The surface electron behavior of the chromium complex has been studied emphatically by surface photovoltage spectroscopy (SPS). Structural analyse indicate that the complex is molecular complex. The result of SPS show that there is positive photovoltage response bands within 300–800 nm, which indicate that it possess obvious photoelectric conversion properties. There was a good correlation between the SPS and UV-Vis absorption spectra.

Solid-State Dinuclear-to-Trinuclear Conversion in an Oxalato-Bridged Chromium(III)−Cobalt(II) Complex as a New Route toward Single-Molecule Magnets

A novel bis(oxalato)chromium(III) salt of a ferromagnetically coupled, oxalato-bridged dinuclear chromium(III)-cobalt(II) complex of formula [CrL(ox)(2)CoL'(H(2)O)(2)][CrL(ox)(2)]·4H(2)O (1) has been self-assembled in solution using different aromatic α,α'-diimines as blocking ligands, such as 2,2'-bipyridine (L = bpy) and 2,9-dimethyl-1,10-phenanthroline (L' = Me(2)phen). Thermal dehydration of 1 leads to an intriguing solid-state reaction between the S = 3/2 Cr(III) anions and the S = 3 Cr(III)Co(II) cations to give a ferromagnetically coupled, oxalato-bridged trinuclear chromium(III)-cobalt(II) complex of formula {[CrL(ox)(2)](2)CoL'} (2). Complex 2 possesses a moderately anisotropic S = 9/2 Cr(III)(2)Co(II) ground state, and it exhibits slow magnetic relaxation behavior at very low temperatures (T(B) < 2.0 K).

Evaluation of the Acute Oral Toxicity Class of Trinuclear Chromium(III) Glycinate Complex in Rat

Chromium(III) is considered as an essential element playing a role in carbohydrate and lipid metabolism, and various chemical forms of this element are widely used in dietary supplements. A new trinuclear chromium(III) glycinate complex [Cr3O(NH2CH2CO2)6(H2O)3]+NO3− (CrGly), an analogue of Cr3 (trinuclear Cr(III) propionate complex) has been synthesized as a potential source of supplementary Cr. In this study, we evaluated the acute toxicity class of CrGly in Wistar rats applying the OECD 423 procedure. Male and female Wistar rats (n = 12, 6 ♀ and 6 ♂) were given by gavage either a single dose of CrGly 2,000 mg/kg body mass (equals to 300 mg Cr(III)/kg body mass; in aqueous solution) or equivalent volumes of distilled water and fed ad libitum commercial Labofeed B diet, and observed carefully for 14 days, then sacrificed to collect blood and internal organs for biochemical and histologic examination. No death cases were detected. No abnormalities in animal behavior, body mass gains, gross organ histology, or blood morphology and biochemistry were observed. The results demonstrate that LD50 of CrGly is greater than 2,000 mg/kg when administrated orally to rat; thus, this compound appears to belong to the fifth category in the GHS system or the fourth class (“unclassified”) in the EU classification system.

Water Stability of Microporous Coordination Polymers and the Adsorption of Pharmaceuticals from Water

The stability of a variety of microporous coordination polymers (MCPs) to water-containing solutions was studied using powder X-ray diffraction. It was determined that the stability of the MCP is related to the metal cluster present in the structure with trinuclear chromium clusters more stable than copper paddlewheel clusters which are more stable than basic zinc acetate clusters. Zn(2-methylimidizolate)(2) was found to be more water stable than zinc MCPs with carboxylate linkers; however, extended exposure to water led to decomposition of all zinc-based MCPs. Matériaux de l'Institut Lavoisier (MIL)-100 was also found to be completely water stable and was used to adsorb the pharmaceuticals furosemide and sulfasalazine from water with large uptakes achievable at low concentrations, indicating that the adsorption of wastewater contaminants may be a feasible application for these materials.

Thiocyanate Ion-Selective PVC Membrane Electrode

A potentiometric selective sensor based on trinuclear chromium(III) complex as a novel ionophore for the thiocyanateselective electrode is reported. The sensor displays a near Nernstian slope of 57 ± 2 mV per decade, over a wide pH range 3 - 11. The working concentration range of the electrode is 1.10-5 – 1.10-1 mol/l with a detection limit of 5.10-6 mol/l. The sensor has a response time of 20 s and can be used for at least 6 months without any considerable fluctuation of the potential. The selectivity coefficients determined at using the fixed interference method indicate a good discriminating ability towards other anions. The prepared sensor was applied as an indicator electrode in the titration of thiocyanate with Ag+.

Binuclear and Trinuclear Chromium Carbonyls with Linear Bridging Carbonyl Groups: Isocarbonyl versus Carbonyl Bonding of Carbon Monoxide Ligands

Isocarbonyl groups bonded to chromium through their oxygen atoms as well as the usual carbonyl groups bonded to carbon atoms have been considered as possible structural features for Cr(CO)(6), Cr(2)(CO)(n) (n = 11, 10, 9), and Cr(3)(CO)(16). In this connection, Cr(CO)(6) structures with one of the six CO groups bonded to the chromium either solely through its oxygen atom or side-on through both its carbon and oxygen atoms are predicted by density functional theory to lie >30 kcal/mol above the well-known Cr(CO)(6) structure, in which all six carbonyl groups are bonded to the chromium atom in the normal manner through their carbon atoms. The binuclear Cr(2)(CO)(11) structure of the type (OC)(5)Cr-C-O-Cr(CO)(5) with a linear bridging carbonyl group bonded to one chromium atom through its carbon atom and to the other chromium atom through its oxygen atom is of lower energy than previously studied Cr(2)(CO)(11) structures and indeed is viable with respect to dissociation into Cr(CO)(5) + Cr(CO)(6). Similar binuclear structures are found for Cr(2)(CO)(10) and Cr(2)(CO)(9) with linear bridging carbonyl groups. However, the Cr(2)(CO)(9) structure with a linear bridging carbonyl group, no Cr-Cr bond, and 16-electron chromium configurations is found to lie higher by 22 +/- 5 kcal/mol than the previously found Cr(2)(CO)(6)(mu-CO)(3) structure with three bridging carbonyl groups, a formal Cr[triple bond]Cr triple bond, and the favorable 18-electron chromium configuration. For the trinuclear Cr(3)(CO)(16), nearly degenerate trans- and cis-Cr(CO)(4)[OCCr(CO)(5)](2) structures are found that are viable with respect to dissociation into 2Cr(CO)(5) + Cr(CO)(6).