Configurational preferences of two 1,2-diamine adducts of bis(1-(2-thienyl)-4,4,4-trifluoro-1,3-butanedionato)cobalt(II)

The preparation, the IR and ligand field spectra and the structures of the mixed-ligand addition compounds [(N,N-dimethyl-1,2-diaminoethane)bis(1-(2-thienyl)-4,4,4-trifluoro-1,3-butanedionato)cobalt(II)], [Co(thtf)2me2en], and [(N,N,N′,N′-tetramethyl-1,2-diaminoethane)bis(1-(2-thienyl)-4,4,4-trifluoro-1,3-butanedionato)cobalt(II)], [Co(thtf)2me4en], are reported. The structures were determined by single crystal X-ray diffraction analysis (monoclinic, space group P21/c, Z=4 with a=10.708(6), b=19.531(6), c=13.352(6) Å, β=111.64(10)°, R1=0.0642 and wR2=0.1719 for [Co(thtf)2(me2en)] and a=12.033(6), b=15.565(6), c=15.339(6) Å, β=92.57(6)°, R1=0.0612 and wR2=0.1504 for [Co(thtf)2me4en]). The structures are distorted octahedral and the shortest cobalt–cobalt separation distances are 5.388(2) Å in [Co(thtf)2me2en] and 8.675(3) Å in [Co(thtf)2me4en]. In both compounds the diamine molecules attain the gauche conformation. The U(Z,Z) conformation of the β-dione leads to a semi-chair conformation of the β-dionato chelate rings. The relative orientation of the groups attached to the β-dionato moiety depends on the extent of stereoelectronic effects the N-substitution of the diamine entails. In [Co(thtf)2me2en] the intraligand distance separating the trifluoromethyl carbon atoms is 5.281(18) Å while in [Co(thtf)2me2en] it increases to 8.338(9) Å. The cobalt–cobalt separation distance, the orientation of the chelate rings and the extent of N-substitution seem to affect hydrogen bonding. While in [Co(thtf)2me2en] inter- and intraligand hydrogen bonding is implicated, it is totally absent in [Co(thtf)2me4en].

Synthesis and evaluation of lipophilic BTBP ligands for An/Ln separation in nuclear waste treatment: the effect of alkyl substitution on extraction properties and implications for ligand design

Four new 6,6′-bis(1,2,4-triazin-3-yl)-2,2′-bipyridine (BTBP) ligands, which contain either additional alkyl groups on the pyridine rings or seven-membered aliphatic rings attached to the triazine rings, have been synthesized, and the effects of the additional alkyl substitution in the 4- and 4′-positions of the pyridine rings on their extraction properties with LnIII and AnIII cations in simulated nuclear waste solutions have been studied. The speciation of ligand 13 with some trivalent lanthanide nitrates was elucidated by 1H NMR spectroscopic titrations and ESI-MS. Although 13 formed both 1:1 and 1:2 complexes with LaIII and YIII, only 1:2 complexes were observed with EuIII and CeIII. Quite unexpectedly, both alkyl-substituted ligands 12 and 13 showed lower solubilities in certain diluents than the unsubstituted ligand CyMe4-BTBP. Compared to CyMe4-BTBP, alkyl-substitution was found to decrease the rates of metal-ion extraction of the ligands in both 1-octanol and cyclohexanone. A highly efficient (DAm > 10) and selective (SFAm/Eu > 90) extraction was observed for 12 and 13 in cyclohexanone and for 13 in 1-octanol in the presence of a phase-transfer agent. The implications of these results for the design of improved extractants for radioactive waste treatment are discussed.

Complexation of lanthanides, actinides and transition metal cations with a 6-(1,2,4-triazin-3-yl)-2,2′:6′,2′′-terpyridine ligand: implications for actinide(III)/lanthanide(III) partitioning

The quadridentate N-heterocyclic ligand 6-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin- 3-yl)-2,2′ : 6′,2′′-terpyridine (CyMe4-hemi-BTBP) has been synthesized and its interactions with Am(III),U(VI), Ln(III) and some transition metal cations have been evaluated by X-ray crystallographic analysis, Am(III)/Eu(III) solvent extraction experiments, UVabsorption spectrophotometry, NMR studies and ESI-MS. Structures of 1 : 1 complexes with Eu(III), Ce(III) and the linear uranyl (UO2 2+) ion were obtained by X-ray crystallographic analysis, and they showed similar coordination behavior to related BTBP complexes. In methanol, the stability constants of the Ln(III) complexes are slightly lower than those of the analogous quadridentate bis-triazine BTBP ligands, while the stability constant for the Yb(III)complex is higher. 1H NMR titrations and ESI-MS with lanthanide nitrates showed that the ligand forms only 1 : 1 complexes with Eu(III), Ce(III) and Yb(III), while both 1 : 1 and 1 : 2 complexes were formed with La(III) and Y(III) in acetonitrile. A mixture of isomeric chiral 2 : 2 helical complexes was formed with Cu(I), with a slight preference (1.4 : 1) for a single directional isomer. In contrast, a 1 : 1 complex was observed with the larger Ag(I) ion. The ligand was unable to extract Am(III) or Eu(III) from nitric acid solutions into 1-octanol, except in the presence of a synergist at low acidity. The results show that the presence of two outer 1,2,4-triazine rings is required for the efficient extraction and separation of An(III)from Ln(III) by quadridentate N-donor ligands.

Hetero-metallic trinuclear nickel(II)–cadmium(II) complexes of a salicylaldimine ligand with thiocyanate, cyanate and azide ions: isolation of a pair of polymorphs with thiocyanate ion

Four new trinuclear hetero-metallic nickel(II)-cadmium(II) complexes [(NiL)(2)Cd(NCS)(2)] (1A and 1B), [(NiL)(2)Cd(NCO)(2)] (2) and [(NiL)(2)Cd(N-3)(2)] (3) have been synthesized using [NiL] as a so-called "ligand complex" (where H2L = N,N'-bis(salicylidene)-1,3-propanediamine) and structurally characterized. Crystal structure analyses reveal that all four complexes contain a trinuclear moiety in which two square planar [NiL] units are bonded to a central cadmium(II) ion through double phenoxido bridges. The Cd(II) is in a six-coordinate distorted octahedral environment being bonded additionally to two mutually cis nitrogen atoms of terminal thiocyanate (in 1A and 1B), cyanate (in 2) and azide (in 3). Complexes 1A and 1B have the same molecular formula but crystallize in very different monoclinic unit cells and can be considered as polymorphs. On the other hand, the two isoelectronic complexes 2 and 3 are indeed isomorphous and crystallize only in one form. Their conformation is similar to that observed in 1A.

Synthesis, crystal structure, and catecholase activity of three trinuclear heterometallic NiII2-MnII complexes derived from a salen-type Schiff base ligand

Three new trinuclear heterometallic nickel(II)manganese(II) complexes, [(NiL)2Mn(NCS)2] (1), [(NiL)2Mn(NCO)2] (2), and [{NiL(EtOH)}2Mn(NO2)2]center dot 2EtOH (3), have been synthesized by using [NiL] as the so-called ligand complex [where H2L = N,N'-bis(salicylidene)-1,3-propanediamine] and have been structurally characterized. Crystal structure analyses revealed that complexes 1 and 2 are angular trinuclear species, in which two terminal four-coordinate square planar [NiL] moieties are coordinated to a central MnII through double phenoxido bridges. The MnII is in a six-coordinate distorted octahedral environment that is bonded additionally to two mutually cis nitrogen atoms of terminal thiocyanate (in 1) and cyanate (in 2). In complex 3, in addition to the double phenoxo bridge, the two terminal NiII ions are linked to the central MnII by means of a nitrite bridge (1?N:2?O) that, together with a coordinated ethanol molecule, gives rise to an octahedral environment around the NiII ions and consequently the structure becomes linear. Catecholase activity of these three complexes was examined by using 3,5-di-tert-butylcatechol (3,5-DTBC) as the substrate. All three complexes mimic catecholase activity and the rate of catechol oxidation follows saturation kinetics with respect to the substrate and first-order kinetics with respect to the catalyst. The EPR spectra of the complexes exhibit characteristic six line spectra, which indicate the presence of high-spin octahedral MnII species in solution state. The ESI-MS positive spectrum of 1 in the presence of 3,5-DTBC has been recorded to investigate possible complexsubstrate intermediates.

Steric effects on uranyl complexation: synthetic, structural, and theoretical studies of carbamoyl pyrazole compounds of the uranyl(VI) ion

New bifunctional pyrazole based ligands of the type [C3HR2N2CONR'] (where R = H or CH3; R' = CH3, C2H5, or (C3H7)-C-i) were prepared and characterized. The coordination chemistry of these ligands with uranyl nitrate and uranyl bis(dibenzoyl methanate) was studied with infrared (IR), H-1 NMR, electrospray-mass spectrometry (ES-MS), elemental analysis, and single crystal X-ray diffraction methods. The structure of compound [UO2(NO3)(2)(C3H3N2CON{C2H5}(2))] (2) shows that the uranium(VI) ion is surrounded by one nitrogen atom and seven oxygen atoms in a hexagonal bipyramidal geometry with the ligand acting as a bidentate chelating ligand and bonds through both the carbamoyl oxygen and pyrazolyl nitrogen atoms. In the structure of [UO2(NO3)(2)(H2O)(2)(C5H7N2CON {C2H5}(2))(2)], (5) the pyrazole figand acts as a second sphere ligand and hydrogen bonds to the water molecules through carbamoyl oxygen and pyrazolyl nitrogen atoms. The structure of [UO2(DBM)(2)C3H3N2CON{C2H5}(2)] (8) (where DBM = C6H5COCHCOC6H5) shows that the pyrazole ligand acts as a monodentate ligand and bonds through the carbamoyl oxygen to the uranyl group. The ES-MS spectra of 2 and 8 show that the ligand is similarly bonded to the metal ion in solution. Ab initio quantum chemical studies show that the steric effect plays the key role in complexation behavior.

Synthesis, characterization and molecular structure of 1,1′ bis (diphenyl phosphino ferrocene) dioxide complex of the cis-uranyl dichloride

A 1,1' bis(diphenyl phosphino ferrocene) dioxide complex of the uranyl dichloride was synthesized and characterized by elemental analysis, H-1, P-31{H-1} NMR and X-ray diffraction methods. The structure of the compound shows that the uranium(VI) ion is surrounded by four oxygen and two chlorine atoms in an octahedral geometry. Two oxygen atoms from the bis (diphenyl phosphino ferrocene) dioxide and two chlorine atoms form a square planar arrangement. Two uranyl oxygen atoms occupy the axial positions. The bis(diphenyl phosphino ferrocene) dioxide ligand acts as a bidentate chelating ligand with a bite angle of 82.90(16)degrees around the uranyl group. The two chlorine atoms are mutually cis with a CI-U-Cl angle of 97.75(7)degrees.

Effect of anionic co-ligands on structure and magnetic coupling of bis(μ-phenoxo-bridged dinuclear copper(II) complexes

Two phenoxo bridged dinuclear Cu(II) complexes, [Cu2L2(NO2)(2)] (1) and [Cu2L2(NO3)(2)] (2) have been synthesized using the tridentate reduced Schiff-base ligand 2-[(2-dimethylamino-ethylamino)-methyl]-phenol (HL). The complexes have been characterized by X-ray structural analyses and variable-temperature magnetic susceptibility measurements. The structures of the two compounds are very similar having the same tridentate chelating ligand (L) and mono-dentate anionic ligand nitrite for 1 and nitrate for 2. In both complexes Cu(II) is penta-coordinated but the square pyramidal geometry of the copper ions is severely distorted (Addison parameter (tau) = 0.33) in 1 while the distortion is quite small (average tau = 0.11) in 2. These differences have marked effect on the magnetic properties of two compounds. Although both are antiferromagnetically coupled, the coupling constants (J = -140.8 and -614.7 cm (1) for 1 and 2, respectively) show that the coupling is much stronger in 2.

Complexes of palladium using di-2-pyridyl ketone as ligand: synthesis, structure and, spectral and catalytic properties

During the reaction of di-2-pyridyl ketone (dpk) with Na(2)[PdCl(4)] in alcoholic media, the C=O fragment of dpk undergoes facile solvolysis and the transformed di-2-pyridyl ketone (dpk(ROH), R = Me or H) binds to palladium as NN-donor. When the reaction is carried out in refluxing methanol, a mono-complex of type [Pd(dpk(MeOH))Cl(2)] is obtained. A similar reaction in ethanol affords a bis-complex of type [Pd(dpk(ROH))(2)]Cl(2). Structure of both the complexes have been determined by X-ray crystallography. In acetonitrile solution the [pd(dpk(MeOH))Cl(2)] and [pd(dpk(ROH))(2)]Cl(2) complexes show intense absorptions in the visible and ultraviolet region, origin of which has been probed through uvr calculations. These two palladium complexes are found to be efficient catalysts for Suzuki cross-coupling reactions.

Synthesis, structural and emission studies of a bis (carbamoyl methyl) sulfone complex of uranyl nitrate

A new tri-functional ligand (Bu2NCOCH2SO2CH2CONBu2)-Bu-i-Bu-i (L) was prepared and characterized. The coordination chemistry of this ligand with uranyl nitrate was studied with IR, (HNMR)-H-1, ES-MS, TG and elemental analysis methods. The structure of the compound [UO2(NO3)(2)L] was determined by single crystal X-ray diffraction techniques. In the structure the uranium(VI) ion is surrounded by eight oxygen atoms in a hexagonal bi-pyramidal geometry. Four oxygen atoms from two nitrate groups and two oxygen atoms from the ligand form a planar hexagon. The ligand acts as a bidentate chelate and bonds through both the carbamoyl groups to the uranyl nitrate. An ES-MS spectrum shows that the complex retains the bonding in solution. The compound displayed vibronically coupled fluorescence emission.

Syntheses, crystal structures and properties of sterically congested heteroleptic complexes of group 10 metal ions with p-tolylsulfonyl dithiocarbimate and 1,2-bis (diphenylphosphino) ethane

Three novel heteroleptic complexes of the type cis- [ML(dppe)] [M = Ni(II), Pd(II), Pt(II); L = p-tolylsulfonyl dithiocarbimate; dppe = 1,2-bis(diphenylphosphino)ethane] have been prepared and characterized. X-ray crystallography revealed the close proximity of one of the ortho phenyl protons of the dppe ligand to the metal in the Ni(II) complex showing existence of the less common C-H center dot center dot center dot Ni anagostic interactions observed for the first time in the dithio-phosphine mixed-ligand systems. The platinum complex showed a strong photoluminescence emission near visible region in CH(2)Cl(2) solution.

Spectroelectrochemical study of complexes [Mo(CO)2(h3-allyl)(adiimine)(NCS)] (a-diimine ¼ bis(2,6-dimethylphenyl)- acenaphthenequinonediimine and 2,20-bipyridine) exhibiting different molecular structure and redox reactivity

The redox properties and reactivity of [Mo(CO)2(η3-allyl)(α-diimine)(NCS)] (α-diimine = bis(2,6-dimethylphenyl)-acenaphthenequinonediimine (2,6-xylyl-BIAN) and 2,2′-bipyridine (bpy)) were studied using cyclic voltammetry and IR/UV–Vis spectroelectrochemistry. [Mo(CO)2(η3-allyl)(2,6-xylyl-BIAN)(NCS)] was shown by X-ray crystallography to have an asymmetric (B-type) conformation. The extended aromatic system of the strong π-acceptor 2,6-xylyl-BIAN ligand stabilises the primary 1e−-reduced radical anion, [Mo(CO)2(η3-allyl)(2,6-xylyl-BIAN•−)(NCS)]−, that can be reduced further to give the solvento anion [Mo(CO)2(η3-allyl)(2,6-xylyl-BIAN)(THF)]−. The initial reduction of [Mo(CO)2(η3-allyl)(bpy)(NCS)] in THF at ambient temperature results in the formation of [Mo(CO)2(η3-allyl)(bpy)]2 by reaction of the remaining parent complex with [Mo(CO)2(η3-allyl)(bpy)]− produced by dissociation of NCS− from [Mo(CO)2(η3-allyl)(bpy•−)(NCS)]−. Further reduction of the dimer [Mo(CO)2(η3-allyl)(bpy)]2 restores [Mo(CO)2(η3-allyl)(bpy)]−. In PrCN at 183 K, [Mo(CO)2(η3-allyl)(2,6-xylyl-BIAN•−)(NCS)]− converts slowly to 2e−-reduced [Mo(CO)2(η3-allyl)(2,6-xylyl-BIAN)(PrCN)]− and free NCS−. At room temperature, the reduction path in PrCN involves mainly the dimer [Mo(CO)2(η3-allyl)(bpy)]2; however, the detailed course of the reduction within the spectroelectrochemical cell is complicated and involves a mixture of several unassigned products. Finally, it has been shown that the five-coordinate anion [Mo(CO)2(η3-allyl)(bpy)]− promotes in THF reduction of CO2 to CO and formate via the formation of the intermediate [Mo(CO)2(η3-allyl)(bpy)(O2CH)] and its subsequent reduction.

Synthesis of linked heterocycles via use of bis-acetylenic compounds

Linked bis-pyrazoles, a pyrazolyl-isoxazole, a pyrazolyl-pyrimidine and a pyrazolyl-triazole were synthesized starting with commercially available 1,4-bis(trimethylsilyl)-1,3-butadiyne 1 or readily available bis-acetylenic diketone 22. A stepwise approach based on the use of 1 allowed the synthesis of nonsymmetrically substituted bis-pyrazoles and linked heterocycles with two different cores whereas a symmetric approach based on the use of 22 allowed a very short synthesis of symmetric bis-pyrazoles.

Hydrophilic sulfonated bis-1,2,4-triazine ligands are highly effective reagents for separating actinides(iii) from lanthanides(iii) via selective formation of aqueous actinide complexes

We report the first examples of hydrophilic 6,6′-bis(1,2,4-triazin-3-yl)-2,2′-bipyridine (BTBP) and 2,9-bis(1,2,4-triazin-3-yl)-1,10-phenanthroline (BTPhen) ligands, and their applications as actinide(III) selective aqueous complexing agents. The combination of a hydrophobic diamide ligand in the organic phase and a hydrophilic tetrasulfonated bis-triazine ligand in the aqueous phase is able to separate Am(III) from Eu(III) by selective Am(III) complex formation across a range of nitric acid concentrations with very high selectivities, and without the use of buffers. In contrast, disulfonated bis-triazine ligands are unable to separate Am(III) from Eu(III) in this system. The greater ability of the tetrasulfonated ligands to retain Am(III) selectively in the aqueous phase than the corresponding disulfonated ligands appears to be due to the higher aqueous solubilities of the complexes of the tetrasulfonated ligands with Am(III). The selectivities for Am(III) complexation observed with hydrophilic tetrasulfonated bis-triazine ligands are in many cases far higher than those found with the polyaminocarboxylate ligands previously used as actinide-selective complexing agents, and are comparable to those found with the parent hydrophobic bis-triazine ligands. Thus we demonstrate a feasible alternative method to separate actinides from lanthanides than the widely studied approach of selective actinide extraction with hydrophobic bis-1,2,4-triazine ligands such as CyMe4-BTBP and CyMe4-BTPhen.