Pseudo-tetrahedral Coordination Research Articles

Synthesis and Characterization of the New Lead Strontium Germanate PbSrGeO4

The new lead strontium germanate PbSrGeO4 was synthesized by a high-temperature solid-state reaction of lead(II) oxide, strontium carbonate, and germanium(IV) oxide at a temperature of 900 °C in a platinum crucible. The compound crystallizes in the orthorhombic space group P212121 (no. 19) being isotypic to the structure of BaNdGaO4 [1]. The primitive cell contains four formula units with lattice parameters of a = 995:40(2), b = 732:44(2), c = 599:42(2) pm, V = 437:02(2)Å3, and residuals of R1 = 0:0385 and wR2 = 0:0997 for all data. The main structural element of PbSrGeO4 is an isolated [GeO4]4- tetrahedron. A circular arrangement of six of these [GeO4]4- tetrahedra leads to the formation of large channels along b in which the strontium cations are eightfold coordinated by oxygen atoms. The lead cations are coordinated by three oxygen atoms, and with a lone pair of electrons they show a pseudo-tetrahedral coordination. Next to the structural investigations, PbSrGeO4 was characterized by Raman-spectroscopic investigations and DFT calculations.

Selective and Nonselective Aza-Michael Additions Catalyzed by a Chiral Zirconium Bis-Diketiminate Complex

Reaction of the chiral bis-diketiminate complex rac- or (R,R)-C6H10(nacnacXyl)2ZrCl2 with AgOTf yielded the corresponding bis-triflate complex. The complex geometry changes from distorted octahedral in the dichloride complex to a pseudotetrahedral coordination involving π coordination of the diketiminate ligands. The bis-triflate complex is highly active for aza-Michael additions with turnover frequencies of 20000/h for the addition of morpholine to acrylonitrile and 1000/h for the addition of morpholine to methacrylonitrile. The enantioselectivities of the latter reaction in various solvents were low, never surpassing 19% ee. The reaction is first-order in olefin concentration and second order in amine concentration, which is explained by its participation as a base in the reaction mechanism. The presence of catalytic amounts of triethylamine slightly increases the observed rate constants and reduces the reaction order in amine to first order. Other activated alkenes such as methacrylonitrile, crotonitri...

Synthesis, characterization, and crystal structures of cobalt(II), copper(II), and zinc(II) complexes of a bidentate iminophenol

A bidentate iminophenol (HL = 2-((4-methoxyphenylimino)methyl)-4,6-di-tert-butylphenol derived from condensation of 4-methoxyaniline and 3,5-di-tert-butyl-2-hydroxybenzaldehyde) was mixed with divalent metal salts to form the corresponding mononuclear metal complexes [MII(L)2] (M = Co (1), Cu (2), and Zn (3)). The complexes are characterized by different spectroscopic and analytical tools. X-ray crystal structures of the complexes revealed homoleptic mononuclear complexes with MN2O2 coordination. The cobalt(II) (1) and zinc(II) (3) complexes display a pseudo-tetrahedral coordination geometry, whereas the copper(II) complex (2) exhibits a distorted square-planar coordination. The zinc(II) complex (3) emits at 460 nm with a twofold enhancement of emission with respect to the free iminophenol.

Comprehensive Uranium Thiophosphate Chemistry: Framework Compounds Based on Pseudotetrahedrally Coordinated Central Metal Atoms

AbstractThe new ternary compounds UP2S6, UP2S7, U(P2S6)2, and U3(PS4)4 were prepared from uranium metal, phosphorus pentasulfide, and sulfur at 700 °C. The crystal structures were determined by single‐crystal X‐ray diffraction methods. UP2S6 (I) crystallizes in the ZrP2S6 structure type [tetragonal, P42/m, a = 6.8058(7) Å, c = 9.7597(14) Å, Z = 2], which consists of central uranium(IV) atoms coordinated by P2S64– anions (staggered conformation). The anions are two‐dimensional connectors for four uranium cations arranged in one plane. The structure of UP2S7 (II) [orthorhombic, Fddd, a = 8.9966(15) Å, b = 15.2869(2) Å, c = 30.3195(5) Å, Z = 16] is closely related to the monoclinic ZrP2S7 structure type. It consists of U4+ cations linked by P2S74– ligands, the resulting 3D network contains large pores (diameter approx. 3.5 × 16.7 Å). In the previously reported compound U(P2S6)2 (III) [I41/a, a = 12.8776(9) Å, c = 9.8367(10) Å, Z = 2], the metal atoms are coordinated by four bidentate P2S62– ligands. This arrangement can be considered as a pseudotetrahedral coordination of the uranium atoms by the linear ligands. Three of the resulting diamondoid frameworks are inseparably interwoven in order to optimize space filling. U3(PS4)4 (IV) [I41/acd, a = 10.7440(9) Å, c = 19.0969(2) Å, Z = 2] crystallizes in a defect variant of the PrPS4 structure type, with 50 % of the U2 sites statistically occupied with uranium atoms. The resulting stoichiometry is U3(PS4)4 with tetravalent uranium atoms. The structure of U3(PS4)4 consists of uranium atoms connected by PS43– groups, each PS4 group linking four central uranium atoms. Vibrational spectra, which were recorded for I–III, show good agreement between the obtained results and the expected values for the anionic units, while magnetic measurements confirm the presence of tetravalent uranium.

Comparative stability of isomeric (565)macrotricyclic chelates of 3d-elements formed in the systems M(II)-thiosemicarbazide-formaldehyde according to DFT B3LYP data

Comparative stability of three types of (565)macrotricyclic chelates of Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and Zn(II) with chelate nodes MN2S2 and MN4 have been analyzed by means of hybrid density functional method B3LYP with the 6-31G(d) basis set using GAUSSIAN-09 software. These chelates may potentially be formed in template interaction between gelatin-immobilized hexacyanoferrate(II) of respective metal ions M(II), thiosemicarbazide H2N-HN-C(=S)-NH2, and formaldehyde H2C=O. It has been demonstrated that for all M(II) considered, the complex with chelate nodes MN2S2 is more stable. Key structural parameters of the complexes (bond lengths, bond and torsion angles) are presented. It is noted that pseudotetrahedral coordination of ligand donor centers around M(II) is typical for Mn(II), Co(II), Cu(II), and Zn(II), whereas for Fe(II) and Ni(II) it is almost planar. Values of standard enthalpy ΔHf,2980 and standard Gibbs energy ΔGf,2980 are positive for nearly all the complexes studied.

Different coordination modes of dipyridyl ketimine ligands in cationic arene ruthenium complexes

Abstract 2,2′-Dipyridyl- N -arylimines L (L 1 = 2,4,6-trimethyl(di-2-pyridylmethylene)aniline, L 2 = 2,6-diisopropyl(di-2-pyridylmethylene)aniline) react with arene ruthenium dichloride dimer in methanol to give cationic arene ruthenium complexes of the general type [(arene)Ru(η 2 - N , N -L)Cl] + (arene = C 6 H 6 , p -MeC 6 H 4 Pr i ). Two coordination modes of the chelating ligands N , N -L are observed. In the major isomer, the ketimine nitrogen atom and one of the two pyridine nitrogen atoms are coordinated to ruthenium, while in the minor isomer the two pyridine nitrogen atoms coordinate to the metal center. In the case of L 1 , the minor isomer of the p -cymene ruthenium chloro complex could be isolated as the tetrafluoroborate salt and characterized by single crystal X-ray analysis. The molecular structure of the major isomer was determined by X-ray crystallography in the case of the tetraphenylborate salt of the benzene ruthenium chloro derivative. In both structures, the ruthenium atom shows the expected pseudo-tetrahedral coordination geometry.

Silver(I) ferrocenylcarboxylate: Reactivity and reaction behavior toward phosphines and phosphites

Silver(I) ferrocenylcarboxylate [Fe(η5-C5H4CO2Ag)(η5-C5H5)] (1) subsequently decarboxylates either in boiling dichloromethane or tetrahydrofuran to give biferrocene [Fe(η5-C5H4)(η5-C5H5)]2 (2) and elemental silver. Phosphine silver(I) ferrocenylcarboxylates of type [Fe(η5-C5H4CO2Ag(PR3)n)(η5-C5H5)] (R = Ph: 4a, n = 1; 4b, n = 2; 4c, n = 3. R = n-Bu: 5a, n = 1; 5b, n = 2; 5c, n = 3. R = OMe: 6a, n = 1; 6b, n = 2; 6c, n = 3) are accessible by treatment of 1 with PR3 (3a, R = Ph; 3b, R = n-Bu; 3c, R = OMe) in the ratio of 1:n. With dppe (7) tetrametallic [Fe(η5-C5H4CO2Ag(μ-dppe))(η5-C5H5)]2 (8) (dppe = Ph2PCH2CH2PPh2) was formed. The structures of 4b and 8 in the solid state have been determined by single X-ray structure determination. In 4b the silver(I) ion possesses a pseudo-tetrahedral environment, whereby the four coordination sites are occupied by the chelated FcCO2 unit and two datively-bonded PPh3 ligands. Compound 8 forms in the solid state a dimer setup by a [Ag(μ-dppe)]2 central building block. The FcCO2 groups are chelated to Ag(I) thus resulting in a pseudo-tetrahedral coordination sphere at silver. The solution behavior of 4–6 was analyzed by temperature-dependent 31P{1H} NMR studies indicating ligand exchange processes.

Azurin as a protein scaffold for a low-coordinate nonheme iron site with a small-molecule binding pocket.

The apoprotein of Pseudomonas aeruginosa azurin binds iron(II) to give a 1:1 complex, which has been characterized by electronic absorption, Mössbauer, and NMR spectroscopies, as well as X-ray crystallography and quantum-chemical computations. Despite potential competition by water and other coordinating residues, iron(II) binds tightly to the low-coordinate site. The iron(II) complex does not react with chemical redox agents to undergo oxidation or reduction. Spectroscopically calibrated quantum-chemical computations show that the complex has high-spin iron(II) in a pseudotetrahedral coordination environment, which features interactions with side chains of two histidines and a cysteine as well as the C═O of Gly45. In the (5)A(1) ground state, the d(z(2)) orbital is doubly occupied. Mutation of Met121 to Ala leaves the metal site in a similar environment but creates a pocket for reversible binding of small anions to the iron(II) center. Specifically, azide forms a high-spin iron(II) complex and cyanide forms a low-spin iron(II) complex.

Synthesis and structural characterization of LiI, ZnII, CdII, and HgII complexes containing a fluorinated β-diketiminate ligand

The reaction of a fluorinated β-aminoimine compound ArN]C(Me)CH]C(Me)NHAr (1) (Ar = 2,6-F2C6H3) with n-BuLi in coordinating solvents (Et2O and THF) leads to the solvated complexes [HC(CMeNAr)2]Li(Et2O) (2) and [HC(CMeNAr)2]Li(THF) (3), respectively. They exist as momonuclear complexes featuring lithium atoms in a distorted trigonal planar environment. The same reaction, which was then carried out in a non-coordinated solvent (pentane), provided complex [HC(CMeNAr)2]2Li2 (4). It crystallized as a dinuclear complex in the solid state, featuring lithium atoms in a pseudo-tetrahedral coordination environment. Notably, one fluorine atom of each ligand was involved to stabilize the lithium center. Taking complex 2 as the precursor, a series of group 12 metal complexes were prepared via the reaction with MX2 (M = Zn, Cd, Hg; X = Br, I). The diketiminate zinc complexes [HC(CMeNAr)2]Zn(μ-I)2Li(Et2O)2 (5) and [HC(CMeNAr)2]Zn(μ-Br)2Li(Et2O)2 (6) were successfully synthesized and characterized by single crystal X-ray diffraction analysis. When 2 reacted with CdI2, the expected double iodide bridging product [HC(CMeNAr)2]Cd(μ-I)2Li(Et2O)2 (7a) was only generated in a small amount, with the single iodide bridging complex {HC(CMeNAr)2}Cd(I)(μ-I)Li(Et2O)3 (7b) as the major product. These results were unambiguously confirmed by NMR spectroscopy and X-ray crystallography. Next, a mercury complex [HC(CMeNAr)2]Hg(μ-I)2Li(Et2O) (8) was prepared by using HgI2 as the metal source. Additionally, [HC(CMeNAr)2]ZnEt (9) was also obtained by mixing ligand 1 with Et2Zn.

Pyrophosphate Complexation of Tin(II) in Aqueous Solutions as Applied in Electrolytes for the Deposition of Tin and Tin Alloys Such as White Bronze

Electrodeposition of tin and tin alloys from electrolytes containing tin(II) and pyrophosphates is an important process in metal finishing, but the nature of the tin pyrophosphate complexes present in these solutions in various pH regions has remained unknown. Through solubility and pH studies, IR and (31)P and (119)Sn NMR spectroscopic investigations of solutions obtained by dissolving Sn(2)P(2)O(7) in equimolar quantities of either Na(4)P(2)O(7)·10H(2)O or K(4)P(2)O(7) the formation of anionic 1:1 complexes {[Sn(P(2)O(7))]}(n)(2n-) has now been verified and the molecular structures of the monomer (n = 1) and the dimer (n = 2) have been calculated by density functional theory (DFT) methods. Whereas the alkali pyrophosphates Na/K(4)P(2)O(7) give strongly alkaline aqueous solutions (pH ∼13), because of partial protonation of the [P(2)O(7)](4-) anion, the [Sn(P(2)O(7))](2-) anion is not protonated and the solutions of Na/K(2)[Sn(P(2)O(7))] are almost neutral (pH ∼8). The monomeric dianion appears to have a ground state with C(2v) symmetry with the Sn atom in a square pyramidal coordination and the lone pair of electrons in the apical position, while the dimer approaches C(2) symmetry with the Sn atoms in a rhombic pyramidal coordination, also with a sterically active lone pair. A comparison of experimental and calculated IR details favors the monomer as the most abundant species in solution. With an excess of pyrophosphate, 3:2 and 2:1 complexes (P(2)O(7)):(Sn) are first formed, which, in the presence of more pyrophosphate, undergo rapid ligand exchange on the NMR time scale. The structure of the 2:1 complex [Sn(P(2)O(7))(2)](6-) was calculated to have a pyramidal complexation by two 1,5-chelating pyrophosphate ligands. Neutralization of these alkaline solutions by sulfuric or sulfonic acids (H(2)SO(4), MeSO(3)H), as also practiced in electroplating, appears to afford the tin(II) hydrogen pyrophosphates [Sn(P(2)O(7)H)](-) and [Sn(H(2)P(2)O(7))](0). The molecular structures of the mononuclear model units have also been calculated and were shown to have an unsymmetrical complexation and to feature trigonal pyramidal (pseudotetrahedral) coordination. NMR observations have shown that, contrary to the results obtained for Sn(II) compounds, Sn(IV) as present in K(2)SnO(3) or its hydrated form (K(2)Sn(OH)(6)) does not form a pyrophosphate complex in aqueous solution near pH 7. There is also no interference of sulfite.

Heterodinuclear Arene Ruthenium Complexes Containing a Glycine-Derived Phosphinoferrocene Carboxamide: Synthesis, Molecular Structure, Electrochemistry, and Catalytic Oxidation Activity in Aqueous Media

Three series of heterodinuclear ruthenium–iron complexes have been synthesized from (η6-arene)ruthenium dichloride dimers and phosphinoferrocene ligands containing glycine-based carboxamido substituents. The neutral complexes [(η6-arene)RuCl2(Ph2PfcCONHCH2CO2Me-κP)] (4, arene = benzene (a), p-cymene (b), hexamethylbenzene (c); fc = ferrocene-1,1′-diyl) were obtained by the bridge cleavage reaction of [(η6-arene)RuCl2]2 with Ph2PfcCONHCH2CO2Me (1) in chloroform solution. The complex [(η6-p-cymene)RuCl2(Ph2PfcCONHCH2CONH2-κP)] (6b) was synthesized in the same way from Ph2PfcCONHCH2CONH2 (3); the preparation of [(η6-p-cymene)RuCl2(Ph2PfcCONHCH2CO2H-κP)] (5b), featuring the ferrocene ligand in the free acid form (2), failed due to side reactions and isolation problems. The salts [(η6-arene)RuCl(MeCN)(1-κP)][PF6] (7a–c) and [(η6-arene)Ru(MeCN)2(1-κP)][PF6]2 (8a–c) were prepared from 1 and the acetonitrile precursors [(η6-arene)RuCl(MeCN)2][PF6] and from 4a–c via halide removal with Ag[PF6] in acetonitrile solution, respectively. Alternative synthetic routes to 7b and 8b were also studied. The compounds were fully characterized by elemental analysis, multinuclear NMR, IR, and electrospray ionization mass spectra, and their electrochemical properties were studied by cyclic voltammetry at a Pt-disk electrode. The single-crystal X-ray analyses of two representatives (4b and 8b) revealed a pseudotetrahedral coordination geometry at the ruthenium centers and eclipsed conformations of the ferrocene moieties, with the substituents at the two cyclopentadienyl rings being anti with respect to each other. All complexes showed high activity for the catalytic oxidation of secondary alcohols with tert-butyl hydroperoxide to give ketones in aqueous media. The most active catalyst was obtained from the neutral p-cymene complex 4b, showing a catalytic turnover frequency of 13 200 h–1 at room temperature for the oxidation of 1-phenylethanol at a substrate/catalyst ratio of 100 000.

Strong Steric Hindrance Effect on Excited State Structural Dynamics of Cu(I) Diimine Complexes

The metal-to-ligand-charge-transfer (MLCT) excited state of Cu(I) diimine complexes is known to undergo structural reorganization, transforming from a pseudotetrahedral D(2d) symmetry in the ground state to a flattened D(2) symmetry in the MLCT state, which allows ligation with a solvent molecule, forming an exciplex intermediate. Therefore, the structural factors that influence the coordination geometry change and the solvent accessibility to the copper center in the MLCT state could be used to control the excited state properties. In this study, we investigated an extreme case of the steric hindrance caused by attaching bulky tert-butyl groups in bis(2,9-di-tert-butyl-1,10-phenanthroline)copper(I), [Cu(I)(dtbp)(2)](+). The two bulky tert-butyl groups on the dtbp ligand lock the MLCT state into the pseudotetrahedral coordination geometry and completely block the solvent access to the copper center in the MLCT state of [Cu(I)(dtbp)(2)](+). Using ultrafast transient absorption spectroscopy and time-resolved emission spectroscopy, we investigated the MLCT state property changes due to the steric hindrance and demonstrated that [Cu(I)(dtbp)(2)](+) exhibited a long-lived emission but no subpicosecond component that was previously assigned as the flattening of the pseudotetrahedral coordination geometry. This suggests the retention of its pseudotetrahedral D(2d) symmetry and the blockage of the solvent accessibility. We made a comparison between the excited state dynamics of [Cu(I)(dtbp)(2)](+) with its mono-tert-butyl counterpart, bis(2-tert-butyl-1,10-phenanthroline)copper(I) [Cu(I)(tbp)(2)](+). The subpicosecond component assigned to the flattening of the D(2d) coordination geometry in the MLCT excited state was again present in the latter because the absence of a tert-butyl on the phenanthroline allows flattening to the pseudotetrahedral coordination geometry. Unlike the [Cu(I)(dtbp)(2)](+), [Cu(I)(tbp)(2)](+) exhibited no detectable emission at room temperature in solution. These results provide new insights into the manipulation of various excited state properties in Cu diimine complexes by certain key structural factors, enabling optimization of these systems for solar energy conversion applications.

Synthesis, characterization, and catalytic properties of new half-sandwich zirconium(iv) complexes

A number of new half-sandwich zirconium(IV) complexes bearing N,N-dimethylaniline-amido ligands with the general formula Cp*ZrCl(2)[ortho-(RNCH(2))(Me(2)N)C(6)H(4)] [R = 2,6-Me(2)C(6)H(3) (1), 2,6-(i)Pr(2)C(6)H(3) (2), (i)Pr (3), (t)Bu (4)] were synthesized by the reaction of Cp*ZrCl(3) with the corresponding ortho-(Me(2)N)C(6)H(4)CH(2)NRLi. All new zirconium complexes were characterized by (1)H and (13)C NMR, elemental analyses and single crystal X-ray diffraction analysis. The molecular structural analysis reveals that the NMe(2) group does not coordinate to the zirconium atom in all cases. Complexes 1-4 all have a pseudo-tetrahedral coordination environment in their solid state structures and adopt a three-legged piano stool geometry for the zirconium atoms with the amide N atom and the two Cl atoms being the three legs and the Cp* ring being the seat. Variable-temperature (1)H NMR experiments for all complexes 1-4 were performed to investigate the possible intramolecular interaction between the N atom in the NMe(2) group and the central zirconium atom in solution. Upon activation with Al(i)Bu(3) and Ph(3)CB(C(6)F(5))(4), complexes 1-4 all exhibit moderate to good catalytic activity for ethylene polymerization and copolymerization with 1-hexene, producing linear polyethylene or poly(ethylene-co-1-hexene) with moderate molecular weight and reasonable 1-hexene incorporation.

An X-ray diffraction, magnetic susceptibility and spectroscopic studies of Yb 2− xCr xO 3

Polycrystalline samples with general formula Yb 2− x Cr x O 3 (0< x<0.03), obtained by sol–gel method and analyzed by X-ray diffraction, formed solid solutions over all the mentioned range. Cr showed a maximum solubility of 2.8 mol% in Yb 2O 3 sesquioxide at 1000 °C. A preferential substitution of Cr 3+ ions over two cationic sites, 8 b and 24 d in the space group Ia-3 was found. The lattice parameters a are found to vary linearly (10.4402(4) Å < a<10.4372(1) Å) with the composition x. The two independent atoms Yb/Cr have octahedral coordination; however, the degrees of distortion of their coordination polyhedron are different. Replacing Yb 3+ by Cr 3+ introduces slight changes in the atomic coordinates leading to an increase of the mean cation-anion distances. The ability of Raman spectroscopy to detect changes in local coordination is utilized. A pseudo-tetrahedral coordination for the Cr 3+ in the 24 d site was found. Magnetic susceptibility measurements of all samples were done in a temperature range of 2–50 K. For T<37 K, the inverse paramagnetic susceptibilities depend linearly on temperature. However, in the high-temperature region, for T>37 K, the inverse paramagnetic susceptibilities are non-linear versus temperature. This deviation from the Curie–Weiss behaviour was discussed.

Methanol oxidation on VSiBEA zeolites: Influence of V content on the catalytic properties

This study deals with the influence of V content on the catalytic properties of V x SiBEA zeolites in the oxidation of methanol. The samples are prepared following a postsynthesis method reported earlier (S. Dzwigaj, M.J. Peltre, P. Massiani, A. Davidson, M. Che, T. Sen, S. Sivasanker, Chem. Commun. (1998) 87). The incorporation of isolated mononuclear V(V) into the framework of SiBEA is evidenced by XRD, FTIR, diffuse reflectance UV–vis and NMR. It is found that, for low V content, V(V) ions are in pseudo-tetrahedral coordination only, either in nonhydroxylated (SiO) 3V O or hydroxylated (SiO) 2(OH)V O species in framework position. For higher V content, additional species appear in extraframework position with vanadium in octahedral coordination. FTIR investigations of pyridine adsorption show that strong Brønsted and Lewis acidic centres are present in SiBEA leading to dimethyl ether only, in methanol oxidation. Upon incorporation of vanadium into the BEA framework, Lewis acidic (V 5+) and basic (O 2−) centres are generated with simultaneous appearance of partial oxidation products mainly, whose total concentration increases with vanadium content. These results suggest that those centres are responsible for the oxidation activity of V x SiBEA zeolites. The selectivity toward formaldehyde increases with the amount of vanadium present as pseudo-tetrahedral hydroxylated (SiO) 2(HO)V O species. This selectivity is suggested to be related to the moderate nucleophilicity of the basic vanadyl oxygen (V O) of (SiO) 2(HO)V O species.

Oxazoles XXII. The Cobalt(II) Coordination Chemistry of 2-(ortho-Anilinyl)-4,4-dimethyl-2-oxazoline: Syntheses, Properties, and Solid-State Structural Characterization

Ethanol solutions of the cobalt(ii) halides react with an excess of 2-(ortho-anilinyl)-4,4-dimethyl-2-oxazoline (1: i.e. 2-(2′-anilinyl)-4,4-dimethyl-4,5-dihydro-1,3-oxazole) to give isolable κ2-N,N′-bonded species of 1 in good to excellent yields. The complexes CoX2(1-κ2-N,N′)·(H2O) n have been isolated for X = Cl (2: n = 1/2), X = Br and I (3 and 4, respectively; n = 0); the solid-state structures (X-ray) are in accordance with those suggested by UV-visible spectroscopy and conductivity measurements (i.e. non-ionic complexes with a pseudo-tetrahedral coordination motif around Co). In contrast, reaction of excess 1 with Co(NCS)2 forms the octahedral (UV-visible, X-ray) bis-isothiocyanato complex Co(NCS-κ1-N′)2(1-κ2-N,N′)2 (5) with cis-oriented NCS groups and trans-disposed oxazolines. Calculations at the PM3(tm) level of theory suggest that this isomer is close in energy to the four other possible (gas-phase) isomers. Treatment of ethanol solutions of hydrated cobaltous nitrate with excess 1 yields a material analyzed as [Co(NO3)(1)(H2O)2](NO3) (6a) and a small amount (less than 1%) of a second complex (6b); the latter has been characterized (X-ray) as the hydrated octahedral complex [Co(NO3-κ1-O)(1-κ2-N,N′)2(OH2)](NO3). In this case, the nitrato and aqua groupings are located cis to one another and trans to the coordinated –NH2 groups. Complex 6a is surmised to have a [Co(NO3-κ2-O,O′)2(1-κ2-N,N′)(OH2)2]NO3 structure. Cobalt compounds 2–5 and 1 have also been screened for their antifungal properties against Aspergillus niger, Aspergillus flavus, Candida albicans, and Saccharomyces cerevisiae but were found to be inactive in this regard.

A Multifrequency High-Field Electron Paramagnetic Resonance Study of CoIIS4Coordination

Advanced electron paramagnetic resonance (EPR) methods have been employed in the study of two high-spin cobalt(II) complexes, Co[(SPPh(2))(2)N](2) (Co(Ph,Ph)L(2)) and Co[(SPPh(2))(SP(i)Pr(2))N](2) (Co(iPr,Ph)L(2)), in which the bidentate disulfidoimidodiphosphinato ligands make up for a pseudotetrahedral sulfur coordination of the transition metal. The CoS(4) core in the two complexes has slightly different structure, owing to the different peripheral groups (phenyl or isopropyl) bound to the phosphorus atoms. To determine the zero-field splitting, notoriously difficult for high-spin cobalt(II), the two complexes required different approaches. For Co(Ph,Ph)L(2), the study of the X-band EPR spectrum of a single crystal as a function of temperature revealed a nearly axial character of the zero-field splitting (ZFS; E/D approximately -0.05). For Co(iPr,Ph)L(2), the combination of the EPR spectra at 9, 95, and 275 GHz revealed a rhombic character of the ZFS (E/D approximately -0.33). The energy difference between the Kramers doublets in Co(Ph,Ph)L(2) and Co(iPr,Ph)L(2) amounts to 24 cm(-1) and 30 cm(-1), respectively. From the X-band EPR spectra of diamagnetically diluted single crystals at fields up to 2.5 T for Co(Ph,Ph)L(2) and 0.5 T for Co(iPr,Ph)L(2), the effective g tensors and cobalt hyperfine tensors have been determined, including the direction of the principal axes in the cobalt sites. The values of the EPR observables are discussed in relation to the structural characteristics of the first (CoS(4)) and second coordination sphere in the complexes.

Structural and vibrational study of C-type doped rare earth sesquioxide Yb 2− xCo xO 3

Polycrystalline samples with general formula Yb 2− x Co x O 3 (0 < x < 0.6), obtained by sol–gel method and analysed by X-ray diffraction, formed solid solutions over all the mentioned range. Co showed a maximum solubility of 30 mol% in Yb 2O 3 sesquioxide. The lattice parameters are found to vary linearly with the composition x. The cationic distribution over the two non-equivalent sites 8b and 24d of the space group Ia−3 is found to be preferentially. Replacing Yb 3+ by Co 3+ introduces slight changes in the atomic coordinates leading to an increase of the mean cation–anion distances. The ability of Raman spectroscopy to detect changes in local co-ordination is utilized. A pseudo-tetrahedral coordination for the Co 3+ in the 24d site was found.

Reductive Activation oftripodMetal Compounds: Preparative Application

AbstractThetripodnickel(0) species [tripod4Ni3] (1) {tripod= CH3C(CH2PPPh2)3} is shown to undergo oxidative addition with disulfides or diselenides REER (E = S, Se, R =tBu, Ph) to produce [tripodNi(ER)] (2). Compounds2show pseudo tetrahedral coordination. They are paramagnetic with one unpaired electron per molecule. Their magnetic behaviour is almost that of an ideal Curie‐type magnet down to temperatures of 2 K. They undergo reversible one electron oxidation to the 16 valence electron species [tripodNi(ER)]+. The isoelectronic pseudo tetrahedral 16 valence electron cobalt species [tripodCo(ER)] (3) are obtained by reduction of CoCl2with KC8in the presence oftripodand subsequent reaction with REER (E = S, Se; R =tBu, Ph). They are paramagnetic with two unpaired electrons per molecule. They can be reversibly oxidised to the 15 valence electron compounds [tripodCo(ER)]+while their reduction to the 17 valence electron species [tripodCo(ER)]–, which would be isoelectronic to the stable compounds2, is not observed. Under appropriate conditions the reactions with REER do not result in the formation of3but yield [tripodCoECotripod] (4) by extrusion of sulfur and selenium from the substrate. Compounds4show a linear Co–E–Co framework with very short Co–E bonds (E = S: 205 pm; E = Se: 216 pm). They are members of a family of dimetallaheterocumulenic compounds [LnMEMLn] (E = main group element of groups III to VI) with a valence electron count of 36 electrons. Quantum chemistry predicts that the HOMO of such compounds should be a degenerated pair of mainly metal centred orbitals. Electrochemistry of4a, [tripodCoSCotripod], shows three quasi‐reversible oxidation steps in the range of –700 mV vs. SCE to 570 mV vs. SCE, which can be understood as metal centred oxidations. Three different types of crystals have been obtained for different types of pseudopolymorphs4a. The geometric parameters of the coordination compounds are almost equal in these pseudopolymorphic crystals. The real difference is the content of solvent molecules and, hence, the packing of the molecules. In the crystals of4acontaining no solvent the coordination compounds form close packed layers stacked on each other in an oblique way. In the crystals containing4a·DME a layer of solvent molecules separates each pair of layers of close packed molecules. In the crystal of4a·3DME a cuboctahedral cage of solvent molecules embedding each coordination compound separates the complex molecules from each other. The different types of crystals observed underpin the globular shape of4and the effective shielding power of thetripodligand. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2008)

Heterotrimetallic and heterotetrametallic transition metal complexes

The synthesis of the ruthenium σ-acetylides (η 5-C 5H 5)L 2Ru–C C–bipy ( 4a, L = PPh 3; 4b, L 2 = dppf; bipy = 2,2′-bipyridine-5-yl; dppf = 1,1′-bis(diphenylphosphino)ferrocene) is possible by the reaction of [(η 5-C 5H 5)L 2RuCl] ( 1) with 5-ethynyl-2,2′-bipyridine ( 2a) in the presence of NH 4PF 6 followed by deprotonation with DBU. Heterobimetallic Fc–C C–NCN–Pt–C C–R ( 10a, R = bipy; 10b, R = C 5H 4N-4; Fc = (η 5-C 5H 5)(η 5-C 5H 4)Fe; NCN = [1,4-C 6H 2(CH 2NMe 2) 2-2,6] −) is accessible by the metathesis of Fc–C C–NCN–PtCl ( 9) with lithium acetylides LiC C–R ( 2a, R = bipy; 2b, R = C 5H 4N-4).The complexation behavior of 4a and 4b was investigated.Treatment of these molecules with [MnBr(CO) 5] ( 13) and {[Ti](μ–σ,π-C CSiMe 3) 2}MX ( 15a, MX = Cu(N CMe)PF 6; 15b, MX = Cu(N CMe)BF 4; 16, MX = AgOClO 3; [Ti] = (η 5-C 5H 4SiMe 3) 2Ti), respectively, gave the heteromultimetallic transition metal complexes (η 5- C 5H 5)L 2Ru–C C–bipy[Mn(CO) 3Br] ( 14a: L = PPh 3; 14b: L 2 = dppf) and [(η 5-C 5H 5)L 2Ru–C C–bipy{[Ti](μ–σ,π-C CSiMe 3) 2}M]X ( 17a: L = PPh 3, M = Cu, X = BF 4; 17b: L 2 = dppf, M = Cu, X = PF 6; 18a: L = PPh 3, M = Ag, X = ClO 4; 18b: L 2 = dppf, M = Ag, X = ClO 4) in which the appropriate transition metals are bridged by carbon-rich connectivities. The solid-state structures of 4b, 10b, 12 and 17b are reported. The main structural feature of 10b is the square-planar-surrounded platinum(II) ion and its linear arrangement. In complex 12 the N-atom of the pendant pyridine unit coordinates to a [ mer, trans-( NN′ N)RuCl 2] ( NN′ N = 2,6-bis-[(dimethylamino)methyl]pyridine) complex fragment, resulting in a distorted octahedral environment at the Ru(II) centre. In 4b a 1,1′-bis(diphenylphosphino)ferrocene building block is coordinated to a cyclopentadienylruthenium-σ-acetylide fragment. Heterotetrametallic 17b contains a (η 5-C 5H 5)(dppf)Ru–C C–bipy unit, the bipyridine entity of which is chelate-bonded to [{[Ti](μ–σ,π-C CSiMe 3) 2}Cu] +. Within this arrangement copper(I) is tetra-coordinated and hence, possesses a pseudo-tetrahedral coordination sphere. The electrochemical behavior of 4, 10b, 12, 17 and 18 is discussed. As typical for these molecules, reversible oxidation processes are found for the iron(II) and ruthenium(II) ions. The attachment of copper(I) or silver(I) building blocks at the bipyridine moiety as given in complexes 17 and 18 complicates the oxidation of ruthenium and consequently the reduction of the group-11 metals is made more difficult, indicating an interaction over the organic bridging units. The above described complexes add to the so far only less investigated class of compounds of heteromultimetallic carbon-rich transition metal compounds.