QTAIM analysis of the bonding in Mo-Mo bonded dimolybdenum complexes

A number of local and integral topological parameters of the electron density of relevant bonding interactions in the binuclear molybdenum complexes [Mo(2)Cl(8)](4-), [Mo(2)(μ-CH(3)CO(2))(4)], [Mo(2)(μ-CF(3)CO(2))(4)], [Mo(2)(μ-CH(3)CO(2))(4)Br(2)](2-), [Mo(2)(μ-CF(3)CO(2))(4)Br(2)](2-), [Mo(2)(μ-CH(3)CO(2))(2)Cl(4)](2-), [Mo(2)(μ-CH(3)CO(2))(2)(μ-Cl)(2)Cl(4)](2-), and [Mo(2)(μ-Cl)(3)Cl(6)](3-) have been calculated and interpreted under the perspective of the quantum theory of atoms in molecules (QTAIM). These data have allowed a comparison between related but different atom-atom interactions, such as different Mo-Mo formal bond orders, ligand-unbridged versus Cl-bridged, CH(3)CO(2)-bridged, and CF(3)CO(2)-bridged Mo-Mo interactions, and Mo-Cl(terminal) and Mo-Cl(bridge) versus Mo-Br and Mo-O interactions. Calculations carried out using nonrelativistic and relativistic approaches afforded similar results.     

“Breathing” in Adsorbate‐Responsive Metal Tetraphosphonate Hybrid Materials

Breathe easy : Reversible H₂O and NH₃ gas uptake by 2D calcium tetraphosphonates (see figure) is accompanied by framework structural changes similar to those previously reported for some carboxylate‐based hybrids. This breathing mechanism is accompanied by a volume increase of 55 %, while maintaining the topology and crystallinity of the material.

     

Cationic Heterocycles as Ligands: Synthesis and Reactivity with Anionic Nucleophiles of Cationic Triruthenium Clusters Containing C‐Metalated N‐Methylquinoxalinium or N‐Methylpyrazinium Ligands

The cationic cluster complexes [Ru₃(CO)₁₀(μ‐H)(μ‐κ²N,C‐L¹Me)]⁺ ( 3 ⁺; HL¹=quinoxaline) and [Ru₃(CO)₁₀(μ‐H)(μ‐κ²N,C‐L²Me)]⁺ ( 5 ⁺; HL²=pyrazine) have been prepared as triflate salts by treatment of their neutral precursors [Ru₃(CO)₁₀(μ‐H)(μ‐κ²N,C‐Lⁿ)] with methyl triflate. The cationic character of their heterocyclic ligands is responsible for their enhanced tendency to react with anionic nucleophiles relative to that of hydrido triruthenium carbonyl clusters that have neutral N‐heterocyclic ligands. These clusters react instantaneously with methyl lithium and potassium tris‐sec‐butylborohydride (K‐selectride) to give neutral products that contain novel nonaromatic N‐heterocyclic ligands. The following are the products that have been isolated: [Ru₃(CO)₉(μ‐H)(μ₃‐κ²N,C‐L¹Me₂)] ( 6 ; from 3 ⁺ and methyl lithium), [Ru₃(CO)₉(μ‐H)(μ₃‐κ²N,C‐L¹HMe)] ( 7 ; from 3 ⁺ and K‐selectride), [Ru₃(CO)₉(μ‐H)(μ₃‐κ²N,C‐L²Me₂)] ( 8 ; from 5 ⁺ and methyl lithium), and [Ru₃(CO)₉(μ‐H)(μ₃‐κ²N,C‐L²HMe)] ( 11 ; from 5 ⁺ and K‐selectride). Whereas the reactions of 3 ⁺ lead to products that arise from the attack of the corresponding nucleophile at the C atom of the only CH group adjacent to the N‐methyl group, the reactions of 5 ⁺ give mixtures of two products that arise from the attack of the nucleophile at one of the C atoms located on either side of the N‐methyl group. The LUMOs and the atomic charges of 3 ⁺ and 5 ⁺ confirm that the reactions of these clusters with anionic nucleophiles are orbital‐controlled rather than charge‐controlled processes. The N‐heterocyclic ligands of all of these neutral products are attached to the metal atoms in nonconventional face‐capping modes. Those of compounds 6 – 8 have the atoms of a ligand C?N fragment σ‐bonded to two Ru atoms and π‐bonded to the other Ru atom, whereas the ligand of compound 11 has a C? N fragment attached to a Ru atom through the N atom and to the remaining two Ru atoms through the C atom. A variable‐temperature ¹H NMR spectroscopic study showed that the ligand of compound 7 is involved in a fluxional process at temperatures above ?93 °C, the mechanism of which has been satisfactorily modeled with the help of DFT calculations and involves the interconversion of the two enantiomers of this cluster through a conformational change of the ligand CH₂ group, which moves from one side of the plane of the heterocyclic ligand to the other, and a 180° rotation of the entire organic ligand over a face of the metal triangle.     

Reactions of Late First-Row Transition Metal (Fe-Zn) Dichlorides with a PGeP Pincer Germylene

The reactivity of the PGeP germylene 2,2’-bis(di-isopropylphosphanylmethyl)-5,5’-dimethyldipyrromethane-1,1’-diylgermanium(II), Ge(pyrmPiPr₂)₂CMe₂, with late first-row transition metal (Fe-Zn) dichlorides has been investigated. All reactions led to PGeP pincer chloridogermyl complexes. The reactions with FeCl₂ and CoCl₂ afforded paramagnetic square planar complexes of formula [MCl{κ³P,Ge,P-GeCl(pyrmPiPr₂)₂CMe₂}] (M=Fe, Co). While the iron complex maintained an intermediate spin state (S¹; μ_eff=3.0 μ_B) over the temperature range 50–380 K, the effective magnetic moment of the cobalt complex varied linearly with temperature from 1.9 μ_B at 10 K to 3.6 μ_B at 380 K, indicating a spin crossover behavior that involves S^1/2 (predominant at T<180 K) and S^3/2 (predominant at T>200 K) species. Both cobalt(II) species were detected by electron paramagnetic resonance at T<20 K. The reaction of Ge(pyrmPiPr₂)₂CMe₂ with [NiCl₂(dme)] (dme=dimethoxyethane) gave a square planar nickel(II) complex, [NiCl{κ³P,Ge,P-GeCl(pyrmPiPr₂)₂CMe₂}], whereas the reaction with CuCl₂ involved a redox process that rendered a mixture of the germanium(IV) compound GeCl₂(pyrmPiPr₂)₂CMe₂ and a binuclear copper(I) complex, [Cu₂{μ-κ³P,Ge,P-GeCl(pyrmPiPr₂)₂CMe₂}₂], whose metal atoms are in tetrahedral environments. The reaction of the germylene with ZnCl₂ led to the tetrahedral derivative [ZnCl{κ³P,Ge,P-GeCl(pyrmPiPr₂)₂CMe₂}].     

Coordination of the natural ligand lapachol to iron(II): synthesis,theoretical study and antiproliferative activity

Transition Metal Chemistry - Lapachol is a natural naphthoquinone known for having a variety of biological properties, and in recent years, it has been used in the synthesis of metal complexes with...     

Reactivity of alkynes containing alpha-hydrogen atoms with a triruthenium hydrido carbonyl cluster: alkenyl versus allyl cluster derivatives

The reactions of the hydrido-triruthenium cluster complex [Ru3(mu-H)(mu3-kappa(2)-HNNMe2)(CO)9] (1; H2NNMe2 = 1,1-dimethylhydrazine) with alkynes that have alpha-hydrogen atoms give trinuclear derivatives containing edge-bridging allyl or face-capping alkenyl ligands. Under mild conditions (THF, 70 degrees C) the isolated products are as follows: [Ru3(mu3-kappa(2)-HNNMe2)(mu-kappa(3)-1-syn-Me-3-anti-EtC3H3)(mu-CO)2(CO)6] (2) and [Ru3(mu3-kappa(2)-HNNMe2)(mu-kappa(3)-1-syn-Me-3-syn-EtC3H3)(mu-CO)2(CO)6] (3) from 3-hexyne; [Ru3(mu3-kappa(2)-HNNMe2)(mu-kappa(3)-3-anti-PhC3H4)(mu-CO)2(CO)6] (4), [Ru3(mu3-kappa(2)-HNNMe2)(mu-kappa(2)-MeCCHPh)(mu-CO)2(CO)6] (5) and [Ru3(mu3-kappa(2)-HNNMe2)(mu3-kappa(2)-PhCCHMe)(mu-CO)2(CO)6] (6) from 1-phenyl-1-propyne; [Ru3(mu3-kappa(2)-HNNMe2)(mu-kappa(2)-3-anti-PrC3H4)(mu-CO)2(CO)6] (7), [Ru3(mu3-kappa(2)-HNNMe2)(mu3-kappa(2)-BuCCH2)(mu-CO)2(CO)6] (8), and [Ru3(mu3-kappa(2)-HNNMe2)(mu3-kappa(2)-HCCHBu)(mu-CO)2(CO)6] (9) from 1-hexyne; [Ru3(mu3-kappa(2)-HNNMe2)(mu3-kappa(2)-HOH2CCCH2)(mu-CO)2(CO)6] (10) from propargyl alcohol; and [Ru3(mu3-kappa(2)-HNNMe2)(mu3-kappa(2)-MeOCH2CCH2)(mu-CO)2(CO)6] (11) from 3-methoxy-1-propyne. The regioselectivity of these reactions depends upon the nature of the alkyne reagent, which affects considerably the kinetic barriers of important reaction steps and the stability of the final products. It has been established that the face-capped alkenyl derivatives are not precursors to the allyl products, which are formed via edge-bridged alkenyl intermediates. At higher temperature (toluene, 110 degrees C), the complexes that have allyl ligands with an anti substituent are isomerized into allyl derivatives with that substituent in the syn position, for example, 4 into [Ru3(mu3-kappa(2)-HNNMe2)(mu-kappa(3)-3-syn-PhC3H4)(mu-CO)2(CO)6] (14). The diene complex [Ru3(mu-H)(mu3-kappa(2)-HNNMe2)(mu-kappa(4)-trans-EtC4H5)(CO)7] (13) has been obtained from the thermolysis of compounds 2 and 7 at 110 degrees C (3 and [Ru3(mu3-kappa(2)-HNNMe2)(mu-kappa(2)-3-syn-PrC3H4)(mu-CO)2(CO)6] (12) are also formed in these reactions). A DFT theoretical study has allowed a comparison of the thermodynamic stabilities of isomeric compounds and has helped rationalize the experimental results. Mechanistic proposals for the synthesis of the allyl complexes and their isomerization processes are also provided.     

Creatinine determination in urine samples by batchwise kinetic procedure and flow injection analysis using the Jaffé reaction: chemometric study

The classical Jaffé reaction for the determination of creatinine in urine samples is tested. A comparative study of the main analytical characteristics focussed to minimize the bias error and improve the precision, for the batchwise and flow injection (FI) methods is realized. Also, the effect of the albumin concentration in the determination of creatinine has been studied. Different analytical signals were studied. Absorbance increments at different times permit to estimate the creatinine concentration free from bias error in urine by the batchwise method using the calibration graph obtained with creatinine standards and no measurement of the blank solution is needed. The lineal interval was 0.92-50 mg l(-1) and seven samples can be processed per hour by an operator. No previous treatment of the urine sample is necessary. The FI method provides also good results. The lineal interval was 30-100 mg l(-1) and the sample rate was around 20 samples per hour. If increased albumin levels are detected in the urine, standard addition method or the calibration graphs with standards in presence of albumin are needed in order to obtain accurate results when FI method is employed. The obtained accuracy of the both methods allows its application as diagnostic tool to establish the urinary creatinine levels.     

Photolysis of diruthenium hexacarbonyl tetrahedrane compounds in Nujol glass matrices

The photochemistry of five diruthenium hexacarbonyl tetrahedrane compounds, Ru₂(CO)₆(μ-S₂C₆H₄) (1), Ru₂(CO)₆(μ-S₂C₂H₄) (2), Ru₂(CO)₆(μ-S₂C₃H₆) (3), Ru₂(CO)₆(μ-SCH₂CH₃)₂ (4), and Ru₂(CO)₆(μ-dmpz)₂, (5), where dmpz=3,5-dimethylpyrazolate, have been examined in frozen Nujol glasses at ca. 90 K. Compounds 1-4 are found to lose CO upon UV photolysis to form two isomeric photoproducts, while 5 is found to form one product almost exclusively. The various photoproducts are assigned to axial and equatorial CO-loss species on the basis of the spectra of analogous triphenylphosphine pentacarbonyl derivatives.     

Structure of trihydrated rare-earth acid diphosphates LnHP2O7·3H2O (Ln=La, Er)

In trihydrated lanthanum acid-diphosphates LnHP₂O₇·3H₂O, prepared from acid LnCl₃ and Na₄P₂O₇ solutions (pH=1), two crystal forms were obtained. Layered structures of two representative members of this family have been determined by single-crystal X-ray diffraction (XRD) technique. In the case of orthorhombic LaHP₂O₇·3H₂O (type I), lanthanum cations are ninefold coordinated and diphosphate groups adopt a staggered (alternated) configuration. In the case of triclinic ErHP₂O₇·3H₂O (type II), erbium cations are eightfold coordinated and diphosphate groups adopt an eclipsed configuration. In agreement with Infrared (IR) spectroscopic data, a bended configuration for diphosphate groups has been deduced. In both structures, one-dimensional chains of edge-sharing rare-earth polyhedra are linked together by diphosphate groups to form the phosphate layers. In both diphosphates, PO₄ and HPO₄ environments have been identified by ³¹P MAS-NMR technique. In the two compounds, OH groups of HPO₄ tetrahedra point out of diphosphate planes interacting with adjacent layers. In La-diphosphate, the interaction between HPO₄ groups and water molecules of adjacent layers is favored; however, in Er-diphosphate, the interaction between phosphate acid groups of contiguous layers is produced. Based on structural information deduced, differences detected in IR and NMR spectra of two disphosphates are discussed.