Utility of all-pyrazole heteroscorpionates in f-element chemistry.

Since their discovery in 1966, scorpionate ligands have been utilized to make coordination compounds for a variety of applications such as: studying organometallic reactions, biomimetic complexes, light-emitting materials and single-ion magnets. The recent development of a solvent-free pyrazole substitution chemistry has yielded the quantitative synthesis of asymmetrically functionalized all-pyrazole heteroscorpionate ligands. In this frontier article, we highlight the utility of all-pyrazole heteroscorpionates, specifically, nitro-trispyrazolylborates, in f-element chemistry.

Tuning the optical and magnetic properties of lanthanide single-ion magnets using nitro-functionalized trispyrazolylborate ligands.

We report the synthesis, crystal structures, photophysical and magnetic properties of 11 novel lanthanide complexes with the asymmetrically functionalized trispyrazolylborate ligand 4-nitrotrispyrazolylborate, 4-NOTp: [Ln(4-NOTp)] (Ln = La-Dy, except Pm). In-depth photophysical characterization of the ligands luminescence, reflectance and absorption spectroscopic techniques, decay lifetimes, quantum yields supported by time-dependent density functional theory (TD-DFT) and natural bond order (NBO) analysis reveal that -NOTp ligands are dominated by intra-ligand charge transfer (ILCT) transitions and that second-sphere interactions are critical to the stabilization of the T state of -NOTp ligands and hence their ability to sensitize Ln emission. The luminescence properties of the complexes indicate that 4-NOTp is a poor sensitizer of Ln emission, unlike 3-NOTp.

Magnetic properties of coordination clusters with {Mn} and {Co} antiferromagnetic cores.

We present a joint experimental and theoretical characterization of the magnetic properties of coordination clusters with an antiferromagnetic core of four magnetic ions. Two different compounds are analyzed, with Co and Mn ions in the core. While both molecules are antiferromagnetic, they display different sensitivities to external magnetic field, according to the different atomic magnetic moments and strength of the intra-molecular magnetic couplings.

Precise control of the degree and regioselectivity of functionalization in nitro- and amino-functionalized di(trispyrazolylborato)iron(II) spin crossover complexes.

Di(trispyrazolylborato)iron(II) ([TpFe]) complexes represent one of the most robust classes of spin-crossover complexes. Their stability renders them particularly suitable for integration in nanoscale devices, as sensors or information storage units. While prior studies of the functionalization of those derivatives have been focused on the electronic and steric effects of alkyl and -CF groups in position 3, a pyrazole exchange reaction between nitropyrazole and either trispyrazolylborate or its iron complex allows the regioselective installation of nitro substituents in positions 3, 4 and 5 of the [TpFe] complexes.

Structural Diversity of Lanthanide 3-Nitrotrispyrazolylborates: Tunable Nuclearity and Intra-Ligand Charge Transfer Sensitization of Visible and NIR Ln Emission.

Reported are the syntheses, crystal structures, and photophysical properties of 28, novel lanthanide compounds across five structural types, [Ln(3-NOTp)(NO)] (-Ln, Ln = La-Tm, except Pm), [BuN][Ln(3-NOTp)(NO)] (-Ln, Ln = Yb, Lu), [Eu(3-NOTp)Cl(HO)]·2PrOH (-Eu), [{Ln(3-NOTp)}(μ-CO)]·MeOH (-Ln, Ln = La-Gd, except Pm), and [{Ln(3-NOTp)}(μ-OMe)(μ-O)] (-Ln, Ln = Pr-Tb, except Pm) with the 3-nitrotrispyrazolylborate (3-NOTp) ligand. The reaction of methanol or isopropanol solutions of LnX (X = Cl, NO) with the tetrabutyl ammonium salt of the flexidentate 3-NOTp ([BuN][3-NOTp]) yields Ln(3-NOTp) complexes of various nuclearities as either monomers (-Ln, -Ln, -Eu), dimers (-Ln), or tetramers (-Ln) owing to the efficient conversion of atmospheric CO to CO (dimers) or ligand controlled solvolysis of lanthanide ions (tetramers). 3-NOTp is an efficient sensitizer for both the visible and near-IR (NIR) emissions of most of the lanthanide series, except thulium.

Amine-Functionalized Spin Crossover Building Blocks.

Bistable spin crossover complexes such as [Fe{HB(pz)}] (pzH = pyrazole) show promise for sensor applications and electrically-controlled data storage units, but exploiting their potential hinges on their integration into a functional environment. We here present a system enabling such covalent post-functionalization steps in both symmetric and asymmetric patterns, based on the amine-functionalized complex [Fe{HB(4-NHpz)(pz)}], obtained by reduction of the nitro analogue. The building block aspects of [Fe{HB(4-NHpz)(pz)}] are showcased by its transformation into amide, imine and azo derivatives, which are structurally and magnetically characterized.

Kinetics and Mechanism of Pyrrolidine Buffer-Catalyzed Fulvene Formation.

Rapid synthesis of fulvenes is achieved using pyrrolidinium/pyrrolidine buffers in anhydrous acetonitrile. Time-dependent UV-vis absorption and NMR spectroscopy reveal that the rate and yield of fulvene formation depend strongly on both the presence of acid in the medium and the choice of solvent, and they are negatively affected by water. Kinetic data have been collected for various substrates, and the synthetic benefits of the adjusted reaction conditions are showcased.

An Ir(IV)-containing polyoxometalate.

[HIr(IV)W6O24](7-), representing the first Ir-containing Anderson-Evans-type polyanion and the first structurally characterized Ir(IV)-based polyoxometalate, has been isolated as its hydrated sodium salt and characterized by single-crystal X-ray diffraction, mass spectrometry, and IR, UV-Vis and EPR spectroscopy. Cyclic voltammetry indicates that the Ir(IV) ions in [HIrW6O24](7-) can undergo reversible one-electron reduction and oxidation, resulting in Ir(III) and Ir(V) derivatives.

Supramolecular recognition influences magnetism in [X@HV(IV) 8 V(V) 14 O54 ](6-) self-assemblies with symmetry-breaking guest anions.

Mixed-valence polyoxovanadates(IV/V) have emerged as one of the most intricate class of supramolecular all-inorganic host species, able to encapsulate a wide variety of smaller guest templates during their self-assembly formation process. As showcased herein, the incorporation of guests, though governed solely by ultra-weak electrostatic and van der Waals interactions, can cause drastic effects on the electronic and magnetic characteristics of the shell complex of the polyoxovanadate. We address the question of methodology for the magnetochemical analysis of virtually isostructural {V(IV/V) 22 O54 }-type polyoxoanions of D2d symmetry enclosing diamagnetic VO2 F2 (-) (C2v ), SCN(-) (C∞v ), or ClO4 (-) (Td ) template anions.

Accessing 4f-states in single-molecule spintronics.

Magnetic molecules are potential functional units for molecular and supramolecular spintronic devices. However, their magnetic and electronic properties depend critically on their interaction with metallic electrodes. Charge transfer and hybridization modify the electronic structure and thereby influence or even quench the molecular magnetic moment.

Base-catalyzed synthesis of substituted indazoles under mild, transition-metal-free conditions.

Back to basics: A transition-metal-free method developed for the synthesis of indazoles involves an inexpensive catalytic system composed of a diamine and K2CO3. Various (Z)-2-bromoacetophenone tosylhydrazones were converted into indazoles at room temperature in excellent yields (see example; Ts = p-toluenesulfonyl). The yield was improved by photoisomerization with UV light when E/Z isomeric mixtures of the starting material were used.

A regioselective Huisgen reaction inside a Keplerate polyoxomolybdate nanoreactor.

A 1,3-dipolar cycloaddition reaction taking place quantitatively between propiolic acid "guests" and azide functions previously attached to binding sites within the cavity of a {Mo(132)}-type Keplerate reproducibly gives a 2 : 1 ratio of 1,4- and 1,5-triazoles.

Chiral hexanuclear ferric wheels.

The homochiral iron(III) wheels [Fe(6){(S)-pedea}(6)Cl(6)] and [Fe(6){(R)-pedea)}(6)Cl(6)] [(R)- and (S)-2; pedea = phenylethylaminodiethoxide] exhibit high optical activities and antiferromagnetic exchange. These homochiral products react with each other, producing the centrosymmetric, crystallographically characterized [Fe(6){(S)-pedea}(3){(R)-pedea}(3)Cl(6)] diastereomer [(RSRSRS)-2]. (1)H NMR and UV-vis studies indicate that exchange processes are slow in both homo- and heterochiral systems but that, upon combination, the reaction between (R)- and (S)-2 occurs quickly.

Addition of N-heterocyclic carbenes to a ruthenium(VI) nitrido polyoxometalate: a new route to cyclic guanidines.

The scope of N-atom transfer from the electrophilic ruthenium(VI) nitrido containing polyoxometalate [PW(11)O(39)Ru(VI)N](4-) has been extended to the N-heterocyclic carbene {CH(2)(Mes)N}(2)C and the coupling product {CH(2)(Mes)N}(2)CNH(2)(+) characterized by (1)H NMR and high-resolution mass spectrometry. Because guanidines display many fields of applications ranging from biology to supramolecular chemistry, this could afford an original route to the synthesis of cyclic guanidines. This also enlarges the potential of nitrido complexes in the synthesis of heterocycles, mainly illustrated in the literature through the formation of aziridines through N-atom transfer to alkenes.

Cs(9)[(gamma-PW(10)O(36))(2)Ru(4)O(5)(OH)(H(2)O)(4)], a new all-inorganic, soluble catalyst for the efficient visible-light-driven oxidation of water.

The tetraruthenium-substituted polyoxometalate Cs(9)[(gamma-PW(10)O(36))(2)Ru(4)O(5)(OH)(H(2)O)(4)] was synthesized and structurally, spectroscopically and electrochemically characterized; it was shown to be a catalyst for visible-light-induced water oxidation.

A fast soluble carbon-free molecular water oxidation catalyst based on abundant metals.

Traditional homogeneous water oxidation catalysts are plagued by instability under the reaction conditions. We report that the complex [Co4(H2O)2(PW9O34)2]10-, comprising a Co4O4 core stabilized by oxidatively resistant polytungstate ligands, is a hydrolytically and oxidatively stable homogeneous water oxidation catalyst that self-assembles in water from salts of earth-abundant elements (Co, W, and P). With [Ru(bpy)3]3+ (bpy is 2,2'-bipyridine) as the oxidant, we observe catalytic turnover frequencies for O2 production > or = 5 s(-1) at pH = 8.

Computational studies of the geometry and electronic structure of an all-inorganic and homogeneous tetra-Ru-polyoxotungstate catalyst for water oxidation and its four subsequent one-electron oxidized forms.

Geometry and electronic structure of five species [{Ru(4)O(4)(OH)(2)(H(2)O)(4)}(gamma-SiW(10)O(36))(2)](10-) (1), [{Ru(4)O(4)(OH)(2)(H(2)O)(4)}(gamma-SiW(10)O(36))(2)](9-) (2), [{Ru(4)O(4)(OH)(2)(H(2)O)(4)}(gamma-SiW(10)O(36))(2)](8-) (3), [{Ru(4)O(4)(OH)(2)(H(2)O)(4)}(gamma-SiW(10)O(36))(2)](7-) (4), and [{Ru(4)O(4)(OH)(2)(H(2)O)(4)}(gamma-SiW(10)O(36))(2)](6-) (5) with different oxidation states of Ru centers were studied at the density functional and COSMO levels of theory. These species are expected to be among the possible intermediates of the recently reported 1-catalyzed water oxidation (Geletii, Y. V.

Structural, physicochemical, and reactivity properties of an all-inorganic, highly active tetraruthenium homogeneous catalyst for water oxidation.

Several key properties of the water oxidation catalyst Rb(8)K(2)[{Ru(IV)(4)O(4)(OH)(2)(H(2)O)(4)}(gamma-SiW(10)O(36))(2)] and its mechanism of water oxidation are given. The one-electron oxidized analogue [{Ru(V)Ru(IV)(3)O(6)(OH(2))(4)}(gamma-SiW(10)O(36))(2)](11-) has been prepared and thoroughly characterized. The voltammetric rest potentials, X-ray structures, elemental analysis, magnetism, and requirement of an oxidant (O(2)) indicate these two complexes contain [Ru(IV)(4)O(6)] and [Ru(V)Ru(IV)(3)O(6)] cores, respectively.

Vicinal dinitridoruthenium-substituted polyoxometalates gamma-[XW10O38{RuN}2]6- (X = Si or Ge).

Reaction of the divacant polyoxometalate K(8)[gamma-XW(10)O(36)] (X = Si, Ge) with two equivalents of the metal-nitrido precursor Cs(2)[Ru(VI)NCl(5)], at room temperature in water, produces K(2)(Me(2)NH(2))(2)H(2)[gamma-XW(10)O(38){RuN}(2)], X = Si (DMA-1 a) or Ge (DMA-1 b). The X-ray crystal structures of both complexes show monomeric complexes with highly unusual vicinal terminal metal-nitrido units. The Ru[triple bond]N bond lengths are 1.

Nitrogen-atom transfer from [PW11O39Ru(VI)N]4- to PPh3.

The nitrido derivative (n-Bu(4)N)(4)[PW(11)O(39)Ru(VI)N] transfers its nitrogen atom to triphenylphosphine to give quantitatively the bis(triphenylphosphane)iminium cation [Ph(3)PNPPh(3)](+). An intermediate can be prepared by the reaction of a single molecule of triphenylphosphine with the polyoxometalate, the iminophosphorane derivative (n-Bu(4)N)(3)[PW(11)O(39)Ru(V){NPPh(3)}]. The reactivity of the latter species has been investigated to complete the general scheme of the nitrogen-transfer reaction.

Synthesis and characterization of the Keggin-type ruthenium-nitrido derivative [PW11O39{RuN}]4- and evidence of its electrophilic reactivity.

The ruthenium-nitrido POM derivative [PW11O39{RuVIN}]4- has been synthesized by reaction between [PW11O39]7- and [RuVINCl5]2- or [RuVINCl4]-. Its molecular structure has been confirmed from multinuclear 31P and 183W NMR spectroscopy together with an EXAFS study, while the oxidation state of the ruthenium bearing the nitrido ligand has been inferred both from 183W NMR and XANES analysis at the Ru-K edge. The potential of [PW11O39{RuVIN}]4- in N-atom transfer reactions has been demonstrated through reaction with triphenylphosphine, which ultimately leads to the release of the bis(triphenylphosphane)iminium cation [PPh3=N=PPh3]+ through several intermediates, among which the phosphoraniminato derivative [PW11O39{RuVNPh3}]3- has been structurally characterized.

A mechanism for transition-metal nanoparticle self-assembly.

The four-step mechanism by which transition-metal nanoclusters or bulk-metal films self-assemble from metal salts under reductive conditions has been discovered. The presence of two autocatalytic steps in the same reaction scheme--double autocatalysis--is the key to the sharp "turn-on" feature after an induction period observed in the signature kinetic curves. Predictions of the new mechanism that are tested experimentally include the following: that low concentrations and high temperatures will favor nanoclusters over bulk-metal film formation; that bulk-metal is formed in some, if not many, literature syntheses reporting only Pt(0) nanoclusters; and that added ligands are one key to turning on the new mechanism.