A tris-oxovanadium pyrogallate complex: synthesis, structure, and magnetic and electronic properties.

With the aim of identifying new cation-phenolate complexes, we herein investigated the reactivity of pyrogallol (H3pgal) with vanadium salts. A trimetallic anionic complex was identified, and found to be formed under a broad set of reaction conditions. This complex, with the formula V3O3(pgal)33-, consists of three oxovanadium(IV) units connected together by three pyrogallate ligands to afford a bowl-shaped species presenting a pseudo 3-fold symmetry axis. Its crystal structure is reported, as well as its characterisation by a broad set of techniques, including powder X-ray diffraction, thermogravimetric analysis, infrared and Raman spectroscopy, and solid state UV-visible diffuse reflectance. Its redox activity both in solution and in the solid state is described, together with its magnetic behavior. Finally, the relevance of this trimetallic unit in the field of phenolic-based biocoatings and Metal Organic Framework (MOF) synthesis is briefly discussed.

Hybrid organic-inorganic mononuclear lanthanoid single ion magnets.

The first family of hybrid mononuclear organic-inorganic lanthanoid complexes is reported, based on [PW11O39]7- and 1,10-phenanthroline ligands. This hybrid approach causes a dramatic improvement of the relaxation time (×1000) with a decrease of the optimal field while maintaining the Ueff of the inorganic analogues.

Substitution Effect on the Charge Transfer Processes in Organo-Imido Lindqvist-Polyoxomolybdate.

Two new aromatic organo-imido polyoxometalates with an electron donor triazole group ([n-Bu4N]2[Mo6O18NC6H4N3C2H2]) (1) and a highly conjugated fluorene ([n-Bu4N]2[Mo6O18NC13H9]) (2) have been obtained. The electrochemical and spectroscopic properties of several organo-imido systems were studied. These properties were analysed by the theoretical study of the redox potentials and by means of the excitation analysis, in order to understand the effect on the substitution of the organo-imido fragment and the effect of the interaction to a metal centre. Our results show a bathochromic shift related to the charge transfer processes induced by the increase of the conjugated character of the organic fragment. The cathodic shift obtained from the electrochemical studies reflects that the electronic communication and conjugation between the organic and inorganic fragments is the main reason of this phenomenon.

Sublimable Single Ion Magnets Based on Lanthanoid Quinolinate Complexes: The Role of Intermolecular Interactions on Their Thermal Stability.

We report the design, preparation, and characterization of two families of thermally robust coordination complexes based on lanthanoid quinolinate compounds: [Ln(5,7-Br2q)4]- and [Ln(5,7-ClIq)4]-, where q = 8-hydroquinolinate anion and Ln = DyIII, TbIII, ErIII, and HoIII. The sodium salt of [Dy(5,7-Br2q)4]- decomposes upon sublimation, whereas the sodium salt of [Dy(5,7-ClIq)4]-, which displays subtly different crystalline interactions, is sublimable under gentle conditions. The resulting film presents low roughness with high coverage, and the molecular integrity of the coordination complex is verified through AFM, MALDI-TOF, FT-IR, and microanalysis. Crucially, the single-molecule magnet behavior exhibited by [Dy(5,7-ClIq)4]- in bulk remains detectable by ac magnetometry in the sublimated film.

Sublimable chloroquinolinate lanthanoid single-ion magnets deposited on ferromagnetic electrodes.

A new family of chloroquinolinate lanthanoid complexes of the formula A+[Ln(5,7Cl2q)4]-, with Ln = Y3+, Tb3+ and Dy3+ and A+ = Na+, NEt4+ and K0.5(NEt4)0.5+, is studied, both in bulk and as thin films. Several members of the family are found to present single-molecule magnetic behavior in bulk. Interestingly, the sodium salts can be sublimed under high vacuum conditions retaining their molecular structures and magnetic properties. These thermally stable compounds have been deposited on different substrates (Al2O3, Au and NiFe). The magnetic properties of these molecular films show the appearance of cusps in the zero-field cooled curves when they are deposited on permalloy (NiFe). This indicates a magnetic blocking caused by the interaction between the single-ion magnet and the ferromagnet. X-ray absorption spectroscopy confirms the formation of hybrid states at the molecule/metal interface.

pH-Controlled Assembly of 3D and 2D Zinc-Based Metal-Organic Frameworks with Tetrazole Ligands.

We report the synthesis and structural diversity of Zn(II) metal-organic framework (MOF) with in situ formation of tetrazole ligand 3-ptz [3-ptz = 5-(3-pyridyl)tetrazolate] as a function pH. By varying the initial reaction pH, we obtain high-quality crystals of the noncentrosymmetric three-dimensional MOF Zn(3-ptz)2 , mixed phases involving the zinc-aqua complex [Zn(H2O)4(3-ptz)2]·4H2O, and two-dimensional MOF crystals Zn(OH)(3-ptz) with a tunable microrod morphology, keeping reaction time, temperature, and metal-ligand molar ratio constant. Structures are characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and UV-vis spectroscopy. We discuss the observed structural diversity in terms of the relative abundance of hydroxo-zinc species in solution for different values of pH.

Crystal lattice effect on the quenching of the intracluster magnetic interaction in [V12B18O60H6](10-) polyoxometalate.

In the present work, the synthesis and structural characterization of four new polyoxovanadoborate (BVO) frameworks based on the [V12B18O60H6](10-) polyanion are reported: (NH4)8(1,3-diapH2)[V12B18O60H6]·5H2O (1), K8(NH4)2[V12B18O60H6]·18H2O (2), K10[V12B18O60H6]·10H2O (3) and K8Cs2[V12B18O60H6]·10H2O (4). A global antiferromagnetic behaviour is observed for these 10V(IV)/2V(V) mixed valence clusters. The magnetic data of 1, 2 and 3, which present different countercation environments, show that 1 is more coupled than 2 and 3. DFT calculations show that the positive charges strongly influence the polarization mechanism of the spin density of the vanadyl groups and the extent of the magnetic orbitals, therefore corroborating the experimental observation of the quenching effect of the magnetic coupling between vanadium centres of 2 and 3.

Theoretical description of the magnetic properties of µ3-hydroxo bridged trinuclear copper(II) complexes.

A theoretical study of the magnetic properties, using density functional theory, of a family of trinuclear µ3-OH copper(II) complexes reported in the literature is presented. The reported X-ray crystal structures of [Cu3(µ3-OH)(aat)3(H2O)3](NO3)2 · H2O (HUKDUM), where aat: 3-acetylamine-1,2,4-triazole; [Cu3(µ3-OH)(aaat)3(H2SO4)(HSO4)(H2O)] (HUKDOG), where aaat: 3-acetylamine-5-amine-1,2,4-triazole; [Cu3(µ3-OH)(PhPyCNO)3(tchlphac)2] (HOHQUR), where PhPyCNO: phenyl 2-pyridyl-ketoxime and tchlphac: acid 2,4,5-trichlorophenoxyacetic; [Cu3(µ3-OH)(PhPyCNO)3(NO3)2(CH3OH)] (ILEGEM); [Cu3(µ3-OH)(pz)3(Hpz)3(ClO4)2] (QOPJIP), where Hpz = pyrazole; [Cu3(µ3-OH)(pz)3(Hpz)(Me3CCOO)2] ∙ 2Me3CCOOH (DEFSEN) and [Cu3(µ3-OH)(8-amino-4-methyl-5-azaoct-3-en-2-one)3][CuI3] (RITXUO), were used in the calculations. The magnetic exchange constants were calculated using the broken-symmetry approach. The calculated J values are for HUKDUM J1 = -68.6 cm(-1), J2 = -69.9 cm(-1), J3 = -70.4 cm(-1); for HUKDOG, J1 = -73.5 cm(-1), J2 = -58.9 cm(-1), J3 = -62.1 cm(-1); for HOHQUR J1 = -128.3 cm(-1), J2 = -134.1 cm(-1), J3 = -120.4 cm(-1); for ILEGEM J1 = -151.6 cm(-1), J2 = -173.9 cm(-1), J3 = -186.9 cm(-1); for QOPJIP J1 = -118.3 cm(-1), J2 = -106.0 cm(-1), J3 = -120.6 cm(-1); for DEFSEN J1 = -74.9 cm(-1), J2 = -64.0 cm(-1), J3 = -57.7 cm(-1) and for RITXUO J1 = -10.9 cm(-1), J2 = +14.3 cm(-1), J3 = -35.4 cm(-1). The Kahn-Briat model was used to correlate the calculated magnetic properties with the overlap of the magnetic orbitals. Spin density surfaces show that the delocalization mechanism is predominant in all the studied compounds.

Electrochemical behavior of copper complexes with substituted polypyridinic ligands: an experimental and theoretical study.

Experimental redox potentials of the couples [Cu(R-L ( n ))(CH 3CN)] (2+,+), where L (1) is bis-(pyridine-2-ylmethyl)-benzylamine, L (2) is (pyridine-2-ylethyl)(pyridine-2-ylmethyl)-benzylamine, and R is H, Me, or CF 3, were determined in dichloromethane solution. The compounds exhibited one simple quasi-reversible wave over the measured potential range of -500 to +1200 mV, and the E 1/2 values varied from +200 to +850 mV versus SCE. These experimental values were correlated with redox potentials calculated using density functional theory. The optimized geometries and the predicted redox potentials were obtained using the BP86 functional and a combination of the basis sets LACV3P** (for Cu) and cc-pVTZ(-f) (for light atoms). A distortion analysis of all of the optimized geometries for both oxidation states was performed using the generalized interconversion coordinate phi. A linear relation was obtained between this parameter and the redox potentials. However, the [Cu(CF 3-L (1))(CH 3CN)] (+) complex showed the largest deviation, which was explained by the more-rigid structure of the ligand.