Synthesis, Mechanism Elucidation and Biological Insights of Tellurium(IV)-Containing Heterocycles.

Inspired by the synthetic and biological potential of organotellurium substances, a series of five- and six-membered ring organotelluranes containing a Te-O bond were synthesized and characterized. Theoretical calculations elucidated the mechanism for the oxidation-cyclization processes involved in the formation of the heterocycles, consistent with chlorine transfer to hydroxy telluride, followed by a cyclization step with simultaneous formation of the new Te-O bond and deprotonation of the OH group. Moreover, theoretical calculations also indicated anti-diastereoisomers to be major products for two chirality center-containing compounds. Antileishmanial assays against Leishmania amazonensis promastigotes disclosed 1,2λ4 -oxatellurane LQ50 (IC50 =4.1±1.0; SI=12), 1,2λ4 -oxatellurolane LQ04 (IC50 =7.0±1.3; SI=7) and 1,2λ4 -benzoxatellurole LQ56 (IC50 =5.7±0.3; SI=6) as more powerful and more selective compounds than the reference, being up to four times more active. A stability study supported by 125 Te NMR analyses showed that these heterocycles do not suffer structural modifications in aqueous-organic media or at temperatures up to 65 °C.

A Rare Example of Four-Coordinate Nonoxido Vanadium(IV) Alkoxide in the Solid State: Structure, Spectroscopy, and Magnetization Dynamics.

The distorted tetrahedral [V(OAd)4] alkoxide (OAd = 1-adamantoxide, complex 1) is the first homoleptic, mononuclear vanadium(IV) alkoxide to be characterized in the solid state by X-ray diffraction analysis. The compound crystallizes in the cubic P4̅3 n space group with two highly disordered, crystallographically independent molecules in the asymmetric unit. Spin Hamiltonian parameters extracted from low temperature X- and Q-band electron paramagnetic resonance (EPR) experiments performed for polycrystalline samples of 1, both in the concentrated (bulk) form and diluted in the diamagnetic [Ti(OAd)4] analogue, reveal a fully axial system with g z < g x, g y and A z ≫ A x, A y. Complex 1 has also been characterized by alternate current susceptometry with varying temperature (3-30 K) and static magnetic field (up to 8.5 T), showing field-induced slow relaxation of the magnetization with relaxation times ranging from ca. 3 ms at 3 K to 0.02-0.03 ms at 30 K, in line with relevant results described recently for other potential molecular quantum bits. Pulsed EPR measurements, in turn, disclosed long coherence times of ca. 4 µs at temperatures lower than 40 K, despite the presence of the H-rich ligands. The slow spin relaxation in 1 is the first observed for a tetracoordinate nonoxido vanadium(IV) complex, and results are compared here to those generated by square-pyramidal VIV(O)2+ and trigonal prismatic V4+ with oxygen donor atom sets. Considering that the number of promising d1 complexes investigated in detail for slow magnetization dynamics is still small, the present work contributes to the establishment of possible structural/electronic correlations of interest to the field of quantum information processing.

Cobalt(II) chloride adducts with acetonitrile, propan-2-ol and tetrahydrofuran: considerations on nuclearity, reactivity and synthetic applications.

High-spin cobalt(II) complexes are considered useful building blocks for the synthesis of single-molecule magnets (SMM) because of their intrinsic magnetic anisotropy. In this work, three new cobalt(II) chloride adducts with labile ligands have been synthesized from anhydrous CoCl2, to be subsequently employed as starting materials for heterobimetallic compounds. The products were characterized by elemental, spectroscopic (EPR and FT-IR) and single-crystal X-ray diffraction analyses. trans-Tetrakis(acetonitrile-κN)bis(tetrahydrofuran-κO)cobalt(II) bis[(acetonitrile-κN)trichloridocobaltate(II)], [Co(C2H3N)4(C4H8O)2][CoCl3(C2H3N)]2, (1), comprises mononuclear ions and contains both acetonitrile and tetrahydrofuran (thf) ligands, The coordination polymer catena-poly[[tetrakis(propan-2-ol-κO)cobalt(II)]-µ-chlorido-[dichloridocobalt(II)]-µ-chlorido], [Co2Cl4(C3H8O)4], (2'), was prepared by direct reaction between anhydrous CoCl2 and propan-2-ol in an attempt to rationalize the formation of the CoCl2-alcohol adduct (2), probably CoCl2(HOiPr)m. The binuclear complex di-µ-chlorido-1:2κ4Cl:Cl-dichlorido-2κ2Cl-tetrakis(tetrahydrofuran-1κO)dicobalt(II), [Co2Cl4(C4H8O)4], (3), was obtained from (2) after recrystallization from tetrahydrofuran. All three products present cobalt(II) centres in both octahedral and tetrahedral environments, the former usually less distorted than the latter, regardless of the nature of the neutral ligand. Product (2') is stabilized by an intramolecular hydrogen-bond network that appears to favour a trans arrangement of the chloride ligands in the octahedral moiety; this differs from the cis disposition found in (3). The expected easy displacement of the bound solvent molecules from the metal coordination sphere makes the three compounds good candidates for suitable starting materials in a number of synthetic applications.

Crystal structures of two mononuclear complexes of terbium(III) nitrate with the tripodal alcohol 1,1,1-tris-(hy-droxy-meth-yl)propane.

Two new mononuclear cationic complexes in which the TbIII ion is bis-chelated by the tripodal alcohol 1,1,1-tris-(hy-droxy-meth-yl)propane (H3LEt, C6H14O3) were prepared from Tb(NO3)3·5H2O and had their crystal and mol-ecular structures solved by single-crystal X-ray diffraction analysis after data collection at 100 K. Both products were isolated in reasonable yields from the same reaction mixture by using different crystallization conditions. The higher-symmetry complex dinitratobis[1,1,1-tris-(hy-droxy-meth-yl)propane]-terbium(III) nitrate di-meth-oxy-ethane hemisolvate, [Tb(NO3)2(H3LEt)2]NO3·0.5C4H10O2, 1, in which the lanthanide ion is 10-coordinate and adopts an s-bicapped square-anti-prismatic coordination geometry, contains two bidentate nitrate ions bound to the metal atom; another nitrate ion functions as a counter-ion and a half-mol-ecule of di-meth-oxy-ethane (completed by a crystallographic twofold rotation axis) is also present. In product aqua-nitratobis[1,1,1-tris-(hy-droxy-meth-yl)propane]-terbium(III) dinitrate, [Tb(NO3)(H3LEt)2(H2O)](NO3)2, 2, one bidentate nitrate ion and one water mol-ecule are bound to the nine-coordinate terbium(III) centre, while two free nitrate ions contribute to charge balance outside the tricapped trigonal-prismatic coordination polyhedron. No free water mol-ecule was found in either of the crystal structures and, only in the case of 1, di-meth-oxy-ethane acts as a crystallizing solvent. In both mol-ecular structures, the two tripodal ligands are bent to one side of the coordination sphere, leaving room for the anionic and water ligands. In complex 2, the methyl group of one of the H3LEt ligands is disordered over two alternative orientations. Strong hydrogen bonds, both intra- and inter-molecular, are found in the crystal structures due to the number of different donor and acceptor groups present.