A spin crossover ferrous complex with ordered magnetic ferric anions

El pdf del artículo es la versión post-print.The first tetrahaloferrate spin crossover compound, [Fe(Metz) 6](FeBr 4) 2 (Metz = 1-methyltetrazole), is reported. The FeBr 4 - ions form ferromagnetically coupled 1D stacks and exhibit an antiferromagnetic order at 2.2 K, which coexists with the gradual spin crossover centred at 165 K. © 2012 The Royal Society of Chemistry.We are grateful to Spanish MINECO (contracts MAT2009-13977-C03 and MAT2011-24284) for funding.Peer Reviewe

Variations to Spin Crossover in [FexZn(1−x)(Me1,3bpp)2(ClO4)2] molecular alloys examined by Magnetometry and Single Crystal X-Ray Diffraction

Spin crossover (SCO) active solid solutions with formula [FexZn1-x(Me1,3bpp)2](ClO4)2 (x = 0.10, 0.15, 0.22, 0.33, 0.41, 0.48, 0.56 and 0.64, Me1,3bpp is a bis-pyrazolylpyridine) and the complex [Zn(Me1,3bpp)2](ClO4)2 have been prepared and characterized by single crystal X-ray diffraction. The structural data and the powder diffraction patterns of all the compounds have been compared with the reported isostructural molecular crystal [Fe(Me1,3bpp)2](ClO4)2. Increasing amounts of Zn diminishes monotonically the cooperativity of the SCO of the parent Fe(II) complex (T1/2=183 K) and cause a decrease of T1/2 in line with the negative chemical pressure exerted by the Zn(II) complexes on the Fe(II) lattice. The gradual variation of the magnetic properties as the composition changes are paralleled by the evolution of the structural parameters at the molecular, intermolecular and crystal lattice scales. Thermal trapping of a portion of the Fe(II) centers of these alloys by quenching the crystals to 2 K unveils that, upon warming, the temperature of relaxation of the metastable states is almost constant for all compositions

Designed Polynuclear Lanthanide Complexes for Quantum Information Processing

The design of dissymmetric organic ligands featuring combinations of 1,3-diketone and 2,6-diacetylpyridine coordination pockets has been exploited to produce dinuclear and trinuclear lanthanide-based coordination compounds. These molecules exhibit two or more non-equivalent Ln ions, most remarkably enabling the access to well-defined heterolanthanide compositions. The site-selective disposition of each metal ion within the molecular entities allows the study of each centre individually as a spin-based quantum bit, affording unparalleled versatility for quantum gate design. The inherent weak interaction between the Ln ions permits the performance of multi-qubit quantum logical operations realized through their derived magnetic states, or implementing quantum-error correction protocols. The different studies performed to date on these systems are revised, showing their vast potential within spin-based quantum information processing

Surface-confined molecular coolers for cryogenics

An excellent molecule-based cryogenic magnetic refrigerant, gadolinium acetate tetrahydrate, is here used to decorate selected portions of silicon substrate. By quantitative magnetic force microscopy for variable applied magnetic field near liquid-helium temperature, we demonstrate that the molecules hold intact their magnetic properties, and therefore their cooling functionality, after their deposition. Our result represents a step forward towards the realization of a molecule-based microrefrigerating device for very low temperatures.Comment: 16 pages, 4+1 figures, S.I. available from author

Controlled Heterometallic Composition in Linear Trinuclear [LnCeLn] Lanthanide Molecular Assemblies.

The combination of two different β-diketone ligands facilitates the size-controlled assembly of pure heterometallic [LnLn'Ln] linear compounds thanks to two different coordination sites present in the molecular scaffold. [HoCeHo], [ErCeEr], and [YbCeYb] analogues are presented here and are characterized both in the solid state and in solution, demonstrating the selectivity of this unique method to produce heterometallic 4f molecular entities

A sequential method to prepare polymorphsand solvatomorphs of [Fe(1,3-bpp)2](ClO4)2·nH2O( n=0, 1, 2) with varying spin-crossover behaviour

Two polymorphs of the spin crossover (SCO) compound [Fe(1,3bpp)2](ClO4)2 (1 and 2; 1,3bpp, 2-(pyrazol-1-yl)-6-(pyrazol-3-yl)-pyridine) are prepared using a novel, stepwise procedure. Crystals of 1 deposit from dry solvents while 2 is obtained from a solid-state procedure, by sequentially removing lattice H2O molecules from the solvatomorph [Fe(1,3bpp)2](ClO4)2·2H2O (2·2H2O), using single-crystal-to-single-crystal (SCSC) transformations. Hydrate 2·2H2O is obtained through the same reaction as 1, now with 2.5% of added water. Compounds 2 and 2·2H2O are unstable in the atmosphere and absorb or lose one equivalent of water, respectively, to both yield the stable solvatomorph [Fe(1,3bpp)2](ClO4)2·H2O (2·H2O), also following SCSC processes. The four derivatives have been characterized by single crystal X-ray diffraction (SCXRD). Furthermore, the homogeneity of the various compounds as well as their SCSC interconversions have been confirmed by powder X-ray diffraction (PXRD). Polymorphs 1/2 exhibit abrupt SCO near room temperature with T1/2↑ = 279/316 K and T1/2↓ = 276/314 K (near 40 K of shift) and different cooperativity

A supramolecular helicate with two independent Fe(II)switchable centres and a[Fe(anilate)3]3 guest

A biphenyl-spaced bis-pyrazolylpyridine ligand interacts with ferrous ions to engender a dimetallic helical coordination cage that encapsulates an Fe3+ tris-anilate complex. The host–guest interaction breaks the symmetry of the Fe2+ centers causing a differential spin crossover behavior in them that can be followed in great detail crystallographically.

Designed intramolecular blocking of the spin crossover of an Fe(II) complex

A ligand derived from 1,3bpp (2-(pyrazol-1-yl)-6-(pyrazol-3-yl)- pyridine) has been prepared to prove that the spin crossover (SCO) of an Fe(II) complex can be blocked by means of intramolecular interactions not related to the crystal field. Calculations show that the blocking is caused by the energy penalty incurred by the rotation of a phenyl ring, needed to avoid steric hindrance upon SCO

Novel Topologies in Vanadium-bis-ß-Diketone Chemistry: A [V4] and a [V6] Metallacyclophane

Exploring the chemistry of vanadyl ions (VO2+) with bis-ß-diketone ligands, in pyridine reactions of vanadyl sulfate with 1, 3-bis-(3-oxo-3-(2-hydroxyphenyl)-propionyl)-benzene (H4L1) and 1, 3-bis-(3-oxo-3-(2-hydroxyphenyl)-propionyl)-pyridine (H4L2), two novel clusters, (VIVO)4(H2L1)4(py)4] (1) and (VVO)4(VIVO)2 (O)4(L2)2(py)6] (2) were prepared and characterized. Due to the conformational flexibility of the ligands, both entities exhibit very peculiar metal topologies and composition, differing significantly from structural patterns established in the related chemistry of divalent 3d metals. Structural analysis also unveils the existence of the most complex metallamacrocycles from this family to date. Studies of the magnetic properties via bulk magnetization measurements and EPR spectroscopy confirmed the existence of uncoupled long-distant S = 1/2 metal centers and the spin ground states S = 2 and S = 1 of the clusters

Novel topologies in vanadium-bis-ß-diketone chemistry: a [V4] and a [V6] metallacyclophane

Exploring the chemistry of vanadyl ions (VO2+) with bis-β-diketone ligands, in pyridine reactions of vanadyl sulfate with 1,3-bis-(3-oxo-3-(2-hydroxyphenyl)-propionyl)- benzene (H4L1) and 1,3-bis-(3-oxo-3-(2-hydroxyphenyl)-propionyl)-pyridine (H4L2), two novel clusters, [(VIVO)4(H2L1)4(py)4] (1) and [(VVO)4(VIVO)2 (O)4(L2)2(py)6] (2) were prepared and characterized. Due to the conformational flexibility of the ligands, both entities exhibit very peculiar metal topologies and composition, differing significantly from structural patterns established in the related chemistry of divalent 3d metals. Structural analysis also unveils the existence of the most complex metallamacrocycles from this family to date. Studies of the magnetic properties via bulk magnetization measurements and EPR spectroscopy confirmed the existence of uncoupled long-distant S = 1/2 metal centers and the spin ground states S = 2 and S = 1 of the clusters.Guillem Aromí thanks the Generalitat de Catalunya for the prize ICREA Academia 2008 and 2013, for excellence in research and the ERC (European Research Council) for a Starting Grant (258060 FuncMolQIP). The authors thank the Spanish MICINN for funding through CTQ2009-06959 (Guillem Aromí, Ivana Borilovic) and MAT2011-24284 (Olivier Roubeau). Ivana Borilovic thanks the Generalitat de Catalunya for a Ph.D. Grant (FI-DGR 2014).We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI).Peer Reviewe