Phenol-pyrazole ligands in the design of manganese(III) compounds : synthesis, structural characterization and study of the magnetic properties

In this thesis project, new manganese(III) compounds containing phenol-pyrazole ligands are presented. Small variations on the phenol-pyrazole ligand have been performed to investigate the role of the ligand in the formation of new complexes. The reaction conditions are also crucial to determine the nuclearity of the obtained compounds, which range from mononuclear to octanuclear compounds. Additionally, the magnetic properties of the synthesized compounds were studied. Magneto-structural correlations are presented to assess the important structural features for tuning the magnetic properties

Hysteresis in a bimetallic holmium complex : A synergy between electronic and nuclear magnetic interactions

We report a bimetallic holmium(III) complex showing a S-shaped magnetic hysteresis at low temperature. The complex is investigated by x-ray crystallography, magnetometry, single crystal microsquid measurements, and first-principles calculations. A model Hamiltonian including electronic and nuclear magnetic moments is used to fit all experimental data. We conclude that the Ho(III) may be described as non-Kramers doublets with respective gaps of Delta(A) = 0.8 and Delta(B) = 10 cm(-1) and that there is a small ferromagnetic coupling of J = 1 cm(-1) ((H) over cap (S) = -JS(A) . S-B). As in previous works, the hysteresis arise from the hyperfine structure of the Ho(III) ions. The S-shaped form of the hysteresis reflects the avoided crossing of the electronic states in the non-Kramers doublets.Peer reviewe

[Cr(dmbipy)(ox)2]−: a new bis-oxalato building block for metal assembling. Crystal structures and magnetic properties of XPh4[Cr(dmbipy)(ox)2]·5H2O (X = P and As), {Ba(H2O)2[Cr(dmbipy)(ox)2]2}n·17/2nH2O and {Ag(H2O)[Cr(dmbipy)(ox)2]}n·3nH2O

The synthesis, X-ray structure and variable-temperature magnetic study of new compounds of formula PPh4 [Cr(dmbipy)(ox)2 ]$5H2O (1), AsPh4 [Cr(dmbipy)(ox)2 ]$5H2O (2), {Ba(H2O)2[Cr(dmbipy)(ox)2]2}n$17/2nH2O (3) and {Ag(H2O)[Cr(dmbipy)(ox)2]}n$3nH2O (4) (PPh4 + ¼ tetraphenylphosphonium cation; AsPh4 + ¼ tetraphenylarsonium cation; dmbipy ¼ 4,4 0 -dimethyl- 2,2 0 -bipyridine; ox 2 ¼ oxalate dianion) are reported herein. The isomorphous compounds 1 and 2 are made up of discrete [Cr(dmbipy)(ox)2] anions, XPh4 + cations [X ¼ P (1) and As (2)] and uncoordinated water molecules. The chromium environment in 1 and 2 is distorted octahedral with Cr–O and Cr–N bond distances varying in the ranges 1.950(2)–1.9782(12) and 2.047(3)–2.0567(14) A˚ , respectively. The angles subtended at the chromium atom by the two bidentate oxalate ligands cover the range 82.58(10)– 83.11(5) , and they are somewhat greater than those concerning the chelating dmbipy [79.04(10) (1) and 79.24(5) (2)]. The [Cr(dmbipy)(ox)2] unit of 1 and 2 also occurs in 3 and 4 but it adopts different coordination modes. It acts as a chelating ligand through its two oxalate groups towards the divalent barium cations in 3 affording neutral chains with diamond-shaped units sharing the barium atoms, while the two other corners are occupied by two crystallographically independent chromium atoms. The barium atom in 3 is coordinated by eight oxygen atoms from four oxalate groups and two aqua ligands. The structure of 4 consists of neutral bimetallic layers where the [Cr(dmbipy)(ox)2] unit acts as a ligand towards the univalent silver(I) cation through its two oxalate groups, one of them being bidentate and the other bidentate/monodentate (outer). Each silver atom is six-coordinated with a water molecule and five oxygen atoms from three oxalate groups building a highly distorted octahedral environment. Magnetic susceptibility measurements for 1–4 in the temperature range 1.9– 300 K show the occurrence of weak ferro- (1 and 2) and antiferromagnetic (3 and 4) interactions which are mediated by p–p stacking between dmbipy ligands through the spin polarization mechanism. A comparative study of the potentiality of the [Cr(AA)(ox)2] unit (AA ¼ bidentate nitrogen donor) as a building bl

Functionalisation of MoS2 2D layers with diarylethene molecules

Functionalisation of two dimensional (2D) materials with stimuli-responsive molecules has been scarcely investigated. Here, MoS2 layers obtained by chemical exfoliation are covalently and non-covalently functionalised using two photoswitchable diarylethene derivatives under their open- and closed-ring isomers. The choice of these light-responsive molecules is based on their excellent thermal irreversibility and fatigue resistance. The characterisation of the resultant molecular/2D heterostructures proves the successful anchoring of the molecules by both approaches as well as the influence that the driving interaction has in the photoswitching behaviour of the diarylethene isomers after their deposition on the 2D layer

Zinc(II), cobalt(II) and manganese(II) networks with phosphoserine ligand: Synthesis, crystal structures magnetic and conduction properties

A series of zinc(II), cobalt(II) and manganese(II) coordination networks with the phosphoserine ligand (Pser) is synthesized and characterized. Whereas in compounds 1 and 2 with the general formula [M(Pser)]n [M = Zn (1) and Co(2)], the metal(II) ion presents a tetrahedral geometry, in [Co(Pser)(H2O)2]n (3) and [Mn(Pser)(H2O)]n (4)], the metal(II) ions are in a distorted octahedral geometry. The 3D frameworks are formed by inorganic layers built up from MO4 or MO6 polyhedra and phosphate groups. These layers are linked by the carboxylate groups of the phosphoserine ligand. The presence of extended hydrogen bonding stabilizes the 3D network and favors the proton transfer leading to moderate proton conductors. The highest proton conductivity, 2.70·10−5 S cm−1 (at 80 ºC and 95% RH), is obtained for compound 3. Temperature dependent magnetic susceptibility measurements for 2−4 reveal predominant antiferromagnetic interactions between the paramagnetic metal(II) ions.Proyectos MAT2013-41836-R y MAT2016-77648-R del MINECO, y proyecto (P12-FQM-1656) de la Junta de Andalucía

Slow magnetic relaxation in dinuclear dysprosium and holmium phenoxide bridged complexes: A Dy2single molecule magnet with a high energy barrier

Slow magnetic relaxation in dinuclear dysprosium and holmium phenoxo bridged complexes: a Dy2 single molecule magnet with a high energy barrier Matilde Fondo,a,* Julio Corredoira-Vázquez,a Ana M. García-Deibe,a Jesús Sanmartín-Matalobos,a Silvia Gómez-Coca,b Eliseo Ruizb and Enrique Colacioc Dinuclear [M(H3L1,2,4)]2 (M = Dy, Dy2; M = Ho, Ho2) complexes were isolated and recrystallised in pyridine. The crystal structures of Dy2·2THF and the pyridine adducts Dy2·2Py and Ho2·2Py show that the complexes are dinuclear, with unsupported double phenoxo bridges, and that the N4O4 environment of the LnIII centres is distorted triangular dodecahedral. The magnetic analysis of Dy2 and Ho2 shows that Dy2 is a single molecular magnet (SMM), with a thermal-activated zero-field effective energy barrier (Ueff) of 367.7 K, the largest barrier shown by double unsupported phenoxo-bridged dinuclear dysprosium complexes. Ho2 is one of the scarce dinuclear complexes showing slow relaxation of the magnetisation, although it does not even show field-induced SMM behaviour. Ab initio calculations were done in order to shed light on the magnetic anisotropy of the complexes and the magnetic relaxation pathways, which support the experimental magnetic results