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Rafael Ruiz-García

Publications and source records attributed to Rafael Ruiz-García.

10 recordsLinked to original sources
PubMed2007

Ligand design for heterobimetallic single-chain magnets: synthesis, crystal structures, and magnetic properties of MIICuII (M=Mn, Co) chains with sterically hindered methyl-substituted phenyloxamate bridging ligands.

Two new series of neutral oxamato-bridged heterobimetallic chains of general formula [MCu(L(x))(2)] m DMSO (m=0-4) (L(1)=N-2-methylphenyloxamate, M=Mn (1 a) and Co (1 b); L(2)=N-2,6-dimethylphenyloxamate, M=Mn (2 a) and Co (2 b); L(3)=N-2,4,6-trimethylphenyloxamate, M=Mn (3 a) and Co (3 b)) have been prepared by reaction between the corresponding anionic oxamatocopper(II) complexes [Cu(Lx)2](2-) with Mn(2+) or Co(2+) cations in DMSO. The crystal structures of [CoCu(L2)2(H2O)2] (2 b') and [CoCu(L3)2(H2O)2]4 H2O (3 b') have been solved by single-crystal X-ray diffraction methods. Compounds 2 b' and 3 b' adopt zigzag and linear chain structures, respectively. The intrachain Cu...Co distance through the oxamate bridge is 5.296(1) A in 2 b' and 5.301(2) A in 3 b', while the shortest interchain Co...Co distance is 5.995(5) A in 2 b' and 8.702(3) A in 3 b', that is, the chains are well isolated in the crystal lattice due to the presence of the bulky methyl-substituted phenyl groups. Although both Mn(II)Cu(II) and Co(II)Cu(II) chains exhibit ferrimagnetic behaviour with moderately strong intrachain antiferromagnetic coupling (-J(Mn,Cu)=24.7-27.9 cm(-1) and -J(Co,Cu)=35.0-45.8 cm(-1); H= Sigma -J(M,Cu)S(M,i)S(Cu,i)), only the Co(II)Cu(II) chains show slow magnetic relaxation at low temperatures (T(B)<3.5 K), which is characteristic of single-chain magnets (SCMs) because of the high magnetic anisotropy of the Co(II) ion. The blocking temperatures T(B) along this series of chains vary according to the steric hindrance of the aromatic substituent of the oxamate ligand in the series L(1)<L(2)<L(3). Analysis of the SCM behaviour for 3 b and 3 b' on the basis of Glauber's theory for a one-dimensional Ising system showed a thermally activated mechanism for the magnetic relaxation (Arrhenius law dependence). The activation energies E(a) to reverse the magnetisation direction are 38.0 (3 b) and 16.3 cm(-1) (3 b'), while the preexponential factors tau(0) are 2.3x10(-11) (3 b) and 4.0x10(-9) s (3 b').

Journal Article↗
PubMed2005

Molecular and electronic structure of square-planar nickel II, nickel III and nickel III pi-cation radical complexes with a tetradentate o-phenylenedioxamidate redox-active ligand.

The molecular and electronic structures of the electron transfer series of four-coordinate square-planar nickel complexes with the ligand o-phenylenebis(N'-methyloxamidate), [NiL]z (z = 2-, 1-, 0), have been evaluated by DFT and TDDFT calculations, and most of their experimentally available structural and spectroscopic properties (X. Ottenwaelder et al., Dalton Trans., 2005, DOI: 10.1039/b502478a) have been reasonably reproduced at the B3LYP level of theory. The anionic species [NiL]2- and [NiL]- are genuine low-spin nickel II and nickel III complexes with diamagnetic singlet (S = 0) and paramagnetic doublet (S = 1/2) states, respectively. The nickel III complex presents shorter Ni-N(amidate) bond distances (1.85-1.90 A) than the parent nickel II complex (1.88-1.93 A) and characteristic LMCT bands in the NIR region (lambda max = 794 and 829 nm) while the analogous MLCT bands for the nickel(II) complex are in the UV region (lambda max = 346 and 349 nm). The neutral species [NiL] is a nickel III o-benzosemiquinonediimine pi-cation radical complex with a diamagnetic singlet (S = 0) and a paramagnetic triplet (S = 1) states fairly close in energy but fundamentally different in orbital configuration. The singlet metal-radical ground state results from the antiferromagnetic coupling between the 3d(yz) orbital of the Ni III ion (S(M) = 1/2) and the pi(b) orbital of the benzosemiquinone-type radical ligand (S(L) = 1/2), which have a large overlap and thus strong covalent bonding. The triplet metal-radical excited state involves the ferromagnetic coupling between the Ni III 3d(zx) orbital and the benzosemiquinone-type pi(b) orbital, which are orthogonal to each other. The singlet and triplet states of the nickel III pi-cation radical complex possess characteristic quinoid-type short-long-short alternating sequence of C-C bonds in the benzene ring, as well as intense MLCT transitions in the VIS (lambda max = 664 nm) and NIR (lambda max = 884 nm) regions, respectively.

Cations↗
PubMed2005

Synthesis, structure, spectroscopy and redox chemistry of square-planar nickel(II) complexes with tetradentate o-phenylenedioxamidates and related ligands.

A series of four-coordinate square-planar nickel(II) complexes of o-phenylenebis(N'-methyloxamidate)(L1) and related o-phenylene(N'-methyloxamidate)oxamate (L2) and o-phenylenebis(oxamate)(L3) tetradentate ligands have been synthesized and characterized structurally, spectroscopically and electrochemically. The parent nickel(II)-L1 complex presents an intense MLCT band in the UV region (lambda max = 357 nm) and a distinctive 1 s --> 4p CT satellite in the Ni K-edge XANES spectrum (E = 8339.2 eV). These features together with the short Ni-N(amidate) bond lengths (1.85-1.93 A) as revealed by the analysis of the Ni K-edge EXAFS spectrum and confirmed by single-crystal X-ray diffraction are typical of square-planar low spin (S = 0) Ni(II) ions. The dianionic nickel(II) complexes, [Ni(II)L(i)](2-)(i = -3), experience two redox processes in acetonitrile at 25 degrees C. The first redox process, at moderately low potentials (E1 = 0.12-0.52 V vs. SCE), is a reversible one-electron metal-centered oxidation to the corresponding monoanionic nickel(III) complexes, [Ni(III)L(i)]-. The second redox process, at relatively high potentials (E2 = 0.86-1.04 V vs. SCE), is a quasireversible to irreversible one-electron oxidation largely centered on the o-benzenediamidate fragment of the non-innocent ligand, yielding the corresponding neutral nickel(iii) complexes with a o-benzosemiquinonediimine pi-cation radical ligand, [Ni(III)(L(i))*+]. The singly and doubly oxidized species of the parent nickel(II)-L1 complex have been prepared by chemical oxidation and characterized spectroscopically in acetonitrile at -40 degrees C. The stable singly oxidized nickel(III)-L1 species presents an intense LMCT band in the NIR region (lambda max = 910 nm) and a rhombic X-band EPR spectrum (g1 = 2.193, g2 = 2.080 and g3 = 2.006) characteristic of square-planar low spin (S = 1/2) Ni(III) ions. The unstable double oxidized nickel(III)-L1 pi-cation radical species exhibits a rather intense visible band (lambda max = 645 nm) that is tentatively assigned as a MLCT transition from the Ni(III)-benzosemiquinone type ground state to the Ni(IV) excited state.

Crystallography, X-Ray↗
PubMed2004

Magnetic anisotropy of a high-spin octanuclear nickel(II) complex with a meso-helicate core.

The octanickel(II) cluster 2b has been synthesized from the novel ferromagnetically coupled dinickel(II) metallacryptand 1b assembled from the m-phenylene-bis(oxamate) ligand. Complex 2b exhibits a dimer-of-tetramers structure, with two oxamate-bridged propeller-shaped tetranuclear units connected through three meta-substituted phenylenediamidate bridges, giving a metallacryptand core of the meso-helicate type. Complex 2b behaves as a ferromagnetically coupled dimer of two S=2 Ni(II)4 units with appreciable magnetic anisotropy.

Journal Article↗
PubMed2004

Spin control in ladderlike hexanuclear copper(II) complexes with metallacyclophane cores.

Two new hexanuclear oxamatocopper(II) complexes 3 and 4 have been synthesized from the binuclear copper(II) complexes of the meta- and para-phenylenebis(oxamate) ligands, respectively. Complexes 3 and 4 possess an overall ladderlike structure made up of two oxamate-bridged linear trinuclear units ("rails") connected through two phenylenediamidate bridges ("rungs") between the central copper atoms to give metallacyclic cores of the meta- and para-cyclophane type, respectively. They show different ground spin states, S = 1 (3) or S = 0 (4), depending on the substitution pattern in the aromatic spacers. The triplet state molecule 3 containing two spin doublet Cu(II)3 units connected by two m-phenylenediamidate bridges represents a successful extension of the concept of "ferromagnetic coupling units" to metal complexes, which is a well-known approach toward high spin organic radicals.

Journal Article↗
PubMed2003

Long-range magnetic coupling through extended pi-conjugated aromatic bridges in dinuclear copper(II) metallacyclophanes.

Self-assembly of 1,4-phenylenebis(oxamate) and 4,4'-biphenylenebis(oxamate) ligands and Cu2+ ions gives two new dinuclear copper(II) metallacyclophanes where the two metal centers are connected by double para-substituted aromatic diamide bridges. Despite the relatively large intramolecular Cu-Cu distance of ca. 8 and 12 A for each complex, magnetic susceptibility measurements evidence strong to moderately strong intramolecular antiferromagnetic couplings (-J values of the order of 100 and 10 cm-1, respectively). Density functional theory calculations on these compounds and their homologues with linear oligo-p-phenylenediamide bridges predict a rather slow exponential decay of magnetic coupling with increasing intermetal distance (r values up to 25 A) along this novel series of dicopper metalla-amidocyclophanes.

Journal Article↗