Laura Cañadillas-Delgado

Study of the Influence of the Bridge on the Magnetic Coupling in Cobalt(II) Complexes

Two new cobalt(II) complexes of formula [Co(2)(bta)(H(2)O)(6)](n) x 2nH(2)O (1) and [Co(phda)(H(2)O)](n) x nH(2)O (2) [H(4)bta = 1,2,4,5-benzenetetracarboxylic acid, H(2)phda = 1,4-phenylenediacetic acid] have been characterized by single crystal X-ray diffraction. Compound 1 is a one-dimensional compound where the bta(4-) ligand acts as 2-fold connector between the cobalt(II) ions through two carboxylate groups in para-conformation. Triply bridged dicobalt(II) units occur within each chain, a water molecule, a carboxylate group in the syn-syn conformation, and an oxo-carboxylate with the mu(2)O(1);kappa(2)O(1),O(2) coordination mode acting as bridges. Compound 2 is a three-dimensional compound, where the phda(2-) group acts as a bridge through its two carboxylate groups, one of them adopting the mu-O,O coordination mode in the syn-syn conformation and the other exhibiting the single mu(2)-O bridging mode. As in 1, chains of cobalt(II) ions occur in 2 with a water molecule, a syn-syn carboxylate group, and an oxo-carboxylate constitute the triply intrachain bridging skeleton. Each chain is linked to other four ones through the phda(2-) ligand, giving rise to the three-dimensional structure. The values of the intrachain cobalt-cobalt separation are 3.1691(4) (1) and 3.11499(2) A (2) whereas those across the phenyl ring of the extended bta(4-) (1) and phda(2-) (2) groups are 10.1120(6) and 11.4805(69 A, respectively. The magnetic properties of 1 and 2 have been investigated in the temperature range 1.9-300 K, and their analysis has revealed the occurrence of moderate intrachain ferromagnetic couplings [J = +5.4 (1) and +2.16 cm(-1) (2), J being the isotropic magnetic coupling parameter], the magnetic coupling through the extended bta(4-) and phda(2-) with cobalt-cobalt separations larger than 10 A being negligible. The nature and magnitude of the magnetic interactions between the high-spin cobalt(II) ions in 1 and 2 are compared to those of related systems and discussed as a function of the complementarity-countercomplementarity effects of the triple bridges.

Crystal structure and magnetic properties of two isomeric three-dimensional pyromellitate-containing cobalt(II) complexes.

The hydrothermal preparation, crystal structure determination, and magnetic study of two isomers made up of 1,2,4,5-benzenetetracarboxylate and high-spin Co(II) ions of formula [Co2(bta)(H2O)4]n x 2n H2O (1 and 2; H4bta = 1,2,4,5-benzenetetracarboxylic acid) are reported. 1 and 2 are three-dimensional compounds whose structures can be described as (4,4) rectangular layers of trans-diaquacobalt(II) units with the bta(4-) anion acting as tetrakis-monodentate ligand through the four carboxylate groups, which are further connected through other trans-[Co(H2O)2](2+) (1) and planar [Co(H2O)4](2+) (2) entities, with the bridging units being a carboxylate group in either the anti-syn (1) or syn-syn (2) conformations and a water molecule (2). The study of the magnetic properties of 1 and 2 in the temperature range 1.9-300 K shows the occurrence of weak antiferromagnetic interactions between the high-spin Co(II) ions, with the strong decrease of chi(M)T upon cooling being mainly due to the depopulation of the higher energy Kramers doublets of the six-coordinated Co(II) ions. The computed values of the exchange coupling between the Co(II) ions across anti-syn carboxylate (1) and syn-syn carboxylate/water (2) bridges are J = -0.060 (1) and -1.90 (2) cm(-1) (with the Hamiltonian being defined as H = -Jsigma(i,j)S(i) x S(j)). These values follow the different conformations of the carboxylate bridge in 1 (anti-syn) and 2 (syn-syn) with the occurrence of a double bridge in 2 (water/carboxylate).

Intramolecular ferro- and antiferromagnetic interactions in oxo-carboxylate bridged digadolinium(III) complexes

Two new digadolinium(III) complexes with monocarboxylate ligands, [Gd2(pac)6(H2O)4] (1) and [Gd2(tpac)6(H2O)4] (2) (Hpac = pentanoic acid and Htpac = 3-thiopheneacetic acid), have been prepared and their structures determined by X-ray diffraction on single crystals. Their structures consist of neutral and isolated digadolinium(III) units, containing six monocarboxylate ligands and four coordinated water molecules, the bridging skeleton being built by a muO(1):kappa2O(1)O(2) framework. This structural pattern has already been observed in the parent acetate-containing compound [Gd2(ac)6(H2O)4] x 4 H2O (3) whose structure and magnetic properties were reported elsewhere (L. Cañadillas-Delgado, O. Fabelo, J. Cano, J. Pasán, F. S. Delgado, M. Julve, F. Lloret and C. Ruiz-Pérez, CrystEngComm, 2009, 11, 2131). Each gadolinium(III) ion in 1 and 2 is nine-coordinated with seven carboxylate-oxygen atoms from four pac (1)/tpac (2) ligands and two water molecules (1 and 2) building a distorted monocapped square antiprism. The values of the intramolecular gadolinium-gadolinium separation are 4.1215(5) (1), 4.1255(6) (2) and 4.1589(3) A (3) and those of the angle at the oxo-carboxylate bridge (theta) are 113.16(13) (1), 112.5(2) (2) and 115.47(7) degrees (3). Magnetic susceptibility measurements in the temperature range 1.9-300 K reveal the occurrence of a weak intramolecular antiferromagnetic interaction [J = -0.032(1) (1) and -0.012(1) cm(-1) (2), the Hamiltonian being defined as H = -JS(A) x S(B)] in contrast with the intramolecular ferromagnetic coupling which occurs in 3 (J = +0.031(1) cm(-1)). The magneto-structural data of 1-3 show the relevance of the geometrical parameters at the muO(1):kappa2O(1)O(2) bridge on the nature of the magnetic coupling between two gadolinium(III) ions.

Dinuclear and two- and three-dimensional gadolinium(III) complexes with mono- and dicarboxylate ligands: synthesis, structure and magnetic properties

Three new gadolinium(III) complexes with carboxylate ligands of formula [Gd2(ac)6(H2O)4]·2H2O (1), [Gd2(ac)2(fum)2(H2O)4]n (2) and [Gd2(ox)(fum)2(H2O)4]n·4nH2O (3) (ac = acetate, fum = fumarate and ox = oxalate) have been prepared and their structures determined by X-ray diffraction on single crystals. The structure of 1 is made up of discrete centrosymmetric di-µ-oxo(carboxylate acetate)digadolinium(III) units with an intramolecular Gd⋯Gd separation of 4.1589(3) A. Each gadolinium atom in 1 is nine-coordinated with two water molecules and seven carboxylate-oxygen atoms from four acetate ligands building a monocapped square antiprism environment. Compound 2 exhibits a sheet-like structure, the repeating intralayer motif being a rectangle of di-µ-oxo(carboxylate acetate)digadolinium(III) units [Gd⋯Gd separation of 3.8659(10) A] where the edges are defined by bridging bis-bidentate and tetrakis-monodentate fumarate groups. Each gadolinium atom in 2 is nine-coordinated with two water molecules and seven carboxylate oxygens from two acetate and three fumarate ligands building a distorted monocapped square antiprism. Compound 3 has a three-dimensional structure where chains of double oxo(carboxylate fumarate)-bridged gadolinium(III) ions are interlinked by bis-bidentate fumarate to afford layers which are further interconnected through bis-bidentate oxalate ligands. The corresponding values of the Gd⋯Gd separation are 4.5816(1), 8.2292(2) and 6.2989(1) A. Each gadolinium atom in 3 is ten-coordinated with two water molecules and eight oxygen atoms from four fumarate ligands and one oxalate group building a distorted bicapped square antiprism. Variable-temperature magnetic susceptibility measurements show the occurrence of weak but significant ferro- (1 and 3) and antiferromagnetic (2) interactions through the double oxo(carboxylate acetate) (1 and 2), double syn-syncarboxylate fumarate (2) and double oxo(carboxylate fumarate) and bis-bidentate oxalate (3) bridges. Monte Carlo calculations were performed in the case of 3 to simulate its magnetic data and to substantiate the best-fit values of the magnetic couplings through the different exchange pathways involved.

Photoswitching of the antiferromagnetic coupling in an oxamato-based dicopper(II) anthracenophane

Thermally reversible photomagnetic (ON/OFF) switching behavior has been observed in a dinuclear oxamatocopper(II) anthracenophane upon UV light irradiation and heating; the two Cu(II) ions (S(Cu) = 1/2) that are antiferromagnetically coupled in the dicopper(II) metallacyclic precursor (ON state) become uncoupled in the corresponding [4+4] photocycloaddition product (OFF state), as substantiated from both experimental and theoretical studies.

Novel cobalt(II) coordination polymers based on 1,2,4,5-benzenetetracarboxylic acid and extended bis-monodentate ligands

Four new high-spin cobalt(II) complexes of formulae [Co2(bta)(4,4′-bpy)2(H2O)2]n (1), {Hbpe[Co(Hbta)(bpe)(H2O)2]}n (2), {[Co(H2bta)(azpy)(H2O)2]·azpy}n (3) and {[Co2(bta)(bpa)2(H2O)4]·8H2O}n (4) with H4bta = 1,2,4,5-benzenetetracarboxylic acid, 4,4′-bpy = 4,4′-bipyridine, bpe = trans-1,2-bis(4-pyridyl)ethene, azpy = 4,4′-azobispyridine and bpa = trans-1,2-bis(4-pyridyl)ethane, have been prepared and characterized by single crystal X-ray diffraction. Compounds 1–4 exhibit two-dimensional networks where the fully (1 and 4) or partially (2 and 3) deprotonated tetracarboxylic ligand connects two (2 and 3) or four (1 and 4) cobalt(II) ions through two trans-carboxylate (1–3) or all the carboxylate groups (4) whereas the co-ligands 4,4′-bpy (1), bpe (2), azpy (3) and bpa (4) act as two-fold connectors in trans- (bpe and azpy) and gauche- (bpa) conformations. The cobalt(II) ions in 1 are five-coordinated with two nitrogen atoms from two 4,4′-bpy ligands in the axial positions and a water molecule and two carboxylate-oxygens building the trigonal plane. Six-coordinated cobalt(II) ions occur in 2–4 with two pyridyl-nitrogen atoms, two carboxylate-oxygens and two trans-coordinated water molecules in a somewhat distorted octahedral surrounding. The magnetic properties of 1–4 have been investigated in the temperature range 1.9–300 K. Compound 1 shows a weak antiferromagnetic interaction between the five-coordinated cobalt(II) ions (0.13 ≤ |J| ≤ 0.28 cm−1, Ĥ = −JŜ1·Ŝ2), the exchange pathway involved being the double carboxylate bridges in the syn–syn conformation [cobalt–cobalt separation] of 3.6465(9) A. As the magnetic interactions between the cobalt(II) ions through the phenyl ring of the bta group in 2–4 and those across the extended bpe (2), azpy (3) and bpa (4) bridges are negligible, the strong decrease of χMT upon cooling observed for 2–4 is mainly due to the depopulation of the higher Kramer doublets of the six-coordinated cobalt(II) ions.

Low-Dimensional Copper(II) Complexes with the Trinucleating Ligand 2,4,6-Tris(di-2-pyridylamine)-1,3,5-triazine: Synthesis, Crystal Structures, and Magnetic Properties†

The preparation and structural characterization of three new copper(II) complexes of formula [Cu(3)(dipyatriz)(2)(H(2)O)(3)](ClO(4))(6) x 2 H(2)O (1), {[Cu(4)(dipyatriz)(2)(H(2)O)(2)(NO(3))(2)(ox)(2)](NO(3))(2) x 2 H(2)O}(n) (2), and [Cu(6)(dipyatriz)(2)(H(2)O)(9)(NO(3))(3)(ox)(3)](NO(3))(3) x 4 H(2)O (3) [dipyatriz = 2,4,6-tris(di-2-pyridylamine)-1,3,5-triazine and ox = oxalate] are reported. The structure of 1 consists of trinuclear units [Cu(3)(dipyatriz)(2)(H(2)O)(3)](6+) and uncoordinated perchlorate anions. The two dipyatriz molecules in 1 act as tris-bidentate ligands with the triazine cores being in a quasi eclipsed conformation. Each copper atom in 1 exhibits a distorted square pyramidal geometry CuN(4)O with four pyridyl-nitrogen atoms from two dipyatriz ligands building the basal plane and a water molecule occupying the axial position. The values of the intratrimer copper-copper separation are 8.0755(6) and 8.3598(8) A. Compound 2 exhibits a layered structure of copper(II) ions which are connected through bis-bidentate dipyatriz ligands and bidentate/outer monodentate oxalato groups. The copper atoms in 2 exhibit six- [Cu(1)N(4)O(2)] and five-coordination [Cu(2)N(2)O(3)]. A water molecule and three pyridyl-nitrogen atoms [Cu(1)] and two pyridyl-nitrogen plus two oxalate-oxygen atoms [Cu(2)] define the equatorial plane whereas either an oxalate-oxygen and a pyridyl-nitrogen [Cu(1)] or a nitrate-oxygen [Cu(2)] fill the axial positions. The copper-copper separation through the bridging oxalato is 5.6091(6) A whereas those across dipyatriz vary in the range 7.801(1)-9.079(1) A. The structure of compound 3 contains discrete cage-like hexacopper(II) units [Cu(6)(dipyatriz)(2)(H(2)O)(9)(NO(3))(3)(ox)(3)](3+) where two trinuclear [Cu(3)(dipyatriz)](6+) fragments are connected by three bis-bidentate oxalate ligands, the charge being balanced by three non-coordinated nitrate anions. The values of the intracage copper-copper distance are 5.112(3)-5.149(2) A (across oxalato) and 7.476(2)-8.098(2) A (through dipyatriz). Magnetic susceptibility measurements of polycrystalline samples of 1-3 in the temperature range 1.9-295 K show the occurrence of a weak antiferromagnetic interaction across dipyatriz in 1 [J = -0.08(1) cm(-1), the Hamiltonian being defined as (wedge)H = -J ((wedge)S(1).(wedge)S(2) + (wedge)S(1) x (wedge)S(3) + (wedge)S(2) x (wedge)S(3))] and weak ferro- (2) and strong antiferromagnetic (3) interactions through the oxalato bridge in 2 [J = +0.45(2) cm(-1)] and 3 [J = -390(1) cm(-1)]. The use of the dipyatriz-containing copper(II) species as a building block to design homo- and heterometallic magnetic compounds is analyzed and discussed.

Well-resolved unusual alternating cyclic water tetramers embedded in a crystal host

Infinite network involving two hydrogen-bonded tetrameric water rings (S4 and D2h) in a (4,4)-square grid crystal host

Oligo‐m‐phenyleneoxalamide Copper(II) Mesocates as Electro‐Switchable Ferromagnetic Metal–Organic Wires

Double-stranded copper(II) string complexes of varying nuclearity, from di- to tetranuclear species, have been prepared by the Cu(II)-mediated self-assembly of a novel family of linear homo- and heteropolytopic ligands that contain two outer oxamato and either zero (1u2009b), one (2u2009b), or two (3u2009b) inner oxamidato donor groups separated by rigid 2-methyl-1,3-phenylene spacers. The X-ray crystal structures of these Cu(II) (n) complexes (n=2 (1u2009d), 3 (2u2009d), and 4 (3u2009d)) show a linear array of metal atoms with an overall twisted coordination geometry for both the outer CuN(2)O(2) and inner CuN(4) chromophores. Two such nonplanar all-syn bridging ligands 1u2009b-3u2009b in an anti arrangement clamp around the metal centers with alternating M and P helical chiralities to afford an overall double meso-helicate-type architecture for 1u2009d-3u2009d. Variable-temperature (2.0-300u2005K) magnetic susceptibility and variable-field (0-5.0u2005T) magnetization measurements for 1u2009d-3u2009d show the occurrence of S=nS(Cu) (n=2-4) high-spin ground states that arise from the moderate ferromagnetic coupling between the unpaired electrons of the linearly disposed Cu(II) ions (S(Cu)=1/2) through the two anti m-phenylenediamidate-type bridges (J values in the range of +15.0 to 16.8u2005cm(-1)). Density functional theory (DFT) calculations for 1u2009d-3u2009d evidence a sign alternation of the spin density in the meta-substituted phenylene spacers in agreement with a spin polarization exchange mechanism along the linear metal array with overall intermetallic distances between terminal metal centers in the range of 0.7-2.2u2005nm. Cyclic voltammetry (CV) and rotating-disk electrode (RDE) electrochemical measurements for 1u2009d-3u2009d show several reversible or quasireversible one- or two-electron steps that involve the consecutive metal-centered oxidation of the inner and outer Cu(II) ions (S(Cu)=1/2) to diamagnetic Cu(III) ones (S(Cu)=0) at relatively low formal potentials (E values in the range of +0.14 to 0.25u2005V and of +0.43 to 0.67u2005V vs. SCE, respectively). Further developments may be envisaged for this family of oligo-m-phenyleneoxalamide copper(II) double mesocates as electroswitchable ferromagnetic metal-organic wires (MOWs) on the basis of their unique ferromagnetic and multicenter redox behaviors.

Luminescent lead(II) complexes: new three-dimensional mixed ligand MOFs

Two new lead(II) butyrate-based compounds with formulae [Pb2(but)4(4,4′-bipy)(H2O)]n (1) and [Pb2(but)4(bpe)(H2O)]n (2) [with but = butyrate; 4,4′-bipy = 4,4′-bipyridine and bpe = 1,2-bis(4-pyridyl)ethene] have been synthesized and characterized, with the aim of obtaining different three-dimensional (3D) structures from the typical two-dimensional (2D) lamellar one of most of metal alkanoates, and enhancing the properties of the products synthesized, using these two different N bridging ligands (4,4′-bipy and bpe). Both new complexes show a similar 3D (42638)-sra network in a monoclinic lattice (C2/c) and present interesting photophysical properties. The two compounds have been fully characterized by single crystal X-ray diffraction (synchrotron radiation), thermogravimetric analysis, differential scanning calorimetry, UV-Vis absorption spectroscopy, and steady-state fluorescence and lifetime measurements.