Joaquín Sanchiz

Crystal structure and magnetic properties of the flexible self-assembled two-dimensional square network complex [Cu2(mal)2(H2O)2(4,4′-bpy)] (H2mal=malonic acid and 4,4′-bpy=4,4′-bipyridine)

Abstract The copper(II) complex [Cu 2 (mal) 2 (H 2 O) 2 (4,4′-bpy)] ( 1 ) (H 2 mal=malonic acid and 4,4′-bpy=4,4′-bipyridine) has been prepared and its structure determined by single crystal X-diffraction methods. Compound 1 has a two-dimensional square grid network structure. The square grids are stacked parallel but in a staggered manner on each other along the c -axis, with an interlayer separation of 3.850(1) A. Each layer contains a large cavity of 15.784(1)×15.784(1) A with each edge shared by one malonate group and one 4,4′-bpy ligand and a small planar square of 4.644(1)×4.644(1) A with Cu(II) ions and malonate groups at each corner and side, respectively. Each copper atom is in a distorted square-pyramidal surrounding with three carboxylate-oxygen atoms from two malonate groups and one nitrogen atom from a 4,4′-bpy ligand building the equatorial plane and a water molecule in the axial position. Each 4,4′-bpy molecule exhibits the bis-monodentate bridging mode whereas the malonate simultaneously adopts the bidentate (at one copper atom) and monodentate (at the adjacent copper atom) coordination modes. The bridging carboxylato exhibits the anti – syn coordination mode. The magnetic properties of 1 have been investigated in the temperature range 1.9–300 K and they correspond to a dominant ferromagnetic coupling through bridging malonato within the small square defined by four copper(II) ions ( J =+12.4(1) cm −1 ) and much weaker intrasheet antiferromagnetic coupling between copper(II) ions through bridging 4,4′-bpy ( j eff =−0.052(1) cm −1 ).

Spontaneous resolution upon crystallization of chiral La(III) and Gd(III) MOFs from achiral dihydroxymalonate

The achiral chelating and bridging dihydroxymalonato (mesoxalato) ligand is a new enantiopurity enforcer in extended structures by yielding the Λ/Δ-metal configured homochiral MOFs 2D-[Ln(2)(μ-mesoxalato)(3)(H(2)O)(6)] (Ln = La(III), Gd(III)) through self-resolution during crystal growth.

Structural versatility of the malonate ligand as a tool for crystal engineering in the design of molecular magnets

The synthesis of ferro- and ferri-magnetic systems with a tunable Tc and three-dimensional (3-D) ordering from molecular precursors implying transition metal ions is one of the active branches of molecular inorganic chemistry. The nature of the interactions between the transition metal ions (or transition metal ions and radicals) is not so easy to grasp by synthetic chemists working in this field since it may be either electrostatic (orbital) or magnetic (mainly dipolar). Therefore, the systems fulfilling the necessary requirements to present the expected magnetic properties are not so easy to design on paper and realize in the beaker. In this work we show how the design of one-, two- and three-dimensional materials can strongly benefit from the use of crystal engineering techniques, which can give rise to structures of different shapes, and how these differences can give rise to different properties. We will focus on the networks constructed by assembling malonate ligands and metal centres. The idea of using malonate (dianion of propanedioic acid, H2mal) is that it can give rise to different coordination modes with the metal ions it binds. Extended magnetic networks of dimensionalities one (1-D), two (2-D) and three (3-D) can be chemically constructed from malonate-bridged metallic complexes. These coordination polymers behave as ferro-, ferri- or canted antiferro-magnets. We are currently trying to obtain analogous compounds using magnetically anisotropic ions, such as cobalt(II), in order to explore how structural differences influence the magnetic properties. In this case the control of the spatial arrangement of the magnetic building blocks is of paramount importance in determining the strength of the magnetic interaction. The possibility of controlling the shape of the networks depends on the coordination bond between the metal ion and the ligands and on supramolecular interactions such as stacking interactions or hydrogen bonding.

Malonate-based copper(II) coordination compounds: ferromagnetic coupling controlled by dicarboxylates

Studies on structural and magnetic properties of polynuclear transition metal complexes, aimed at understanding the structural and chemical factors governing electronic exchange coupling mediated by multiatom bridging ligands, are of continuing interest to design new molecular materials exhibiting unusual magnetic, optical and electrical properties, bound to their molecular nature. Looking at potentially flexible bridging ligands, the malonate group seems a suitable candidate. The occurrence of two carboxylate groups in the 1,3 positions allows this ligand to adopt simultaneously chelating bidentate and different carboxylato bridging modes (syn–syn, anti–anti and syn–anti trough one or two carboxylate groups) In the course of our research we have structurally and magnetically characterized several carboxylato bridged copper(II) complexes. In the present study we start describing briefly the structure and the magnetic behaviour of the compounds, subsequently we analyze the magneto-structural correlations concluding that the parameter that governs, in first order, the magnetic interaction between metal centres is the relative position of the carboxylato bridge of the malonate respect to the copper(II) ions: equatorial–equatorial (strong interaction), equatorial–apical (weak interaction) and apical–apical (negligible interaction). Inside this division another parameters become important such as β (angle between copper(II) basal planes) in the equatorial–equatorial, or the distortion t in the equatorial–apical.

Synthesis, crystal structure and magnetic properties of two-dimensional malonato-bridged cobalt(II) and nickel(II) compounds

Two isostructural malonato-bridged complexes of formula {[M(H2O)2][M(mal)2(H2O)2]}n [M = Co(II) (1), Ni(II) (2); H2mal = malonic acid] have been synthesised and characterized by X-ray diffraction. Their structure consists of corrugated layers of trans-diaquabismalonatemetalate(II) and trans-diaquametal(II) units bridged by carboxylate–malonate groups in the anti–syn conformation. Two crystallographycally independent metal atoms occur in 1 and 2. The malonate anion acts simultaneously as a bidentate and bis-monodentate ligand. Variable-temperature (1.9–295 K) magnetic susceptibility measurements indicate the occurrence of weak antiferro- (1) and ferromagnetic (2) interactions between the cobalt(II) (1) and nickel(II) ions (2) through the anti–syn caboxylate–malonate bridge. A brief discussion on the structural diversity and crystal engineering possibilities of the malonate complexes with divalent first-row transition metal ions other than copper(II) is carried out.

Crystal engineering of 3-D coordination polymers by pillaring ferromagnetic copper(II)-methylmalonate layers

Three new copper(II) complexes of formula [Cu(Memal)(H2O)]n (1), [Cu2(pyz)(Memal)2] (2) and [Cu2(4,4′-bpy)(Memal)2(H2O)2] (3) (Memal = methylmalonate, pyz = pyrazine and 4,4′-bpy = 4,4′-bipyridine) were obtained and structurally characterized by X-ray diffraction. Complex 1 is a square grid of aquacopper(II) units which are linked by carboxylate-methylmalonate groups in the anti–syn (equatorial–equatorial) coordination mode. The crystal structures of 2 and 3 consist of corrugated layers of copper(II) (2) and aquacopper(II) (3) units with intralayer carboxylate-methylmalonate bridges in the anti–syn (equatorial–apical) coordination mode which are linked through pyrazine (2) and 4,4′-bipyridine (3) ligands; to build up a 3-D network. Magnetic susceptibility measurements of complexes 1–3 in the temperature range 2–300 K show the occurrence of an overall ferromagnetic behaviour with a weak intralayer ferromagnetic coupling (J = +1.61(1) cm−1) in 1 whereas two opposite magnetic interactions occur in 2 and 3, one ferromagnetic through the anti–syn carboxylate (2 and 3) and the other antiferromagnetic through pyz (2) and 4,4′-bpy) (3).

2∞[Cu2(μ5-btb)(μ-OH)(μ-H2O)]: a two-dimensional coordination polymer built from ferromagnetically coupled Cu2 units (btb = benzene-1,2,3-tricarboxylate)

Hydrothermal reaction of Cu(NO3)(2).3H2O, Cd(OH)2 or Zn(OH)2 with benzene-1,2,3-tricarboxylic acid (H3btb, hemimellitic acid) produced the 2D coordination polymer (MOF) (infinity)(2)[Cu2(mu5-btb)(mu-OH)(mu-H2O)] (1) and the 2D hydrogen-bonded complexes [Cd(H2btb)2(H2O)4].2H2O (2) and [Zn(H2O)6](H2btb)(2).4H2O (3) which are characterized by single-crystal X-ray diffraction, X-ray powder diffraction and thermoanalysis. Magnetic susceptibility measurements between 1.9-300 K for 1 revealed three magnetic active exchange pathways that link the copper(II) ions through a long mu-aqua bridge, an anti-syn carboxylate bridge [j2 = 0.161(1) cm(-1)], and through a mixed mu-hydroxo + syn-syn carboxylate bridge [J = 83(1) cm(-1)]. At temperatures higher than 30 K the system behaves as isolated Cu2 units with strong ferromagnetic Cu-Cu coupling through the mu-hydroxo and syn-syn carboxylate bridge. The strong ferromagnetic coupling is explained with Hoffmanns approach by means of the concept of counter-complementarity introduced by Nishida et al.[Chem. Lett., 1983, 1815-1818].

Ferromagnetic coupling in the malonato-bridged copper(II) chains [Cu(Im)2(mal)]n and [Cu(2-MeIm)2(mal)]n(H2mal = malonic acid, Im = imidazole and 2-MeIm = 2-methylimidazole)

Two new malonato-bridged copper(II) complexes of formula [Cu(Im)2(mal)]n (1) and [Cu(2-MeIm)2(mal)]n (2) (Im=imidazole, 2-MeIm=2-methylimidazole and mal=malonate dianion) have been prepared and their structures solved by X-ray diffraction methods. The [Cu(Im)2(mal)] and [Cu(2-MeIm)2(mal)] neutral entities act as monodentate ligands towards the adjacent copper(II) units through one of the two carboxylate groups, the OCO bridge exhibiting an anti-anti conformation. The environment of each copper atom in 1 and 2 is distorted square pyramidal: two carboxylate oxygen atoms from a bidentate malonate and two nitrogen atoms from two imidazole (1) or 2-methylimidazole (2) ligands form the equatorial plane whereas the apical position is occupied by a carboxylate oxygen from the malonate group of the neighbouring complex unit. The intrachain copper-copper separation is 6.036(2) (1) and 6.099(2) A (2). The magnetic properties of 1 and 2 have been investigated in the temperature range 1.9–290 K. Overall, ferromagnetic behaviour is observed in both cases and the intrachain magnetic coupling (J) between the copper(II) ions through the carboxylato group is found to be 1.64 (1) and 0.39 cm−1 (2) (the Hamiltonian being H=−JΣiSi·Si+1).

Malonic acid: a multi-modal bridging ligand for new architectures and properties on molecule-based magnets

Abstract In this work, we show how the design of one-, two- and three-dimensional materials can strongly benefit from the use of crystal engineering techniques, which can give rise to structures of different shapes, and how these differences can give rise to different properties. We will focus on the networks constructed by assembling malonate ligands and metal centres. The idea of using malonate (dianion of propanedioic acid, H 2 mal) is that they can give rise to different coordination modes with the metal ions bind. Extended magnetic networks of dimensionalities 1 (1D), 2 (2D) and 3 (3D) can be chemically constructed from malonato-bridged metallic complexes. These coordination polymers behave as ferro-, ferri- or canted antiferromagnets. The control of the spatial arrangement of the magnetic building blocks is of paramount importance in determining the strength of the magnetic interaction. It depends on the coordination bond between the metal ion and the ligands, and on supramolecular interactions such as stacking interactions or hydrogen bonds.

Magnetic Ordering in Two Molecule-Based (10,3)-a Nets Prepared from a Copper(II) Trinuclear Secondary Building Unit

Two new molecule-based materials of formulas 3D-{[K(H(2)O)(6)](0.5)[K(18-crown-6)](0.5)[MnCu(3)(Hmesox)(3)].5.25H(2)O} (1) and 3D-{(Ph(4)P)(2)[MnCu(3)(Hmesox)(3)Cl].3.5H(2)O} (2) have been prepared from a tricopper(II) secondary building unit (SBU), [Cu(3)(Hmesox)(3)](3-) (H(4)mesox = mesoxalic acid, 2-dihydroxymalonic acid). Compound 1 is obtained by means of the reaction of the SBU with manganese(II) acetate in the presence of potassium cations and the 18-crown-6 ether, whereas compound 2 is obtained by means of the reaction of the SBU with manganese(II) acetate in the presence of Ph(4)PCl. The [MnCu(3)(Hmesox)(3)](-) and [MnCu(3)(Hmesox)(3)Cl](2-) moieties in compounds 1 and 2, respectively, yield chiral 3-connected three-dimensional (3D) anionic (10,3)-a (srs, SrSi(2)) nets. In the cubic and centrosymmetric structures (Pa3) of 1, two inversion-symmetry-related anion nets interpenetrate to a racemic structure. The Ph(4)P(+) cations in 2 are organized in a supramolecular (10,3)-a net through the 6-fold phenyl embrace. In 2, both the cationic and anionic nets are homochiral and enantiopure with opposite handedness and form interpenetrating supramolecular and covalent (10,3)-a nets in the noncentrosymmetric Sohncke space group P 2(1)2(1)2(1). Both compounds display ferrimagnetic interaction with long-range magnetic ordering below 2.5 and 15.2 K for 1 and 2, respectively. A dehydrated phase of 2 exhibits a T(c) of 21.8 K. The saturation of magnetization, M(S), indicates two different ground states, S = (1)/(2) and (3)/(2), for the tricopper(II) units in 1 and 2, respectively. The different spin states of the tricopper(II) unit in 1 and 2 has been explained by means of a density functional theory (DFT) study performed in the [Cu(3)(Hmesox)(3)](3-) and [Cu(3)(Hmesox)(3)Cl](4-) fragments, for 1 and 2, respectively. A further DFT study has allowed one to analyze the structural parameters that lead to the different spin ground states for the trinuclear units in both compounds.