Joan Ribas

Polynuclear NiII and MnII azido bridging complexes. Structural trends and magnetic behavior

Abstract The azide anion is a good bridging ligand for divalent metal ions, mainly Cu II , Ni II and Mn II . It may give end-to-end (1,3) or end-on (1,1) coordination modes. As a general trend, the 1,1 mode exhibits ferromagnetic coupling while the 1,3 mode creates antiferromagnetic coupling. This review focuses on polynuclear Ni II and Mn II azido bridging complexes. Polynuclear structures known to have these two cations are: discrete (normally dinuclear), one-, two- and three-dimensional nets. The main characteristics of these structures are reported together with their magnetic behavior. From a large number of known structures, magneto-structural correlations are made. Taking into account that M–N 3 distances are always similar, the angles within the M–(N 3 ) n –M unit are the main determinant of the type and magnitude of the exchange coupling. Moreover, some one-, two- and three-dimensional complexes exhibit cooperative effects (long-range magnetic order), behaving as molecular magnets. This behavior is also analyzed.

Flexiblemeso-Bis(sulfinyl) Ligands as Building Blocks for Copper(II) Coordination Polymers: Cavity Control by Varying the Chain Length of Ligands

Fillings and cavities: Three novel pseudo-octahedral metal-organic frameworks, 1-3, consisting of macrometallacyclic noninterpenetrating meso networks and exhibiting weak antiferromagnetic interactions, have been constructed from CuII centers and structurally flexible R,S-bis(sulfinyl) ligands. Varying the chain length of ligands is found to control the cavity sizes of the networks.

Synthesis, structure and magnetism of a new dicubane-like ferromagnetic tetranuclear nickel cluster containing versatile azido-only bridges and a bis(bidentate) Schiff base blocker

A new tetranuclear double-open dicubane complex [Ni4(mu 2-N3)4(mu 3-N3)2(N3)2(enbzpy)2].2H2O (enbzpy = [N,N-bis(pyridin-2-yl)benzylidene]ethane-1,2-diamine) has been characterised structurally and magnetostructurally.

Metal–organic framework structures of Cu(II) with pyridine-2,6-dicarboxylate and different spacers: identification of a metal bound acyclic water tetramer

The ligand pyridine-2,6-dicarboxylic acid (pdcH2) reacts under hydrothermal conditions, with Cu(NO3)2·6H2O in the presence of different N-heterocycles used as spacers to form 1D, 2D or 3D metal–organic framework structures depending on the nature of the spacer. These network structures are characterized by X-ray crystallography, variable temperature magnetic measurements, powder X-ray diffraction, infrared and thermal gravimetric analyses. With 4,4′-bipyridine spacer, a 2D network is formed where every alternate Cu(II) ion in the chain is coordinated terminally to an acyclic tetrameric water cluster.

Unprecedented Marriage of a Cationic Pentanuclear Cluster and a 2D Polymeric Anionic Layer Based on a Flexible Tripodal Ligand and a CuII Ion

The anionic CdI(2)-type topological net, [Cu(2)(tci)(2)](2-), and the pentanuclear copper cluster cation [Cu(5)(tci)(2)(OH)(2)(H(2)O)(8)](2+) [tci = tris(2-carboxyethyl)isocyanurate] form a complementary 3D supramolecular framework. Interestingly, there exist centrosymmetric cyclic (H(2)O)(18) clusters in the cavities.

An azido–metal–isonicotinate complex showing long-range ordered ferromagnetic interaction: synthesis, structure and magnetic properties

A new 3D Cu(II) complex [Cu1.5(N3)2(isonicotinate)]n [1], which features two types of bridging modes for azide (mu(1,1) and the rare asymmetric mu(1,1,3)) where the three bonds of the mu(1,1,3)-N3(-) group to Cu exhibit three different distances, has been synthesized and characterized, and magnetic measurements indicate that [1] experiences long-range ferromagnetic ordering at approximately 6 K.

Synthesis, crystal structure and magnetic behavior of three polynuclear complexes: [Co(pyo)2(dca)2]n, [Co3(ac)4(bpe)3(dca)2]n and [{Co(male)(H2O)2}(H2O)]n [pyo, pyridine-N-oxide; dca, dicyanamide; ac, acetate; bpe, 1,2-bis-(4-pyridyl)ethane and male, maleate]

Three polymeric cobalt(II) complexes of formulae [Co(pyo)2(dca)2]n (1), [Co3(ac)4(bpe)3 (dca)2]n (2) and [{Co(male)(H2O)2(H2O)]n (3) [pyo, pyridine-N-oxide; dca, dicyanamide; ac, acetate; bpe, 1,2-bis-(4-pyridyl)ethane and male, maleate] have been synthesized and characterized structurally as well as magnetically. The structure determination of complex 1 shows that each octahedral Co(II) in the 1D coordination chain is attached with four μ-1,5-dicyanamide and two pendant pyridine-N-oxide ligands, which form mutual relationships with other 1D chains through non-covalent π-π interactions, giving rise to a 2D infinite sheet-like structure. The molecular structure reveals that complex 2 adopts an infinite three-leg ladder-like structure in which three parallel 1D Co(bpe) chains are connected by syn-syn and oxo bridging acetate ligands. The dicyanamide ligands are pendant to the terminal Co(II) centers. Complex 3 is an infinite 3D network in which carboxylate groups of the maleate ligand are linked to Co(II) centers in syn-anti fashion. The structure of complex 3 has already been reported. The variable temperature (300–2 K) magnetic measurements have been performed for all three complexes. In the case of 2, the full structure can be rationalized as quasi-isolated trimers; the exchange Hamiltonian that describes magnetic interactions between the effective S′ = 1/2 spins, at low temperature is . Fixing g⊥ = 6.01 and g∣∣ = 2.25, according to the EPR measurements at 4 K, 2J = −3.3 cm−1 is the best-fit parameter. For 1 and 3, complete fits are not possible for calculating the corresponding J parameters for the one- and three-dimensional structures, respectively. Only an approximate J value has been calculated for 1.

Polymeric networks of copper(II) using succinate and aromatic N–N donor ligands: synthesis, crystal structure, magnetic behaviour and the effect of weak interactions on their crystal packing

Four succinato-bridged complexes of copper(II) have been synthesized. Complex 1, [Cu(2)(mu-OH(2))(2)L(bpy)(2)(NO(3))(2)](n) and 2, [Cu(2)(mu-OH(2))(2)L(phen)(2)(NO(3))(2)](n)(bpy = 2,2[prime or minute]-bipyridine; phen = 1,10-phenanthroline and LH(2)= succinic acid) exhibit 1D coordination polymer structures where both the nitrate ions are directly linked to the copper(ii) producing synthons in a 2D sheet. A novel 2D grid-like network, ([Cu(4)L(2)(bpy)(4)(H(2)O)(2)](ClO(4))(4)(H(2)O))n3, is obtained upon changing the nitrate by perchlorate anion in complex 1, where the channels are occupied by the anions. On changing the nitrate by tetrafluoroborate anion in complex 2, a novel octanuclear complex, [Cu(8)L(4)(phen)(12)](BF(4))(8).8H(2)O 4, is isolated. The coligand bpy and phen in these complexes show face-to-face (in 1,2,3,4) or edge-to-face (in 4 )pi-pi interactions forming the multidimensional supramolecular architectures. Interestingly, the appearance of edge-to-face pi-pi interactions in complex facilitates the formation of discrete octanuclear entities. Variable-temperature (300-2 K) magnetic measurements of complexes have been done. Complexes 1 and 2 show very weak antiferromagnetic (OOC-CH(2)-CH(2)-COO) and ferromagnetic coupling (mu-H(2)O). Complex 3 also shows antiferromagnetic (syn-syn mu-OCO), and ferromagnetic coupling (mu-O of the -COO group). Complex 4 with two types (syn-syn and syn-anti) of binding modes of the carboxylate group shows strong antiferromagnetic interaction.

Single-Molecule Magnets: Different Rates of Resonant Magnetization Tunneling in Mn12 Complexes**

Two new molecular magnets, the dodecanuclear manganese complexes of the type [Mn12 O12 (O2 CR)16 (H2 O)4 ] (known for R = CH3 , new for R = o-ClC6 H4 , o-BrC6 H4 ) have contributed to a better quantum mechanical understanding of single-molecule magnets. For instance, appreciable differences in the steps seen in the magnetization hysteresis loops of these high-spin clusters are attributed to changes in the rates of magnetization tunneling from one complex to another.

Synthesis, characterization and properties of highly conducting organometallic polymers derived from the ethylene tetrathiolate anion

Abstract The preparation and electrical conductivity studies of a series of organometallic polymers, (MC2S4x−)n (M = Ni, Pd, Pt, Au), derived from the ethylene tetrathiolate anion are described. The synthesis of the precursor molecules or molecular complexes (PhCH2)4(C2S4), (AsPh4)2[M(C3OS4)2], (C3)OS4Pd(dppe) and (AsPh4)2[(C3OS4)Cu(C2S4)Cu(C3OS4)] is also described. From these results the different possible formation mechanisms of the polymers are discussed. The polymers show high compaction powder conductivity at room temperature (from 10−5 to 5Ω−1 cm−1). [Na0.31(NiC2S4)]ν, one of the most conductive polymers, exhibits a metal-like temperature dependence of conductivity, as evidenced by voltage shorted compaction (VSC) experiments. These conductivity properties are to be related with the degree of partial oxidation (DPO) observed in the polymers studied.