Tridentate Schiff-base carboxylate-containing ligands, derived from the condensation of 2-imidazolecarboxaldehyde with the amino acids beta-alanine (H2L1) and 2-aminobenzoic acid (H2L5) and the condensation of 2-pyridinecarboxaldehyde with beta-alanine (HL2), D,L-3-aminobutyric acid (HL3), and 4-aminobutyric acid (HL4), react with copper(II) perchlorate to give rise to the helical-chain complexes [[Cu(mu-HL1)(H2O)](ClO4)]n (1), [[Cu(mu-L2)(H2O)](ClO4).2H2O]n (2), and [[Cu(mu-L3)(H2O)](ClO4).2H2O]n (3), the tetranuclear complex [[Cu(mu-L4)(H2O)](ClO4)]4 (4), and the mononuclear complex [Cu(HL5)(H2O)](ClO4).1/2H2O (5). The reaction of copper(II) chloride with H2L1 leads not to a syn-anti carboxylate-bridged compound but to the chloride-bridged dinuclear complex [Cu(HL1)(mu-Cl)]2 (6). The structures of these complexes have been solved by X-ray crystallography. In complexes 1-4, roughly square-pyramidal copper(II) ions are sequentially bridged by syn-anti carboxylate groups. Copper(II) ions exhibit CuN2O3 coordination environments with the three donor atoms of the ligand and one oxygen atom belonging to the carboxylate group of an adjacent molecule occupying the basal positions and an oxygen atom (from a water molecule in the case of compounds 1-3 and from a perchlorate anion in 4) coordinated in the apical position. Therefore, carboxylate groups are mutually cis oriented and each syn-anti carboxylate group bridges two copper(II) ions in basal-basal positions with Cu...Cu distances ranging from 4.541 A for 4 to 5.186 A for 2. In complex 5, the water molecule occupies an equatorial position in the distorted octahedral environment of the copper(II) ion and the Cu-O carboxylate distances in axial positions are very large (>2.78 A). Therefore, this complex can be considered as mononuclear. Complex 6 exhibits a dinuclear parallel planar structure with Ci symmetry. Copper(II) ions display a square-pyramidal coordination geometry (tau = 0.06) for the N2OCl2 donor set, where the basal coordination sites are occupied by one of the bridging chlorine atoms and the three donor atoms of the tridentate ligand and the apical site is occupied by the remaining bridging chlorine atom. Magnetic susceptibility measurements indicate that complexes 1-4 exhibit weak ferromagnetic interactions whereas a weak antiferromagnetic coupling has been established for 6. The magnetic behavior can be satisfactorily explained on the basis of the structural data for these and related complexes.

The reaction of M(hfac)2 with the tridentate Schiff base H2L (where H2L stands for the 1:1 condensation product of 2‐imidazolecarboxaldehyde with β‐alanine) leads to the complexes [M(HL)(hfac)]n [M = MnII, NiII, and CuII; hfac = hexafluoroacetylacetonate anion] (1–3). The structures of the complexes 1 and 3 have been solved by X‐ray crystallographic methods. The structures are very similar and consist of infinite zig‐zag chains, running parallel to the b axis, in which the metal ions are bridged sequentially by anti‐anti carboxylate groups with intrachain metal–metal distances of 6.134 Å for 1 and 6.239 Å for 3. Each monodeprotonated HL ligand acts as a tridentate one to a metal(II) ion and as a monodentate one to a neighbouring metal(II) centre. Metal atoms exhibit distorted octahedral coordination spheres comprised of two oxygen atoms from the hexafluoroacetylacetonate ligand, three donor atoms from the HL ligand and the oxygen atom belonging to the carboxylate group of an adjacent molecule. The complexes 1–3 have been confirmed to be isomorphous and isostructural on the basis of X‐ray powder diffraction and IR spectra. The magnetic properties of the three compounds were studied by susceptibility measurements as a function of the temperature and successfully analyzed in terms of the isotropic spin Hamiltonian for one‐dimensional infinite chain systems to give the coupling parameters J = –0.91 cm−1, g = 2.03 (1); J = –13.2 cm−1, g = 2.24 (2); and J = 0.40 cm−1, g = 2.11 (3). The magnetic behaviour for all three complexes can be satisfactorily explained in terms of the conformation of the bridge and the interaction between the d orbitals of the metal centre and the bridge.

The 2D honeycomb-like layered iron(iii)-nickel(ii) cyanidebridged complex [Ni(cyclam)] 3 [Fe(CN)6] 2 ·nH 2 O exhibits ferromagnetic intralayer and antiferromagnetic interlayer interactions; above 3 K the magnetic properties are typical of a metamagnet with H c = 5000 G, whereas below 3 K a canted structure is formed, leading to a long range ferromagnetic ordering.Bimetallic assemblies with Prussian blue-like structure form a family of materials that exhibit spontaneous magnetization at T c as high as 315 K, 1 and interesting electro-chemical, optoelectronic and magneto-optical properties. 2 The crystallization of Prussian blue analogues, however, is very difficult and it has been only quite recently that Kahn and coworkers 3 have succeeded in growing crystals of [Mn 2 (H 2 O) 5 Mo(CN) 7 ]·nH 2 O (a and b forms), which ferromagnetically order at 51 K.One alternative route to bimetallic cyanide-bridged extended arrays is that of using hexacyanometalate building blocks with metal complexes containing polydentate ligands. This hybrid approach favours the crystallization and then their magnetostructural study. Depending on the nature of the building blocks different and fascinating extended network structures can be obtained, some of which are magnetically ordered. 4 On O (n = 12 and 22.5). X-ray analysis † reveals that both phases exhibit similar structures, which only differ in the number of water molecules (hereafter we shall discuss the results for n = 22.5, whose structure is more accurately determined). The structure consists of honeycomb-like layers (Fig. 1) and crystal water molecules that occupy the interlayer space.

Coordination polymers and metal-organic frameworks are appealing as synthetic hosts for mediating chemical reactions. Here we report the preparation of a mesoscopic metal-organic structure based on single-layer assembly of aluminium chains and organic alkylaryl spacers. The material markedly accelerates condensation reactions in water in the absence of acid or base catalyst, as well as organocatalytic Michael-type reactions that also show superior enantioselectivity when comparing with the host-free transformation. The mesoscopic phase of the solid allows for easy diffusion of products and the catalytic solid is recycled and reused. Saturation transfer difference and two-dimensional 1H nuclear Overhauser effect NOESY NMR spectroscopy show that non-covalent interactions are operative in these host–guest systems that account for substrate activation. The mesoscopic character of the host, its hydrophobicity and chemical stability in water, launch this material as a highly attractive supramolecular catalyst to facilitate (asymmetric) transformations under more environmentally friendly conditions.