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[Co(4)(phcina)(6)(OH)(2)(H(2)O)(4)]·2H(2)O (1) (phcina = α-phenylcinnamate), obtained as pink needles by hydrothermal technique, consists of two edge-sharing pairs of octahedral CoO(6) connected by their apexes to form diamond-chains. The magnetic chains are isolated from one another without chemical bond at 17 Å by the nonmagnetic bulky organic ligand. It exhibits hidden canting below the long-range antiferromagnetic (AF) ordering at 5.5 K. A metamagnetic critical field of only 30 Oe at 2 K suffices to overcome the weak through space magnetic interaction between chains and reverse the moments within the chains to give a canted AF reaching only (1)/(4) of the required moment for all parallel moment alignment. The anisotropy measured on aligned crystals, using dc and ac modes, estimates g(||b) = 6.5 and g(⊥b) = 3.25, thus eliminating an Ising or a Heisenberg magnetic dimensionality while suggesting an easy-plane AF. Weak frequency dependence of the ac-susceptibilities below the transition temperature is associated with domain structure in the ordered state, and absence of it well above T(N) eliminates single-chain magnetism. It is inferred that the competition between the strong AF coupling between the edge-sharing pairs, which dominates the high temperature susceptibility, and the ferromagnetic coupling within the pairs, results in a canting of the moments within each chain, where the moments are out of the ac-plane by an estimated 13°. In zero-field the moments of adjacent chains are antiparallel resulting in a compensated system, i.e., hidden canting.

The hydrothermal synthesis, single crystal X-ray structures and magnetic properties of two layered cobalt-carboxylate complexes, ∞2[CoII(O2C*CH(OH)C6H5)2] (1) and ∞2[CoII(O2C*CH(NH2)C6H5)2] (2), where O2CCH(OH)C6H5 is mandalate and O2CCH(NH2)C6H5 is phenylglycinate, are described. Pale pink crystals of 1 and 2 were obtained by the reaction of cobalt nitrate and the enantiomer-pure acids at 120 °C. In each case, the structure consists of stacks of quasi square-grid polymeric sheets consisting of carboxylato- bridges, M–O–C–O–M, and the presence of both d- and l-enantiomers of the ligands segregated on each face of the layer. The ligands exhibit both chelating and bridging functions with the carboxylate group adopting an anti–anti mode. The magnetic properties are characteristic of weakly interacting paramagnets where the moments are elevated by an important orbital contribution via spin-orbit coupling. [Copyright &y& Elsevier]

The hydrothermal synthesis, structures and magnetic properties of the isostructural coordination polymers ∞3[M2II(pm)], M=Co, Fe or Mn and pm=pyromellitate, 1,2,4,5-benzenetetracarboxylate, are described. The structure consists of 1D chains of edge-sharing MO6 octahedra that are connected into layers via O&z.sbnd;C&z.sbnd;O bridges. The layers are held together by the pyromellitate (pm4−) backbone to give a 3D structure where each ligand participates in an unprecedented 12 coordination M&z.sbnd;O bonds to ten metal atoms. The Fe and Mn analogues are antiferromagnets whereas the Co compound displays a more complex behaviour, existing in one of three magnetic ground states at low temperature (collinear antiferromagnetism, canted antiferromagnetism and field induced ferromagnetism). [Copyright &y& Elsevier]

Reaction of Co(II) with phenylcinnamic acid and sodium hydroxide under hydrothermal conditions yields a new hexanuclear Co(II) complex, [Co6(OH)2(L)10] (L=phenylcinnamate). [Co6(OH)2(L)10] consists of two edge-sharing octahedral {CoO6} and four tetrahedral {CoO4} units linked through μ-carboxylate ligands and μ-hydroxide ions. The magnetic moment shows a large decrease from 300 to 25 K which amounts to antiferromagnetic coupling between cobalt ions in octahedral and tetrahedral sites leading to an s=3 ground-state at low temperatures. [Copyright &y& Elsevier]

Studies the construction of hydrogen-bonded and coordination-bonded networks of cobalt with pyromellitate. Presence of very dense inorganic paramagnetic layers on hybrid compounds; Development of metal—carboxylate hybrid materials; Preparation of crystals of the synthetic minerals.

The hydrothermal synthesis, single crystal X-ray structure and magnetic properties of a new cobalt(II)-carboxy-cinnamate complex is described. Reaction of Co(II), Carboxy-cinnamic acid (C 10 H 8 O 4 ) and NaOH at 120°C yield the coordination network, Co(H 2 O) 2 carboxy-cinnamate ( 1 ). 1 crystallizes in the monoclinic system, a =11.3236(4), b =6.6084(4), c =7.2011(6) Å, β=101.948(5)°, V =527.2(1) Å 3 , space group P 2 1 /c, Z =2. 1 possesses a three-dimensional coordination-bonding network consisting of layers of CoO 6 bridged by the tetra-dendate carboxy-cinnamate. Its magnetic moment decreases on lowering temperature due to spin-orbit coupling and no interaction between cobalt ions is observed. carboxylate cobalt coordination polymer magnetic properties [ABSTRACT FROM AUTHOR]

The synthesis, structure and magnetic properties of a novel series of layered compound containing interlayer dicarboxylate anions, where the interlayer separation has been tuned from 9.9 to 13.8 Å, are reported. They display collinear antiferromagnetism (AF) just below the Néel temperature and in small applied fields canted AF below a second transition. At higher fields metamagnetic behavior is observed which exhibits no hysteresis in the collinear state and wide hysteresis, attaining 5.2 Tesla at 2K, below the canting temperature. The phase diagram is also presented. [ABSTRACT FROM AUTHOR]

We herein report the synthesis, single-crystal structures of coordination polymers, and structural transformations of complexes employing 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarbonitrile (tdpd2−) and pyrazine (pyz) as bridging ligands. {[M(H2O)4(pyz)][M(tdpd)2(pyz)]·6(H2O)}n, [1·10H2O and 2·10H2O where M = Co (1) and Zn (2)], consists of two types of crystallographically independent one-dimensional (1D) structures packed together. One motif, [M(tdpd)2(pyz)]2− (A), is an anionic infinite pyz bridged 1D array with chelating tdpd2− ligands, and the other motif is a cationic chain, [M(H2O)4(pyz)]2+ (B), which is decorated with four terminal water molecules. The 1D arrays (A) and (B) are arranged in parallel by multi-point hydrogen-bonding interactions in an alternate (A)(B)(A)(B) sequence extending along the c-axis. Both compounds exhibit structural transformations driven by thermal dehydration processes around 350 K to give partially dehydrated forms, 1·2H2O and 2·2H2O. The structural determination of the partially dehydrated form, 2·2H2O, reveals a solid-state structural transformation from a 1D chain structure to a two-dimensional (2D) coordination sheet structure, [Zn2(tdpd)2(H2O)2(pyz)]n (2·2H2O). Further heating to 500 K yields the anhydrous form 2. While the virgin samples of 1·10H2O and 2·10H2O crystallize in different crystal systems, powder X-ray diffraction (PXRD) measurements of the dehydrated forms, 1·2H2O and 2·2H2O, are indicative of the same structure. The structural transformation is irreversible for 1·10H2O at ambient conditions. On the other hand, compound 2·10H2O shows a reversible structural change. The solid-state structural transformation for 1·10H2O was also confirmed by monitoring in-situ magnetic susceptibility, which is consistent with other thermally-induced measurements. [ABSTRACT FROM AUTHOR]

We present the hydrothermal synthesis, characterization (IR, DT-TGA), single-crystal structures, and magnetic properties of two polymorphs of trans-3(3-pyridyl)acrylate of cobalt(II) and of nickel(II), MII(C8H6NO2)2(H2O)2. Hydrothermal reaction at 120 or 170 °C results exclusively in the different polymorphs. The infrared spectra and thermogravimetric analyses of the complexes are almost similar for the two polymorphs but show a difference between cobalt and nickel in energies of the vibrational modes and in the decomposition temperatures. The crystal structures of the two polymorphs are quite different; one crystallizes in a monoclinic space group and the other in a triclinic. This major difference is due to the different stereochemistry, cis or trans, of the coordination at the metal sites. When it is trans-MN2O4, it results in the monoclinic cell consisting of a 3D-network of metals bridged by the ligands through single bonds (M-N and M-O). There is threading of three sublattices up to 2a × 4b × 2c, at which point the three sublattices are knotted into one infinite framework. When it is cis-MN2O4, it results in the triclinic cell and consists of Zwitterionic linear chains of metals bridged by one single ligand via the pyridine and a bidentate carboxylate group and the other ligand is bonded only via the pyridine while its carboxylate end is free. All four compounds are paramagnetic with Weiss constants suggesting weak interactions. [ABSTRACT FROM AUTHOR]

Examines the synthesis and characterization of layered cobalt hydroxysulfates with both rigid and flexible organic pillars. Interaction between pillaring agents and compositionally complex inorganic layer; Influence of multiple metal sites and geometrical frustration on cobalt hydroxides magnetism.