Magnetic [n × n] (n = 2−5) Grids by Directed Self-Assembly

Syntheses, Structures and Photoluminescence of a Series of Transition Metal-Cyanopyridine Polymers

A series of transition metal- n cyanopyridines ( i.e. pyridine- n-carbonitrile; n = 2, 3, 4) complexes with one-dimensional (1-D) structures, [CuCl2(pyridine-3-carbonitrile)2] n, [CuCl2(pyridine-4-carbonitrile)2] n and [CoCl2(pyridine-4-carbonitrile)2] n, have been synthesised via hydrothermal reactions and structurally characterised by single-crystal X-ray diffraction. All these complexes feature infinite 1-D chain-like structures. Photoluminescent investigation reveals that the title complexes display strong emissions which may originate from π→π* charge-transfer interaction of the ligands.

Tuning the spin ground state in heterononanuclear nickel(II)-copper(II) cylinders with a triangular metallacyclophane core

Two new heterometallic Ni(II)(n)Cu(II)((9-n)) complexes [n = 1 (2) and 2 (3)] have been synthesized following a multicomponent self-assembly process from a n:(3 - n):2:6 stoichiometric mixture of Ni(2+), Cu(2+), L(6-), and [CuL'](2+), where L and L' are the bridging and blocking ligands 1,3,5-benzenetris(oxamate) and N,N,N',N'',N''-pentamethyldiethylenetriamine, respectively. Complexes 2 and 3 possess a unique cyclindrical architecture formed by three oxamato-bridged trinuclear linear units connected through two 1,3,5-substituted benzenetris(amidate) bridges, giving a triangular metallacyclophane core. They behave as a ferromagnetically coupled trimer of two (2)/one (3) S = (1)/(2) Cu(II)(3) plus one (2)/two (3) S = 0 Ni(II)Cu(II)(2) linear units with overall S = 1 Ni(II)Cu(II)(8) (2) and S = (1)/(2) Ni(II)(2)Cu(II)(7) (3) ground states.

Combining azide, carboxylate, and 2-pyridyloximate ligands in transition-metal chemistry: ferromagnetic Ni(II)5 clusters with a bowtie skeleton

The combined use of the anion of phenyl(2-pyridyl)ketone oxime (ppko(-)) and azides (N(3)(-)) in nickel(II) carboxylate chemistry has afforded two new Ni(II)(5) clusters, [Ni(5)(O(2)CR')(2)(N(3))(4)(ppko)(4)(MeOH)(4)] [R' = H (1), Me (2)]. The structurally unprecedented {Ni(5)(μ-N(3))(2)(μ(3)-N(3))(2)}(6+) cores of the two clusters are almost identical and contain the five Ni(II) atoms in a bowtie topology. Two N(3)(-) ions are end-on doubly bridging and the other two ions end-on triply bridging. The end-on μ(3)-N(3)(-) groups link the central Ni(II) atoms with the two peripheral metal ions on either side of the molecule, while the Ni···Ni bases of the triangles are each bridged by one end-on μ-N(3)(-) group. Variable-temperature, solid-state direct- (dc) and alternating-current (ac) magnetic susceptibility, and magnetization studies at 2.0 K were carried out on both complexes. The data indicate an overall ferromagnetic behavior and an S = 5 ground state for both compounds. The ac susceptibility studies on 1 reveal nonzero, frequency-dependent out-of-phase (χ(M)") signals at temperatures below ~3.5 K; complex 2 reveals no χ(M)" signals. However, single-crystal magnetization versus dc field scans at variable temperatures and variable sweep rates down to 0.04 K on 1 reveal no noticeable hysteresis loops, except very minor ones at 0.04 K assignable to weak intermolecular interactions propagated by nonclassical hydrogen bonds.

Recent Advances in Molecular Magnetic Materials

This review describes advances made in three areas of molecular magnetic materials of the types A: extended frameworks (coordination polymers) showing long-range magnetic order, B: spin-coupled clusters with emphasis on single molecule magnets and (n × n) grid species, C: polynuclear spin-switching (spin crossover) compounds of FeII with emphasis on dinuclear compounds and one-dimensional (1D) and three-dimensional (3D) (framework) materials, including porous ‘hybrid’ systems. The work of the author and his group is largely used to provide examples, together with results from other groups and collaborators that are included for comparison and completeness. Supramolecular aspects such as cluster–cluster and chain–chain interactions are discussed where relevant. A brief discussion is also given of the recent studies, carried out elsewhere, dealing with aspects of spintronics and the possible future relevance to molecular computers (type B materials) and with memory and other device possibilities (type C materials)