The synthesis and structural chemistry of a series of new divalent transition metal complexes of the bis-bidentate ligand 3,3Ј-diamino-2,2Ј-bipyridine (L1) and its dication L1H 2 are described. Ligand L1 reacts with salts of divalent transition metals to afford the (1:1) metal-ligand complexes (2a−2d) as well as the tris complexes (3a−3f). All complexes were fully characterised by spectroscopic methods and the following compounds [Cu(L1)Cl 2 ] 2 (2a), [Cu(L1)(OAc) 2 ] (2b), [Zn(L1) 3 ][OTf] 2 (3a), and [Zn(L1) 3 ][ZnCl 4 ] (3e and 3f) were structurally characterised. Results from single crystal X-ray diffraction measurements indicate that formation of an intramolecular hydrogen bond between the two amino groups allows the ligand to coordinate divalent metal ions through their diimine binding sites. Furthermore, the structure of compound 2a reveals that it crystallises as a dimer in which each copper ion is bound to two pyridine nitrogen atoms and [a]

Mn(II)9 grid complexes with a [Mn9(mu-O)12] core, obtained by self-assembly of a series of tritopic picolinic dihydrazone ligands with Mn(II) salts, have been oxidized by both chemical and electrochemical methods to produce mixed oxidation state systems. Examples involving [Mn(III)3Mn(II)6] and [Mn(III)4Mn(II)5] combinations have been produced. Structures are reported for [Mn9(2poap-2H)6](NO3)6.14H2O (1), [Mn9(2poap-2H)6](ClO4)10.10H2O (3), and [Mn9(Cl2poap-2H)6](ClO4)9.14H2O.3CH3CN (10). Structural studies show distinct contraction of the corner grid sites on oxidation, with overall magnetic properties consistent with the resulting changes in electron distribution. Antiferromagnetic exchange in the outer ring of eight metal centers creates a ferrimagnetic subunit, which undergoes antiferromagnetic coupling to the central metal, leading to S=1/2 (3) and S2/2 (10) ground states. Two moderately intense absorptions are observed on oxidation of the Mn(II) grids in the visible and near-infrared (1000 nm, 700 nm), associated with charge transfer transitions (LMCT, IVCT respectively). Compound 1 crystallized in the monoclinic system, space group P2 1/n, with a=21.308(2) A, b=23.611(2) A, c=32.178(3) A, beta=93.820(2) degrees . Compound 3 crystallized in the tetragonal system, space group I, with a=b=18.44410(10) A, c = 24.9935(3) A. Compound 10 crystallized in the triclinic system, space group P, with a=19.1150(10) A, b=19.7221(10) A, c=26.8334(14) A, alpha=74.7190(10) degrees, beta=77.6970(10) degrees, gamma=64.7770(10) degrees. The facile oxidation of the Mn(II)9 grids is highlighted in terms of their potential use as molecular based platforms for switching and data storage.

A new ligand containing a linear sequence of four-tridentate chelating subunits built around alkoxide and pyrimidine bridging groups undergoes a spontaneous self-assembly process with Pb(CF3SO3)2 to produce a unique hexadecanuclear [4 x (2 x 2)] 'grid of grids' type structure with external dimensions of 26 A.

A Co(II) quaterpyridine-type complex has been prepared via a one-pot transformation of a 2,29-bipyridine Schiff-base ligand in the presence of a Lewis acidic metal salt.

The majority of self-assembled metallic helicates contain two metal centers, whilst those containing three or more remain quite rare.[1] The limitation to synthesizing high-nuclearity helicates appears to be the design of the organic ligand, since double-and quadruple-stranded helicates containing five [2] and nine [3] metal centers, respectively, have been reported. This is in contrast to triple-stranded helicates, which have not progressed beyond the inclusion of three metal centers.[4] The apparent lack of high-nuclearity helicates has undoubtedly limited the exploitation of these systems, which is currently driven towards the development of molecular devices having predetermined properties and functions such as chirality, [5] energy transfer, [6] metal-metal bonding, [7] and DNA groove binding. [8] Surprisingly, helicates exhibiting magnetic exchange remain scarce, [9] since the adjacent metal ions are often bridged by long spacers that preclude viable superexchange pathways. However the preparation of high-nuclearity helicates with adjacent metal centers bridged by a single atom, or groups of atoms, provide an ideal opportunity to study the magnetic exchange between fixed numbers of paramagnetic metal centers in an isolated finite one-dimensional (1D) system. These systems could serve as useful models to provide further insights into the magnetic properties of infinite 1D magnetic-chain compounds, [10] which occupy an intermediate position between zero-dimensional clusters and 3D extended lattices, and as building blocks for future supramolecular devices.[11] Consequently we have embarked upon a program to exploit the helical structural

The majority of self-assembled metallic helicates contain two metal centers, whilst those containing three or more remain quite rare.[1] The limitation to synthesizing high-nuclearity helicates appears to be the design of the organic ligand, since double-and quadruple-stranded helicates containing five [2] and nine [3] metal centers, respectively, have been reported. This is in contrast to triple-stranded helicates, which have not progressed beyond the inclusion of three metal centers.[4] The apparent lack of high-nuclearity helicates has undoubtedly limited the exploitation of these systems, which is currently driven towards the development of molecular devices having predetermined properties and functions such as chirality, [5] energy transfer, [6] metal-metal bonding, [7] and DNA groove binding. [8] Surprisingly, helicates exhibiting magnetic exchange remain scarce, [9] since the adjacent metal ions are often bridged by long spacers that preclude viable superexchange pathways. However the preparation of high-nuclearity helicates with adjacent metal centers bridged by a single atom, or groups of atoms, provide an ideal opportunity to study the magnetic exchange between fixed numbers of paramagnetic metal centers in an isolated finite one-dimensional (1D) system. These systems could serve as useful models to provide further insights into the magnetic properties of infinite 1D magnetic-chain compounds, [10] which occupy an intermediate position between zero-dimensional clusters and 3D extended lattices, and as building blocks for future supramolecular devices.[11] Consequently we have embarked upon a program to exploit the helical structural

No abstract

Cyclic metal arrays containing multiples of spin-coupled paramagnetic metal centers are frequently synthesized from a large number of components in an uncontrolled assembly process that employs relatively simple bridging ligands in conjunction with smaller bridging fragments, such as hydroxide, oxide, halide, and methoxide.[1] A controlled approach that excludes these extraneous bridging fragments can be adopted when designed polytopic ligands are employed, as