Structural and functional evolution of metallacrowns.

A series of tetranuclear copper(II) and nickel(II) complexes is described, all of which form by a strict self-assembly process involving just a single ligand and the metal salt The ligands POAP, POAPZ, PZOAP, and 6POAP contain terminal pyridine and pyrazine residues bound to a central flexible diazine subunit (N−N) and contain two potentially bridging groups (alkoxo and diazine) In all cases but one the metals are linked by alkoxo oxygens alone, forming essentially square [M4(μ2-O)4] clusters A rectangular copper(II) complex [Cu4(μ2-N2)2(μ2-O)2] involves a mixture of two alkoxo and two diazine bridges The square Cu4O4 clusters exhibit ferromagnetic coupling between the metal centers, associated with the orthogonal arrangement of magnetic orbitals, while for the Ni4O4 clusters the nickel(II) centers are coupled antiferromagnetically The [Cu4(μ2-N2)2(μ2-O)2] cluster exhibits strong antiferromagnetic coupling through a trans Cu(N-N)Cu bridging arrangement, typical for systems of this sort X-ray structu

Tetranuclear Copper(II) and Nickel(II) Cluster Complexes Derived by Self-Assembly from a Series of Tetradentate Diazine Ligands: Structural and Magnetic Studies

A series of ZnII and CdII complexes with a flexible dicarboxylate building block and various heterocyclic co-ligands, formulated as {[Zn2(pda)2(phen)2]·2H2O}n (1), {[Zn(pda)(dpe)]·H2O}n (2), [Zn(pda)(bpp)]n (3), {[Cd2(pda)2(2,2′-bipy)2]·2H2O}n (4), {[Cd(pda)(4,4′-bipy)(H2O)]·H2O}n (5) and {[Cd2(pda)2(bpp)3]·14H2O}n (6) (pda = 1,3-phenylenediacetate, phen = 1,10-phenanthroline, dpe = 1,2-di(4-pyridyl)ethylene, bpp = 1,3-bi(4-pyridyl)propane, 2,2′-bipy = 2,2′-bipyridine, and 4,4′-bipy = 4,4′-bipyridine), have been synthesized and structurally characterized. In 1, the (H2O)8clusters interlink the cyclic coordination dimers to give a 3D network through hydrogen bonding. Both 2 and 3 feature 2D corrugated (4,4) layers, which are of 2-fold interpenetrating for 3. In 4, the dimeric CdII subunits are connected by the 1,3-pda ligands to generate a rampart-shaped 1D chain motif. As for 5, the [Cd(pda)]2 rings are connected by the paired 4,4′-bipy ligands to afford a tube-shaped 1D motif. In contrast to 1–5, complex 6 displays a 3D diamond network and, interestingly, the T5(0)A(0)A(2) water tapes are found to locate in the channels of this 3-D array. A structural comparison of these complexes demonstrates that the characteristics of auxiliary ligands (from chelating to bridging) play a key role in governing the coordination motifs as well as the 3-D supramolecular lattices. Solid-state properties such as photoluminescence and thermal stability of 1–6 have also been studied.

Structural diversity and properties of ZnII and CdII complexes with a flexible dicarboxylate building block 1,3-phenylenediacetate and various heterocyclic co-ligands

Malonate-based copper(II) coordination compounds: ferromagnetic coupling controlled by dicarboxylates

The synthesis of transition-metal and rare-earth clusters has become a very active research field, mainly because these compounds can behave as molecule-based magnets. The formation of such compounds strongly depends on the choice of the bridging ligand. This review covers the progress made by pyrazole-based ligands in the formation of new transition-metal and rare-earth clusters. Synthetic approaches, structural diversity and magnetic properties are described. The formation of other interesting supramolecular structures, such as metallocycles or metallohelicates is also described to emphasize the richness of this type of ligands.

Coordination Versatility of Pyrazole‐Based Ligands towards High‐Nuclearity Transition‐Metal and Rare‐Earth Clusters

A new pyrazolate-bridged tetranuclear copper(II) complex [{CuL(H2O)}4]·12H2O (H2L = 5-methoxycarbonylpyrazole-3-carboxylic acid) was synthesized and its crystal structure determined. The molecule has C2 symmetry and consists of four copper atoms bridged by four planar L ligands through the nitrogen atoms of the pyrazole groups to form a (–Cu–N–N–)4 12-membered ring. The co-ordination of each copper is distorted square planar. The basal plane of each copper atom is nearly parallel to a neighbouring pyrazole plane and perpendicular to another neighbouring pyrazole plane. In the crystal there is a hydrogen-bond network between water molecules and carboxylate groups which may control the packing. The magnetic properties of the complex have also been investigated down to 5 K. The fitting of the experimental data using a Heisenberg Hamiltonian shows that the exchange interaction between the copper atoms propagated through the monopyrazolate bridge is antiferromagnetic with J=–12.34 cm–1. The reason for this small value relative to those in di-µ-pyrazolato-dicopper(II) complexes is discussed.

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Tianyang Yao

Papers

A pyrazolate-bridged cyclic tetranuclear copper(II) complex: synthesis, crystal structure and magnetic properties