A three-dimensional copper(II) coordination polymer featuring the 2,3-dioxyquinoxalinate(-2) ligand: Preparation,structural characterization and magnetic study

The synthesis, single-crystal X-ray structure and magnetic properties of [Cu₃L₂Cl₂(DMF)₄]_n (1), where L^2? is the 2,3-dioxyquinoxalinate(-2) ligand, are reported. The complex was prepared by the reaction of CuCl₂ and 1,4-dihydro-2,3-quinoxalinedione (H₂L′) under basic conditions using either solvothermal or normal laboratory techniques. Compound 1 is a 3D coordination polymer with an (8².10)-a, lig (LiGe) topology, containing the ligand in a novel 3.1111 (Harris notation) coordination mode. Variable-temperature and variable-field magnetic studies reveal that the ligand L^2? propagates weak antiferromagnetic exchange interactions through its “quinoxaline” part. IR data are discussed in terms of the structural features of 1 and the coordination mode of L^2?.     

The effect of preflux bath additives on the morphology and structure of the hot‐dip galvanized coatings

The effect of CdCl₂, NiCl₂ and SnCl₂ on the morphology and on the structure of hot‐dip galvanized coatings was examined with optical microscopy, scanning electron microscopy and X‐ray diffraction, when these salts are added in the preflux bath. From this investigation it turned out, that the morphology of the coatings formed after fluxing in a preflux bath containing CdCl₂ is very similar to the morphology of the coatings formed in the usual flux, regardless of the concentration of the Cd salt and the solvent used (water or aqueous solution containing 50% ZnCl₂^.NH₄Cl) in the preflux bath. By contrast, Ni enhances the growth of small‐sized crystallites of the zeta‐phase instead of the columnar growth, and finally it results in reduction of the coating thickness. This phenomenon is likely to be affected by the NiCl₂ concentration but not by the solvent used (pure water or aqueous solution containing 50% ZnCl₂^.NH₄Cl). Finally, Sn addition seems to be inert with regard to the coating structure. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dinuclear versus trinuclear complex formation in zinc(II) benzoate/pyridyl oxime chemistry depending on the position of the oxime group

The initial employment of pyridine-3-carbaldehyde oxime, (3-py)C(H)NOH, and pyridine-4-carbaldehyde oxime, (4-py)C(H)NOH, in zinc(II) carboxylate chemistry is reported. The syntheses, crystal structures and IR characterization are described for [Zn₃(O₂CPh)₆{(3-py)C(H)NOH}₂] (1) and [Zn₂(O₂CPh)₄{(4-py)C(H)NOH}₂] (2). The trinuclear molecule of 1 has a linear structure, with one monoatomically bridging η¹:η²:μ and two syn, syn-η¹:η¹:μ benzoate groups spanning each pair of Zn^II ions; the terminal metal ions are each capped by one (3-py)C(H)NOH ligand coordinating through its pyridyl nitrogen. Complex 2 exhibits a dinuclear paddle–wheel structure with a Zn···Zn distance of 2.990(2) Å; each Zn^II ion has a square pyramidal geometry with four carboxylate oxygens in the basal plane and the pyridyl nitrogen of one monodentate (4-py)C(H)NOH ligand at the apex. Both complexes form 1D architectures by virtue of hydrogen bonding interactions involving the free oxime group as donor and the oxime nitrogen (1) or carboxylate oxygens (2) as acceptors. IR data are discussed in terms of the known structures and coordination modes of the ligands.     

Forcing Twisted 1,7-Dibromoperylene Diimides to Flatten in the Solid State: What a Difference an Atom Makes

Perylene diimides (PDI) are workhorses in the field of organic electronics, owing to their appealing n-semiconducting properties. Optimization of their performances is widely pursued by bay-atom substitution and diverse imide functionalization. Bulk solids and thin-films of these species crystallize in a variety of stacking configurations, depending on the geometry of the stable conformation of the polyaromatic core. We here demonstrate that 1,7-dibromo-substituted perylene diimides, PDI(H₂Br₂), possessing a heavily twisted conformation in the gas phase, in solution and in the solids, can be easily flattened in the solid state into centrosymmetric molecules if the polyaromatic cores form π–π stabilized chains. This is achieved by using axial residues with low stereochemical hindrance, as guaranteed by a single CH₂/NH spacer directly linked to the imide function. Structural powder diffraction and DFT calculations on four newly designed species of the PDI(H₂Br₂) class coherently show that, thanks to the flexibility of the N−X−Ar link (X=CH₂/NH), flat cores are indeed obtained by overcoming the interconversion barrier between twisted atropoisomers, of only 26.5 kJ mol⁻¹. This strategy may then be useful to induce “anomalously flat” polyaromatic cores of different kinds (substituted acenes/rylenes) in the solid state, towards suitable crystal packing and orbital interactions for improved electronic performances.     

Metal ion-assisted transformations of 2-pyridinealdoxime and hexafluorophosphate

Metal-ion mediated reactions of 2-pyridinealdoxime and hexafluorophosphate lead to Zn(II) complexes containing picolinic acid, picolinamide and monofluorophosphate (-2) as ligands.     

Investigation of the zinc(II)-benzoate-2-pyridinealdoxime reaction system

The employment of pyridine-2-carbaldehyde oxime (paoH) in zinc(II) benzoate chemistry, in the absence or presence of azide ions, is described. The syntheses, crystal structures and spectroscopic characterization are reported for the complexes [Zn(O(2)CPh)(2)(paoH)(2)] (1), [Zn(12)(OH)(4)(O(2)CPh)(16)(pao)(4)] (2) and [Zn(4)(OH)(2)(pao)(4)(N(3))(2)] (3). The Zn(II) centre in octahedral 1 is coordinated by two monodentate PhCO(2)(-) groups and two N,N'-chelating paoH ligands. The metallic skeleton of 2 describes a tetrahedron encapsulated in a distorted cube. The {Zn(12)(μ-OH)(4)(μ(3)-ΟR)(4)}(16+) core of the cluster can be conveniently described as consisting of a central {Zn(4)(μ(3)-ΟR)(4)}(4+) cubane subunit (RO(-) = pao(-)) linked to four {Zn(2)(μ-OH)}(3+) subunits via the OH(-) group of each of the latter, which becomes μ(3). The molecule of 3 has an inverse 12-metallacrown-4 topology. Two triply bridging hydroxido groups are accommodated into the metallacrown ring. Each pao(-) ligand adopts the η(1)?:?η(1)?:?η(1)?:?μ coordination mode, chelating one Zn(II) atom and bridging a Zn(II)(2) pair. Complexes 1 and 2 display photoluminescence with maxima at ～355 nm and ～375 nm, upon maximum excitation at 314 nm; the origin of the photoluminescence is discussed.     

Dinuclear Lanthanide(III) Complexes from the Use of Methyl 2-Pyridyl Ketoxime: Synthetic,Structural, and Physical Studies

The first use of methyl 2-pyridyl ketoxime (mepaoH) in homometallic lanthanide(III) [Ln(III)] chemistry is described. The 1:2 reactions of Ln(NO₃)₃·nH₂O (Ln = Nd, Eu, Gd, Tb, Dy; n = 5, 6) and mepaoH in MeCN have provided access to complexes [Ln₂(O₂CMe)₄(NO₃)₂(mepaoH)₂] (Ln = Nd, 1; Ln = Eu, 2; Ln = Gd, 3; Ln = Tb, 4; Ln = Dy, 5); the acetato ligands derive from the Ln^III—mediated hydrolysis of MeCN. The 1:1 and 1:2 reactions between Dy(O₂CMe)₃·4H₂O and mepaoH in MeOH/MeCN led to the all-acetato complex [Dy₂(O₂CMe)₆(mepaoH)₂] (6). Treatment of 6 with one equivalent of HNO₃ gave 5. The structures of 1, 5, and 6 were solved by single-crystal X-ray crystallography. Elemental analyses and IR spectroscopy provide strong evidence that 2–4 display similar structural characteristics with 1 and 5. The structures of 1–5 consist of dinuclear molecules in which the two Ln^III centers are bridged by two bidentate bridging (η¹:η¹:μ₂) and two chelating-bridging (η¹:η²:μ₂) acetate groups. The Ln^III atoms are each chelated by a N,N’-bidentate mepaoH ligand and a near-symmetrical bidentate nitrato group. The molecular structure of 6 is similar to that of 5, the main difference being the presence of two chelating acetato groups in the former instead of the two chelating nitrato groups in the latter. The geometry of the 9-coordinate Ln^III centers in 1, 5 and 6 can be best described as a muffin-type (MFF-9). The 3D lattices of the isomorphous 1 and 5 are built through H-bonding, π⋯π stacking and C-H⋯π interactions, while the 3D architecture of 6 is stabilized by H bonds. The IR spectra of the complexes are discussed in terms of the coordination modes of the organic and inorganic ligands involved. The Eu(III) complex 2 displays a red, metal-ion centered emission in the solid state; the Tb^III atom in solid 4 emits light in the same region with the ligand. Magnetic susceptibility studies in the 2.0–300 K range reveal weak antiferromagnetic intramolecular Gd^III…Gd^III exchange interactions in 3; the J value is −0.09(1) cm⁻¹ based on the spin Hamiltonian Ĥ = −J(Ŝ_Gd1·Ŝ_Gd2).     

One-dimensional cadmium(II)/bicinate(−1) complexes : The role of the alkali metal ion used in the reaction medium

The initial employment of N,N-bis(2-hydroxyethyl)glycine (bicine; bicH₃) in CdCl₂ chemistry is reported, and the syntheses, IR spectra and crystal structures of the 1D coordination polymers [CdCl(bicH₂)]_n·nH₂O (1·H₂O) and [CdNaCl₂(bicH₂)(MeOH)]_n (2) are described. The identity of the products depends on the solvent, the reaction temperature and the alkali metal ion of the base used. The structure of 1·H₂O consists of zig-zag chains. The 7-coordinate Cd^II atoms are bridged by η¹:η¹:μ₂ carboxylate groups of the 2.21111 (Harris notation) bicH₂⁻ ligand. The coordination geometry of the metal center can be either described as a very distorted pentagonal bipyramidal or as a distorted capped octahedral. In the structure of 2 the Cd^II atoms form an almost linear chain with neighboring Na^I atoms on opposite sites of the chain. Every pair of Cd^II atoms is linked by two chloro ligands and the two oxygen atoms of the bicinate carboxylate group. The Cd^II and Na^I atoms are bridged by one μ₂ carboxylate bicinate oxygen and one μ₃ chloro ligand. The 3.2_1,21₁1₂1₂1₂ coordination mode of bicH₂⁻ is unprecedented. The CdCl₄(O_carboxylate)₂ and Na(O_hydroxyl)₂(O_carboxylate)(O_MeOH)NCl coordination spheres are octahedral and trigonal prismatic, respectively. IR data of the complexes are discussed in terms of the coordination modes of bicH₂⁻ and the known structures.     

The First Use of a ReX5 Synthon to Modulate FeIII Spin Crossover via Supramolecular Halogen⋅⋅⋅Halogen Interactions

We have added the {Re^IVX₅}⁻ (X=Br, Cl) synthon to a pocket-based ligand to provide supramolecular design using halogen⋅⋅⋅halogen interactions within an Fe^III system that has the potential to undergo spin crossover (SCO). By removing the solvent from the crystal lattice, we “switch on” halogen⋅⋅⋅halogen interactions between neighboring molecules, providing a supramolecular cooperative pathway for SCO. Furthermore, changes to the halogen-based interaction allow us to modify the temperature and nature of the SCO event.