Piperazine linked salicylaldoxime and salicylaldimine-based dicopper(ii) receptors for anions.

The syntheses and single crystal X-ray analyses of five strapped salicylaldoxime/salicylaldimine based dicopper(ii) receptors utilising a new piperazine linker are described. The complexes form 2 + 2 metallocycles and the molecular structures of all four complexes possess a small internal cavity with the utilisation of a short piperazine linker. The molecular structures of complexes [Cu2(L(4) - H)(L(4) - 2H) ⊂ DMF]BF4·DMF, and [Cu2(L(4) - H)2Br]Br·1.25DMSO·H2O·MeOH, show that intramolecular H-bonding interactions due to the presence of -OH (oxime moiety) groups lead to a Pacman-like cleft arrangement of the two metal coordinating subunits in the metallo-macrocycle. The geometrical constraints brought about by this constrained cleft make the receptor coordinate strongly to a bromide anion involving both metal centres as evidenced by whereas in the larger tetrafluroborate anion is excluded. Absence of the oxime moiety around the metal coordination site of the ligand as demonstrated in the complexes [Cu2(L(5))2BF4](BF4)3, and [Cu2(L(5))2Br]Br3·2MeOH, resulted in less constrained dicopper(ii) helicate forms. For these complexes no anion size discrimination was observed. The addition of pyridine solvent to a slightly modified piperazine-linked ligand produces an expanded 3 + 3 tube-like tricopper complex [Cu3(L(4a) - H)3Py3](BF4)2·(MeOH)3·PF6·(H2O)3, , with two coordinated pyridine molecules occupying the newly formed cavity.

Tetra-kis(pyridine-κN)bis-(tetrafluorido-borato-κF)copper(II).

In the title complex, [Cu(BF4)2(C5H5N)2], the Cu(II) ion is in an octa-hedral coordination environment and is surrounded by four pyridine and two tetra-fluoridoborate mol-ecules. The four pyridine mol-ecules are coordinated to the copper ion through their N atoms in the equatorial plane and display a right-handed screw arrangement around the Cu(II) ion. The remaining two trans positions in the octa-hedron are occupied by the BF4 (-) anions, each coordinating weakly through an F atom. The crystal packing shows a two-dimensional sheet structure parallel to the ab plane that is formed by C-H⋯F hydrogen-bonding inter-actions.

Aryl-linked salicylaldoxime-based copper(II) helicates and "boxes": synthesis, X-ray analysis, and anion influence on complex structure.

The synthesis and spectroscopic analysis of both "metal-only" and anion encapsulated salicylaldoxime-based complexes utilizing a new 1,3-xylyl strap are described. X-ray crystallographic analysis reveals that the aromatic spacer restricts the confirmation flexibility of the resulting complexes leading to dicopper(II) double helicate and dicopper(II) 2 + 2 "box" structural forms. The choice of the structural motif is influenced by the anion present, with the copper(II) nitrate-containing complex [NO3⊂(Cu2L(3)2)](NO3)3, 4, adopting a double helicate form, whereas the analogous copper(II) bromide complexes [2Br⊂(Cu2L(3)2)](Br)2, 5, and [2Br⊂(Cu2L(3)2)](BF4)2, 6, both adopt 2 + 2 "box" structural configurations. Spectroscopic analysis has shown an enhancement in the binding strength of ClO4(-) over the anions SO4(2-) and NO3(-). The enhanced rigidity caused by the use of the 1,3-xylyl spacer in this series of complexes has favored the formation of the "double loaded" dibromide complex.

Diaqua-bis-(pyrazine-2-carboxamide-κ(2)N(1),O)cobalt(II) dinitrate.

The asymmetric unit of the title complex, [Co(C(5)H(5)N(3)O)(2)(H(2)O)(2)](NO(3))(2), contains one half of a Co(II) cationic unit and a nitrate anion. The entire [Co(C(5)H(5)N(3)O)(2)(H(2)O)(2)](2+) cationic unit is completed by the application of inversion symmetry at the Co(II) site, generating a six-coordinate distorted octa-hedral environment for the metal ion. The chelating pyrazine-2-carboxamide mol-ecules are bound to cobalt via N and O atoms, forming a square plane, while the remaining two trans positions in the octa-hedron are occupied by two coordinated water mol-ecules.

Magneto-structural studies of two new cobalt(II)-N,N-diisobutylisonicotinamide compounds: [CoLCl2]n and [Co(L)2(H2O)4][CoLBr3]2·2H2O.

Two similar synthetic pathways using the ligand N,N-diisobutylisonicotinamide (L) with anhydrous CoX(2) salts (being X = Cl(-), Br(-)) led to different species: a one-dimensional system, [CoLCl(2)](n), 1, and an ionic product [Co(L)(2)(H(2)O)(4)][CoLBr(3)](2)·2H(2)O, 2, respectively. Compound 1 is a polymer in which ligand L coordinates to tetrahedral Co(II) ions in a bidentate bridging fashion using the pyridine nitrogen and carbonyl oxygen atoms. Compound 2 consists of one octahedral cationic [Co(L)(2)(H(2)O)(4)](2+) entity and two tetrahedral anionic [CoLBr(3)](-) units. In this system, the ligand molecules coordinate only through the pyridine nitrogen atoms. The magnetic properties of 1 and 2 were investigated in the temperature range of 2.0 to 300.0 K and correlations between both (due to the existence of similar features) examined. The study of the magnetic properties of 1 was carried out by considering each Co(II) ion as a perfectly isolated system, hence, J = 0, but taking into account a significant zero-field splitting contribution due to distortions on the tetrahedral environment of the cobalt atoms. The fit of the magnetic susceptibility data together with reduced magnetization vs H/T measurements provided similar parameters (|D| = 10.8 cm(-1), g(⊥) = 1.92, g(‖) = 2.92 for the former and |D| = 11.04 cm(-1)and g = 2.05 for the latter, respectively). On the other hand, the magnetic response of compound 2 has been analyzed using a model which considers the presence of two tetrahedral and one octahedral Co(ii) ions (Co(Td) and Co(Oh)). The study was carried out in two separated blocks, above and below 80 K, where only the most significant effects at each interval of temperature were considered. As a result, the analysis of the magnetic data shows weak antiferromagnetic interactions between the Co(Oh)and the two Co(Td) ions (J = -0.41 cm(-1)) in 2. The best fit parameters were g(Co(Td)) = 2.89, g(Co(Oh)) = 3.50, |D(Co(Td))| = 10.62 cm(-1), |E(Co(Td))| = 2.95 cm(-1), Δ = 240.9 cm(-1) and J(L-S) = -107.1 cm(-1), from where λ was calculated with a final value of -144.8 cm(-1) (J(L-S) = Aκλ). The approximations performed to obtain these values provide reasonable results in agreement with compound 1 and also to other systems in the literature.

Entrapment and kinetic resolution of stabilized axial and equatorial conformers of spiro-ß-lactams.

The facile synthesis of the stabilized axial and equatorial conformers of spiro-ß-lactams was achieved via entrapment of cyclohexanone imines (Schiff bases) with acetoxyacetyl chloride in a [2 + 2]-cycloaddition reaction followed by their kinetic resolution. The immobilization of the racemic substrates on an inert solid support significantly reduced the reaction time and improved the enantioselectivity of conformers during kinetic resolution. The mechanism of the formation of the spiro-ß-lactams was explored using B3LYP/6-31+G* level quantum chemical calculations.

First report on N,N'-diisoalkylisonicotinamide 1D coordination network containing linear trinuclear [Co3L4Cl6] units with mixed Co(II)(Td)-Co(II)(Oh)-Co(II)(Td) geometries: structure and magnetic properties.

Reaction of anhydrous CoCl(2) with N,N'-diisopropylisonicotinamide (L) has yielded a coordination polymer containing linear trinuclear [Co(3)L(4)Cl(6)] units with a rare, mixed Co(T(d))-Co(O(h))-Co(T(d)) assembly (compound 1). The central Co(II) ion, of each trinuclear entity, exhibits a distorted octahedral geometry, with two ligand molecules coordinating through their carbonyl oxygen atoms along with two bridging Cl(-) ions and two pyridine N atoms from the neighboring molecules. Also, in each unit, two outer Co(II) ions display distorted tetrahedral geometry, coordinating to one ligand molecule through the pyridine N atom and to three Cl(-) ions (one of them bridged to the central Co(II) and the two acting as a terminal ligands). The magnetic properties of this compound were investigated in the temperature range of 2.0 to 300.0 K. Owing to the complexity of the system and the weak interactions among trinuclear aggregates, the magnetic response has been analyzed using a model which considers these units as isolated systems. In addition, magnetic data has been examined in two separated blocks, above and below 50 K, applying programs VPMAG FORTRAN and MAGPACK-fit, respectively. This way, only the most significant effects at each interval of temperature were considered: spin-orbit coupling of the Co(O(h)), at high temperatures and zero-field splitting parameters of the Co(T(d)) at the low. Spin-spin magnetic interaction has been taken into account for the whole range of temperatures. As a result, the analysis of the magnetic data shows that, within every trinuclear unit, the central position matches well with a high-spin Co(II) (S = 3/2) and also reveals weak ferromagnetic interactions between the Co(O(h)) and the two terminal Co(T(d)) ions (J = +0.34 cm(-1)).