Dinuclear Cobalt(III) Complexes Showing a Co2O2 Metallacycle

The heptadentate Schiff base H₃L reacts with cobalt(II) acetate in methanol to form the discrete dinuclear complex Co₂L(OAc)₂(OMe)(H₂O)₂ ( 1 ·2H₂O). The reaction of 1 ·2H₂O with NMe₄OH·5H₂O in methanol gives rise to displacement of the acetate by methanolate groups, yielding Co₂L(OMe)₃(H₂O) ( 2 ·1H₂O). Recrystallizations of the Schiff base, 1 ·2H₂O and 2 ·H₂O in different solvents, produce single crystals of H₃L, 1 ·2.5H₂O and 2 ·2MeOH, respectively. The crystal structures of 1 ·2.5H₂O and 2 ·2MeOH show the cobalt atoms double bridged by and endogenous phenol oxygen atom and an exogenous methanolate oxygen donor, giving rise to Co₂O₂ cores with Co···Co distances of ca. 2.87 Å.     

Insights into the absorption of carbon dioxide by zinc substrates: isolation and reactivity of di- and tetranuclear zinc complexes

The heptadentate Schiff base H(3)L can react with zinc acetate to form the discrete dinuclear complex Zn(2)L(OAc)(H(2)O), 1.H(2)O. The reaction of 1.H(2)O with NMe(4)OH.5H(2)O both in air and under an argon stream has been investigated. On one hand, this reaction in air yields the tetranuclear complex (Zn(2)L)(2)(CO(3))(H(2)O)(6), 2.5H(2)O, by spontaneous absorption of adventitious carbon dioxide. This process can be reverted in an acetic acid medium, whereas the treatment of 2.5H(2)O with methanoic acid yields crystals of [Zn(2)L(HCOO)].0.5MeCN.1.25MeOH.2H(2)O, 3.0.5MeCN.1.25MeOH.2H(2)O. On the other hand, the interaction under an argon atmosphere of 1.H(2)O with NMe(4)OH.5H(2)O in methanol allows the isolation of the dinuclear complex Zn(2)L(OMe)(H(2)O)(4), 4.4H(2)O. Recrystallisations of 1.H(2)O, 2.5H(2)O and 4.4H(2)O, in different solvents, yielded single crystals of 1.MeCN.2.5H(2)O, 2.4MeOH and 4.3MeOH.H(2)O, respectively. The crystal structure of 2.4MeOH can be understood as resulting from an unusual asymmetric tetranuclear self-assembly from two dinuclear units, and shows three different geometries around the four zinc atoms.     

Unexpected ferromagnetic interaction in a new tetranuclear copper(II) complex: synthesis, crystal structure, magnetic properties, and theoretical studies

The new tetranuclear carbonate complex [Cu2L)2(CO3)] x 8H2O (1 x 8H2O) (H3L = (2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) has been obtained by two different synthetic routes and fully characterized. Recrystallization of 1 x 8H2O in methanol yields single crystals of {[(Cu2L)2(CO3)]}2 x 12H2O (1 x 6H2O), suitable for X-ray diffraction studies. The crystal structure of 1 x 6H2O shows two crystallographically different tetranuclear molecules in the asymmetric unit, 1a and 1b. Both molecules can be understood as self-assembled from two dinuclear [Cu2L]+ cations, joined by a mu4-eta(2):eta(1):eta(1) carbonate ligand. The copper atoms of each crystallographically different [(Cu2L)2(CO3)] molecule present miscellaneous coordination polyhedra: in both 1a and 1b, two metal centers are in square pyramidal environments, one displays a square planar chromophore and the other one has a geometry that can be considered as an intermediate between square pyramid and trigonal bipyramid. Magnetic studies reveal net intramolecular ferromagnetic coupling between the metal atoms. Density functional calculations allow the assignment of the different magnetic coupling constants and explain the unexpected ferromagnetic behavior, because of the presence of an unusual NCN bridging moiety and countercomplementarity of the phenoxo (or carbonate) and NCN bridges.     

Dinuclear nickel complexes with a Ni(2)O(2) core: a structural and magnetic study

The acetylacetonate complexes [Ni(2)L(1)(acac)(MeOH)] x H(2)O, 1 x H(2)O and [Ni(2)L(3)(acac)(MeOH)] x 1.5H(2)O, 2 x 1.5H(2)O (H(3)L(1) = (2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine and H(3)L(3) = (2-(5-bromo-2-hydroxyphenyl)-1,3-bis[4-(5-bromo-2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) were prepared and fully characterised. Their crystal structures show that they are dinuclear complexes, extended into chains by hydrogen bond interactions. These compounds were used as starting materials for the isolation of the corresponding [Ni(2)HL(x)(o-O(2)CC(6)H(4)CO(2))(H(2)O)] x n MeOH and [Ni(2)HL(x)(O(2)CCH(2)CO(2))(H(2)O)]x nH(2)O dicarboxylate complexes (x = 1, 3; n = 1-3). The crystal structures of [Ni(2)HL(1)(o-O(2)CC(6)H(4)CO(2))(H(2)O)] x MeOH, 3 x MeOH, [Ni(2)HL(3)(o-O(2)CC(6)H(4)CO(2))(H(2)O)] x 3 MeOH, 4 x 3 MeOH and [Ni(2)HL(1)(O(2)CCH(2)CO(2))(H(2)O)] x 2.5H(2)O x 0.25 MeOH x MeCN, 5 x 2.5H(2)O x 0.25 MeOH x MeCN, were solved. Complexes 3-5 show dinuclear [Ni(2)HL(x)(dicarboxylate)(H(2)O)] units, expanded through hydrogen bonds that involve carboxylate and water ligands, as well as solvate molecules. The variable temperature magnetic susceptibilities of all the complexes show an intramolecular ferromagnetic coupling between the Ni(II) ions, which is attempted to be rationalized by comparison with previous results and in the light of molecular orbital treatment. Magnetisation measurements are in accord with a S = 2 ground state in all cases.     

Self-assembly of a tetranuclear Ni4 cluster with an S = 4 ground state: the first 3d metal cluster bearing a mu4-eta2:eta2-O,O carbonate ligand

Reaction of nickel(II) acetate with H(3)L (2-(5-bromo-2-hydroxyphenyl)-1,3-bis[4-(5-bromo-2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) yields [Ni(2)L(OAc)(H(2)O)(2)].3MeCN.2H(2)O (1.3MeCN.2H(2)O), crystallographically characterized. 1 is unstable in solution for a long time and hydrolyzes to give [Ni(2)L(o-OC(6)H(3)BrCHO)(H(2)O)].2.25MeCN.H(2)O (2.2.25MeCN.H(2)O). In addition, 1 uptakes CO(2) from air in a basic methanol/acetonitrile solution, yielding [[Ni(2)L(MeOH)](2)(CO(3))].1.5MeOH.MeCN.H(2)O (3.1.5MeOH.MeCN.H(2)O). The X-ray characterization of 3 reveals that it is a tetranuclear nickel cluster, which can be considered as the result of a self-assembly process from two dinuclear [Ni(2)L](+) blocks, joined by a mu(4)-eta(2):eta(2)-O,O carbonate ligand. The coordination mode of the carbonate anion is highly unusual and, to the best of our knowledge, it has not been described thus far for first-row transition metal complexes or magnetically studied until now. Magnetic characterization of 1 and 3 shows net intramolecular ferromagnetic coupling between the metal atoms in both cases, with S = 2 and S = 4 ground states for 1 and 3, respectively.     

Encapsulation of atmospheric CO(2) by a self-assembled decanuclear cadmium complex via unfamiliar perchlorato and carbonato bridges

A decanuclear Cd complex has been found as a carbonate-containing capsule. The structure strongly resembles a ten-blade waterwheel with a central carbonate ligand surrounded by two superimposed Cd(5)O(5) crowns with a pentagonal antiprism-like disposition. The capsule is doubly capped by two pentadentate perchlorate anions.     

Copper(II) Complexes with Asymmetrical Schiff Base Ligands Derived from 2‐Acetylpyrazine

New copper(II) complexes of asymmetrical tetradentate Schiff bases containing pyrazine have been prepared and thoroughly characterised by elemental analysis, IR and electronic spectroscopy, mass spectrometry and magnetic measurements. Two alternative methods were used in the isolation of the complexes: template synthesis in the preparation of Cu(SalDpyz)ClO₄ (HSalDPyz = derived from the condensation of salicylaldehyde, acetylpyrazine and 1,2‐ethylendiamine, 2‐methyl‐1,2‐propylendiamine, 1,2‐phenylendiamine) and direct interaction between copper perchlorate and the corresponding Schiff base, as in the isolation of Cu(AEPyz)(ClO₄) (HAEPyz = (Z)‐4‐[2‐{[2‐{[(E)‐1‐(pyrazinyl)ethylidene]amino} ethyl)amino]‐3‐penten‐2‐one)]. [Cu(SalEn)(py)(OClO₃)][Cu(SalEn)(py)]ClO₄ ( 1 ) (SalEn = 4‐(2‐hydroxyphenyl)‐3‐aza‐3‐buten‐1‐amino, py = pyridine), metal precursor in the preparation of Cu(SalEnpyz)(ClO₄) (HSalEnpyz = 2‐{E(2‐{[(E)‐1‐(2‐pyrazinyl)ethylidene]amino}ethyl)imino]methyl}phenol), was crystallographically characterised. The crystal structure of [Cu(AEpyz)]ClO₄ ( 2 ) is also reported.     

Ferromagnetic exchange in a dinuclear copper(II) complex mediated by a methanolate bridging ligand

The copper(II) complex Cu(2)L(OMe)(H(2)O)(3), [middle dot]3H(2)O [H(3)L = 2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine] was obtained and recrystallised in methanol to yield crystals of [[Cu(2)L(OMe)]](2).2.5MeOH.4H(2)O, 1.2.5MeOH.4H(2)O. Its single X-ray study shows that it contains two crystallographically different but chemically equivalent dinuclear [Cu(2)L(OMe)] 1 molecules in the asymmetric unit cell. The copper atoms of each dinuclear moiety are in distorted square-pyramidal environments, with both pyramids sharing an apical phenolate and a basal methanolate oxygen atom. Magnetic characterisation of 1.3H(2)O shows a quite strong intramolecular ferromagnetic coupling between both metal atoms. Extended Huckel calculations reveal that the intradinuclear magnetic interaction seems to be mediated by the exogenous methanolate bridging ligand.     

One pot-synthesis of chiral Ni6 clusters involving Ni3 subunits: a combined structural, magnetic and DFT study

Ni(6) clusters of the general formula [{Ni(3)L(n)(OAc)(OH)}(2)(X)(OAc)(H(2)O)(2)] (n = 1, 2; X = Cl(-) or N(3)(-), (L(n))(3-) = hexadentate tritopic ligands) can be isolated by spontaneous self-assembly, from mixtures of Ni(OAc)(2), H(3)L(n), NMe(4)OH·5H(2)O and NaX in adequate molar ratios. Thus, four new hexanuclear complexes [{Ni(3)L(1)(OAc)(OH)}(2)Cl(OAc)(H(2)O)(2)]·7.5H(2)O (1·7.5H(2)O), [{Ni(3)L(2)(OAc)(OH)}(2)Cl(OAc)(H(2)O)(2)]·2H(2)O·7.5MeOH (2·2H(2)O·7.5MeOH), [{Ni(3)L(1)(OAc)(OH)}(2)(N(3))(OAc)(H(2)O)(2)]·6H(2)O (3·6H(2)O) and [{Ni(3)L(2)(OAc)(OH)}(2)(N(3))(OAc)(H(2)O)(2)]·4H(2)O (4·4H(2)O) were obtained and fully characterised. 1·7.5H(2)O and 2·2H(2)O·7.5MeOH were isolated in the form of single crystals, the latter losing solvate on drying, to yield 2·2H(2)O. Recrystallisation of 3·6H(2)O in MeCN/MeOH also generates single crystals of 3·H(2)O·2MeOH·2MeCN. Their X-ray characterisation shows that these Ni(6) clusters can be considered to be built from two triangular trinuclear [Ni(3)L(n)(OAc)(OH)](+) subunits with different connectors. In addition, these studies demonstrate that the (L(n))(3-) ligands behave as trinucleating, adopting such a conformation that induces chirality in the isolated compounds. In this way, 3·H(2)O·2MeOH·2MeCN appears particularly interesting, since it emerges as homochiral after undergoing spontaneous resolution upon crystallisation. The magnetic characterisation of 1·7.5H(2)O to 3·6H(2)O reveals that the three compounds present an overall antiferromagnetic coupling. The intricate magnetic behaviour of these clusters, mediated by a total of 14 bridges of different kinds, was analysed and satisfactorily interpreted in light of DFT calculations.     

Ferromagnetic heterotrinuclear Cu-Ni complexes of a compartmental chiral Schiff base

Nickel(II) and copper(II) acetate react with the trinucleating compartmental Schiff base H(4)L (H(4)L = 6,6'-(E)-3,3'-(ethane-1,2-diyl)bis(1-(2-((E)-3-bromo-5-chloro-2-hydroxybenzylideneamino)ethyl)imidazolidine-3,2-diyl)bis(2-bromo-4-chlorophenol)) to produce the heterotrinuclear complexes [Ni(2)CuL(OAc)(2)]·0.25H(2)O·2.5MeOH (1·0.25H(2)O·2.5MeOH) and [NiCu(2)L(OAc)(2)]·3.25H(2)O·0.5MeOH (2·3.25H(2)O·0.5MeOH) as a function of the Ni(OAc)(2)?:?Cu(OAc)(2) molar ratio. The crystal structures of H(4)L, 1·0.25H(2)O·2.5MeOH and 2·3.25H(2)O·0.5MeOH could be solved. The free ligand presents two stereogenic methine groups on the imidazolidine heterocycles. X-Ray diffraction studies on H(4)L determined that the solved crystal structure corresponds to a racemate formed by the (2R,2'R) and (2S,2'S) enantiomers, without detecting the (2R,2'S) diastereoisomer. The crystal structures of both heterotrinuclear complexes reveal that Ni(II) has a preference for the central ligand pocket, showing that this cavity discriminates between Ni(II) and Cu(II) when both species are present in the reaction medium. These results are validated by DFT calculations. As a consequence of the coordination, 1·0.25H(2)O·2.5MeOH and 2·3.25H(2)O·0.5MeOH are also chiral, but crystallise as racemates. In addition to their asymmetric methine groups, these complexes present four other stereogenic centres: the four coordinated imidazolidine N atoms. The luminescent properties of the ligand and both complexes were analysed, showing that the presence of the metals partially inhibits the emission of the ligand and apparently tunes the position of the secondary fluorescence emission band. The magnetic characterisation of 1·0.25H(2)O·2.5MeOH and 2·3.25H(2)O·0.5MeOH was also performed, showing the ferromagnetic behaviour of both complexes.