Noelia Ocampo

Dinuclear nickel complexes with a Ni2O2 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.

Dinuclear Co(III)/Co(III) and Co(II)/Co(III) mixed-valent complexes: synthetic control of the cobalt oxidation level

The reactivity of cobalt(II) salts towards H(3)L (2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) was studied in different reaction conditions. Accordingly, the interaction of cobalt(II) acetate with H(3)L in methanol gives rise to the discrete complex [Co(III)(2)L(OAc)(2)(OMe)]*1.5H(2)O.MeOH, 1. Reaction of cobalt(II) acetylacetonate with H(3)L in the presence of dicarboxylic acids was also investigated. Thus, when cobalt(II) acetylacetonate and H(3)L are mixed with terephthalic or malonic acid in 4 : 2 : 1 molar ratios, the mixed valent [Co(II/III)(2)L(acac)(p-O(2)CC(6)H(4)CO(2)H)][Co(II/III)(2)L(acac)(OH)]*2H(2)O*2MeOH, 2 and [Co(II/III)(2)L(acac)(O(2)CCH(2)CO(2)H)][Co(II/III)(2)L(acac)(OH)]*7H(2)O, complexes are isolated. Decreasing the pH of the medium, by addition of a second mol of dicarboxylic acid, leads to [Co(II/III)(2)L(O(2)CCH(2)CO(2))(MeOH)]*2MeOH, 4, while the reaction with terephthalic acid does not proceed. 1, 2 and 4 were crystallographically characterised and all the complexes are dinuclear, with hydrogen bonds that expand the initial nodes. The magnetic characterisation, as well as the NMR spectroscopy, indicates a diamagnetic nature for 1, in agreement with the presence of Co(III), showing the aerial oxidation suffered by the cobalt(II) ions. Nevertheless, are paramagnetic. Temperature variable magnetic measurements were recorded for the crystallographically characterised complexes 2 and 4 and these studies confirm the mixed valence Co(II)/Co(III) nature of the compounds. The best fits of the magnetic data give an axial distortion parameter Delta = 628.7 cm(-1) for 2 and 698.8 cm(-1) for 4, and spin-orbit coupling constant lambda = -117.8 cm(-1) for 2 and -107.0 cm(-1) for 4. Therefore, this study shows that the oxidation degree of the initial cobalt(ii) salt by atmospheric oxygen can be controlled according to the pH of the medium.

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.

Discovering the Complex Chemistry of a Simple NiII/H3L System: Magnetostructural Characterization and DFT Calculations of Di- and Polynuclear Nickel(II) Compounds

The simple nickel(II) acetate/H(3)L system (H(3)L = 2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) presents an unusually complicated reactivity scheme, which strongly depends on the Ni(OAc)(2)/H(3)L molar ratio and on the pH of the medium. Thus, in addition to the formerly reported compounds [Ni(2)L(OAc)(H(2)O)(2)][Ni(2)L(OAc)(H(2)O)(HOAc)].3.25H(2)O, 1.3.25H(2)O; [{Ni(3)L(OAc)(OH)(H(2)O)(MeOH)(2)}(CO(3)){Ni(2)L(OAc)(MeOH)(2)}].2.7H(2)O.1.5MeOH, 2.2.7H(2)O.1.5MeOH; and [Ni(3)L(OAc)(2)(OH)(H(2)O)(MeOH)(2)].3H(2)O.0.5MeOH, 3.3H(2)O.0.5MeOH, this system can also yield some other complexes as [Ni(2)L(o-O-C(6)H(4)-CHO)(H(2)O)].1.75H(2)O, 4.1.75H(2)O; [Ni(2)L(OH)(H(2)O)(MeOH)].3H(2)O.1.5MeOH, 5.3H(2)O.1.5MeOH; [Ni(2)L(OAc)(MeOH)(2)].H(2)O.3MeOH, 6.H(2)O.3MeOH; and [{Ni(2)L(MeOH)}(CO(3)){Ni(2)L(MeOH)(2)}].4.75H(2)O.2MeOH, 7.4.75H(2)O.2MeOH. A detailed study of the reaction scheme that allows obtaining all of these complexes is presented herein, as well as the structural characterization of the novel compounds 4.1.75H(2)O to 7.4.75H(2)O.2MeOH. X-ray analyses show that all of them present stereoisomery in the solid state. In this way, 6.H(2)O.3MeOH appears particularly interesting, as its molecular and supramolecular chirality is only controlled by hydrogen bonds. Magnetic studies of 5.3H(2)O to 7.4.75H(2)O.2MeOH are also discussed, and the complicated magnetic superexchange pathway shown by 7.4.75H(2)O.2MeOH is analyzed in light of DFT calculations.

From dinuclear to tetranuclear zinc complexes through carboxylate donors: structural and luminescence studies

Carboxylate zinc complexes of general formula [Zn2Lx(p-OOC–C6H4–CHO)], [Zn2Lx(o-OOC–C6H4–COOH)], [(Zn2Lx)2(OOC–CH2–COO)], [(Zn2Lx)2(OOC–CH2CH2–COO)] and [(Zn2Lx)2(p-OOC–C6H4–COO)] (x = 1, 2; H3L1 = 2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine and H3L2 = 2-(5-bromo-2-hydroxyphenyl)-1,3-bis[4-(5-bromo-2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) were isolated with different solvates. The crystal structures of [Zn2L1(p-OOC–C6H4–CHO)]·2.5DMSO·2H2O, [(Zn2L1)2(OOC–CH2CH2–COO)]·4.25H2O·0.75MeOH·0.5MeCN, [(Zn2L2)2(OOC–CH2CH2–COO)]·7H2O·0.25MeOH and [(Zn2L1)2(p-OOC–C6H4–COO)]·2.5H2O·MeOH·6EtOH demonstrate that their different nuclearities are a function of the carboxylate donor, with the aldehyde residue remaining uncoordinated in [Zn2L1(p-OOC–C6H4–CHO)]·2.5DMSO·2H2O. The solution studies further support the dissimilar nuclearity of the complexes and agree with a dinuclear nature for those complexes containing ortho-phthalate or 4-formylbenzenecarboxylate, and a tetranuclear arrangement when malonate, succinate or terephthalate are used as co-ligands. The ability of both Schiff base ligands to recognize Zn(II) in solution was studied by UV-vis and emission spectroscopies. The luminescent properties of the ligands and their isolated complexes are also discussed in detail.

Zn3, Ni3, and Cu3 Complexes of a Novel Tricompartmental Acyclic Ligand

A new tricompartmental acyclic ligand (H(4)L) was prepared and fully characterized. It reacts with zinc, nickel, and copper(II) acetate to yield [Zn(3)L(OAc)(2)].H(2)O (1.H(2)O), [Ni(3)L(OAc)(2)(MeOH)(2)].2MeCN.2MeOH (2.2MeCN.2MeOH), and [Cu(3)L(OAc)(2)].3H(2)O (3.3H(2)O), respectively. 2.2MeCN.2MeOH precipitates as single crystals, which lose the solvates upon drying to give 2. The reactivity of the acetate complexes in a methanol/acetonitrile basic medium in air was investigated. Thus, 1.H(2)O and 2 are unstable in this medium, both suffering partial hydrolysis to produce single crystals of [Zn(3)L(3-Br-5-Cl-Sal)(2)].2MeCN (4.2MeCN; 3-Br-5-Cl-Sal(-) = 3-bromo-5-chlorosalicylaldehydate) and [Ni(3)L(3-Br-5-Cl-Sal)(2)].2MeCN (5.2MeCN) as one of the reaction byproducts, while 3.3H(2)O gives rise to a reaction of ligand displacement, generating crystals of [Cu(3)L(OMe)(2)].MeOH (6.MeOH). Complexes 2.2MeCN.2MeOH, 4.2MeCN, 5.2MeCN, and 6.MeOH were crystallographically characterized, and these studies demonstrate not only the trinucleating ability of the fully deprotonated L(4-) ligand but also its tendency to induce chirality in the isolated compounds. The magnetic characterization of 2, 3.3H(2)O and 6.MeOH shows that the magnetic coupling between adjacent metal ions is weak, with 2 being ferromagnetic and 3.3H(2)O and 6.MeOH antiferromagnetic.

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.

Ferromagnetism in dinuclear copper(II)-phenolate complexes with exogenous O-donor bridges: a comparative study

The copper(II) complex Cu2L(OAc)(H2O)3.5, 1 x 3.5H2O was obtained and its reactivity in a basic medium investigated. Complex 1 x 3.5H2O shows different reaction patterns in air and in an inert atmosphere. Accordingly, interaction of 1 x 3.5H2O with Me4NOH x 5H2O in methanol-acetonitrile in air yields the hydroxide complex Cu2L(OH)(H2O)1.125, 2 x 1.125H2O while Cu2L(OMe)(MeOH)0.5(H2O), 3 x 0.5MeOH x H2O is isolated under an argon atmosphere. The products 1-3 were fully characterised and single crystals of {[Cu2L(OAc)] x MeCN x 3.5H2O}2, 1 x MeCN x 3.5H2O, {[Cu2L(OH)] x MeCN x 1.125H2O}2, 2 x MeCN x 1.125H2O and [Cu2L(OMe)] x 0.5MeOH x H2O, 3 x 0.5MeOH x H2O solved. The single X-ray study shows that 1-3 are dinuclear complexes with an endogenous phenol oxygen and an exogenous O-bridge. Magnetic characterisation of the three dinuclear complexes was performed, showing an apparent anomalous intramolecular ferromagnetic coupling between the metal atoms in all cases.

Design of chiral homodinuclear complexes based on the coordinating behaviour of some symmetric ligands

The crystal structures determined for [Zn2L1(acac)]·H2O and [Zn2L2(acac)]·H2O·MeCN·MeOH show that both compounds are chiral, although crystallising as racemates. This was not unexpected, as these complexes had been designed on the basis of the coordinating behaviour of acac in combination with 2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine (H3L1) and 2-(5-bromo-2-hydroxyphenyl)-1,3-bis[4-(5-bromo-2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine (H3L2). The reactivity of Zn(acac)2·nH2O with compartmental H3Lx (x = 1 or 2) has been investigated under different reaction conditions. Thus, depending on the temperature, the reaction with H3L1 can yield [Zn2L1(acac)]·H2O or [Zn2L1(OAc)]·H2O, whilst the interaction of Zn(acac)2·nH2O with H3L2 only gives rise to crystalline [Zn2L2(acac)]·H2O·MeCN·MeOH. This latter species loses the most volatile solvates on drying to yield [Zn2L2(acac)]·H2O. Both [Zn2Lx(acac)]·H2O complexes have been fully characterised by analytical and spectroscopic methods.