Exploring the Spatial Arrangement of Simple 18-Membered Hexaazatetraamine Macrocyclic Ligands in Their Metal Complexes.

Hexaazamacrocyclic Schiff bases have been extensively combined with lanthanoid (Ln) ions to obtain complexes with a highly axial geometry. However, the use of flexible hexaazatetraamine macrocycles containing two pyridines and acyclic spacers is rather uncommon. Accordingly, we obtained [DyL(OAc)2]OAc·7H2O·EtOH and [DyLMe2(Cl)2]Cl·2H2O, where L and LMe2 are the 18-membered macrocycles 3,6,10,13-tetraaza-1,8(2,6)-dipyridinacyclotetradecaphane and 3,10-dimethyl-3,6,10,13-tetraaza-1,8(2,6)-dipyridinacyclotetradecaphane, respectively, which contain ethylene and methylethylene spacers between their N3 moieties. [DyL(OAc)2]OAc·7H2O·EtOH represents the first crystallographically characterized lanthanoid complex of L, while [DyLMe2(Cl)2]Cl·2H2O contributes to increasing the scarce number of LnIII compounds containing LMe2. Furthermore, the crystal structure of L·12H2O was solved, and it was compared with those of other related macrocycles previously published. Likewise, the crystal structures of the DyIII complexes were compared with those of the lanthanoid and d-metal complexes of other 18-membered N6 donor macrocycles. This comparison showed some effect of the spacers employed, as well as the influence of the size of the ancillary ligands and the metal ion. Additionally, the distinct folding behaviors of these macrocycles influenced their coordination geometries. Moreover, the luminescent properties of [DyL(OAc)2]OAc·7H2O·EtOH and [DyLMe2(Cl)2]Cl·2H2O were also investigated, showing that both complexes are fluorescent, with the emission being sensitized by the ligands.

Dy4, Dy5, and Ho2 Complexes of an N3O2 Aminophenol Donor: A Dy5-µ3-Peroxide Single Molecule Magnet.

The reactivity of the new flexible potentially pentadentate N3O2 aminophenol ligand H4Lr (2,2'-((pyridine-2,6-diylbis(methylene))bis(azanediyl))diphenol) towards different dysprosium salts and holmium(III) nitrate was investigated. Accordingly, this reactivity seems to greatly depend on the metal ion and salt employed. In this way, the reaction of H4Lr with dysprosium(III) chloride in air leads to the oxo-bridged tetranuclear complex [Dy4(H2Lr)3(Cl)4(µ3-O)(EtOH)2(H2O)2]·2EtOH·H2O (1·2EtOH·H2O), while the same reaction just changing the chloride salt by the nitrate one renders the peroxo-bridged pentanuclear compound [Dy5(H2Lr)2(H2.5Lr)2(NO3)4(µ3-O2)2]·2H2O (2·2H2O), where both peroxo ligands seem to come from the fixation and reduction of atmospheric oxygen. However, if holmium(III) nitrate is used instead of dysprosium(III) nitrate, no evidence of a peroxide ligand is observed, and the dinuclear complex {[Ho2(H2Lr)(H3Lr)(NO3)2(H2O)2](NO3)} 2.5H2O (3·2.5H2O) is isolated. The three complexes were unequivocally characterized by X-ray diffraction techniques, and their magnetic properties were analyzed. Thus, while the Dy4 and Ho2 complexes do not show magnet-like behavior even in the presence of an external magnetic field, 2·2H2O is a single molecule magnet, with an Ueff barrier of 61.2 K (43.2 cm-1). This is the first homonuclear lanthanoid peroxide SMM, which also shows the highest barrier among the reported 4f/3d peroxide zero field SMMs to date.

Experimental and Computational Studies on the Interaction of a Dansyl-Based Fluorescent Schiff Base Ligand with Cu2+ Ions and CuO NPs.

We studied the interaction of Cu2+ ions and CuO nanoparticles with the fluorescent Schiff base ligand H3L, which derives from the condensation of 4-formyl-3-hydroxybenzoic acid with N-(2-aminobenzyl)-5-(dimethylamino)naphthalene-1-sulfonamide (DsA). A detailed assignment of the most significant bands of the electronic and infrared spectra of H3L and DsA was performed using DFT methods, based on both crystal structures. The affinity of H3L to react with Cu2+ ions in solution (KB = 9.01 103 L mol-1) is similar to that found for the Cu2+ ions present on the surface of CuO NPs (KB = 9.84 103 L mol-1). Fluorescence spectroscopic measurements suggest five binding sites for H3L on the surface of the CuO NPs used. The µ-XRF analysis indicates that a polycrystalline sample of CuO-H3L NPs contains 15:1 Cu:S molar ratio (CuO:H3L). ATR-FTIR spectroscopy, supported by DFT calculations, showed that the HL2- (as a phenolate and sulfonamide anion) is coordinated to superficial Cu2+ ions of the CuO NPs through their azomethine, sulphonamide, and phenolic groups. A solution of H3L (126 ppb) shows sensitive responses to CuO NPs, with a limit of detection (LOD) of 330 ppb. The working range for detection of CuO NPs with [H3L] = 126 ppb was 1.1-9.5 ppm. Common metal ions in water, such as Na+, K+, Mg2+, Ca2+, Fe3+, and Al3+ species, do not interfere significantly with the detection of CuO NPs.

Luminescence thermometry in a Dy4 single molecule magnet.

The tetranuclear linear complex [Dy4(1,1,4-H3Lr)2(OAc)6]·CH3OH (1·CH3OH) was satisfactorily prepared and characterized. Its X-ray structure shows that it contains two types of octacoordinated DyIII ions, with distorted triangular dodecahedral and square antiprism geometries. This complex is an SMM, with multiple relaxation pathways, and with an anisotropic energy barrier of 39.7 K. 1·CH3OH also operates as a luminescent thermometer in the 11-295 K range, with a maximum relative thermal sensitivity of 1.6% K-1 and a minimum temperature uncertainty of 1.1 K at 295 K. Thus, 1·CH3OH is the first Dy4 SMM with luminescent thermometry, and this system is a rare example of dysprosium SMM that accesses the thermometric characteristics involving the ligand ascribed to the triplet emission in combination with DyIII emission.

Semiconductor Quantum Dots as Target Analytes: Properties, Surface Chemistry and Detection.

Since the discovery of Quantum Dots (QDs) by Alexey I. Ekimov in 1981, the interest of researchers in that particular type of nanomaterials (NMs) with unique optical and electrical properties has been increasing year by year. Thus, since 2009, the number of scientific articles published on this topic has not been less than a thousand a year. The increasing use of QDs due to their biomedical, pharmaceutical, biological, photovoltaics or computing applications, as well as many other high-tech uses such as for displays and solid-state lighting (SSL), has given rise to a considerable number of studies about its potential toxicity. However, there are a really low number of reported studies on the detection and quantification of QDs, and these include ICP-MS and electrochemical analysis, which are the most common quantification techniques employed for this purpose. The knowledge of chemical phenomena occurring on the surface of QDs is crucial for understanding the interactions of QDs with species dissolved in the dispersion medium, while it paves the way for a widespread use of chemosensors to facilitate its detection. Keeping in mind both human health and environmental risks of QDs as well as the scarcity of analytical techniques and methodological approaches for their detection, the adaptation of existing techniques and methods used with other NMs appears necessary. In order to provide a multidisciplinary perspective on QD detection, this review focused on three interrelated key aspects of QDs: properties, surface chemistry and detection.

Dinuclear Fluoride Single-Bridged Lanthanoid Complexes as Molecule Magnets: Unprecedented Coupling Constant in a Fluoride-Bridged Gadolinium Compound.

A new synthetic method allows isolating fluoride-bridged complexes Bu4N{[M(3NO2,5Br-H3L1,1,4)]2(µ-F)} (M = Dy, 1; M = Ho, 2; M = Gd, 3) and Bu4N{[Dy(3Br,5Cl-H3L1,2,4)]2(µ-F)}·2H2O, 4·2H2O. The crystal structures of 1·5CH3C6H5,·2·2H2O·0.75THF, 3, and 4·2H2O·2THF show that all of them are dinuclear compounds with linear single fluoride bridges and octacoordinated metal centers. Magnetic susceptibility measurements in the temperature range of 2-300 K reveal that the GdIII ions in 3 are weakly antiferromagnetically coupled, and this constitutes the first crystallographically and magnetically analyzed gadolinium complex with a fluoride bridge. Variable-temperature magnetization demonstrates a poor magnetocaloric effect for 3. Alternating current magnetic measurements for 1, 2, and 4·2H2O bring to light that 4·2H2O is an SMM, 1 shows an SMM-like behavior under a magnetic field of 600 Oe, while 2 does not show relaxation of the magnetization even under an applied magnetic field. In spite of this, 2 is the first fluoride-bridged holmium complex magnetically analyzed. DFT and ab initio calculations support the experimental magnetic results and show that apparently small structural differences between 1 and 4·2H2O introduce important changes in the dipolar interactions, from antiferromagnetic in 1 to ferromagnetic in 4·2H2O.

Eight coordinated mononuclear dysprosium complexes of heptadentate aminophenol ligands: the influence of the phenol substituents and the ancillary donors on the magnetic relaxation.

The mononuclear complexes [Dy(3Br,5Cl-H3L1,1,4)(D)]·solvate (D = H2O, solvate = 0.25MeOH, 1W·0.25MeOH; D = Py without solvate, 1Py), and [Dy(3NO2,5Br-H3L1,1,4)(H2O)] (2W) were isolated. The crystal structures of 1W·0.25MeOH, 1Py and 2W·2CH3C6H5 show that the DyIII ion is octacoordinated, in N4O4 or N5O3 environments, with distorted geometries, between square antiprism, biaugmented trigonal prism and triangular dodecahedral. A similar environment for the metal ion is shown in the chiral crystals of the diamagnetic yttrium analogue [Y(3Br,5Cl-H3L1,1,4)(MeOH)] (3M), which were spontaneously resolved. Magnetic analyses of the three dysprosium complexes, and their diluted analogous 1W@Y, 1Py@Y and 2W@Y, reveal that none of them seem to relax through an Orbach mechanism at Hdc = 0. However, the three complexes show Orbach relaxation under Hdc = 1000 Oe, and 1Py is the in-field SIM with the highest energy barrier among these complexes, with a Ueff value of 358 K. Analysis of ac magnetic data shows that the electron-withdrawing substituents on the phenol rings of the aminophenol ligands, as well as the auxiliary oxygen donors from water ligands, reduce the energy barriers of the complexes, which is attributed to a charge reduction in the coordinating atoms of the aminophenol donor. Ab initio calculations support the experimental results.

Dysprosium-based complexes with a flat pentadentate donor: a magnetic and ab initio study.

The reactivity of the well-known pentadentate N3O2 Schiff base H2L (2,6-bis(2-hydroxyphenyliminomethyl)pyridine) towards a lanthanoid metal, in this case DyIII, has been investigated for the first time. This reactivity markedly depends on the pH of the medium and, accordingly, two different complexes, [Dy(HL)(NO3)2]·H2O (1·H2O) and [Dy(L)(NO3)(EtOH)(H2O)]·2H2O (2·2H2O), could be isolated from dysprosium(iii) nitrate and H2L. In addition, reaction of H2L with dysprosium(iii) chloride in methanol yields [Dy(HL')2][Dy(L)(Cl2)] (3), where H2L' ((6-(2-hydroxyphenyliminomethyl)-2-methoxyhydroxymethyl)pyridine) is an N2O2 hemiacetal donor derived from the partial hydrolysis of the H2L ligand, and subsequent addition of the methanol solvent to the carbonyl group. This latter reaction has been firstly observed for a lanthanoid metal. Single crystal X-ray diffraction studies of 1·1.15Py·0.3CH3C6H5, 2·2H2O and 3 show that the Schiff base is acting as a nearly flat pentadentate donor in all the cases, this behaviour being independent of the deprotonation degree of the phenolic oxygen atoms, both mono- or bisdeprotonated. Complexes 1·1.15Py·0.3CH3C6H5 and 2·2H2O show DyN3O6 cores, with distorted geometries closer to spherical tricapped trigonal prism or spherical capped square antiprism for 1·1.15Py·0.3CH3C6H5 and 2·2H2O, respectively. In the case of 3, the [Dy(HL')2]+ cation shows a dysprosium ion in an N4O4 triangular dodecahedron environment, while the [Dy(L)(Cl2)]- anion displays a DyN3O2Cl2 core with distorted pentagonal bipyramidal geometry. Moreover, attempts to dilute 1·H2O with yttrium yielded single crystals of (Et3NH)[Dy0.09Y0.91(L)(NO3)2] (4), where the Schiff base shows a similar pentadentate coordination mode. Dynamic magnetic studies of 1·H2O, 2·2H2O and 3 show that 2·2H2O and 3 present field-induced slow relaxation of the magnetisation, with Ueff barriers of 46.1(9) and 31.0(7) K for 2·2H2O and 3, respectively, while 1·H2O does not exhibit frequency-dependent peaks of the out of phase susceptibility, even in the presence of an external dc magnetic field. By contrast, the dilute sample 4 behaves as a SIM at zero dc field, with an energy barrier of ca. 49 K. Ab initio calculations using CASSCF methods including spin-orbit effects qualitatively support the obtained magnetic results, indicating that axiality is not the only factor that should be taken into account in order to increase effective energy barriers.

Field-Induced Single Molecule Magnets of Phosphine- and Arsine-Oxides.

The coordination chemistry of dysprosium and terbium toward phosphine and arsine oxides was further explored. Thus, the new nitrate [M(NO3)3(Ph3PO)3] (M = Tb, 1; Dy, 2), [Dy(NO3)3(EtOH)(Ph3XO)2] (X = P, 3; As, 4), chloride [DyCl2(Ph3AsO)4]Cl (5), triflate [Dy(OTf)2(MePh2PO)4]OTf (6; OTf = triflate) and hexafluoroacetylacetonate [M(hfa)3(Ph3PO)2] (hfa = hexafluoroacetylacetonate; M = Tb, 7; Dy, 8) complexes were isolated and fully characterized. The crystal structures of 1·CH3CN, 2·CH3CN, 4, 5·2.75EtOH·1.25H2O, 6, 7, and 8 show MO9 cores in 1, 2, and 4, with highly distorted geometry, between spherical capped square antiprism and muffin-like, hexacoordinated environments for the dysprosium ions in 5 and 6, with octahedral geometry, and octa-coordination for the lanthanoid metals in 7 and 8, with geometry closer to square antiprism. Comparison of the magnetic behavior of all the complexes allows analyzing which metal ion (Tb or Dy), phosphine or arsine oxide, or anionic ligand favor more the slow relaxation of the magnetization. Alternating current magnetic measurements show that only 2, 4, and 8 present slow relaxation of the magnetization in the presence of an external magnetic field, 8 being the complex with the highest U eff (44.85 K) of those described herein.

Tb2, Dy2, and Zn2Dy4 Complexes Showing the Unusual Versatility of a Hydrazone Ligand toward Lanthanoid Ions: a Structural and Magnetic Study.

Three dinuclear complexes, [Tb2(H2daps)2(CH3OH)5.5(H2O)0.5](Cl)2 (Tb2Cl), [Dy2(H2daps)2(Cl)(CH3OH)3(H2O)]Cl (Dy2Cl), and [Dy2(H2daps)2(H2O)6](CF3SO3)2 (Dy2CF3SO3), as well as the heterohexanuclear compound [Zn2Dy4(daps)2(Hdaps)(Cl)3(OH)2(CH3OH)(H2O)5] (Zn2Dy4) (H4daps: 2,6-bis(1-salicyloylhydrazonoethyl)pyridine), which crystallize with different lattice molecules, show their hexa- or heptadentate hydrazone ligands acting with hitherto unknown µ2-κ5:κ1, µ3-κ5:κ4:κ1, µ4-κ5:κ4:κ1:κ1, or µ4-κ5:κ2:κ1:κ1 bridging modes. The single X-ray crystal structures of the dinuclear complexes show nine-coordinated N3 O6 environments for lanthanoid atoms in Tb2Cl and Dy2CF3SO3, with distorted geometries, between spherical capped square antiprism and muffin-like, while the dysprosium atoms in Dy2Cl are eight-coordinated, with distorted triangular dodecahedron geometries. In the case of Zn2Dy4, both eight-coordinated, O8 and O7 Cl, as well as nine-coordinated N3 O6 environments coexist in the crystal structure, with biaugmented trigonal prism, triangular dodecahedron, and muffin-like pseudogeometries. The magnetic study of all the complexes shows that none of the pure samples behaves as a single molecular magnet (SMM) and that the quantum tunnel cannot be removed by dilution of any of the dinuclear complexes, but except in diluted [Y1.904Dy0.096(H2daps)2(Cl)(H2O)4]Cl (Dy2Cl@Y), behaves as a weak field induced SMM. The heterohexanuclear Zn2Dy4 complex also lacks slow relaxation of the magnetization.

Improving the SMM and luminescence properties of lanthanide complexes with LnO9 cores in the presence of ZnII: an emissive Zn2Dy single ion magnet.

Mononuclear complexes of stoichiometry [Ln(H3L)(H2O)(NO3)](NO3)2 (Ln = Tb, 1; Dy, 2, Er, 3), which crystallise with different solvates, and the heterotrinuclear compound [Zn2Dy(L)(NO3)3(OH)] (4) can be obtained with the same H3L compartmental ligand. The single X-ray crystal structure of the mononuclear complexes shows a LnO9 core with a muffin-like disposition while the geometry of the DyO9 core in 4 seems to be closer to spherical capped square antiprism. The analysis of the magnetic properties of all the complexes demonstrates that the mononuclear lanthanide compounds do not show slow relaxation of the magnetization, even when the samples are diluted with a diamagnetic matrix and subjected to a dc applied field of 1000 Oe. Nevertheless, the heterotrinuclear dysprosium complex 4·3H2O is a field-induced single ion magnet, with an estimated Ueff barrier of 59 K. The luminescence characterisation of all the metal complexes in methanol solution at 298 K also shows a notable increase in the fluorescence emission of the heterotrinuclear complex with respect to the mononuclear ones, in such a way that 4 can be defined as a fluorescent single ion magnet.

Exploration of an easily synthesized fluorescent probe for detecting copper in aqueous samples.

An easily synthesized fluorescent probe for detecting copper in aqueous samples, with a short response time and at neutral pH, has been investigated. Through the chelation of Cu2+ ions or by binding to CuO nanoparticles, the fluorescence emission of the 2-(aminomethyl)aniline derivative H2L is quenched by over 50%. Spectroscopic determination of the association constants of H2L with some metal ions showed that the ligand has a higher affinity toward Cu2+ than toward other d-block metal ions. The comparative bonding ability of the aniline-based fluorescent probe in d-block metal complexes was studied in solution by a combination of UV-Vis, 1H NMR and mass spectrometry analyses. Besides these, the bonding behavior has been investigated in the solid state by X-ray diffraction, FT-IR spectroscopy and elemental analysis. The crystal structures of Pd2(L)2 and Co(L)(HL)(H2O) were elucidated.

Designing Ligands to Isolate ZnLn and Zn2Ln Complexes: Field-Induced Single-Ion Magnet Behavior of the ZnDy, Zn2Dy, and Zn2Er Analogues.

A new H3L Schiff base ligand with three defined compartments, namely, two internal NNO and one external O6, was designed to allocate metal ions of different size. This ligand allows isolating heterodinuclear [ZnLn(HL)(NO3)(OAc)(D)](NO3) (Ln = Tb, D = H2O, ZnTb; Ln = Dy, D = CH3OH, ZnDy; and Ln = Er, D = CH3OH, ZnEr) complexes, where one of the NNO pockets allocates a zinc(II) ion, while the other one is empty, or heterotrinuclear [Zn2Ln(L)(NO3)2(OAc)2(H2O)] (Ln = Dy, Zn2Dy and Ln = Er, Zn2Er) compounds, where each NNO compartment accommodates ZnII. All these compounds crystallize with different solvates, and their structures were unequivocally determined by single-crystal X-ray diffraction studies. Complexes ZnDy, Zn2Dy, and Zn2Er behave as single-molecule magnets in the presence of an external dc field of 1000 Oe, with Ueff values of 41.05, 47.69, and 20.81 K, respectively, while ZnTb and ZnEr do not.

Predetermined Ferromagnetic Coupling via Strict Control of M-O-M Angles.

An imidazolidine-phenolate ligand HL yields quadruple-bridged (µ-NCNimidazolidine)2(µ-Ophenolate)2 ferromagnetic dinuclear nickel and cobalt complexes. Both kinds of bridges contribute to the ferromagnetic coupling, but the ferromagnetism of these samples is mainly ascribed to the double µ-Ophenolate links, on the basis of density functional theory calculations. These studies demonstrate not only that the short M-O-M angles of the M2O2 cores favors the parallel alignment of the electrons but also that these angles are the optimal ones for maximizing the ferromagnetic contribution in these complexes. And these acute angles, close to 90°, are predetermined by the geometrical constrictions imposed by the ligand itself. Thus, HL is an uncommon polydentate donor that induces ferromagnetism per se in its metal complexes by strict control of one geometric parameter, the M-O-M angle.

Dual role of 2-tosylaminomethylaniline as a ligand and a nucleophile in the copper-mediated oxidation of methanol.

Some reactivity in the oxidation of methanol to formaldehyde has been spectroscopically detected on the methanolic mother liquors of a copper(ii) complex of a Schiff base ligand derived from the condensation of 8-hydroxyquinoline-2-carboxaldehyde and 2-tosylaminomethylaniline. An investigation has shown that 2-tosylaminomethylaniline (HA(TS)) plays a dual role in the oxidative process acting as a N-donor ligand and reacting in situ with formaldehyde, which leads to 3-tosyl-1,2,3,4-tetrahydroquinazoline (1). This was characterized by using both spectroscopic and X-ray diffraction techniques. The influence of 8-hydroxyquinoline derivatives, water and ligand stoichiometry on the yield of 1 was studied.

Encapsulation of atmospheric CO2 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.

Structural variety of zinc and copper complexes based on a 2,3-disubstituted 1,2,3,4-tetrahydroquinazoline ligand.

The ring-chain tautomerism of 2-(3-tosyl-1,2,3,4-tetrahydroquinazolin-2-yl)quinolin-8-ol (H(2)L(ring)) has been exploited to produce mononuclear complexes or, alternatively, dinuclear complexes, as desired, by varying the stoichiometry of the ligand. Cu(2+) and Zn(2+) stabilise the ring tautomeric form of the ligand in their mononuclear complexes M(HL(ring))(2). The structural characterisation of Zn(HL(ring))(2)·2MeOH·0.5H(2)O shows O,N-donor behaviour of the ring tautomer. The 1,2,3,4-tetrahydroquinazoline undergoes a ring-opening reaction upon formation of phenoxo-bridged dinuclear complexes M(2)(L(chain))(2) in which the chain tautomer is acting as O,N,N,N-donor. The crystal structure of Cu(2)(L(amide))(L(quinazoline))(MeOH)·2MeOH evidenced the sensitivity of H(2)L(ring) to the copper-mediated aerobic oxidation, which results in two derivatives of the ligand, a quinazoline and an amide. The quinazoline ligand is acting as monoanionic and mononucleating through its O,N,N binding site, while the amide ligand behaves as a trianionic and binucleating through its O,N,N,N and O,O binding sites in Cu(2)(L(amide))(L(quinazoline))(MeOH)·2MeOH.

Metal-assisted ring-closing/opening process of a chiral tetrahydroquinazoline.

The ring-chain tautomerism of a 2-aryl-1,2,3,4-tetrahydroquinazoline has been exploited to induce reversible changes in the aminal-imine equilibrium, as desired, by coordination of a suitable metal ion. This process was studied by NMR and UV-vis spectroscopies, X-ray crystallography, and molecular modeling approach. The results obtained show that the imine H(2)L(i) undergoes a selective ring-closing reaction upon complexation with Ni(2+). As a result, complexes of the type Ni(HL(a))(2) are obtained, whose chirality arises from the chiral ligand H(2)L(a) and the helicity of the structure. Hence, helical enantiomers form the following racemates: [Δ-C(R,R)N(S,S),Λ-C(S,S)N(R,R)]-Ni(HL(a))(2)·2HOAc and [Δ,Λ-C(S,R)N(R,S)]-Ni(HL(a))(2)·4MeOH. In contrast to the situation observed for Ni(2+), the cyclic tautomer of the ligand, H(2)L(a), undergoes a selective ring-opening reaction upon complex formation with Pd(2+), ultimately yielding Pd(HL(i))(2)·MeOH, in which the open-chain imine ligand is bidentate through the N,O donor set of the quinoline residue. Density functional theory calculations were conducted to provide insight into the different behavior of both coordinated metals (Ni(2+) and Pd(2+)) and to propose a mechanism for the metal-assisted opening/closing reaction of the tetrahydroquinazoline ring.

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.