Diana Visinescu

Self-assembly of [CuIITbIII]3+ and [W(CN)8]3− tectons: a case study of a mixture containing two complexes showing slow-relaxation of the magnetization

The reaction of [Cu(valen)] with Tb(NO(3))(3) and (Bu(3)NH)(3)[W(CN)(8)] affords two types of crystals: [{W(CN)(8)}Cu(valen)Tb(OH(2))(5)]·2H(2)O (1, a discrete trinuclear complex) and [{W(CN)(8)}Cu(valen)Tb(OH(2))(4)]·CH(3)CN·H(2)O (2, an infinite zig-zag chain), both compounds showing slow relaxation of the magnetization (H(2)valen is the Schiff base resulting from the reaction of o-vanillin with 1,2-ethanediamine).

A straightforward synthetic route towards tetranuclear copper(II) complexes: reactions between binuclear complexes and exo-bidentate or exo-bis(bidentate) ligands

Abstract The reactions between binuclear copper(II) complexes of the type [L(μ-OH)Cu2](ClO4)2 with exo-dentate ligands lead to tetranuclear complexes with both short and long distances between the metallic centers (L=the compartmental end-off ligand, 2,6-bis[N-2-pyridylethyl)formimidoyl]-phenolato). Three new copper(II) complexes have been obtained by using the following spacers: bis(4-pyridyl)ethane (1), the dianion of the acetylenedicarboxylic acid (2) and 4,4′-bipyridine-N,N′-dioxide (3). The crystal structures of the three compounds have been solved. Compound 1 contains cationic [Cu4] rectangles, with the short edges constructed from the preexisting μ-OH and μ-phenoxo groups, and the long ones constructed from bis(4-pyridyl)ethane molecules. The crystal 2 contains centrosymmetric tetranuclear cationic species, which result by connecting two binuclear units with one dicarboxylato linker. Each carboxylato group forms a third bridge between the copper(II) ions within the binuclear moiety (syn–syn bridging more). In compound 3, one 4,4′-bipyridine-N,N′-dioxide molecule (4,4′-bpno) connects two copper(II) ions arising from two binuclear cationic entities. The two binuclear moieties are almost parallelly disposed above and below the 4,4′-bpno bridge. The Cu(II) ions bridged by 4,4′-bpno show a square-pyramidal stereochemistry, with the oxygen atom arising from 4,4′-bpno in the apical position. The other two copper(II) ions, which are not bridged by 4,4′-bpno, exhibit a square-planar coordination geometry.

[Fe(phen)(CN)4] − : a suitable metalloligand unit to build 3d–4f heterobimetallic complexes with mixed bpym-cyano bridges (phen = 1,10-phenantroline, bpym = 2,2′-bipyrimidine)

The synthesis, crystal structure and magnetic properties of a new series of mixed 3d–4f complexes with the formula [{FeIII(phen)(CN)3(μ-CN)}4Ln2III(NO3)2(H2O)6(μ-bpym)]·nH2O [Ln = Eu (1), Gd (2), Dy (3) and Ho (4); n = 8 (1, 3 and 4) and 11 (2); phen = 1,10-phenantroline; bpym = 2,2′-bipyrimidine] are discussed here. Compounds 1–4 are centrosymmetric hexanuclear species whose structure is made up of two cyano-bridged {Fe2IIILnIII} heterobimetallic moieties which are connected through a bis-bidentate bpym molecule between the two rare-earth centers. The values of the iron–lanthanide distance across the single cyano-bridge are Fe(1)⋯Eu(1) = 5.5587(8) and Fe(2)⋯Eu(1) = 5.4908(8) A (1), Fe(1)⋯Gd(1) = 5.5456(6) and Fe(2)⋯Gd(1) = 5.4831(6) A (2), Fe(1)⋯Dy(1) = 5.5223(7) and Fe(2)⋯Dy(1) = 5.4509(7) A (3) and Fe(1)⋯Ho(1) = 5.5094(12) and Fe(2)⋯Ho(1) = 5.4420(14) A (4), whereas those of the lanthanide–lanthanide separation through the bpym bridge are 6.8196(8) (1), 6.7971(6) (2), 6.7511(7) (3) and 6.7395(6) A (4). The two crystallographically independent iron(III) ions in 1–4 are six-coordinated with two nitrogen atoms from a bidentate phen ligand and four carbon atoms from four cyanide groups building somewhat distorted octahedral surroundings. The trivalent lanthanide cations in 1–4 are nine-coordinated with two bpym and two cyano-nitrogen atoms, three water molecules and a chelating nitrate describing distorted monocapped square antiprism environments. Compounds 1–4 are isomorphous species where the neutral hexanuclear motifs are assembled through an extensive network of hydrogen bonds involving all the water molecules to afford a supramolecular three-dimensional structure. Interestingly, the crystal packing of 2 shows the occurrence of unprecedented centrosymmetric twelve-atom water aggregates which are integrated by two interlinked pentanuclear water rings, each one having a dangling water molecule. The investigation of the magnetic properties of 1–4 in the temperature range 1.9–300 K reveals the presence of intramolecular magnetic interactions for 2–4 [antiferro- (through single cyano and bpym bridges) in 2 and ferromagnetic (across single cyano and/or bpym bridges) in 3 and 4] whereas the magnetic behaviour of 1 corresponds to that of the magnetically isolated low-spin iron(III) and europium(III) centers.

Design of molecular rectangles by using compartmental and exo-bidentate ligands

Abstract Molecular rectangles with different sizes can be obtained by reacting a binuclear copper(II) complex, [L(μ-OH)Cu2](ClO4)2 (L=the compartmental end-off ligand, 2,6-bis[N-(2-pyridylethyl)formimidoyl]-phenolato), with bis-(4-pyridyl) derivatives (4,4′-bipyridine, 1,2-bis(4-pyridyl)ethylene). Two tetranuclear complexes have been obtained and characterized by single-crystal X-ray diffraction: [{L(μ-OH)Cu2}-(μ-4,4′-bipy)2-{Cu2(μ-OH)L}](ClO4)4·3H2O (1), and [{L(μ-OH)Cu2}-(μ-bpe)2-{Cu2(μ-OH)L}](ClO4)4·4H2O (2). Compounds 1 and 2 have been obtained also through a multicomponent self-assembly process, namely by mixing together the stoichiometric amounts of compartmental Schiff base, exo-bidentate ligand and lithium hydroxide, followed by the addition of copper(II) perchlorate.

New tetranuclear copper(II) complexes obtained by using compartmental and exo-dentate ligands

The synthesis and crystal structures of two new tetranuclear complexes are described: [{L(g-OH)Cu-2}(mu-fum){Cu-2(mu-OH)L}]1(ClO4)(2) (1) and [{L(mu-OH)Cu-2}(mu-IN)(2){Cu-2(mu-OH)L}](ClO4)(2).2C(2)H(5)OH.0.5H(2)O (2). The two complexes have been obtained through self-assembly processes involving a binuclear copper(II) complex, [L(mu-OH)Cu-2](ClO4)(2) (L stands for a compartmental end-off ligand, 2,6-bis[N-2-pyridylethyl)formimidoyl]-phenolato), and exo-dentate ligands (the fumarate anion, fum(2-), and the isonicotinato anion, IN-). The crystal structure of 1 consists of centrosymmetric tetranuclear cationic species, which result by connecting two binuclear units with one dicarboxylato linker. Each carboxylato group forms a third bridge between the copper(II) ions within the binuclear moiety (syn -syn bridging mode). The closest (CuCu)-Cu-... distances in tetramer are 2.930(1) and 9.313(3) Angstrom. Compound 2 contains cationic [Cu-4] rectangles, with the short edges constructed from the preexisting [L-OH and Aphenoxo groups [3.062(1) Angstrom], and the long ones constructed from the isonicotinato linkers [9.352(1) Angstrom]. In both compounds the copper(II) ions are pentacoordinated with a square-pyramidal stereochemistry

Synthesis, Crystal Structures, and Magnetic Properties of Two Novel Cyanido-Bridged Heterotrimetallic {CuIIMnIICrIII} Complexes

The self-assembly process between the heteroleptic [CrIII(phen)(CN)4]- and [CrIII(ampy)(CN)4]- metalloligands and the heterobimetallic {CuII(valpn)MnII}2+ tecton afforded two heterotrimetallic complexes of formula [{CuII(valpn)MnII(μ-NC)2CrIII(phen)(CN)2}2{(μ-NC)CrIII(phen)(CN)3}2]·2CH3CN (1) and {[CuII(valpn)MnII(μ-NC)2CrIII(ampy)(CN)2]2·2CH3CN}n (2) [phen = 1,10-phenanthroline, ampy = 2-aminomethylpyridine, and H2valpn = 1,3-propanedyilbis(2-iminomethylene-6-methoxyphenol)]. The crystal structure of 1 consists of neutral CuII2MnII2CrIII4 octanuclear units, where two [Cr(phen)(CN)4]- anions act as bis-monodentate ligands through cyanide groups toward two manganese(II) ions from two [CuII(valpn)MnII]2+ units to form a [{Cu(valpn)Mn}2Cr2(CN)4]6+ square motif. Two [Cr(phen)(CN)4]- pendant anions in 1 are bound to the copper(II) ions with cis-trans geometry with respect to the bridging [Cr(phen)(CN)4]- anion. Compound 2 is a sheet-like coordination polymer, where chains constituted by {CrIII(ampy)(CN)4} spacers act as bis-monodentate ligands toward the manganese(II) ions belonging to the {CuII(valpn)MnII} nodes, which are interlinked by another {CrIII(ampy)(CN)4} unit that acts as a bridge between the copper(II) and manganese(II) ions of adjacent chains. Magnetic susceptibility measurements in the temperature range of 1.9-300 K were performed for 1 and 2. An overall antiferromagnetic behavior is observed for 1, the ground spin state being described by a spin triplet from the square motif plus two magnetically isolated spin triplets from the two peripheral chromium(III) ions. Ferrimagnetic chains with interacting spins 1/2 (resulting spin of the trimetallic {CuII(valpn)MnII(μ-NC)CrIII} fragment) and 3/2 (spin from the bis-monodentate [CrIII(ampy)(CN)4]- with weak interchain ferromagnetic interactions across the cyanide bridge between the chromium(III) and the copper(II) ion from adjacent chains [θ = +3.83(2) cm-1]) occur in 2, resulting into a ferromagnetic ordering below 3.5 K. The values of the magnetic coupling between the Cu(II) and Mn(II) ions through the double phenoxide bridge [J = -63.1(2) (1) and -62(3) cm-1 (2)] and those between the Cr(III) and the Mn(II) across the single cyanide bridge [J = -7.08(5) and -4.86(6) cm-1 (1) and -8.59(3) cm-1 (2)] agree with the values reported for these exchange pathways in other magnetostructural studies.

Polysaccharides Route: A New Green Strategy for Metal Oxides Synthesis

The present paper reviews some of the most important polysaccharide-based synthetic strategies of metal oxides, highlighting the polysaccharides multitasking abilities in the synthesis of nanosized oxide particles. The perspectives but also the unexplored areas of this new and promising green chemistry topic are also examined.

{CoIIIMnIII}n corrugated chains based on heteroleptic cyanido metalloligands

The use of the cyanide-bearing complexes PPh4[CoIII(4,4′-dmbipy)(CN)4] and PPh4[CoII(dmphen)(CN)3] as metalloligands towards [Mn(salen)(H2O)]ClO4 affords one-dimensional coordination polymers with the formulas {[MnIII(salen)(μ-NC)2CoIII(4,4-dmbipy)(CN)2]·H2O}n (1) and {[MnIII(salen)(μ-NC)2CoIII(dmphen)(CN)2]}n (2) [PPh4+ = tetraphenylphosphonium cation, 4,4′-dmbipy = 4,4′-dimethyl-2,2′-bipyridine, dmphen = 2,9-dimethyl-1,10-phenanthroline and H2salen = N,N′-ethylenebis(salicylideneimine)]. Compounds 1 and 2 were structurally characterized. Their structures consist of neutral chains with regular alternating [Mn(salen)]+ and [CoIII(4,4′-dmbipy)(CN)4]− (1)/[CoIII(dmphen)(CN)4]− (2) moieties, the latter ones acting as bis-monodentate ligands towards the Mn(III) units through two of their four cyanide groups. During the synthesis, the cobalt(II) ion of the starting [CoII(dmphen)(CN)3]− metalloligand is oxidized to Co(III) and it takes an additional cyanide ligand to transform into {CoIII(dmphen)(CN)4} in 2. Magnetic studies have been carried out on 1 and 2 in the temperature range 1.9–300 K which yielded local negative zero-field splitting parameters of −3.26 (1) and −4.38 cm−1 (2). Frequency-dependent alternating current susceptibility signals under an external applied magnetic field (dc) were clearly observed for 1 and 2 indicating slow magnetic relaxation, that is, Single Ion Magnet (SIM) behaviour. The energy barriers (Ea) to reverse the magnetization direction under an applied dc magnetic field of 2000 Oe were 12.0(2) (1) and 9.4(3) cm−1 (2), whereas the values of the pre-exponential factor (τo) were 1.40(2) × 10−8 (1) and 2.5(2) × 10−8 s (2).

Additive-free 1,4-butanediol mediated synthesis: a suitable route to obtain nanostructured, mesoporous spherical zinc oxide materials with multifunctional properties

A family of mesoporous, self-aggregated zinc oxide materials with spherical morphologies of high crystalline quality, is obtained through a facile, additive-free polyol procedure. The forced hydrolysis of zinc acetylacetonate in 1,4-butanediol (BD), in various reaction conditions, affords ZnO materials with versatile morphologies and optical properties. The reaction parameters (temperature, time and zinc source concentration) modulate the ZnO nanocrystallites size (from 8.1 to 13.2 nm), the spheres diameter (ranging from 50 up to 250 nm), the internal structure of the spherical aggregates (hollow or solid) and their specific surface area (from 31 to 92 m2 g−1). Polycrystalline spheres with hollow cores are obtained at the lowest temperature (90 °C) and zinc cation concentration (0.1 M), while at higher reaction temperatures (140–180 °C), solid spherical aggregates are developed. A reaction mechanism for ZnO formation via zinc layered hydroxide (LDH-Zn) is proposed based on nuclear magnetic resonance (1H NMR and 13C NMR) and powder X-ray diffraction (XRD) studies. The obtained ZnO materials have a functionalized surface, derived from the polyol and act as a nitrogen selective photocatalyst in the reduction reaction of NO3−. The organic residual attached on the ZnO surface plays a crucial role in the denitrification reaction, since the photo-cleaned sample showed negligible photocatalytic activity. The ZnO materials also exhibited microbicidal and anti-biofilm activity against reference and clinical strains, highlighting their potential for the development of novel antimicrobial formulations.

Synthesis, crystal structure and magnetic properties of a cyanide-bridged heterometallic {CoIIMnIII} chain

The assembly reaction between the low-spin [CoII(dmphen)(CN)3]- metalloligand and the [MnIII(salen)(H2O)]+ complex cation yielded the one-dimensional compound {[MnIII(salen)(μ-NC)2CoII(dmphen)(CN)]·2H2O}n (1), which behaves as a ferrimagnetic chain, the intrachain magnetic coupling being J = -1.71(1) cm-1.