Nadia Marino

A self-assembled tetrameric water cluster stabilized by the hexachlororhenate(IV) anion and diprotonated 2,2′-biimidazole: X-ray structure and magnetic properties

A self-assembled tetrameric water cluster stabilized by [ReCl6]2− anions and [H4biim]2+ cations occurs in the new compound [H4biim][ReCl6]·4H2O, which exhibits a weak ferromagnetic coupling between the Re(IV) centers through an unusual ReIV–Cl⋯(H2O)⋯Cl–ReIV pathway.

[Cr(dmbipy)(ox)2]−: a new bis-oxalato building block for metal assembling. Crystal structures and magnetic properties of XPh4[Cr(dmbipy)(ox)2]·5H2O (X = P and As), {Ba(H2O)2[Cr(dmbipy)(ox)2]2}n·17/2nH2O and {Ag(H2O)[Cr(dmbipy)(ox)2]}n·3nH2O

The synthesis, X-ray structure and variable-temperature magnetic study of new compounds of formula PPh4[Cr(dmbipy)(ox)2]·5H2O (1), AsPh4[Cr(dmbipy)(ox)2]·5H2O (2), {Ba(H2O)2[Cr(dmbipy)(ox)2]2}n·17/2nH2O (3) and {Ag(H2O)[Cr(dmbipy)(ox)2]}n·3nH2O (4) (PPh4+ = tetraphenylphosphonium cation; AsPh4+ = tetraphenylarsonium cation; dmbipy = 4,4′-dimethyl-2,2′-bipyridine; ox2− = oxalate dianion) are reported herein. The isomorphous compounds 1 and 2 are made up of discrete [Cr(dmbipy)(ox)2]− anions, XPh4+ cations [X = P (1) and As (2)] and uncoordinated water molecules. The chromium environment in 1 and 2 is distorted octahedral with Cr–O and Cr–N bond distances varying in the ranges 1.950(2)–1.9782(12) and 2.047(3)–2.0567(14) A, respectively. The angles subtended at the chromium atom by the two bidentate oxalate ligands cover the range 82.58(10)–83.11(5)°, and they are somewhat greater than those concerning the chelating dmbipy [79.04(10) (1) and 79.24(5)° (2)]. The [Cr(dmbipy)(ox)2]− unit of 1 and 2 also occurs in 3 and 4 but it adopts different coordination modes. It acts as a chelating ligand through its two oxalate groups towards the divalent barium cations in 3 affording neutral chains with diamond-shaped units sharing the barium atoms, while the two other corners are occupied by two crystallographically independent chromium atoms. The barium atom in 3 is coordinated by eight oxygen atoms from four oxalate groups and two aqua ligands. The structure of 4 consists of neutral bimetallic layers where the [Cr(dmbipy)(ox)2]− unit acts as a ligand towards the univalent silver(I) cation through its two oxalate groups, one of them being bidentate and the other bidentate/monodentate (outer). Each silver atom is six-coordinated with a water molecule and five oxygen atoms from three oxalate groups building a highly distorted octahedral environment. Magnetic susceptibility measurements for 1–4 in the temperature range 1.9–300 K show the occurrence of weak ferro- (1 and 2) and antiferromagnetic (3 and 4) interactions which are mediated by π–π stacking between dmbipy ligands through the spin polarization mechanism. A comparative study of the potentiality of the [Cr(AA)(ox)2]− unit (AA = bidentate nitrogen donor) as a building block for designing heterometallic species is carried out in the light of the available structural information.

Self-assembly of a chiral carbonate- and cytidine-containing dodecanuclear copper(II) complex: a multiarm-supplied globular capsule.

A dodecanuclear copper(II) globular-shaped structure has been obtained with the cytidine nucleoside and the templating carbonate anion. It shows receptor properties through anion-cation and multiple anion-pi interactions toward ClO 4 (-) as well as an overall antiferromagnetic coupling.

Cubane-Type CuII4 and MnII2MnIII2 Complexes Based on Pyridoxine: A Versatile Ligand for Metal Assembling

By using Vitamin B6 in its monodeprotonated pyridoxine form (PN-H) [PN = 3-hydroxy-4,5-bis(hydroxymethyl)-2-methylpyridine], two tetranuclear compounds of formula [Mn4(PN-H)4(CH3CO2)3Cl2]Cl·2CH3OH·2H2O (1) and [Cu4(PN-H)4Cl2(H2O)2]Cl2 (2) have been synthesized and magneto-structurally characterized. 1 crystallizes in the triclinic system with space group P1 whereas 2 crystallizes in the orthorhombic system with Fdd2 as space group. They exhibit Mn(II)2Mn(III)2 (1) and Cu(II)4 (2) cubane cores containing four monodeprotonated pyridoxine groups simultaneously acting as chelating and bridging ligands (1 and 2), three bridging acetate ligands in the syn-syn conformation (1), and two terminally bound chloride anions (1 and 2) plus two coordinated water molecules (2). The electroneutrality is achieved by the presence of chloride counterions in both compounds. Tri- [Mn(1) and Mn(3)] and divalent [Mn(2) and Mn(4)] manganese centers coexist in 1, all being six-coordinate with distorted Mn(1/3)O6 and Mn(2/4)O5Cl octahedral surroundings, respectively, the equatorial Mn-O bonds being about 0.2 Å shorter at the former ones. The two crystallographically independent copper(II) ions in 2 are five-coordinate in somewhat distorted CuO5 [Cu(1)] and CuO4Cl [Cu(2)] square pyramidal geometries. The values of the intracore metal-metal separation cover the ranges 3.144(1)-3.535(1) (1) and 2.922(6)-3.376(1) Å (2). The magnetic properties of 1 and 2 were investigated in the temperature range 1.9-300 K, and they correspond to an overall antiferromagnetic behavior with susceptibility maxima at 5.0 (1) and 65.0 K (2). The analysis of the magnetic susceptibility data showed the coexistence of intracore antiferro- and ferromagnetic interactions in the two compounds. Their values compare well with those existing in the literature for the parent systems.

Cytosine Nucleobase Ligand: A Suitable Choice for Modulating Magnetic Anisotropy in Tetrahedrally Coordinated Mononuclear CoII Compounds

A family of tetrahedral mononuclear CoII complexes with the cytosine nucleobase ligand is used as the playground for an in-depth study of the effects that the nature of the ligand, as well as their noninnocent distortions on the Co(II) environment, may have on the slow magnetic relaxation effects. Hence, those compounds with greater distortion from the ideal tetrahedral geometry showed a larger-magnitude axial magnetic anisotropy (D) together with a high rhombicity factor (E/D), and thus, slow magnetic relaxation effects also appear. In turn, the more symmetric compound possesses a much smaller value of the D parameter and, consequently, lacks single-ion magnet behavior.

Ethylene transposition: ruthenium hydride catalyzed intramolecular trans-silylvinylation of internal alkynes.

A highly selective intramolecular trans-silylvinylation of internal alkynes catalyzed by RuHCl(CO)(SIMes)(PPh3) has been accomplished. The use of methyl vinyl ketone as an additive increased the efficiency of this transformation. This process was used to successfully form five-, six-, and seven-membered oxasilacycles by a formal anti-exo-dig cyclization.

Expanding Monomeric Pyrophosphate Complexes beyond Platinum

Four new monomeric pyrophosphate complexes, namely [Co(phen)(2)(H(2)P(2)O(7))] x 4 H(2)O (1 x 4 H(2)O), [Ni(phen)(2)(H(2)P(2)O(7))] x 8 H(2)O (2 x 8 H(2)O), [Cu(phen)(H(2)O)(H(2)P(2)O(7))] (3) and {[Cu(phen)(H(2)O)(P(2)O(7))][Na(2)(H(2)O)(8)]} x 6 H(2)O (4 x 14 H(2)O) have been isolated and structurally characterized. The impact of pH and stoichiometry in obtaining 1-4 is described. These complexes have been tested against the adriamycin-resistant ovarian cancer cell line A2780/AD, revealing highly significant (nM) IC(50) values, compared to microM IC(50) values for cisplatin controls.

Solid-state cis–trans isomerism in bis(oxamato)palladate(II) complexes: synthesis, structural studies and catalytic activity

A new generation of bis(oxamato)palladate(II) monomeric complexes has been prepared by using N-2,6-dimethylphenyloxamate (2,6-Me2pma) as the ligand. Four alkaline salts of the complex, namely {[Na(H2O)]2trans-[PdII(2,6-Me2pma)2]}n (1a), {[Na4(H2O)2]cis-[PdII(2,6-Me2pma)2]2}n (1b), {[K4(H2O)3]cis-[PdII(2,6-Me2pma)2]2}n (2), {[Rb4(H2O)3]cis-[PdII(2,6-Me2pma)2]2}n (3) and {[Cs6(H2O)7]trans-[PdII(2,6-Me2pma)2]2cis-[PdII(2,6-Me2pma)2]}n·3nH2O (4), were obtained and structurally characterized by single crystal X-ray diffraction. Both the cis and trans stereoisomers of the [PdII(2,6-Me2pma)2]2− complex anion were isolated in the solid state, in a cation-dependent manner. The trans-isomer as the sodium salt (1a) crystallizes in the monoclinic space group I2/a with half of the molecule in the asymmetric unit. The cis isomer as sodium (1b), potassium (2) or rubidium (3) salt crystallizes in the acentric monoclinic space group Cc, with two whole molecules in the asymmetric unit. In the presence of cesium(I) (4), both the cis and trans stereoisomers co-crystallize in the orthorhombic system with Pbca as the space group, with two whole and two half molecules in the asymmetric unit. Previously reported square-planar bis(oxamato)metallate(II) [M = Cu(II) or Pd(II)] species with similar N-aryl substituted oxamate ligands only showed the occurrence of the trans isomer, complexes 1b and 2–4 offering unique examples of the alternative cis stereochemistry. The catalytic properties of 1a, 2–4 have been investigated in the palladium-catalyzed arylation of phenylboronic acid with a variety of aryl halides referred to as the Suzuki reaction, yielding biaryl compounds in very higher yields when iodobenzene [turnover number (TON) = 88–99 and turnover frequency (TOF) = 1056–1188 h−1] was used compared to commercial palladium(II) catalysts.

{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).

Ca2+ metal ion adducts with cytosine, cytidine and cytidine 5′-monophosphate: a comprehensive study of calcium reactivity towards building units of nucleic acids

Six new Ca(II) adducts of formulae [Ca(cyt)2(H2O)4][ClO4]2·2cyt·2H2O (1), [Ca2(cyt)2(H2O)4(ClO4)4] (2), [Ca2(cyt)4(H2O)4Cl2]Cl2 (3), [Ca(H2cyd)2(H2O)4][ClO4]2·3H2O (4), [Ca(H2cyd)2(H2O)4]Cl2·3H2O (5) and [Ca2(CMP)2(H2O)11]·5H2O (6) [cyt = cytosine, H2cyd = cytidine, CMP = cytidine 5′-monophosphate] have been synthesized and structurally characterized. They reveal classical as well as uncommon structures, with H2cyd and CMP showing unprecedented binding sites for the calcium ion. The structure of compound 1 consists of monomeric [Ca(cyt)2(H2O)4]2+ cations and uncoordinated ClO4− anions as well as lattice nucleobase molecules. The structures of compounds 2 and 3 contain either neutral (2) or cationic (3) dinuclear entities. They have in common a bis-μ-carboxylate bridged [Ca2(cyt)2]4+ dinuclear core, where each cytosine molecule shows coordination simultaneously through O2–N3. The coordination sphere of each calcium ion in 2 is completed by two cis water molecules and two ClO4− groups, the latter either in a mono- or in a bis-monodentate fashion. In the structure of 3, the dinuclear entities are cationic due to the direct metal coordination of only two of four Cl− anions, the remaining two being engaged as counterions in hydrogen bonds with the metal complex. The coordination sphere of each calcium ion in 3 is completed by two trans water molecules and an additional cytosine molecule, coordinated this time via O2 only. Compounds 4 and 5 are, like 1 and 3, ionic salts. They share the same [Ca(H2cyd)2(H2O)4]2+ cationic unit and differ by the supramolecular packing motif generated with the aid of water molecules of crystallization and the specific counterions in each case [ClO4− in 4 and Cl− in 5]. The structure of compound 6 consists of neutral [Ca2(CMP)2(H2O)11] asymmetric moieties and crystallization water molecules. Each dimer contains two Ca(II) ions in a slightly different coordination environment and two CMP di-anions exhibiting the chelating coordination mode through the ribose O2′ and O3′ hydroxyl groups and each interacting with a calcium ion. One of them is further coordinated via the nucleobase O2 oxygen atom toward the exogenous calcium ion, thus building up the dinuclear unit. The lack of coordination of Ca2+ ions to phosphate groups observed in 6 is unusual.