Reversible solvatomagnetic switching in a spongelike manganese(II)-copper(II) 3D open framework with a pillared square/octagonal layer architecture

The concept of "molecular magnetic sponges" was introduced for the first time in 1999 by the creative imagination of the late Olivier Kahn. It refers to the exotic spongelike behavior of certain molecule-based materials that undergo a dramatic change of their magnetic properties upon reversible dehydration/rehydration processes. Here we report a unique example of a manganese(II)-copper(II) mixed-metal-organic framework of formula [Na(H(2)O)(4)](4)[Mn(4){Cu(2)(mpba)(2)(H(2)O)(4)}(3)]·56.5H(2)O (1) (mpba=N,N'-1,3-phenylenebis(oxamate)). Compound 1 possesses a 3D Mn(II)(4)Cu(II)(6) pillared layer structure with mixed square and octagonal pores of approximate dimensions 1.2×1.2 nm and 2.1×3.0 nm, respectively, hosting a large amount of crystallization H(2)O molecules and hydrated Na(I) countercations as guests. It reversibly switches from a crystalline hydrated phase with long-range ferromagnetic ordering at a rather high critical temperature (T(c)) of 22.5 K to an amorphous dehydrated phase with T(c) as low as 2.3 K, which is accompanied by a breathing-type dynamic effect involving a large crystal volume (ca. 45%) and color changes after water desorption/adsorption. The combination of both the open-framework structure and the spongelike optical, mechanical, and magnetic switching behavior in this new class of oxamato-based porous magnets offers fascinating possibilities in designing multifunctional materials for host-guest molecular sensing.     

Ethenedithione (S=C=C=S): trapping and isomerization in a cobalt complex

Swing bridge: The triplet species ethenedithione has been generated within the coordination sphere of cobalt, leading to a dinuclear μ-η(2)-η(2)-C(2)S(2) complex (see picture: C?gray, Co?blue, P?purple, S?yellow). Depending on the solvent, the C(2)S(2) moiety displays a transoid or a cisoid geometry. This isomerization step changes the sign of the magnetic coupling between the cobalt centers.     

Synthesis and structure of pseudotetrahedral Co(II) zwitterionic complexes: trichloro(1-methylpiperazin-1-ium-N4)cobalt(II) and trichloro(1,4-dimethylpiperazin-1-ium-N4)cobalt(II)

The pseudotetrahedral cobalt(II) zwitterionic complexes, [CoCl₃(H₂Meppz)] (1) [H₂Meppz⁺=1-methylpiperazin-1-ium cation] and [CoCl₃(HMe₂ppz)] (2), [HMe₂ppz⁺=1,4-dimethylpiperazin-1-ium cation] have been synthesized and characterized in the solid state by X-ray single crystal analysis, IR spectra, magnetic measurements and electronic spectra. In both the compounds the cobalt(II) center is coordinated in a distorted tetrahedral fashion by the three chloride ions and by one nitrogen of the piperazine ring that retains the more stable chair conformation. The distorted coordination polyhedron in complex 1 preserves the C_3v symmetry while in complex 2 it retains only the m symmetry. In complex 1, the (H₂Meppz)⁺ cation binds the Co(II) ion in the equatorial position of the piperazine ring using the unmethylated N1–H nitrogen atom that is less hindered than the methylated one. Complex 2, on the contrary, is a novelty being the first example of a Co(II) ion bound in the axial position of a piperazine ring, this produces a long Co(II)–N bond, 2.108(4) Å. Electronic spectra in the solid state are in perfect accordance with the X-ray crystallographic results indicating a C_3v symmetry for complex 1 and a C_s(m) symmetry for complex 2. These complexes present strong two-center and three-center hydrogen bonds of N⁺–H⋯Cl type.     

Nickel(II)-azido ferromagnetic chains in a 3D porous metal-organic framework with breathing guest molecules

A new 3D porous Ni(II)-azido complex has been synthesized and characterized and exhibits guest sorption properties explored by single-crystal to single-crystal transformations and linear ferromagnetic chains held together by a Ni-isonicotinate framework.     

Unusual layer structure in an ion-paired compound containing tetra(isothiocyanate) cobalt(II) dianion and 4-nitrobenzylpyridinium: Crystal structure and magnetic properties

A new ion-paired compound [4NO₂BzPy]₂[Co(NCS)₄] (1) ([4NO₂BzPy]⁺ = 1-(4′-nitrobenzyl)pyridinium, NCS^? = isothiocyanate) is synthesized and characterized by elemental analysis, IR and UV-Vis spectra, ESI-MS and single crystal X-ray diffraction. Compound 1 is orthorhombic, space group Pbcn, with a = 13.188(2) Å, b = 8.458(1) Å, c = 29.281(4) Å, V = 3266.2(7) ų, D _calc = 1.468 g/cm³, Z = 4, F(000) = 1476, R ₁ = 0.0332. The [Co(NCS)₄]_2? anions form an unusual layer structure by S…N and S…Co interactions, while the [4NO₂BzPy]⁺ cations stack into a 1D column by the p…π stacking interaction in the solid state of 1. A magnetic measurement in the range 2–300 K shows a weak antiferromagnetic exchange with θ = ?2.42 K in 1.     

Carbonyl compounds of cobalt(II) and nickel(II). Reversible arene-carbon monoxide exchange and similarities to analogous η6-arene complexes

Displacement of η⁶-arene in (C₆F₅)₂Co(η⁶-toluene), (Cl₃Si)₂Ni(η⁶-toluene), and (F₃Si)₂Ni(η⁶-toluene) by CO yielded very labile (C₆F₅)₂Co(CO)₃, (Cl₃Si)₂Ni(CO)₃, and (F₃Si)₂Ni(CO)₃, which are rare examples of isolated, characterized, simple carbonyl complexes of cobalt(II) and nickel(II). According to infrared ν(CO) studies the cobalt(II) tricarbonyl and the nickel(II) tricarbonyl derivatives are trigonal bipyramidal with the CO ligands in the axial positions. These η⁶-arene substitutions with CO are reversible under mild conditions. However, the cobalt system slowly degrades to cobalt(I) while the nickel system degrades to nickel(0) carbonyl compounds.     

Hydrothermal synthesis and structure of a three-dimensional cobalt(II) triazolate magnet

The reaction of CoCl2.6H2O, 1,2,4-triazole, and H(2)O at 200 degrees C for 96 h yields purple rods of [Co2(trz)3Cl] (1; trz = 1,2,4-triazolate) in 90% yield. The structure of 1 consists of {Co(trz)3}n(n-) chains of Co(II) sites linked through tetrahedral sites of {CoN(3)Cl} geometry into a three-dimensional framework. The competing antiferromagnetic interactions of the octahedral and tetrahedral Co(II) centers result in weak ferromagnetic behavior below Tc = 9 K.     

Synthesis and guest exchange reactions of inclusion compounds of cucurbit[8]uril with nickel(II) and copper(II) complexes

Inclusion compounds of the macrocyclic cavitand cucurbit[8]uril (CB[8]) with the nickel(II) complex, {trans-[Ni(en)₂(H₂O)₂]@CB[8]}Cl₂ · 23.5H₂O, the copper(II) complex, {2[Cu(dien)(bipy)(H₂O)]@CB[8]}(ClO₄)₄ · 11H₂O, and the organic molecules, 2(pyCN)@CB[8]} · 16H₂O and {2(bpe)@CB[8]} · 17H₂O, where bipy is 4,4′-bipyridyl, pyCN is 4-cyanopyridine, and bpe is trans-1,2-bis(4-pyridyl)ethylene, were synthesized. The inclusion compounds with organic molecules were synthesized starting from inclusion compounds of cucurbit[8]uril with cyclam and ethylenediamine complexes of copper(II) and nickel(II) by the guest exchange method, which is based on the replacement of one guest with another in the cavity of the cavitand The resulting compounds were characterized by X-ray diffraction, ESR, ¹H NMR, IR, and electronic absorption spectroscopy, and electrospray mass spectrometry. Photochemically induced [2+2]-cycloaddition of two 1,2-bis(4-pyridyl)ethylene molecules included in cucurbit[8]uril was studied. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 25–34, January, 2006.     

Fast and mild palladium(II)-catalyzed 1,4-oxidation of 1,3-dienes via activation of molecular oxygen with a designed cobalt(II) porphyrin

The use of a Co(porphyrin)-amide ligand, , in the palladium(II)-catalyzed 1,4-diacetoxylation of conjugated dienes under O2 results in aerobic oxidation. The catalyst was highly active under O2, and the 1,4-diacetoxylation reaction could also be performed under air.     

Water exchange dynamics of manganese(II), cobalt(II), and nickel(II) ions in aqueous solution

The first row transition metal ions Mn(2+), Co(2+), and Ni(2+) have been studied by classical umbrella sampling molecular dynamics simulations. The water exchange mechanisms, estimates of reaction rates, as well as structural changes during the activation process are discussed. Mn(2+) was found to react via an I(A) mechanism, whereas Co(2+) and Ni(2+) both proceed via I(D). Reaction rate constants are generally higher than those obtained by experiment but the simply constructed metal(II) ion-water potential reproduces the relative order quite well.     

Octahedral-tetrahedral equilibrium and solvent exchange of cobalt(II) ions in primary alkylamines

The enthalpy differences (Delta H degrees ) of the equilibrium between the octahedral and tetrahedral solvated cobalt(II) complexes were obtained in some primary alkylamines such as propylamine (pa, 36.1 +/- 2.3 kJ mol(-1)), n-hexylamine (ha, 34.9 +/- 1.0 kJ mol(-1)), 2-methoxyethylamine (meea, 44.8 +/- 3.1 kJ mol(-1)), and benzylamine (ba, 50.1 +/- 3.6 kJ mol(-1)) by the spectrophotometric method. The differences in the energy levels between the two geometries of the cobalt(II) complexes in the spherically symmetric field (Delta E(spher)) were estimated from the values of Delta H degrees by offsetting the ligand field stabilization energies. It was indicated that the value of Delta E(spher) is the decisive factor in determining the value of Delta H degrees and is largely dependent on the electronic repulsion between the d-electrons and the donor atoms and the interelectronic repulsion in the d orbitals. The comparison between activation enthalpies (Delta H(++)) for the solvent exchange reactions of octahedral cobalt(II) ions in pa and meea revealed that the unexpectedly large rate constant and small Delta H(++) in pa are attributed to the strong electronic repulsion in the ground state and removal of the electronic repulsion in the dissociative transition state, which can give the small Delta E(spher) between the ground and transition states. Differences in the solvent exchange rates and the DeltaH(++) values of the octahedral metal(II) ions in some other solvents are discussed in connection with the electronic repulsive factors.     

Crystal structure of a new mononuclear complex of Mn(II) with a bbbi ligand (bbbi = 1,4-bis(benzimidazol-1-yl)-2-butene)

A new mononuclear complex Mn(bbbi)₂(H₂O)₄(ClO₄)₂·(bbbi)₂·(H₂O)₂ 1 (bbbi = 1,4-bis(benzimidazol-1-yl)-2-butene) is synthesized under hydrothermal conditions and characterized by IR spectroscopy, elemental analysis, and single crystal X-ray structural analysis. Crystal data for 1: triclinic, , a = 8.8478(7) ?, b = 15.0550(11) ?, c = 16.4310(12) ?, α = 108.657(7)°, β = 104.044(7)°, Γ = 99.317(7)°, V = 1942.2(3) ?³, Z = 1, final R = 0.0621. Each manganese atom is octahedrally coordinated by four aqua ligands and two nitrogen atoms of two distinct bbbi ligands. The molecule is stabilized by hydrogen bonding and π…π interactions.     

Reaction of oxygen with a binuclear cobalt(II) hexaphosphine complex. Single-crystal X-ray structure of an extended chain cobalt(II) hexaphosphine oxide system

Molecular oxygen reacts rapidly with Co₂Cl_4-x,(eHTP)^x+ [x = 0 or 2; eHTP = (Et₂PCH₂CH₂)₂PCH₂P(CH₂CH₂PEt₂)₂] in dry acetonitrile to produce in approximately 66% yield the fully-oxygenated phosphine oxide eHTP (eHTPO) Co(II) complex [Co(eHTPO)²⁺][CoCl₄²⁻. The X-ray structure on this novel system shows an extended chain system in which the monomeric repeating unit has an octahedral Co(II) centre. The eHTPO ligand is adopting an unusual conformation with the phosphine oxide groups P(2)P(1)P(3) (P(1) is one of the internal phosphorus atoms) forming a P(1)P(2) chelate to the metal atom while P(3) bridges to another Co(eHTPO)²⁺ monomer unit making up the extended chain, instead of acting as an independent bis chelating group. The third unique coordination site on the cobalt centre is occupied by a phosphine oxide group from the other half of the eHTPO ligand which bridges over to the cobalt centre forming a facial set of three PO donor ligands. This mixed bridging/chelating conformation gives rise to fused seven- and nine-membered ring systems with a CoCo separation of 7.613(0) Å between symmetry related cobalt sites on the extended chain. This structure is the first reported for a Co(R₃PO)₆ⁿ⁺ (R = alkyl, phenyl) system.     

Synthesis,structure and cytotoxic activity of cobalt(II), nickel(II) and copper(II) chloride complexes with acetamidrazones

Co^II, Ni^II and Cu^II chloride complexes with acetamidrazone derivatives (L ¹ )–(L ⁸ ) have been prepared, by reacting the corresponding metal chloride with the ligand in a 1:2 ratio, and characterised by chemical analysis and physical measurements. The ligand behaviour and the geometry have been assigned on the basis of i.r. spectroscopy, electronic reflectance spectra and molar conductivity values and only, where possible, the geometry has been confirmed as octahedral by X-ray structure determination. Complexes cytotoxicity on a human cellular line of adenocarcinoma was also tested. Three of the complexes present a weak cytotoxicity in vitro.     

Synthesis,crystal structure and antifungal activity of a divalent cobalt(II) complex with uniconazole

Azole compounds have attracted commercial interest due to their high bactericidal and plant‐growth‐regulating activities. Uniconazole [or 1‐(4‐chlorophenyl)‐4,4‐dimethyl‐2‐(1H‐1,2,4‐triazol‐1‐yl)pent‐1‐en‐3‐ol] is a highly active 1,2,4‐triazole fungicide and plant‐growth regulator with low toxicity. The pharmacological and toxicological properties of many drugs are modified by the formation of their metal complexes. Therefore, there is much interest in exploiting the coordination chemistry of triazole pesticides and their potential application in agriculture. However, reports of complexes of uniconazole are rare. A new cobalt(II) complex of uniconazole, namely dichloridotetrakis[1‐(4‐chlorophenyl)‐4,4‐dimethyl‐2‐(1H‐1,2,4‐triazol‐1‐yl‐κN⁴)pent‐1‐en‐3‐ol]cobalt(II), [CoCl₂(C₁₅H₁₈ClN₃O)₄], was synthesized and structurally characterized by element analysis, IR spectrometry and X‐ray single‐crystal diffraction. The crystal structural analysis shows that the Co^II atom is located on the inversion centre and is coordinated by four uniconazole and two chloride ligands, forming a distorted octahedral geometry. The hydroxy groups of an uniconazole ligands of adjacent molecules form hydrogen bonds with the axial chloride ligands, resulting in one‐dimensional chains parallel to the a axis. The complex was analysed for its antifungal activity by the mycelial growth rate method. It was revealed that the antifungal effect of the title complex is more pronounced than the effect of fungicide uniconazole for Botryosphaeria ribis, Wheat gibberellic and Grape anthracnose.     

Structure and magnetic ordering of a 2-D Mn(II)(TCNE)I(OH2) (TCNE = tetracyanoethylene) organic-based magnet (T(c) = 171 K)

Mn(II)(TCNE)I(OH(2)) was isolated from the reaction of tetracyanoethylene (TCNE) and MnI(2)(THF)(3), and has a 2-D structure possessing an unusual, asymmetric bonded μ(4)-[TCNE]˙(-). Direct antiferromagnetic coupling between the S = 5/2 Mn(II) and S = 1/2 [TCNE]˙(-) leads to magnetic ordering as a canted antiferrimagnet at a T(c) of 171 K.     

Increasing nuclearity of secondary building units in porous cobalt(II) metal-organic frameworks: variation in structure and H2 adsorption

Reaction of Co(NO(3))(2)·6H(2)O with H(2)L [H(2)L = pyridine-4-(phenyl-3',5'-dicarboxylic acid)] under different reaction conditions gives three closely-related metal-organic framework polymers, {[Co(2)(L)(2)(DMF)]·n(solv)}(∞) (1), {[Co(L)]·2DMF}(∞) (2) and {[Co(3)(L)(3)(DMF)(0.5)(H(2)O)(1.5)]·n(solv)}(∞) (3). Variation in reaction conditions thus has a decisive impact on the materials isolated, producing frameworks based upon either binuclear (1, 2) or trinuclear (3) cobalt cluster nodes. Analysis of their crystal structures shows that all three contain considerable solvent-accessible volumes, an indication of porosity that is confirmed for desolvated 1 and 3, which can store up to 2.75 and 2.33 wt% of H(2) at 78 K and 20 bar, respectively.     

Preparation and x-ray crystal structure of a seven-coordinate cobalt(II) complex with 2,6-diacetylpyridine bis(2-picolinoylhydrazone)

Summary A new seven-coordinate cobalt(II) complex has been synthesized with 2,6-diacetylpyridine bis(2-picolinoylhydrazone) (H₂dappc) and its crystal and molecular structure has been determined by x-ray diffraction methods from counter data and refined toR 0.0449 for 2128 observed reflections. The complex crystallizes in a triclinic cell, space group P¯1, with dimensions:a=13.759(8),b=7.685(3),c=13.816(7) Å, =86.50(5), =66.48(5), =85.28(5)° andZ=2. The complete structure consists of [Co(H₂dappc)(OH₂)₂] cations, chloride anions and solvating H₂O molecules, interlinked by hydrogen bonds. The geometry around the cobalt is that of a distorted pentagonal bipyramid with the H₂dappc ligand forming the equatorial plane and two H₂O molecules occupying the axial positions.     

Syntheses, characterizations and crystal structures of two new lead(II) amino and carboxylate-sulfonates with a layered and a pillared layered structure

Reactions of lead(II) acetate with m-aminobenzenesulfonic acid (HL¹) and 5-sulfoisophthalic acid (H₃L²) afforded two new lead(II) sulfonates, Pb(L¹)₂1 and Pb₂(L²)(μ₃-OH)(H₂O) 2. In compound 1, the lead(II) ion is eight-coordinated by two sulfonate groups bidentately, two sulfonate groups unidentately and two amino groups from six ligands. Each L¹ ligand is tetradentate and bridges with three Pb(II) ions. The interconnection of the Pb(II) ions via bridging sulfonate ligands resulted in 〈100〉 and 〈200〉 layers. In compound 2, one Pb(II) ion is six-coordinated by a carboxylate group bidentately, by two carboxylate groups unidentately, by a sulfonate oxygen atom and by an OH anion, whereas the other one is six-coordinated by a bidentate chelating carboxylate group, two μ₃-OH anions, a sulfonate oxygen atom and an aqua ligand. The interconnection of irregular PbO₆ polyhedra via carboxylate-sulfonate ligands resulted in the formation of a pillared layered structure with the 2D layer being formed; the lead(II) ions, hydroxyl groups, carboxylate and sulfonate groups and the benzene ring as the pillar agent.