New versatile ligand family, pyrazine-modulated oligo-α-pyridylamino ligands, from coordination polymer to extended metal atom chains

The Origin of Magnetic Anisotropy and Single-Molecule Magnet Behavior in Chromium(II)-Based Extended Metal Atom Chains

Chromium(II)-based extended metal atom chains have been the focus of considerable discussion regarding their symmetric versus unsymmetric structure and magnetism. We have now investigated four complexes of this class, namely, [Cr3(dpa)4X2] and [Cr5(tpda)4X2] with X = Cl- and SCN- [Hdpa = dipyridin-2-yl-amine; H2tpda = N2,N6-di(pyridin-2-yl)pyridine-2,6-diamine]. By dc/ac magnetic techniques and EPR spectroscopy, we found that all these complexes have easy-axis anisotropies of comparable magnitude in their S = 2 ground state (|D| = 1.5-1.8 cm-1) and behave as single-molecule magnets at low T. Ligand-field and DFT/CASSCF calculations were used to explain the similar magnetic properties of tri- versus pentachromium(II) strings, in spite of their different geometrical preferences and electronic structure. For both X ligands, the ground structure is unsymmetric in the pentachromium(II) species (i.e., with an alternation of long and short Cr-Cr distances) but is symmetric in their shorter congeners. Analysis of the electronic structure using quasi-restricted molecular orbitals (QROs) showed that the four unpaired electrons in Cr5 species are largely localized in four 3d-like QROs centered on the terminal, "isolated" Cr2+ ion. In Cr3 complexes, they occupy four nonbonding combinations of 3d-like orbitals centered only on the two terminal metals. In both cases, then, QRO eigenvalues closely mirror the 3d-level pattern of the terminal ions, whose coordination environment remains quite similar irrespective of chain length. We conclude that the extent of unpaired-electron delocalization has little impact on the magnetic anisotropy of these wire-like molecular species.

Novel Cobalt Complex as an Efficient Catalyst for Converting CO2 into Cyclic Carbonates under Mild Conditions

Based on the ligand H2dpPzda (1), a novel cobalt complex [Co(H2dpPzda)(NCS)2]·CH3OH(2) has been synthesized and characterized. The Complex 2 exhibited excellent catalytic performance for converting CO2 into cyclic carbonates under mild conditions. For propylene oxide (PO) and CO2 synthesis of propylene carbonate (PC), the catalytic system showed a remarkable TOF as high as 29,200 h−1. The catalytic system also showed broad substrate scope of epoxide. Additionally, the catalyst could be recycled to maintain the integrity of the structure and remained equal to the level of its catalytic activity even after seven catalytic rounds. Additionally, a possible catalytic mechanism was proposed due to the high catalytic activity which might be owing to the synergism of Lewis acidic metal centers and N group.

Solution structure of a pentachromium(ii) single molecule magnet from DFT calculations, isotopic labelling and multinuclear NMR spectroscopy

Solution NMR spectroscopy on isotopically-labelled samples of [Cr₅(tpda)₄Cl₂] unveils a D₄ symmetric molecule, implying fast shuttling between the two unsymmetric ground configurations over NMR timescale.

Fine-Tuning of Magnetic Properties in Nickel(II) Trinuclear EMACs via Modifications of Equatorial Ligands

The relationship between equatorial ligands structures and magnetic response of [Ni3]6+ extended metal atom chain core has been investigated. The distances between metal ions in Ni metal strings are largely predefined by framework provided through equatorial ligands. The equatorial ligands thus have primary influence on the magnitude of magnetic coupling between terminal high spin centers. Since the σ channel has greatest contribution to J, the variations in Ni–Ni bond lengths have immediate and strong effect on magnetic properties. The secondary, yet important role is played by ligand field strength and nucleophilicity. It has been shown that energy difference between singly occupied σ-type MOs composed of d(z2) of terminal ions and doubly occupied σ-type MO evolved from d(z2) of the central ion in antiferromagnetic state solution is inversely proportional to magnitude of J. Hence, the alignment between energies of d(z2) orbitals on HS and LS centers directly affected by ligand field strength governs the magnetic response. Moreover, the greater basicity of lone pairs coordinating terminal metal atoms correlates with the larger absolute value of magnetic coupling constant.

Bis[tris(propane-1,3-diamine-κ(2) N,N')-nickel(II)] di-aqua-bis(propane-1,3-di-amine-κ(2) N,N')nickel(II) hexa-bromide dihydrate

In the title compound, [Ni(C₃H₁₀N₂)₃]₂[Ni(C₃H₁₀N₂)₂(H₂O)₂]Br₆·2H₂O, one Ni²⁺ cation, located on an inversion centre, is coordinated by four N atoms from two ligands and by two water O atoms. The other Ni²⁺ cation, located in a general position, is coordinated by six N atoms from three ligands. In both cases, the Ni²⁺ cation has an octa­hedral coordination environment. The overall structural cohesion is ensured by three types of hydrogen bonds, N—H⋯Br, O—H⋯Br and O—H⋯O, which connect the two types of complex cations, the bromide counter-anions and the lattice water molecules into a three-dimensional network.

A magnetic and conductive study on a stable defective extended cobalt atom chain

A defective extended cobalt atom chain complex has been synthesized and the magnetism and conductance are studied. The formation and the electron transporting pathway of EMACs are investigated.

2-Amino-5-methyl-pyridinium nitrate

In the title salt, C₆H₉N₂⁺·NO₃⁻, the 2-amino-5-methyl­pyridinium cation and the nitrate anion are cyclically linked through pyridinium and amine N—H⋯O hydrogen bonds [graph set R₄³(12)]. These units are extended into a zigzag chain structure lying parallel to the a axis, through a second cyclic R₂²(8) association involving amine N—H⋯O and aromatic C—H⋯O hydrogen bonds to nitrate O-atom acceptors.

Bis(morpholin-4-ium) tetrachloridocobalt(II)

The title compound, (C₄H₁₀NO)₂[CoCl₄], is an ionic compound consisting of two protonated tetra­hydro-1,4-oxazine (morpholine) cations and a [CoCl₄]²⁻ dianion. The Co^II ion is in a tetra­hedral coordination geometry. The cations exhibit chair-shaped conformations. A three-dimensional supra­molecular architecture is formed through N—H⋯Cl and C—H⋯Cl hydrogen bonds between the dianions and the cations.

2-Amino-5-chloro-pyridinium nitrate

The title structure, C(5)H(6)ClN(2) (+)·NO(3) (-), is held together by extensive hydrogen bonding between the NO(3) (-) ions and 2-amino-5-chloro-pyridinium H atoms. The cation-anion N-H⋯O hydrogen bonds link the ions into a zigzag- chain which develops parallel to the b axis. The structure may be compared with that of the related 2-amino-5-cyano-pyridinium nitrate.

2-Amino-5-cyano-pyridinium nitrate

In the title compound, C₆H₆N₃⁺·NO₃⁻, the packing is consolidatedby N—H⋯N and N—H⋯O hydrogen bonds.

4-Benzhydryl-1-cinnamylpiperazin-1-ium nitrate

In the title compound, C₂₆H₂₉N₂⁺·NO₃⁻, the dihedral angle formed by the phenyl rings of the benzhydryl group is 66.18 (9)°. Crystal cohesion is enforced by cation–anion C—H⋯O and N—H⋯O hydrogen bonds.

2-Cyano-anilinium nitrate

In the title compound, C₇H₇N₂⁺·NO₃⁻, all atoms of the cation, with the exception of two H atoms of the NH₃ group, lie on a mirror plane, while the anion lies across this plane with the N and one O atom on the mirror plane. In the crystal structure, the organic cations and NO₃⁻ anions are linked by N—H⋯N and N—H⋯O hydrogen bonds, forming a two-dimensional network parallel to (100).

3-Cyano-anilinium chloride

In the title salt, C₇H₇N₂⁺·Cl⁻, all non-H atoms of the cation are essentially coplanar (r.m.s. deviation = 0.005 Å). In the crystal structure, the organic cations and chloride ions are linked to form a two-dimensional network parallel to the (001) plane by N—H⋯Cl hydrogen bonds.

2-Amino-5-cyano-pyridinium chloride

In the crystal structure of the title compound, C₆H₆N₃⁺·Cl⁻, cohesion is maintained by cation–anion N—H⋯Cl and cation–cation N—H⋯N hydrogen bonds, which link the ions into a three-dimensional network.