Cobalt(II) Single-Ion Magnet Coordinated by Double Deprotonation of 2,2'-Bipyridine-6,6'-diol Ligands.

In this study, we synthesized a new Co(II) complex, [NMe][Co(bpyO)] (), using deprotonated 2,2'-bipyridine-6,6'-diol ligands (bpyO ). This compound exhibits a significant zero-field splitting () value. The far-infrared magneto spectroscopy and high-frequency and field electron paramagnetic resonance (HFEPR) measurements indicated that compound possesses = -54.

Phonon-induced relaxation mechanisms are changed by a chelating effect in a Co single-ion magnet.

It is well known that phonon-induced relaxation processes play a significant role in accelerating magnetization relaxation in the low-temperature regime. Unfortunately, many SIMs (single-ion magnets) suffer from being quenched by these mechanisms such that neither out-of-phase signals nor magnetization hysteresis can be readily observed. Nevertheless, because it involves molecular motions at low-frequency (low-energy) levels, methods for synthetically controlling this factor have not yet been addressed by chemists.

Toward Heteronuclear Molecular Re(I)-Cu(II) Boxes: Structural, Luminescent, and Magnetic Properties.

The bifunctional ligands of isonicotinic acid (Py-4-COOH) and 4-pyrid-4-ylbenzoic acid (Pybz-4-COOH) instead of polypyridines were therefore reacted with (Re(CO))(CNS) (CNS = cyanurate trianion), resulting in the formation of two trinuclear [(Re(CO))(CNS)(Py-4-COOH)] () and [(Re(CO))(CNS)(Pybz-4-COOH)] (), respectively. In the meantime, both complexes and are connected by three bifurcated hydrogen bonds between their carboxylic acid moieties Py-4-COOH and Pybz-4-COOH to form the supramolecular trigonal-prismatic and -antiprismatic structures, respectively. It is noted that complex can further react with copper(II) nitrate upon deprotonation to give nonanuclear [(Re(CO))(CNS)(Py-4-COO)]Cu(HO) (), where two trinuclear [(Re(CO))(CNS)(Py-4-COO)] moieties are connected by three penta-coordinate copper(II) ions, each coordinating to two carboxylates and three water molecules, to form the trigonal-prismatic structure.

Slow magnetization relaxation in a tetrahedrally coordinated mononuclear Co(II) complex exclusively ligated with phenanthroline ligands.

This paper describes a tetrahedral mononuclear Co(ii) complex [CoL2](ClO4)2 (1) in which L = 2,9-diphenyl-1,10-phenanthroline. The structure of 1, which was determined by single crystal X-ray diffraction, indicates that it exists in the triclinic space group P1[combining macron]. Magnetic property studies were conducted by reduced magnetization measurements, ab initio calculations and X-band EPR experiments, the results of which revealed a large zero-field splitting, with D ∼ -45.

A Pair of Co Supramolecular Isomers Based on Flexible Bis-Pyridyl-Bis-Amide and Angular Dicarboxylate Ligands.

Thermal reactions of cobalt(II) salts with flexible -bis(pyrid-3-ylmethyl)adipoamide () and angular 4,4'-sulfonyldibenzoic acid (HSDA) in HO and CHOH afforded a pair of supramolecular isomers: [Co()(SDA)], , and [Co()(SDA)]⋅CHOH⋅HO, . The structure of complex can be simplified as a one-dimensional (1D) looped chain with ligands penetrating into the middles of squares, forming a new type of self-catenated net with the (4⋅5)(4)(5) topology, whereas complex displays a 2-fold interpenetrated 2D net with the rare (4⋅6⋅8⋅10)(4)-2,6L1 topology. While both complexes and display antiferromagnetism with strong spin-orbital coupling, the antiferromagnetism of is accompanied by a cross-over behavior and probably a spin canting phenomenon.

A new member of a class of rod-like Mn single molecule magnets using 2-(pyridine-2-ly)propan-2-ol.

This paper reports on the synthesis, structure and magnetic properties of a new type of rod like Mn metal cluster, [MnO(OH)(OMe)(dmhmp)(OCPh)(HO)] (6) where the ligand (dmhmpH) is 2-(pyridine-2-yl)propan-2-ol. Compound (6) was obtained by reacting MnCl·4HO with dmhmpH in the presence of benzoic salt and EtN. The resulting crystalline material is assigned to the triclinic space group 1̄.

Sponge-Like Water De-/Ad-Sorption versus Solid-State Structural Transformation and Colour-Changing Behavior of an Entangled 3D Composite Supramolecuar Architecture, [Ni₄(dpe)₄(btc)₂(Hbtc)(H₂O)₉]·3H₂O.

An entangled composite compound, [Ni₄(dpe)₄(btc)₂(Hbtc)(H₂O)₉]·3H₂O (), where H₃btc = 1,3,5-benzenetricarboxylic acid and dpe = 1,2-bis(4-pyridyl)ethane, has been synthesized and structurally characterized. Single-crystal structural determination reveals that compound consists of four coordination polymers (CPs), with two two-dimensional (2D) (4,4) layered metal-organic frameworks (MOFs) of [Ni(dpe)(Hbtc)(H₂O)] and [Ni(dpe)(btc)(H₂O)] anion, and two one-dimensional (1D) polymeric chains of [Ni(dpe)(btc)(H₂O)₃] anion and [Ni(dpe)(H₂O)₄] cation, respectively. The three-dimensional (3D) supramolecular architecture of is constructed via the inter-penetration of inter-digited, double-layered, 2D rectangle-grid MOFs by two 1D coordination polymeric chains, and tightly entangled together via the combination of inter-CPs π⁻π stacking and hydrogen bonding interactions.

Structural, Spectroscopic, and Theoretical Investigation of a T-Shaped [Fe(μ-O)] Cluster.

The synthesis, X-ray crystal and electronic structures of [Fe(μ-O)(mpmae)(OAc) Cl], 1, where mpmae-H = 2-(N-methyl-N-((pyridine-2-yl)methyl)amino)ethanol, are described. This cluster comprises three high-spin ferric ions and exhibits a T-shaped site topology. Variable-frequency electron paramagnetic resonance measurements performed on single crystals of 1 demonstrate a total spin S = 5/2 ground state, characterized by a small, negative, and nearly axial zero-field splitting tensor D = -0.

Systematic studies of the structures and magnetic properties for a family of cubane complexes with the formula: [M2Ln2] (Ln = Dy, Gd; M = Ni, Zn) and [Ni2Y2].

Studies of magnetic properties of a family of tetranuclear M(II)(2)Ln(III)(2) (M = Ni, Zn; Ln = Dy, Gd and Y) complexes with hmp (anion of 2-hydroxymethylpyridine) and benzoate as ligands are reported. In these complexes, metal ions (M or Ln) occupy the four alternative corners of a distorted cubane with oxygen atoms from alkoxyl groups on the others. Complexes 1, 2 and 3 crystallized in P2(1)/c and complexes 4 and 5 in C2/c space groups.

Half-integer spin heptanuclear single-molecule magnet with an unusual Mn(III)6Mn(II) exchange-coupled core.

The synthesis, X-ray crystallography, magnetic properties, and high-field electron paramagnetic resonance (HFEPR) of a new heptanuclear manganese complex [Mn(7)(heamp)(6)](ClO(4))(2)·4CH(2)Cl(2)·H(2)O (complex 2), in which heampH(3) is 2-[N,N-di(2-hydroxyethyl)aminomethyl]phenol (compound 1), is reported. Complex 2 has a hexagonal, disk-shaped topology and contains six Mn(III) ions and a central Mn(II) ion. It crystallizes in the monoclinic space group P2(1)/c with two molecular orientations.

Studies of magnetic properties and HFEPR of octanuclear manganese single-molecule magnets.

A new octanuclear manganese cluster [Mn(8)(Hpmide)(4)O(4)(EtCOO)(6)](ClO(4))(2) (1) is achieved by employing Hpmide as the ligand, and this paper examines the synthesis, X-ray structure, high-field electron paramagnetic resonance (HFEPR), magnetization hysteresis loops and magnetic susceptibilities. Complex 1 was prepared by two different methods, and hence, was crystallized in two space groups: P3(2)21 for 1a and P3(1)21 for 1b. Each molecule possesses four Mn(II) and four Mn(III) ions.

1H NMR study of the influence of mutation on the interaction of the C-terminus with the active site in heme oxygenase from Neisseria meningitidis: implications for product release.

The HO from the pathogenic bacterium Neisseria meningitidis, NmHO, possesses C-terminal His207, Arg208, and His209 residues that are undetected in crystal structures. NMR found the C-terminus ordered and interacting with the active site and shown to undergo a spontaneous cleavage of the C-terminal Arg208-His209 bond that affects the product off rate. A preliminary model for the interaction based on the wild-type (WT) NmHO complexes has been presented [Liu, Y.

Disorder and intermolecular interactions in a family of tetranuclear Ni(II) complexes probed by high-frequency electron paramagnetic resonance.

High-frequency electron paramagnetic resonance (HFEPR) data are presented for four closely related tetranuclear Ni(II) complexes, [Ni(hmp)(MeOH)Cl]4.H2O (1a), [Ni(hmp)(MeOH)Br]4.H2O (1b), [Ni(hmp)(EtOH)Cl]4.

ESEEM studies of peptide nitrogen hyperfine coupling in tyrosyl radicals and model peptides.

Tyrosyl radicals are important in long-range electron transfer in several enzymes, but the protein environmental factors that control midpoint potential and electron transfer rate are not well understood. To develop a more detailed understanding of the effect of protein sequence, we have performed 14N and 15N electron spin echo envelope modulation (ESEEM) measurements on tyrosyl radical, generated either in polycrystalline tyrosinate or in its 15N-labeled isotopomer, by UV photolysis. 14N-ESEEM was also performed on tyrosyl radical generated in tyrosine-containing pentapeptide samples.

Fast magnetization tunneling in tetranickel(II) single-molecule magnets.

A series of Ni(4) cubane complexes with the composition [Ni(hmp)(ROH)Cl](4) complexes 1-4 where R= -CH(3) (complex 1), -CH(2)CH(3) (complex 2), -CH(2)CH(2)(C(4)H(9)) (complex 3), -CH(2)CH(2)CH(2)(C(6)H(11)) (complex 4), hmp(-) is the anion of 2-hydroxymethylpyridine, t-Buhmp(-) is the anion of 4-tert-butyl-2-hydroxymethylpyridine, and dmb is 3,3-dimethyl-1-butanol] and [Ni(hmp)(dmb)Br](4) (complex 5) and [Ni(t-Buhmp)(dmb)Cl](4) (complex 6) were prepared. All six complexes were characterized by dc magnetic susceptibility data to be ferromagnetically coupled to give an S = 4 ground state with significant magnetoanisotropy (D approximately equal to -0.6 cm(-1)).

Single-molecule magnets: high-field electron paramagnetic resonance evaluation of the single-ion zero-field interaction in a Zn(II)3Ni(II) complex.

High-field electron paramagnetic resonance spectra were collected at several frequencies for a single crystal of [Zn3.91Ni0.09(hmp)4(dmb)4Cl4] (1), where dmb is 3,3-dimethyl-1-butanol and hmp- is the monoanion of 2-hydroxymethylpyridine.

One-dimensional chain of tetranuclear manganese single-molecule magnets.

A one-dimensional chain of interconnected single-molecule magnets (SMMs) is obtained that consists of [Mn(4)(hmp)(6)](4+) units bridged by chloride ions. Slow magnetization relaxation is evident in the AC susceptibility data and in magnetization hysteresis measurements for [Mn(4)(hmp)(6)Cl(2)](n)(ClO(4))(2)(n). The magnetization hysteresis loops for this complex are similar to those for an SMM and show significant coercive field and steps at regular magnetic intervals.