Tetra-butyl-ammonium 2-[2,5-dimethyl-3-(4-nitro-phen-yl)-2,3-dihydro-1,2,4-oxadiazo-lium-4-yl]nona-hydro-closo-deca-borate

The title ionic compound, C16H36N(+)·C10H20B10N3O3(-), consists of a tetra-butyl-ammonium cation and a closo-deca-borate cluster anion, which is bound to the substituted 2,3-dihydro-1,2,4-oxadiazole ring through a B-N bond [1.540 (2) Å]. The distances between connected B atoms in the deca-borate cluster range from 1.689 (2) to 1.844 (2) Å. The 2,3-dihydro-1,2,4-oxadiazole ring adopts an envelope conformation with the N atom as the flap atom.

Crystal structure of μ-oxalodi-hydroxamato-bis-[(2,2'-bipyrid-yl)(di-methyl sulfoxide-κO)copper(II)] bis-(perchlorate)

The centrosymmetric binuclear complex, [Cu2(C2H2N2O4)(C10H8N2)2(C2H6OS)2](ClO4)2, contains two copper(II) ions, connected through an N-deprotonated oxalodi-hydroxamic acid dianion, two terminal 2,2'-bi-pyridine ligands, and two apically coordinating dimethylsulfoxide mol-ecules. Two non-coordinating perchlorate anions assure electrical neutrality. The copper(II) ions in the complex dication [Cu2(C10H8N2)2(μ-C2H2N2O4)(C2H6SO)2](2+) are in an O2N3 square-pyramidal donor environment, the Cu-Cu separation being 5.2949 (4) Å. Two hydroxamate groups in the deprotonated oxalodi-hydroxamic acid are located trans to one each other. In the crystal, O-H⋯O and C-H⋯O hydrogen bonds link the complex cations to the perchlorate anions. Further C-H⋯O hydrogen bonds combine with π-π contacts with a centroid-to-centroid separation of 3.6371 (12) Å to stack the mol-ecules along the a-axis direction.

The crystal structures of {LnCu5}3+ (Ln = Gd, Dy and Ho) 15-metallacrown-5 complexes and a reevaluation of the isotypic EuIII analogue

Three new isotypic heteropolynuclear complexes, namely penta-aqua-carbonato-penta-kis-(glycinehydroxamato)nitrato-penta-copper(II)lanthanide(III) x-hydrate, [LnCu5(GlyHA)5(CO3)(NO3)(H2O)5]·xH2O (GlyHA2- is glycine-hydrox-amate, N-hy-droxy-glycinamidate or amino-aceto-hydroxamate, C2H4N2O2 2-), with lanthanide(III) (Ln III) = gadolinium (Gd, 1, x = 3.5), dysprosium (Dy, 2, x = 3.28) and holmium (Ho, 3, x = 3.445), within a 15-metallacrown-5 class were obtained on reaction of lanthanide(III) nitrate, copper(II) acetate and sodium glycinehydroxamate. Complexes 1-3 contain five copper(II) ions and five bridging GlyHA2- anions, forming a [CuGlyHA]5 metallamacrocyclic core. The Ln III ions are coordinated to the metallamacrocycle through five O-donor hydroxamates. The electroneutrality of complexes 1-3 is achieved by a bidentate carbonate anion coordinated to the Ln III ion and a monodentate nitrate anion coordinated apically to one of the copper(II) ions of the metallamacrocycle. The lattice parameters of complexes 1-3 are similar to those previously reported for an EuIII-CuII 15-metallacrown-5 complex with glycine-hydroxamate of proposed composition [EuCu5(GlyHA)5(OH)(NO3)2(H2O)4]·3.5H2O [Stemmler et al. (1999 ▸). Inorg. Chem. 38, 2807-2817]. High-quality X-ray data obtained for 1-3 have allowed a re-evaluation of the X-ray data solution proposed earlier for the EuCu5 complex and suggest that the formula is actually [EuCu5(GlyHA)5(CO3)(NO3)(H2O)5]·3.5H2O.

Tetra-kis[bis-(pyridin-2-yl)amine-κN (2)](nitrato-κO)silver(I)

In the title complex, [Ag(NO₃)(C₁₀H₉N₃)₄], the nitrate ligand is found to be disordered over two sets of positions, with occupancy factors of 0.473 (5) and 0.527 (5). The Ag^I ion is located in a square-pyramidal coordination environment formed by four N atoms from four bis­(pyridin-2-yl)amine ligands and one O atom from a nitrate ligand. Weak inter­actions between the Ag^I ions and the nitrate anions acting in a monodentate mode [Ag⋯O = 2.791 (13) and 2.816 (9) Å for the major component of the nitrate ligand, and 2.865 (8) and 2.837 (8) Å for the minor component] link the complex mol­ecules into a chain along [001]. N—H⋯O hydrogen bonds are observed.

Bis-{(E)-3-[2-(hy-droxy-imino)-propan-amido]-2,2-dimethyl-propan-1-aminium} bis[μ-(E)-N-(3-amino-2,2-dimethyl-prop-yl)-2-(hy-droxy-imino)-propanamido-(2-)]bis-{[(E)-N-(3-amino-2,2-dimethyl-prop-yl)-2-(hy-droxy-imino)-propanamide]-copper(II)} bis-((E)-{3-[2-(hy-droxy-imino)-propanamido]-2,2-dimethyl-prop-yl}carbamate) acetonitrile disolvate

The reaction between copper(II) nitrate and (E)-N-(3-amino-2,2-dimethyl­prop­yl)-2-(hy­droxy­imino)­propanamide led to the formation of the dinuclear centrosymmetric copper(II) title complex, (C₈H₁₈N₃O₂)₂[Cu₂(C₈H₁₅N₃O₂)₂(C₈H₁₇N₃O₂)₂](C₉H₁₆N₃O₄)₂·2CH₃CN, in which an inversion center is located at the midpoint of the Cu₂ unit in the center of the neutral [Cu₂(C₈H₁₅N₃O₂)₂(C₈H₁₇N₃O₂)₂] complex fragment. The Cu²⁺ ions are connected by two N—O bridging groups [Cu⋯Cu separation = 4.0608 (5) Å] while the Cu^II ions are five-coordinated in a square-pyramidal N₄O coordination environment. The complex mol­ecule co-crystallizes with two mol­ecules of acetonitrile, two mol­ecules of the protonated ligand (E)-3-[2-(hy­droxy­imino)­propanamido]-2,2-dimethyl­propan-1-aminium and two negatively charged (E)-{3-[2-(hy­droxy­imino)­propanamido]-2,2-dimethyl­prop­yl}carbamate anions, which were probably formed as a result of condensation between (E)-N-(3-amino-2,2-dimethyl­prop­yl)-2-(hy­droxy­imino)­propanamide and hydro­gencarbonate anions. In the crystal, the complex fragment [Cu₂(C₈H₁₅N₃O₂)₂(C₈H₁₇N₃O₂)₂] and the ion pair C₈H₁₈N₃O₂^+.C₉H₁₆N₃O₄⁻ are connected via an extended system of hydrogen bonds.

CoII Complexes with a Tripyridine Ligand, Containing a 2,6-Di-tert-butylphenolic Fragment: Synthesis, Structure, and Formation of Stable Radicals

Interaction of a tripyridine ligand bearing a 2,6-di-tert-butylphenolic fragment (L, 2,6-di-tert-butyl-4-(3,5-bis(4-pyridyl)pyridyl)phenol) with Co^II pivalate or chloride led to the formation of one-dimensional coordination polymers [Co(L)Cl₂] _n ·nEtOH (1) and [Co₃(L)₂(OH)(Piv)₅] _n (2) or a trinuclear complex Co₃(H₂O)₄(L)₂Cl₆ (3) (Piv^- = pivalate). Chemical oxidation of L and 1-3 by PbO₂ or K₃[Fe(CN)₆], as well as exposure of L (in solution or solid state) and 2 (in solid state) to UV irradiation, led to the formation of free radicals with g = 2.0024, which probably originated because of oxidation of 2,6-di-tert-butylphenolic groups. These radicals were stable for several days in solutions and more than 1 month in solid samples. Irradiation and oxidation of the solid samples probably caused formation of the phenoxyl radical only on their surface. It was shown by density functional theory calculations that exchange coupling between the unpaired electron of the phenoxyl radical and Co^II ions was negligibly weak and could not affect the electron paramagnetic resonance signal of the radical, as well as exchange coupling of Co^II ions could not be transmitted by L. The latter conclusion was confirmed by the analysis of magnetic properties of 1: temperature dependency of magnetic susceptibility (χ_M) of 1 could be simulated by a simple model for isolated Co^II ions.

Crystal structure of a TbIII-CuII glycine-hydroxamate 15-metallacrown-5 sulfate complex

The core of the title complex, bis-[hexa-aqua-hemi-aqua-penta-kis-(μ3-glycine-hydroxamato)sulfato-penta-copper(II)terbium(III)] sulfate hexa-hydrate, [TbCu5(SO4)(GlyHA)5(H2O)6.5]2(SO4)·6H2O (1), which belongs to the 15-metalla-crown-5 family, consists of five glycine-hydroxamate dianions (GlyHA2-; C2H4N2O2) and five copper(II) ions linked together forming a metallamacrocyclic moiety. The terbium(III) ion is connected to the centre of the metallamacrocycle through five hydroxamate oxygen atoms. The coordination environment of the Tb3+ ion is completed to an octa-coordination level by oxygen atoms of a bidentate sulfate and an apically coordinated water mol-ecule, while the copper(II) atoms are square-planar, penta- or hexa-coordinate due to the apical coordination of water mol-ecules. Continuous shape calculations indicate that the coordination polyhedron of the Tb3+ ion in 1 is best described as square anti-prismatic. The positive charge of each pair of [TbCu5(GlyHA)5(H2O)6.5(SO4)]2 2+ fragments is compensated by a non-coordinated sulfate anion, which is located on an inversion center with 1:1 disordered oxygen atoms. Complex 1 is isomorphous with the previously reported compounds [LnCu5(GlyHA)5(SO4)(H2O)6.5]2(SO4), where Ln III = Pr, Nd, Sm, Eu, Gd, Dy and Ho.

Metal-Assembled Collagen Peptide Microflorettes as Magnetic Resonance Imaging Agents

Magnetic resonance imaging (MRI) is a medical imaging technique that provides detailed information on tissues and organs. However, the low sensitivity of the technique requires the use of contrast agents, usually ones that are based on the chelates of gadolinium ions. In an effort to improve MRI signal intensity, we developed two strategies whereby the ligand DOTA and Gd(III) ions are contained within Zn(II)-promoted collagen peptide (NCoH) supramolecular assemblies. The DOTA moiety was included in the assembly either via a collagen peptide sidechain (NHdota) or through metal–ligand interactions with a His-tagged DOTA conjugate (DOTA-His6). SEM verified that the morphology of the NCoH assembly was maintained in the presence of the DOTA-containing peptides (microflorettes), and EDX and ICP-MS confirmed that Gd(III) ions were incorporated within the microflorettes. The Gd(III)-loaded DOTA florettes demonstrated higher intensities for the T1-weighted MRI signal and higher longitudinal relaxivity (r1) values, as compared to the clinically used contrast agent Magnevist. Additionally, no appreciable cellular toxicity was observed with the collagen microflorettes loaded with Gd(III). Overall, two peptide-based materials were generated that have potential as MRI contrast agents.

Crystal structure of bis-(pivaloyl-hydroxamato-κ2O,O')copper(II)

Reaction of copper(II) nitrate with pivaloyl-hydroxamic acid yielded the title compound, [Cu(pivHA)2] (where pivHA- is pivaloyl hydroxamate, C5H10NO2). The centrosymmetric mononuclear complex consists of a CuII ion, which is located on a center of inversion, with two coordinated pivaloyl hydroxamate monoanions. The CuII ion has a square-planar coordination environment consisting of four O atoms - two carbonyl O atoms and two hydroxamate O atoms from two hydroxamate pivHA- ligands. The pivHA- anions are coordinated to copper(II) in a trans-mode, forming two five-membered O,O'-chelate rings.

Crystal structure of poly[(μ3-4-amino-1,2,5-oxa-diazole-3-hydroxamato)thallium(I)]

The title compound represents the thallium(I) salt of a substituted 1,2,5-oxa-diazole, [Tl(C3H3N4O3)] n , with amino- and hydroxamate groups in the 4- and 3- positions of the oxa-diazole ring, respectively. In the crystal, the deprotonated hydroxamate group represents an inter-mediate between the keto/enol tautomers and forms a five-membered chelate ring with the thallium(I) cation. The coordination sphere of the cation is augmented to a distorted disphenoid by two monodentately binding O atoms from two adjacent anions, leading to the formation of zigzag chains extending parallel to the b axis. The cohesion within the chains is supported by π-π stacking [centroid-centroid distance = 3.746 (3) Å] and inter-molecular N-H⋯N hydrogen bonds.

Magnetocaloric effect in 1D-polymers bearing 15-metallacrown-5 {GdCu5}3+ units and anionic oxalate complexes

Two complexes {[GdCu5(GlyHA)5(H2O)7Cr(C2O4)3]·11.02H2O}n (1) and {{[GdCu5(GlyHA)5(H2O)6]μ2-[Cu(C2O4)2(H2O)]}2μ4-[Cu(C2O4)2]·15.8H2O}n (2), were obtained as outcomes of the reactions between the cationic hexanuclear {GdCu5(GlyHA)5}3+ 15-metallacrown-5 complex (where GlyHA2- = glycinehydroxamate) and the anionic oxalate complexes K3[Cr(C2O4)3] or K2[Cu(C2O4)2]. Both 1 and 2 possess polymeric 1D-chain structures according to X-ray structural analysis. As a consequence of the geometric orientations of the donor atoms in the oxalates from [Cr(C2O4)3]3-, the Cu5 mean planes of neighboring 15-metallacrown-5 units {GdCu5(GlyHA)5}3+ are angled at 75.5° to each other, which leads to formation of a zig-zag motif in the 1D-chains of complex 1. The centrosymmetric complex 2 contains two structurally different bis(oxalato)cuprate anions μ2-[Cu(C2O4)2(H2O)]2-, for one of which, coordination to two adjacent {GdCu5(GlyHA)5}3+ units leads to formation of linear 1D-chains in 2, while the second type, μ4-[Cu(C2O4)2]2-, is coordinated to four {GdCu5(GlyHA)5}3+ units, causing the cross-linking of single 1D-chains into a double-chain 1D coordination polymer. Studies of χMT vs. T data for 1 and 2 in a 2-300 K temperature range revealed the presence of both ferromagnetic and antiferromagnetic interactions amongst paramagnetic centres. The experimental χMT vs. T data for 1 were fitted using a model which takes into account exchange interactions between adjacent copper(II) ions, the Gd-Cu exchange interactions within {GdCu5(GlyHA)5}3+ units and additionally Gd-Cr exchange interactions. Fitting of the χMT vs. T data for 2 was not possible, since coordination of μ4-[Cu(C2O4)2]2- to {GdCu5(GlyHA)5}3+ led to the non-equivalence of several Cu-Cu exchange interactions within the metallacrown units and hence a superfluity of fittable parameters. Complexes 1 and 2 are the first examples of 15-metallacrown-5 complexes demonstrating a magnetocaloric effect (-ΔSM at 13 T reaches 24.26 J K-1 kg-1 at 5 K and 19.14 J K-1 kg-1 at 4 K for 1 and 2, respectively).

The crystal structure of a mononuclear PrIII complex with cucurbit[6]uril

A new mononuclear complex, penta-aqua-(cucurbit[6]uril-κ2 O,O')(nitrato-κ2 O,O')praseodymium(III) dinitrate 9.56-hydrate, [Pr(NO3)(CB6)(H2O)5](NO3)2·9.56H2O (1), was obtained as outcome of the hydro-thermal reaction between the macrocyclic ligand cucurbit[6]uril (CB6, C36H36N24O12) with a tenfold excess of Pr(NO3)3·6H2O. Complex 1 crystallizes in the P21/n space group with two crystallographically independent but chemically identical [Pr(CB6)(NO3)(H2O)5]2+ complex cations, four nitrate counter-anions and 19.12 inter-stitial water mol-ecules per asymmetric unit. The nona-coordinated PrIII in 1 are located in the PrO9 coordination environment formed by two carbonyl O atoms from bidentate cucurbit[6]uril units, two oxygen atoms from the bidentate nitrate anion and five water mol-ecules. Considering the differences in Pr-O bond distances and O-Pr-O angles in the coordination spheres, the coordination polyhedrons of the two PrIII atoms can be described as distorted spherical capped square anti-prismatic and muffin polyhedral.