Michel M. Bélombé

4-(Dimethyl-amino)-pyridinium trans-diaqua-bis-[oxalato(2-)-κO,O]chromate(III).

In the title salt, (C7H11N2)[Cr(C2O4)2(H2O)2], the asymmetric unit contains one half-cation and one half-anion. The Cr atom, the C and N atoms involved in C— N(exocyclic) bonding and the N and H atoms of N—H groups lie on twofold rotation axis. The CrIII atom of the complex anion is six-coordinated in a distorted (4 + 2) octahedral geometry with four equatorial O atoms of two nearly coplanar oxalate and two quasi-axial aqua O atoms. In the crystal, the protonated N atoms of the pyridine rings are hydrogen bonded to the carbonyl O atoms of the anions, forming chains along [010]. These chains are connected by lateral O—H⋯O hydrogen bonds, stabilizing the structure.

Hydrogen-bonded pillars of alternating chiral complex cations and anions: 1. Synthesis, characterization, X-ray structure and thermal stability of catena-{[Co(H(2)oxado)(3)][Cr(C(2)O(4))(3)].5H(2)O} and of its precursor (H(3)oxado)[Co(H(2)oxado)(3)](SO(4))(2).2H(2)O.

Compound (H(3)oxado)[Co(H(2)oxado)(3)](SO(4))(2).2H(2)O () (H(3)oxado(+) = oxamide dioximemonoximium) reacted metathetically with Ba(6)(H(2)O)(17)[Cr(C(2)O(4))(3)](4).7H(2)O in water to give the one-dimensional complex salt {[Co(H(2)oxado)(3)][Cr(C(2)O(4))(3)].5H(2)O}(infinity) () (H(2)oxado = oxamide dioxime). Compounds and were characterized by elemental analysis, FTIR, UV-Vis and by single crystal X-ray structure determination. The structure of consists of infinite pillars of alternating chiral complex cations and anions linked together along [100] by electrostatic and longitudinal O-HO interactions, with an average intrachain CoCr separation of 4.94 A. Equatorial N-HO bridges cross-link neighboring pillars (which are of opposite chirality) and consolidate a three-dimensional lattice framework which delineates elliptic nanochannels parallel to the a axis, encapsulating highly disordered water molecules. The thermal stability of both compounds was assessed by TGA, and the effective magnetic moment of , checked at room temperature, revealed considerable spin-orbit coupling.

Electrochemical and electronic spectroscopic behaviour of trans-bis(ethanedial dioximato(1-),N,N′) diiodocobaltate(III), [Co(GH)2I2]− in connection with the cations H+, NH4+, Et4N+, Hqn+ (quinoleinium)

The electrochemistry of six-coordinated cobalt(III) cobaloximatic salts is reported in acetonitrile containing 0.1 M tetrabutylammonium hexafluorophosphate as supporting electrolyte. The investigated compounds are represented as R[Co(GH)2I2] where GH− is ethanedial dioximate or glyoximate and R = H+, NH4+, Et4N+, Hqn+ (quinoleinium). Each complex undergoes up to three oxidative processes and two metal-centered reduction steps within the potential range of the solvent. Except for Et4N[Co(GH)2I2], all the other complexes display an additional redox system situated between the two metal centered processes. The more likely origin for this additional redox signal is the reduction of the proton contained in the cations H+, NH4N+, and Hqn+ associated to [Co(GH)2I2]− in the corresponding complexes. The electrochemical behaviour of the cobaloximatic ion is only slightly influenced by the counter cation. The electronic spectra of these compounds show three bands similar to those generally found for cobaloximes.

A Dimeric Copper(II) Complex of Oxalate and Oxamide Dioxime Ligands: Synthesis, Crystal Structure, Thermal Stability, and Magnetic Properties

The dimeric copper(II) complex [Cu(C2O4)(H2oxado)(H2O)]2 (1), where H2oxado=oxamide dioxime, has been synthesized in water and characterized by elemental and thermal analyses, IR spectroscopy, and single-crystal X-ray diffraction. Complex 1 is composed of two neutral [Cu(C2O4)(H2oxado)(H2O)] entities connected by Cu-O bonds between oxalate oxygen atoms and copper(II) ions, thereby producing a centrosymmetric dimer, with the Cu(II) centers exhibiting a strongly distorted octahedral coordination. Neighboring dimers are hydrogen-bonded through O- H···O interactions leading overall to a layer structure. Thermal analyses of complex 1 showed two significant weight losses corresponding to the coordinated water molecules, followed by the decomposition of the network. Variable-temperature (10 - 300 K) magnetic susceptibility measurements revealed very weak antiferromagnetic interactions (θ = 0:86 K from Curie-Weiss law behavior) within the dinuclear unit Graphical Abstract A Dimeric Copper(II) Complex of Oxalate and Oxamide Dioxime Ligands: Synthesis, Crystal Structure, Thermal Stability, and Magnetic Properties

2-Amino­pyridinium trans-diaqua­bis­(oxalato-κ2O,O)chromate(III)

In the title hybrid salt, (C5H7N2)[Cr(H2O)2(C2O4)2], the CrIII ion is coordinated in a slightly distorted octahedral environment by four O atoms from two oxalate ligands in the equatorial plane and by two water O atoms in the axial sites. The 2-aminopyridinium cation is disordered over two sets of sites in a 0.800 (7):0.200 (7) ratio. In the crystal, N—H⋯O and O—H⋯O hydrogen bonds connect the components into a three-dimensional network. The crystal studied was an inversion twin with components in a ratio 0.75 (2):0.25 (2).

Crystal structure of quinolinium trans-diaquabis(oxalato-0,0')- chromate(III), [C9H8N][Cr(H2O)2(C2O4)2]

Discussion The oxalate ion has recently moved into the focus of a considerable research activity around the world, due to its unique potential as a remarkably flexible ligand system in complexations with a wide range of metal ions [1]. In the past decades, many coordination compounds based on this ligand system were shown to play a crucial role in the rational design and development of novel materials that may combine, within a given system, a range of interesting solid state functionalities [2], such as molecular magnetism, optical activity, nano-channels in metal-organic frameworks (MOFs) [3], extended hydrogen-bonding. Such polyfunctional materials are needed to boost the advancement of the new millennium technologies. The unit cell of the title salt contains four formula units, each of which consists of a quinolinium cation and a [Cr(H20)2(C204>2]~ anion (figure, top). These discrete ions are stacked into segregated positive and negative layers parallel to (001), whereby the planar positive and the corrugated negative layers alternate along the [001] direction, being interconnected via N-H—O bridgings (¿(Nl-Ol) = 2.887(4) Â) that link the quinolinium N-H groups to the coordinated oxalato O atoms (dashed lines, figure, bottom). The quinolinium stacks are centered on a 2-fold axis which extends throughout the lattice across the centers of the superimposed benzenic ring systems, in eclipsed configuration and 3.77 À apart, revealing weak π-π interactions within these stacks. The cations and the main planes of the complex anions of this salt are disposed in a fish-bone fashion, defining the respective dihedral angles of 63.50° and 56.91° with respect to (001). The bond lengths and angles within the quinolinium cation are in accord with reported values [4]. The complex anions contain Cr(m) centers in a prolate (4+2) octahedral coordination of two chelating, equatorial oxalato ligands and two axial water molecules, the equatorial Cr—O bond lengths ranging from 1.955(1) to 1.976( 1) Â, and the axial Cr—O distances being virtually identical at 2.000(2) and 2.002(2) À. The shortest intralayer Cr-Cr spacing is d(Cr-Cr) = 6.635(1) Â. Abstract Ci3Hi2CrNOio, monoclinic, P12i/cl (no. 14), a = 7.541(1) À, b = 10.936(2) Â, c = 18.594(3) λ,β = 94.261(3)°, V = 1529.2 Â, Ζ = 4, Rgt(F) = 0.035, wR^F*) = 0.115, Γ =294 Κ.

Tris(oxamide dioxime-κ2N,N′)nickel(II) sulfate penta­hydrate

The asymmetric unit of the title compound, [Ni(C2H6N4O2)3]SO4·5H2O, contains two complex cations, two sulfate anions and ten lattice water molecules. In both independent cations, the central NiII ion adopts a distorted octahedral coordination involving six imino N atoms of three bidentate oxamide dioxime ligands. The bulk structure is achieved by a three-dimensional network of O—H⋯O and N—H⋯O hydrogen bonds which interlink the ionic partners and some water molecules in such a manner that the lattice framework thus formed defines channels parallel to [100]. The other water molecules are lodged inside these channels. Two of the ten water molecules in the asymmetric unit are disordered over three sites, in 0.356 (3):0.324 (5):0.320 (5) and 0.247 (3):0.293 (6):0.460 (6) occupancy ratios, and one O atom of a sulfate ion is also disordered over two sites, with occupancies of 0.621 (5) and 0.379 (5).

Anionic Nanochanneled Silver-Deficient Oxalatochromate(III) Complex with Hydroxonium as Counter Ion: Synthesis, Characterization and Crystal Structure

Reaction of Ba0.50[Ag2Cr(C2O4)3]·5H2O with Ag2SO4 in an aqueous solution of sulfuric acid (pH ≈ 3) yielded the silver(I)/chromium(III) oxalate salt H0.50[Ag2.50Cr(C2O4)3]·5H2O (1). Compound 1 can be best described as an anionic silver-deficient oxalatochromate(III) complex [Ag2.50Cr(C2O4)3]0.5- with nanochannels containing hydrogen-bonded water molecules and protons. Thermal analyses show significant weight losses corresponding to the elimination of water molecules of crystallization followed by the decomposition of the network.

{[Na1(μ-H(2)O)Na2](2)[(C(2)O(4))(2)Cr(μ-OH)(2)Cr(C(2)O(4))(2)]·H(2)O}(n), a novel hydrated form.

The unit cell of the title compound, poly[[μ-aqua-μ-hydroxido-di-μ-oxalato-chromium(III)disodium] monohydrate], {[CrNa2(C2O4)2(OH)(H2O)]·H2O}n, contains four [Na1(μ-H2O)Na2][(C2O4)2Cr(μ-OH)·H2O] formula units, each of which consists of two crystallographically independent Na+ sites (bridged by one aqua ligand), one half of a centrosymmetric di-μ-hydroxido-bis[cis-bis(oxalato)chromate(III)] dimer, [(C2O4)2Cr(μ-OH)2Cr(C2O4)2]4−, and one uncoordinated water molecule. The structure is best described as a coordination polymer in which the three-dimensional lattice framework is realized by the interconnection of the metallic atoms via the O atoms of the aqua, hydroxide and oxalate ligands. One Na atom is heptacoordinated by one water, one hydroxide and five oxalate O atoms, whilst the other is pentacoordinated by one water and four oxalate O atoms. The coordination around the Cr3+ sites is pseudo-octahedral, involving four aqua and two hydroxide O atoms. Adjacent Na atoms are separated by 3.593 (2) Å, whereas the intradimer Cr⋯Cr spacing is 2.978 (1) Å. The crystal structure is consolidated by extended relatively weak O—H⋯O hydrogen bonding with O⋯O distances ranging from 2.808 (4) to 3.276 (5) Å.

{[Na1(μ-H2O)Na2]2[(C2O4)2Cr(μ-OH)2Cr(C2O4)2]·H2O}n, a novel hydrated form

The unit cell of the title compound, poly[[μ-aqua-μ-hydroxido-di-μ-oxalato-chromium(III)disodium] monohydrate], {[CrNa2(C2O4)2(OH)(H2O)]·H2O}n, contains four [Na1(μ-H2O)Na2][(C2O4)2Cr(μ-OH)·H2O] formula units, each of which consists of two crystallographically independent Na+ sites (bridged by one aqua ligand), one half of a centrosymmetric di-μ-hydroxido-bis[cis-bis(oxalato)chromate(III)] dimer, [(C2O4)2Cr(μ-OH)2Cr(C2O4)2]4−, and one uncoordinated water molecule. The structure is best described as a coordination polymer in which the three-dimensional lattice framework is realized by the interconnection of the metallic atoms via the O atoms of the aqua, hydroxide and oxalate ligands. One Na atom is heptacoordinated by one water, one hydroxide and five oxalate O atoms, whilst the other is pentacoordinated by one water and four oxalate O atoms. The coordination around the Cr3+ sites is pseudo-octahedral, involving four aqua and two hydroxide O atoms. Adjacent Na atoms are separated by 3.593 (2) Å, whereas the intradimer Cr⋯Cr spacing is 2.978 (1) Å. The crystal structure is consolidated by extended relatively weak O—H⋯O hydrogen bonding with O⋯O distances ranging from 2.808 (4) to 3.276 (5) Å.