Irina A. Golenya

A new Cu(II) [12]metallocrown-4 pentanuclear complex based on a Cu (II ) -malonomonohydroxamic acid unit

The first example of a Cu(II) [12]-MC-4 hydroxamic metallacrown compound containing a carboxyl group as a supporting donor function is described. The solution equilibria of malonomonohydroxamic acid (MACZ, H2L) with Cu(II) are investigated in aqueous solution using a combination of potentiometry, UV-vis absorption spectrophotometry, EPR spectroscopy and ESI mass spectrometry. Among the four complexes fitting the best speciation model ([CuL], [Cu5L4H−4]2−, [CuL2]2− and [CuL2H−1]3−), a pentameric metallacrown molecule of composition Cu : L = 5 : 4 predominates in solution over the pH 4 to 11 range, and the corresponding complex was isolated in the solid state. The crystallization of the complex [Cu5L4H−4]2− in the presence of [Cu(en)2(H2O)2]2+ cations resulted in the isolation of [Cu(en)2(H2O)2]n[Cu(en)2(H2O)(μ-H2O){Cu5(L4H−4)(H2O)3}2]n·20nH2O (1), whose crystal structure has been determined by X-ray analysis. The structure of 1 consists of centrosymmetric complex cations [Cu(en)2(H2O)2]2+, infinite complex anionic chains [Cu(en)2(H2O)(μ-H2O){Cu5(L4H−4)(H2O)3}2]n2n− and solvate water molecules. Within the complex anionic chains, the decanuclear double-decked bis([12]-MC-4) complex anions {Cu5(L4H−4)(H2O)3}24− are united by the [Cu(en)2(H2O)2]2+ complex cations due to the bridging function of the axial water molecule O(5). The magnetic behaviour of 1, studied in the temperature range 1.8–300 K, suggests the presence of both antiferromagnetic and ferromagnetic contributions to the observed magnetic susceptibility, resulting in a ground state of S = 2 per formula unit.

Collapsed Cu(II)-Hydroxamate Metallacrowns

Degradation of a strained, thermodynamically destabilized pentanuclear copper(II) 12-metallacrown-4 complex based on a picoline hydroxamic acid resulted in the formation of the tetranuclear compounds which are the first examples of solely hydroxamate-based Cu(II) metallacrown complexes with a collapse of the metallamacrocyclic cavity.

Pyridine-2,6-dihydroxamic acid, a powerful dihydroxamate ligand for Ni2+ and Cu2+ ions

Pyridine-2,6-dihydroxamic acid was found to be the most effective ligand for Ni2+ and Cu2+ ions among the known dihydroxamates. The stability constants of the title complexes are many orders of magnitude higher than those obtained for the other dihydroxamates. Only equimolar species are formed with Cu2+ ions, while NiL and bis-complexes are formed in the case of Ni2+. The [NiL2]2− complex anion contains compressed octahedral hexanitrogen surroundings of two meridionally coordinated ligands. The equatorial Ni–N(Py) bonds are significantly shorter than the axial Ni–N(hydroxamate) distances although the latter are formed by the deprotonated groups.

Encapsulation of a guest sodium cation by iron(III) tris-(hydroxamate)s.

An unprecedented encapsulation of an exogenous sodium ion by iron(III) tris(hydroxamate)s was observed upon crystallization of an iron(III) complex with isonicotinylhydroxamic acid. The sodium cation is bound by bridging coordination of the amide oxygen atoms from two mononuclear iron(III) fac-tris(hydroxamate)s.

Copper(II) complexes of 3- and 4-picolinehydroxamic acids: from mononuclear compounds to 1D- and 2D-coordination polymers

A series of copper(II) complexes with 3- and 4-picolinehydroxamic acids has been synthesized and characterized by a variety of spectroscopic methods, X-ray structure analysis and magnetic susceptibility measurements. The ligands show the tendency to form 1D- and 2D-polymeric structures with copper(II) ions due to the chelating-and-bridging binding mode involving the (O,O′)-hydroxamate chelate formation combined with N-coordination of the pyridine moiety. In some cases the (O, μ2-O′) chelating-and-bridging modes are realized, in which either amide or hydroxamic oxygen atoms play a μ2-bridging role. Molecular and crystal structures of two discrete complexes: mononuclear [Cu(3-HPicHA)2(ClO4)2] (1) and binuclear [{Cu(4-HPicHA)(bpy)(ClO4)}2](ClO4)2 (4a), and five coordination polymers catena-[Cu(3-PicHA)(phen)]n(ClO4)n (7), catena-[Cu(4-PicHA)(bpy)]n(OH)n·3.25nH2O (8), catena-[Cu(4-PicHA)(DMSO)2]2n(ClO4)2n (9), [Cu(3-PicHA)(DMSO)(ClO4)]nm·nmDMSO (10), and [{Cu(4-PicHA)(phen)}2]n(ClO4)2n (11) were determined by single crystal X-ray analysis. In structures 1 and 4a the hydroxamate ligands exist in a zwitterionic form with the O-deprotonated hydroxamate groups and protonated pyridine rings. The following types of coordination polymers have been structurally characterized: (i) single-stranded zigzag-shaped 1D polymers (7 and 8); (ii) double-stranded 1D polymer comprising binuclear subunits formed on account of μ2(O)-carbonyl oxygen bridging coordination to the axial position of the copper(II) ion (9); (iii) 2D netted coordination polymers of two different types comprising μ2(O)-bridged binuclear subunits (10 and 11). Magnetic susceptibility measurements (2–300 K) of powdered samples revealed the presence of moderate antiferromagnetic interaction in the binuclear complex 4a (2J = −7.164(6) cm−1), while the coordination polymers exhibit weak antiferromagnetic interaction with a cryomagnetic behaviour obeying the Curie–Weiss law.

Pyridinium bis­(pyridine-κN)tetra­kis­(thio­cyanato-κN)ferrate(III)–pyrazine-2-carbo­nitrile–pyridine (1/4/1)

In the title compound, (C5H6N)[Fe(NCS)4(C5H5N)2]·4C5H3N3·C5H5N, the FeIII ion is located on an inversion centre and is six-coordinated by four N atoms of the thiocyanate ligands and two pyridine N atoms in a trans arrangement, forming a slightly distorted octahedral geometry. A half-occupied H atom attached to a pyridinium cation forms an N—H⋯N hydrogen bond with a centrosymmetrically-related pyridine unit. Four pyrazine-2-carbonitrile molecules crystallize per complex anion. In the crystal, π–π stacking interactions are present [centroid–centroid distances = 3.6220 (9), 3.6930 (9), 3.5532 (9), 3.5803 (9) and 3.5458 (8) Å].

(2RS)-3-Hydr-oxy-2-methyl-2-(2-pyrid-yl)imidazolidine-4-one.

The title structure, C9H11N3O2, is a racemate. The chiral centre is situated at the N—C—N C atom of the imidazolidine ring. The interplanar angle between the mean planes of the pyridine and imidazolidine rings is 89.41 (5)°. The methyl group is in a trans position with respect to the pyridine N atom. In the crystal, the molecules are arranged in zigzag layers parallel to the b axis. The molecules within the layers are interconnected by strong O—H⋯N and weak N—H⋯O hydrogen bonds; the former take place between OH groups and amine N atoms and the latter between the amine N atom and the carbonyl O atom. In addition, C—H⋯O interactions are also present.

cyclo-Tetra­kis(μ-3-acetyl-4-methyl-1H-pyrazole-5-carboxyl­ato-κ4N2,O3:N1,O5)tetra­kis[aqua­copper(II)] tetra­deca­hydrate

The title compound, [Cu4(C7H6N2O3)4(H2O)4]·14H2O, a tetranuclear [2 × 2] grid-type complex with S4 symmetry, contains four CuII atoms which are bridged by four pyrazolecarboxylate ligand anions and are additionally bonded to a water molecule. Each CuII atom is coordinated by two O atoms of the carboxylate and acetyl groups, two pyrazole N atoms of doubly deprotonated 3-acetyl-4-methyl-1H-pyrazole-5-carboxylic acid and one O atom of a water molecule. The geometry at each CuII atom is distorted square-pyramidal, with the two N and two O atoms in the equatorial plane and O atoms in the axial positions. O—H⋯O hydrogen-bonding interactions additionally stabilize the structure. One of the uncoordinated water molecules shows half-occupancy.

Crystal structure of (E)-9-({[4-(di­ethyl­amino)­phen­yl]imino}­meth­yl)-2,3,6,7-tetra­hydro-1H,5H-pyrido[3,2,1-ij]quinolin-8-ol

In the title compound, the hydroxy group forms a intramolecular hydrogen bond to the imine N atom and generates an S(6) ring motif. The conformation about the C=N bond is E, and the aromatic ring of the julolidine moiety is inclined to the benzene ring by 3.74 (14)°.

cis-Dichlorido(dimethyl sulfoxide-κS)(N,N,N′,N′-tetra­methyl­guanidine-κN′′)platinum(II)

In the title compound, cis-[PtCl2(C5H13N3)(C2H6OS)], the four-coordinate PtII atom is bonded to one N atom of the N,N,N′,N′-tetramethylguanidine ligand, one dimethyl sulfoxide S atom and two chloride ligands, forming a cis-square-planar geometry. The bond lengths and angles of the N—Pt—Cl functionality are typical for imine dichloridoplatinum(II) complexes. The H atom of the imino group is oriented towards the O atom of the sulfoxide group of a neighboring molecule and forms an N—H⋯O hydrogen bond.