Igor O. Fritsky

One-Pot Synthesis of a New Magnetically Coupled Heterometallic Cu2Mn2 [2 × 2] Molecular Grid

The heterometallic [2 x 2] grid-type complex [Cu(2)Mn(2)(pop)(4)(OAc)(4)].7H(2)O (1) has been selectively synthesized in a targeted one-pot reaction. Single-crystal X-ray analysis shows the expected structure with identical metal ions located at diagonal vertices of the grid. Magnetochemical studies reveal that 1 has a ferrimagnetic spin ground state with some admixture of low-lying excited states.

Synthesis of Spin‐Crossover Nano‐ and Micro‐objects in Homogeneous Media

New methods are proposed for the synthesis of spin-crossover nano- and micro-objects. Several nano-objects that are based upon the spin-crossover complex [Fe(hptrz)(3)](OTs)(2) (hptrz=4-heptyl-1,2,4-triazole, Ts=para-toluenesulfonyl) were prepared in homogeneous media. The use of various reagents (Triton X-100, PVP, TOPO, and PEGs of different molecular weights) as stabilizing agents yielded materials of different size (6 nm-2 μm) and morphology (nanorods, nanoplates, small spherical particles, and nano- and micro-crystals). In particular, when Triton X-100 was used, a variation in the morphology from nanorods to nanoplates was observed by changing the nature of the solvent. Interestingly, the preparation of the nanorods and nanoplates was always accompanied by the formation of small spherical particles. Alternatively, when PEG was used, 200-400 nm crystals of the complex were obtained. In addition, a very promising polymer-free synthetic method is discussed that was based on the preparation of relatively stable Fe(II)-triazole oligomers in CHCl(3). Their specific treatment led to micro-crystals, small nanoparticles, or gels. The size and morphology of all of these objects were characterized by TEM and by dynamic light scattering (DLS) where possible. Their spin-crossover behavior was studied by optical and magnetic measurements. The spin-transition features for large particles (>100 nm) were very similar to that of the bulk material, that is, close to room temperature with a hysteresis width of up to 8 K. The effects of the matrix and/or size-reduction led to modification of the transition temperature and an abruptness of the spin transition for oligomeric solutions and small nanoparticles of 6 nm in size.

Study of complex formation with 2-hydroxyiminocarboxylates: specific metal binding ability of 2-(4-methylthiazol-2-yl)-2-(hydroxyimino)acetic acid

Abstract Complex formation properties of a novel water soluble thiazolyloxime 2-(4-methylthiazol-2-yl)-2-(hydroxyimino)acetic acid (H3L1) with Cu2+ and Ni2+ were investigated in solution by potentiometrical and spectral (UV–Vis, EPR, NMR) methods. All Cu2+ and most of Ni2+ complex species detected in solution were found to have square-planar MN4 core with oxime and heterocyclic nitrogen atoms which was rationalized in terms of destabilizing effect of repulsive interaction between oxygen atom of carboxylic group and nitrogen atom of thiazole ring in N,O-coordinated ligand conformation. It has been found that stability of metal complexes in a series of oxime ligands is dependent upon basicity of nitrogen atom of oxime group. The thiazolyloxime forms less stable complexes with Cu2+ but stronger ones with Ni2+ ions when compared to parent 2-(hydroxyimino)propanoic acid. The lower stability obtained for Cu2+ complexes was elucidated in terms of negative inductive effect of the thiazole and nitrile substituents as well as an effect of intramolecular attractive interaction between thiazolyl sulfur and oxime oxygen atoms in thiazolyloxime. In the case of Ni2+ the complexes formed are square-planar and it is why thiazolyl ligand is more effective in metal ion binding than simple 2-(hydroxyimino)propanoic acid forming only octahedral species. The solid state structure of the Co3+ complex K3[Co(HL1)3]·5.5H2O (1) was studied by X-ray analysis. The thiazolyloxime ligand is coordinated to Co3+ via oxime nitrogen and carboxylate oxygen atoms forming five-membered chelate rings.

Direct synthesis and crystal structure of zinc thiocyanate complexes with 1,4diazabicyclo(2,2,2)octane

Abstract A direct method of synthesis of zinc thiocyanate complexes with 1,4-diazabicyclo(2,2,2) octane (or triethylenediamine, Ten) is reported. The main peculiarities of interaction of zinc oxide with non-aqueous (methanol, acetonitrile, N,N-dimethylformamide = DMF, dimethylsulfoxide = DMSO) solutions of ammonium thiocyanate in the presence of Ten were investigated. The crystal structures of the compounds [Zn2(NCS)4(NH3)2Ten] (I), (HTen)2[Zn(NCS)4] (II) and [Zn(NCS)2(Ten)DMSO] (III) were determined by X-ray diffraction. The complexes contain four (I) and five (III) coordinate zinc atoms linked by μ2-bridging nitrogen atoms of Ten forming the dimeric and polymeric molecules respectively; the complex (II) has an ionic-type crystal lattice with (HTen)+ cations and [Zn(NCS)4]2− anions.

Efficient stabilization of copper(III) in tetraaza pseudo-macrocyclic oxime-and-hydrazide ligands with adjustable cavity size

Substitution of the amide donors in open-chain {2N(oxime), 2N(amide)} ligands by hydrazide donors gives new pseudo-macrocyclic copper complexes that show a significant decrease of the Cu(3+/2+) redox potentials in both mono- and polynuclear systems, thus demonstrating a pronounced capacity of such ligand systems to efficiently stabilize the trivalent copper.

Synthesis and structure of diaqua-bis(ethylenediamine)copper(II) salts with anions of carbamic acids

Abstract Two complexes of diaqua-bis(ethylenediamine)copper(II) with anions of N-car☐yglycine and ethylenediaminebiscar☐ylic acid [Cu(en)2(H2O)](OOCCH2NHCOO) · H2O (1) and [Cu(en)2(H2O)2](OOCNHCH2CH2NHCOO) · 2H2O (2) were synthesized and investigated by single-crystal X-ray analysis and IR spectroscopy. Compound 1 was obtained by direct synthesis upon interaction of copper powder with glycine hydrochloride in methanol solution upon heating in air. Compound 2 was isolated as a result of a reaction between a copper(II) anionic complex with pyruvoylamide oxime (H2pox) of composition K[Cu(pox)(Hpox)] with ethylenediamine and formaldehyde in methanol solution. In both cases formation of carbamate anions is connected with uptake of atmospheric carbon dioxide by the reaction mixtures. The crystal structures of 1 and 2 comprise [Cu(en)2H2O)2]2+ cations, carbamic acids anions and solvate water molecules. The complex cations of 1 and 2 consist of two ethylenediamine molecules coordinated in the equatorial plane [Cu-N = 2.007(3)–2.024(3)A for 1 and 1.996(2) and 2.022(2)A˚ for 2], and water molecules occupying the apical positions of distorted octahedral [Cu-O = 2.591(3) and 2.741(3)A˚ for 1 and 2.556(3)A˚ for 2]. The extended hydrogen bond system in 1 and 2 unites the elements of the structures.

Evaluating the Conformational Role of an Allosteric CuII Ion in Anion Recognition and Catalysis by a Tricopper Complex

Structural and anion binding studies have provided an insight into the conformational role of an allosteric CuII ion in the trinuclear catalyst (L 2–2H). L 2 is a novel trinucleating ligand with pyridyl, pyrimidyl and amide donor groups. (L 2–2H)Cu (1) has been characterized by X-ray crystallography. The Cu ion is located at the allosteric site and coordinated by two amide N and two pyrimidine N atoms, the CuN4 plane is tetrahedrally distorted, and the complex adopts a helically twisted conformation. In contrast, the (L 2–2H)Cu3(μ4-C2O4) subunit of the dodecanuclear complex [(L 2–2H)4Cu12(μ4-C2O4)2(μ-OH)4(μ-Cl)4Cl4(H2O)2] (5) is roof-shaped, and the allosteric Cu is located on the top of a square-based pyramid. The oxalate coligand is coordinated by the two catalytic Cu ions in an unusual 1,4-μ-O,O bridging mode with an O ⃛O “bite length” of 2.6 Å and a Cu ⃛Cu distance of 6.4 Å. Intramolecular transesterification of the phosphodiester 2-(hydroxypropyl)-p-nitrophenyl phosphate (HPNP) by [(L 2–2H)Cu3]4+ was investigated, in comparison with the closely related complex [(L 3–2H)Cu3]4+ in which the ligand framework is somewhat less flexible. From a kinetic analysis of cleavage rate at varying HPNP concentrations, K HPNP (the equilibrium constant for binding of HPNP to the complex) and k cat (first-order rate constant for cleavage of HPNP when bound to the complex) parameters were derived: K HPNP=190 M-1 ([(L 2–2H)Cu3]4+) and 305 M-1 ([(L 3–2H)Cu3]4+), k cat=10×10-3 s-1 ([(L 2–2H)Cu3]4+) and 3.3×10-3 s-1 ([(L 3–2H)Cu3]4+). Anion binding constants of the complexes were determined by monitoring competitive inhibition of HPNP cleavage. The complexes have a high affinity to , , and , which appear to be of the appropriate size for bridging coordination, while “smaller” anions and are bound less efficiently. [(L 3–2H)Cu3]4+ has a higher affinity than [(L 2–2H)Cu3]4+ to HPNP but a lower affinity to the rather large anion . This is interpreted as a consequence of the reduced flexibility of [(L 3–2H)Cu3]4+, which slightly disfavours widening of the Cu ⃛Cu distance for incorporation of perrhenate. Similarly, the somewhat lower reactivity of [(L 3–2H)Cu3]4+ is attributed to the larger energy gap between the ground state and sterically more demanding (and less efficiently stabilized) transition state. Synthesis of L 2. Intramolecular cleavage of the phosphodiester 2-(hydroxypropyl)-p-nitrophenyl phosphate (HPNP). Proposed mechanism of HPNP cleavage by [(L n –2H)Cu3]4+, including estimated O ⃛O distances of bridging HPNP in the ground and transition state.

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.

Electronic communication between fluorescent pyrene excimers and spin crossover complexes in nanocomposite particles

Bistable [Fe(H-trz)2(trz)]BF4 core and silica shell hybrid nanoparticles with different sizes between 50–150 nm were grafted with a pyrene-derivative fluorophore. The fluorescent composites exhibited both monomer and excimer luminescence (with a controllable ratio), whilst their spin transition properties remained unaltered. When switching the particles from the diamagnetic to the paramagnetic state the excimer lifetime and luminescence intensity increased and the emission spectra were redshifted, while the monomer emission exhibited negligible spin-state dependence. The strong coupling of the pyrene excimers with the spin-state of the ferrous ions was shown to occur via a non-radiative mechanism, brought about, to a large extent, by the spin transition induced mechanical strain.

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.