Novel oxovanadium(iv) heterochelate complexes: synthesis, structure, ESR spectra, and photoluminescence properties

The reactions of oxovanadium(iv) salts with dimethylmalonate anions (H₂Dmm — C₃H₆(COOH)₂) and chelating N-donor ligands (2,2′:6′,2″-terpyridine (terpy), 2,2′-bipyridine (bpy)) led to the formation of new mononuclear heterochelate complexes [VO(Dmm)(terpy)]·4H₂O (1) and [VO(Dmm)(bpy)(H₂O)] (2). The structures of the synthesized compounds were determined by X-ray diffraction. The ESR spectra of the compounds at 293 and 100 K were analyzed and simulated. The photoluminescence properties were investigated.     

Synthesis, structure, electrochemical and magnetic properties of 2,6-bis(5-trifluoromethylpyrazol-3-yl)pyridine and its NiII complexes

2,6-Bis(5-trifluoromethylpyrazol-3-yl)pyridine (H₂L) and its mono-, tri-, and tetranuclear NiII complexes were synthesized for the first time. All the obtained compounds were characterized by single-crystal X-ray diffraction analysis. In the complexes, 2,6-bis(5-trifluoromethylpyrazol-3-yl)pyridine exists in the neutral and dianionic forms and exhibits different coordination modes (??³-, ??²-??³:??¹-, and ??³-??³:??¹:??¹). The electrochemical and magnetic properties of all compounds were studied. The tetranuclear Ni^II complex with the L^2? dianion is reduced in two sequential reversible one-electron steps.     

Polymeric heterometallic CuII dimethylmalonate complexes with potassium and cadmium ions

A reaction of (HPiv)₂Cu₂(Piv)₄ with dimethylmalonic acid dipotassium salt (K₂Me₂mal) leads to the formation of a cage coordination polymer {(μ-H₂O)₆K₈[(μ-H₂O)Cu-(μ₃,κ²-Me₂mal)(μ₆,κ²-Me₂mal)]₂[Cu₂(μ₅,κ²-Me₂mal)₂(μ₅,κ²-Me₂mal)₂]}n (1). It was found that when 1 reacted with CdSO₄·8H₂O in a mixture of EtOH-H₂O (3: 1), the potassium ions in 1 were displaced with cadmium(ii) ions with the formation of a heterometallic 1D-polymer [(κ¹-H₂O)₄CdCu(μ,κ²-Me₂mal)₂] _n (2). Compounds 1 and 2 were characterized by X-ray crystallography and ESR spectroscopy.     

Synthesis,structure, and luminescent properties of lanthanide coordination compounds with 3-methyl-4-formyl-1-phenylpyrazol-5-one

An exchange reaction of the sodium salt of 3-methyl-1-phenyl-4-formylpyrazol-5-one (HL) with chlorides or nitrates of lanthanides (Ln = La, Nd, Sm, Eu, Gd, Tb, Dy, and Yb) was used to synthesize coordination compounds of composition LnL₃·nSolv (Solv = H₂O or EtOH). According to powder X-ray diffraction data, these compounds constitute two series: one comprises lanthanum and neodymium complexes, and the other, samarium, europium, gadolinium, terbium, dysprosium, and ytterbium complexes. For the complexes of the first series, the structure was solved in a single-crystal diffraction experiment carried out on [La₂(μ-L)₃(L)₃(H₂O)₃]·2MeOH. The lanthanum atoms in the complex are at a distance of 4.222(2) — from each other, and they are structurally nonequivalent and linked by three 5-hydroxy-4-formylpyrazole anions. Solid-phase samples of the coordination compounds under study feature weak luminescence in the spectral regions intrinsic to lanthanide cations.     

Proof of a conjecture of Pólya on the zeros of successive derivatives of real entire functions

We prove Pólya’s conjecture of 1943: For a real entire function of order greater than 2 with finitely many non-real zeros, the number of non-real zeros of the nth derivative tends to infinity, as . We use the saddle point method and potential theory, combined with the theory of analytic functions with positive imaginary part in the upper half-plane.     

Influence of the nature of organic components in dinuclear copper(II) pivalates on the composition of thermal decomposition products

Tetrabridged dinuclear complexes ((2-NH₂)C₅H₄N)₂Cu₂(μ₂-OOCCMe₃)₄ (2·С₆Н₆) and ((3-NH₂)C₅H₄N)₂Cu₂(μ₂-OOCCMe₃)₄ (3) and the cocrystallization product ((4-NMe₂)C₅H₄N)₂Cu(η²–OOCCMe₃)₂·2((4-NMe₂)C₅H₄N)₂Cu₂(μ₂-OOCCMe₃)₄ (4) were synthesized by the reaction of the polymer [Cu(OOCCMe₃)₂]_n (1) with aminopyridine ligands (L) of different nature (Cu: L = 1:1) in С₆Н₆. The solid-state thermal decomposition of these compounds was studied by differential scanning calorimetry and thermogravimetry, and their electrochemical behavior was investigated by cyclic voltammetry. All newly synthesized complexes were studied by X-ray diffraction, the magnetic properties of the complexes were investigated, and ESR measurements were performed.     

Pivalates with the M<Superscript>II</Superscript><Subscript>4</Subscript>O<Subscript>4</Subscript> cubane core (M = Co,Ni): synthesis,structure, magnetic properties,and solid-state thermolysis

Methods were developed for the controlled thermal synthesis of high-spin cubane-like pivalates {M^II ₄(μ₃−OR)₄} (M = Co or Ni; R = H or Me) starting from mono-and polynuclear complexes. The solid-state thermal decomposition of the known pivalate clusters [M^II ₄(μ₃−OMe)₄−(μ₂−OOCBu^t)₂(η²−OOCBu^t)₂(MeOH)₄] and the new clusters [M₄^II(μ₃)−OH₄(η¹−OOCBu^t)₃−(μ−(NH₂)₂C₆H₂Me₂)₃(η¹−(NH₂)₂C₆H₂Me₂)₃]⁺(OOCBu^t)− (M = Co or Ni) was studied by differential scanning calorimetry and thermogravimetry. The thermolysis of cubane-like CoII and NiII pivalates is a destructive process. The phase composition of the decomposition products is determined by the nature of coordinated ligands and the structural features of the metal core.     

Influence of nanoparticles and thin layers of gold, europium phthalocyanine, and erbium nanoparticles on the formation of luminescence spectra of structures with InGaN/GaN quantum wells

The influence of nanoparticles and thin layers of Au, Eu phthalocyanine, and Er nanoparticles on the formation of luminescence spectra of InGaN/GaN quantum-well structures has been investigated. It has been shown that the influence of localized plasmons on the generation of charge carriers is determined by the size of Au nanoparticles under the assumption that the interaction of plasmons with surface states of the structures plays a dominant role. The influence of Au nanoparticles on the formation of luminescence spectra of multiple quantum-well structures based on InGaN/GaN, unlike the case of Au layers, is determined by the indium concentration. The influence of Eu phthalocyanine films, which are deposited onto the surface of the studied structures, on their photoluminescence spectra is similar to the influence of doping of these structures with europium.