Investigations in the xanthine series and among its condensed derivatives

A method has been developed for obtaining derivatives of 8-methyl-2,3-dihydro-6H-imidazo[1,2-f]xanthine. It has been established that 2,3-dihydroimidazo[1,2-f]-xanthines alkylate in position 6 of the uracil fragment. A method has been developed for obtaining derivatives of 2,3-dihydroimidazo[1,2-f]purin-7-one. The structure of the compounds synthesized have been confirmed by IR and PMR spectroscopy. Zaporozh'e Medical Institute. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 623–626, September–October, 1980.     

Aminoguanidinium cations and the square-bipyramidal hexachlorocuprate(II) anion in the (CH8N4)2[CuCl6] crystal structure

Synthesis and structure of a novel thermochromic complex (CH₈N₄)₂[CuCl₆] are reported. X-ray analysis of the compound was carried out for a single crystal 0.4×0.2×0.05 mm in size (a bright-yellow plate). The monoclinic unit cell parameters are a=7.167(1), b=15.561(3), c=7.328(1) Å, β=118.73(3)°, V=716.7(2) ų, space group P2₁, Z=2 (CH₈N₄)₂[CuCl₆] d_calc=1.99 g/cm³, μ(MoK_α)=2.65 mm^?1, R=0.0264, and R_w=0.0290 for 1411 I_hkl>2σ_I.     

Unusual Polymers Containing Alternating <Emphasis Type="Italic">s</Emphasis> and <Emphasis Type="Italic">d</Emphasis> Elements Connected by Bridging Pivalate

From tetrahydrofurane solutions containing Cu(II) or Co(II) and potassium pivalate (KPiv) (molar ratios Cu/K=1/10, Co/K=1/5) one can isolate polynuclear [K₃Co₂Piv₇(THF)₃] (1) and [K₆Cu₂Piv₁₀(HPiv)(THF)(H₂O)₂]\(\cdot\)2THF (2), respectively. In the solid state the structures of the compounds consist of alternating, oppositely winding helices with a step of 46.085 Å for 1 and 25.260 Å for 2. In 2, the bridging pivalates link the infinite helices into layers. For both compounds, an important peculiarity of the structure is wide separation of transition metal ions (at least 5.327 Å for 1 and 6.791 Å for 2). Due to the presence of excess KPiv in the reaction system, the Cu(II) and Co(II) ions do not “coalesce” into polynuclear complexes typically observed in transition metal pivalates; instead they form unusual polymer systems containing alternating atoms of s and d elements. For transition metal pivalates, this type of structure was found for the first time.     

Copper(II) Complexes with N-(3-Hydroximino-2-methylbutan-2-yl)methylamine (HL): Synthesis and Properties. Crystal and Molecular Structures of [Cu(HL)Cl2] and [Cu(HL)(H2O)2SO4]n

Paramagnetic copper(II) complexes with N-(3-hydroximino-2-methylbutan-2-yl)methylamine (HL), namely, Cu(HL)Cl₂(I), Cu(HL)(SO₄) · 2H₂O (II), and Cu(HL)(NO₃)₂(III), were obtained. The crystal structures of I and II were determined. The blue crystals of these compounds are monoclinic. For I(C₆H₁₄Cl₂CuN₂O): a = 8.820(1) Å, b = 6.511(1) Å, c = 18.255(2) Å, = 92.86(1)° V = 1047.0(2) ų, space group P2₁/c, _calcd = 1.679 g/cm³, Z = 4 for R ₁ = 0.0250; for II(C₆H₁₈CuN₂O₇S): a = 9.999(2) Å, b = 9.927(2) Å, c = 12.963(3) Å, = 106.37(3)°, V = 1234.5(4) ų, space group P2₁/c, _calcd = 1.753 g/cm³, Z = 4 for R ₁ = 0.0324. Crystals of I have a molecular structure. The Cu coordination polyhedron is a square bipyramid (2N + 2Cl + Cl + Cl) due to additional contacts with two Cl atoms from the neighboring molecules. Structure II is built from polymeric chains. The environment of the Cu atom is a distorted cis-octahedron (2N + 2O(H₂O) + 2O(SO₄)). Complexes I–IIIare characterized by IR and EPR spectroscopy.     

Crystal structure of cobalt(II) complexes with imidazoline nitroxide

The crystal structures of Co(II) coordination compounds CoL ₂-α modification (I), CoL₂(CH₃OH)₂ (II), and CoL₂Py₂(III) — where L is a stable nitroxide 4-(3′,3′,3′-trifluoro-2′-oxypropylene)-2,2,5,5-tetramethyl-3-imidazoline-l-oxyl (L), were determined. It was found that the tetrahedral surroundings of cobalt in I consist of the O and N donor atoms of the deprotonated enaminoketone groups of L. In II and III, the same atoms form the equatorial plane of the centrosymmetric octahedral environment of the central atom in which the axial positions are occupied by the methanol O atoms or the pyridine N donor atoms. In the octahedral coordination centers of II and III, the Co-O and Co-N distances exceed analogous distances in the tetrahedral coordination center of I, substantially increasing the chelate angle in I compared to II and III. In I, the Co-O and Co-N bond lengths and the OCoN chelate angles are, respectively, 1.921(4), 2.006(4) Å, 93.6(2)° in II, 2.014(4), 2.177(4), Co-O_OH 2.146(4) Å, 86.9(2)° in the two crystallographically independent molecules of III, 2.031(2) and 2.022(2), 2.170(2) and 2.193(2), Co-N_Py 2.213(2) and 2.219(2)Å, 87.04(7) and 87.20(7)°. Compounds I and III are molecular. Compound II in the solid state has a layered polymer structure due to hydrogen bonding between the O atoms of the nitroxyl groups of L and the O atoms of the coordinated alcohol molecules.     

Peculiarities of NMR spectra of heterospin complexes

Experimental investigation and theoretical simulation of the unusual phenomenon of multiple broadening and narrowing of NMR signals due to the temperature variation of a solution of the stereochemically non-rigid heterospin Ni²⁺ complex with stable nitroxide were performed. The investigation of the temperature dependence of the NMR signals of stereochemically non-rigid heterospin systems can be used for choosing conditions for growing heterospin single crystals containing molecules in a definite conformation.     

Dynamics of solutions of the simplest nonlinear boundary-value problems

We investigate two classes of essentially nonlinear boundary-value problems by using methods of the theory of dynamical systems and two special metrics. We prove that, for boundary-value problems of both these classes, all solutions tend (in the first metric) to upper semicontinuous functions and, under sufficiently general conditions, the asymptotic behavior of almost every solution can be described (by using the second metric) by a certain stochastic process. Institute of Mathematics, Ukrainian Academy of Sciences, Kiev. Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 51, No. 6, pp. 810–826, June, 1999.     

Copper(II) complexes with pyrazolyl-substituted nitronyl and imino nitroxides

It was established that the reactions of pyrazol-3-yl-substituted nitronyl nitroxide (HL¹) and pyrazol-3-yl-substituted imino nitroxide (HL³) with Cu(II) acetate lead to self-assembly of the Cu₄(OH)₂(OAc)₄(DMF)₂(L¹)₂ tetranuclear and Cu₂(OAc)₂(H₂O)₂(L³)₂ dinuclear complexes, respectively. The reaction of Cu(II) acetate with 5-ethoxycarbonyl-pyrazol-3-yl-substituted nitronyl nitroxide (HL²) gave unexpected solid Cu₂(H₂O)₂(L⁶)₂ · 2DMF, in which L⁶ is a deprotonated 5-carboxy-pyrazol-3-yl-substituted nitronyl nitroxide, formed as a result of cleavage of an ester bond in the starting HL². A similar transformation of the paramagnetic ligand was observed in the reaction of Cu(II) acetate with 5-ethoxycarbonyl-pyrazol-3-yl-substituted imino nitroxide (HL⁴). It led to the formation of Cu₂(DMF)₂(L⁷)₂, where L⁷ is deprotonated 2-(5-carboxy-1H-pyrazol-3-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole 3-oxide. An X-ray diffraction study indicated that in Cu₄(OH)₂(OAc)₄(DMF)₂(L¹)₂ and Cu₂(OAc)₂(H₂O)₂(L³)₂, the L¹ and L³ paramagnetic ligands perform the bridging cyclic tridentate function, while in Cu₂(H₂O)₂(L⁶)₂ · 2DMF and Cu₂(DMF)₂(L⁷)₂, the paramagnetic L⁶ and diamagnetic L⁷ are bridging bicyclic tetradentate ligands. The magnetic behavior of complexes with coordinated nitronyl nitroxide – Cu₄(OH)₂(OAc)₄(DMF)₂(L¹)₂ and Cu₂(H₂O)₂(L⁶)₂ · 2DMF is dictated by the dominant antiferromagnetic exchange interactions, which is confirmed by quantum-chemical data. The magnetic susceptibility of Cu₂(OAc)₂(H₂O)₂(L³)₂ reflects the competition between the antiferromagnetic and ferromagnetic components, of which the latter is due to electron coupling in the Cu(II) ← N=C–N ? O exchange channels. EPR data confirm the results received from static magnetic measurements for multispin solids.     

Unique [(1)infinityNi(8)Bi(8)S] metallic wires in a novel quasi-1D compound. Synthesis, crystal and electronic structure, and properties of Ni(8)Bi(8)SI.

A new quasi-one-dimensional compound Ni(8)Bi(8)SI has been synthesized and its crystal structure determined from single-crystal X-ray diffraction data. The structure of Ni(8)Bi(8)SI consists of [(1)infinityNi(8)Bi(8)S] columns separated by iodine atoms. Conductivity and magnetic susceptibility measurements (down to 4.2 K) show that Ni(8)Bi(8)SI is a one-dimensional metal and exhibits Pauli paramagnetic properties. These observations are in good agreement with the results from electronic structure calculations. An analysis of the chemical bonding employing difference electron charge density maps reveals strong multicenter Ni-Bi bonds and pair Ni-S interactions within the [(1)infinityNi(8)Bi(8)S] columns. Only electrostatic interactions are inferred between the columns and iodine atoms.