Thermal studies on metal complexes of 5-nitroso-pyrimidine derivatives

The following cadmium(II) complexes of deprotonated 6-amino-5-nitroso-uracil (AH), deprotonated 6-amino-3-methyl-5-nitroso-uracil (BH) and neutral 6-amino-1-methyl-5--nitroso-uracil (CH) have been prepared and their thermal behaviour studied by TG and DSC techniques: CdA₂ · 3 H₂O, CdB₂ · 2 H₂O, CdB₂ and CdCl₂(CH)₂ · 2 H₂O.Dehydration processes of these complexes take place in only one step and the enthalpy values associated with them are comprised in the 42.7–80.5 kJ · mole^–1 H₂O range. The pyrolytic reactions finish in the 630–900 C temperature range, remaining as final residue in the case of CdA₂ · 3 H₂O, CdB₂ · 2 H₂O and CdB₂ complexes, cadmium oxide. The pyrolytic decomposition of CdCl₂(CH)₂ · 2 H₂O complex does not yield any residue, due to the elimination of cadmium chloride.

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Zusammenfassung Folgende Cadmium(II)-Komplexe von deprotoniertem 6-Amino-5-nitrosouracil (AH), deprotoniertem 6-Amino-3-methyl-5-nitroso-uracil (BH) und neutralem 6-Amino-1-methyl-5-nitroso-uracil (CH) wurden hergestellt: CdA₂ · 3 H₂O, CdB₂· 2 H₂O, CdB₂ und CdCl₂(CH)₂ · 2 H₂O. Das thermische Verhalten dieser Komplexe wurde mittels TG und DSC untersucht. Die Dehydratisierung der Komplexe verlÄuft in nur einem Schritt. Die Enthalpiewerte für diese Prozesse liegen im Bereich von 42.7–80.5 kJ · mol^–1 H₂O. Die pyrolytischen Reaktionen verlaufen im Temperaturbereich von 630–900C zu Ende, wobei im Falle der Komplexe CdA₂ · 3 H₂O, CdB₂ · 2 H₂O und CdB₂ Cadmiumoxid als Rückstand zurückbleibt. Die pyroytische Zersetzung von CdCl₂(CH)₂ · 2 H₂O verlÄuft wegen der Flüchtigkeit von CdCl₂ rückstandslos.

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CdA₂ · 3 H₂O, CdB₂ · 2 H₂O, CdB₂ CdCl₂(CH)₂ · 2 H₂O, A — 6--5-, B — 6--3--5- CH — 6--1--5- . . 42.7–80.5 · ^–1. 630–900, . CdCl₂(CH)₂ · 2 H₂O - , .

     

Thermal and spectral studies on some tetrachloroaurates of 8-alkyltheophylline derivatives

Tetrachloroaurates of 8-ethyl-, 8-isopropyl-, 8-propyl- and 8-pentyltheophylline were synthesized and studied by¹H-NMR, TG and DSC techniques. The metal is not coordinated to the 8-alkyltheophylline derivatives and forms a salt-like structure.

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Zusammenfassung Tetrachloroaurate von 8-Äthyl-, 8-Isopropyl-, 8-Propyl- und 8-Pentyltheophillin wurden synthetisiert und mittels¹H-NMR, TG und DSC untersucht. Die 8-Alkyltheophillin-Derivate sind nicht koordinativ an das Metall gebunden, es liegt vielmehr eine salzartige Struktur vor.

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8--, 8--, 8-- 8- , . , 8- .

     

Copper(II) complexes with the N,N,O-tridentate ligand 6-amino-5-formyl-1,3-dimethyluracilato-(N6)-benzoylhydrazone: synthesis, spectral and XRD studies

From reactions between different Cu(II) salts and the Schiff base 6-amino-5-formyl-1,3-dimethyluracil-benzoylhydrazone (H₂BEZDO) in alcohol, six new copper complexes with simplified formulas [Cu(HBEZDO)(H₂O)(MeOH)]NO₃ (1), [CuCl(HBEZDO)(DMF)] (2), [CuBr(HBEZDO)]·2H₂O (3), CuBr(HBEZDO) (4), Cu(ClO₄)(HBEZDO)·H₂O (5), and Cu(SO₄)_1/2(HBEZDO)·1 H₂O (6) were isolated. The structures of compounds 1, 2 and 3 have been established by means of XRD diffraction methods. In the three compounds, the Schiff base acts as a tridentate monodeprotonated ligand through the N(6), N(51) and O(52) atoms, making two five- and six-membered chelate rings. In the structure of 1 and 2, the solvent molecules are coordinated giving square-based pyramidal environments, with the basal plane completed by a MeOH (1) or Cl (2) and the apical positions occupied by the oxygen atom of a water (1) or a DMF molecule (2). The molecular unit of the complex [CuBr(HBEZDO)]·2H₂O (3) is defined by a square-plane containing the three donor atoms of the organic ligand and a bromide ligand (Cu–Br 2.384 Å), but there is a stronger tetragonally elongated pyramidal geometry around the metal, the apical position of the polyhedron being occupied by a weakly bound-to-copper bromine atom (3.086 Å) of a neighbouring molecule. This fact gives the appearance of an apparent dimer with very asymmetric bromine bridges, in which there are no exchange interactions between metal centres. Also, infrared, magnetic and EPR data of the isolated complexes are reported.     

Gold(III)-pteridine compounds: synthesis, spectral, and X-ray diffraction studies on new adducts between sodium tetrabromoaurate(III) and lumazine derivatives

In aqueous hydrobromic medium, Na[AuCl₄] reacts with 1,3-dimethyllumazine (1,3-dimethyl-pteridine-2,4(1H,3H)-dione, DLM) or 1,3,6,7-tetramethyllumazine (DLMD) to give three adducts with simplified formulas Na[AuBr₄](DLMD), Na[AuBr₄](DLM), and Na[AuBr₄](DLM)₂. These compounds have been characterized by means of analytical techniques, and IR and NMR spectroscopies. Single-crystal x-ray diffraction studies have been made on the Na[AuBr₄](DLM)₂ compound. The crystals belong to the orthorhombic Pbca space group, with a = 15.249(1), b = 15.238(2), c = 21.563(2) Å, Z = 8, and R = 0.053. The structure consists of planar [AuBr₄]^– anions and Na⁺ cations weakly linked to two crystallographically independent DLM molecules. The Na⁺ cation interacts weakly with four oxygen and one nitrogen atoms from four different pteridine molecules, its environment may be described as a very distorted square pyramid.     

Novel coordination behavior of a pteridine-benzoylhydrazone ligand (BZLMH): Theoretical calculations, XRD structures and luminescence studies

The XRD structure and the influence of the conformation in the molecular orbitals of the pteridine-benzoylhydrazone ligand (BZLMH = benzoylhydrazone of 6-acetyl-1,3,7-trimethyllumazine, lumazine = (1H,3H)-pteridin-2,4-dione) have been studied. Complexes of BZLMH with nickel(II), zinc(II) and mercury(II) have been prepared and spectroscopically characterized by IR, NMR and fluorescence spectroscopy; also XRD studies have allowed to establish two different coordinative patterns in the complexes [Ni₃(BZLMH)₃(OH)(H₂O)(CH₃CN)₂](ClO₄)₅ · 2H₂O · CH₃CN (2) and [Zn(NO₃)(BZLMH)(H₂O)](NO₃) (3). Compound (2) is a trinuclear hydroxo-centered complex with a central hydroxo group bridging the three nickel(II) ions. The [Ni₃(μ₃-OH)]⁵⁺ core is planar with the benzoylhydrazone ligands coordinated in the bis-bidentate [O(4),N(5)]-[N(61),O(63)] mode. The zinc(II) compound displays a BPT coordination geometry in which the BZLMH ligand acts in a tridentate fashion using N(5), N(61) and O(63) donor atoms. Fluorescence spectroscopic properties of benzoylhydrazone (BZLMH) are studied and the fluorescence band shift and changes in intensity is modulated by complexation with different metal ions (Ni²⁺, Zn²⁺ and Hg²⁺), so the binding is signaled such a possible cause.     

Thermal studies on metal complexes of 5-nitroso-pyrimidine derivatives

Four Hg(II) complexes, containing as ligands 6-amino-5-nitrosouracil (AH), 6-amino-3-methyl-5-nitrosouracil (BH) or 6-amino-1-methyl-5-nitrosouracil (CH), have been synthesized and their thermal behaviour studied by TG and DSC techniques: Hg₃Cl₆(AH)₄, HgCl₂(BH)₂· 2 H₂O, HgCl₂(BH)₂ · H₂O and HgC₂· 2 H₂O.The dehydration processes take place in only one step, with enthalpies in the range 40.2–60.0 kJ · mole^–1 H₂O.Pyrolytic processes start between 200 and 250°, in all cases the thermal stability of the corresponding pyrimidine derivative being lower than that of the free ligand. These processes finish between 600 and 750°, with no residue.

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Zusammenfassung Vier 6-Amino-5-nitrosouracil (AH), 6-Amino-3-methyl-nitrosouracil (BH) oder 6-Amino-1-methyl-5-nitrosouracil (CH) als Liganden enthaltende Hg(II)-Komplexe wurden synthetisiert: Hg₃Cl₆(AH)₄, HgCl₂(BH)₂ · 2 H₂O, HgCl₂(BH)₂ · H₂O und HgC₂ · 2 H₂O. Die Dehydratisierungsprozesse verlaufen in nur einem Schritt mit Enthalpien im Bereich von 40.2–60.0 kJ pro mol H₂O. Pyrolitische Prozesse setzen zwischen 200 und 250° ein. In allen Fällen ist die thermische Stabilität der entsprechenden Pyrimidin-Derivate geringer als die der freien Liganden. Diese Prozesse sind zwischen 600 und 750° beendet, wobei kein Rückstand zurückbleibt.

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g₃l₆()₄, gl₂( )₂ · 2 ₂O, gl₂()₂ · ₂O, g₂ · 2 ₂, — 6- -5-, — 6--3- — 6---5- . , 40.2–60.0 · ^–1 ₂. 200 250° 600–750° - . , .

     

Thermal behaviour of silver/I/ complexes of 4-amino-5-nitroso-uracil derivatives

The silver(I) complexes of 4-amino-5-nitroso-uracil, 4-amino-1-methyl-5-nitroso-uracil, 4-amino-3-methyl-5-nitroso-uracil and 4-amino-1,3-dimethyl-5-nitroso-uracil have been prepared and their thermal behaviour studied. All the isolated compoounds show 1∶1 stoichiometry.     

XRD structure of two heptacoordinated Mn(II) complexes containing 2,9-dimethyl-1,10-phenanthroline (phen), nitrato and nicotinato bidentate anions: [Mn(phen)(nicot)(NO3)(H2O)]·EtOH·H2O and [Mn(phen)(NO3)2(H2O)]

The XRD structure of two seven-coordinated Mn(II) complexes with the formula [Mn(phen)(nicot)(NO₃)(H₂O)]·EtOH·H₂O (1) and [Mn(phen)(NO₃)₂(H₂O)] (2) are reported. The 2,9-dimethyl-1,10-phenanthroline, nitrato and nicotinato anions act as bidentate ligands, with Mn–N distances of 2.21–2.29 Å and Mn–O distances of 2.17–2.40 Å. In both compounds, the water molecule seems to be the strongest coordinated ligand, with bond distances of 2.139(2) Å in 1 and 2.195(2) Å in 2. The average ratio between coordinated unidentate and bidentate bond lengths less than the unity justifies, from an energetical point of view, the shape of the coordination polyhedra. In the structure of 1, the coordination polyhedron may be best-described as a distorted pentagonal bipyramid with a nitrogen from phenanthroline and the water molecule occupying the apical sites. The polyhedron shape for 2 is close to a square-capped trigonal prism, the capping site being occupied by the water molecule. The crystal structures are built by H-bonded bidimensional sheets piled up by π–π stacking of the partially interpenetrated aromatic moieties of adjacent layers.     

Gold(III)–Pteridine Compounds: Preparation,Spectroscopic, and XRD Studies on a New Compound Containing Tetrabromoaurate(III) Anions and Hydrogen-Bonded 1,6,7-Trimethyllumazine-Oxonium Dihydrate Cations

In concentrated aqueous hydrobromic medium, Na[AuCl₄] reacts with 1,6,7-trimethyllumazine (1,6,7-trimethyl-pteridine-2,4(1H,3H)-dione, MLMD) to give an adduct with simplified formula (H₇O₃)[AuBr₄](DLMD)₃ in which the negative charge of the tetrabromoaurate(III) anion is neutralized by an oxonium dihydrate cation (H₇O₃ ⁺). The compound has been characterized by means of analytical techniques and IR and NMR spectroscopies. The crystals belong to the triclinic P ^—1 space group, with a = 11.321(1), b = 11.908(2), c = 16.460(1) Å, = 71.54(2), = 71.675(7), = 78.68(1)°, Z = 2, R = 0.089. The structure is formed by uncoordinated pteridine derivatives hydrogen-bonded, in a ladder-like polymeric fashion, to trinuclear oxonium-dihydrate cations; free square-planar tetrabromoaurate(III) anions are allocated in the holes of the H-bond network.