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

Versatile Coordinative Abilities of a New Hybrid Pteridine−Thiosemicarbazone Ligand: Crystal Structure, Spectroscopic Characterization, and Luminescent Properties

“…The second angle corresponds to the bite angle of the rigid chelating lumazine moiety. The Cu−O(4) bond distance of 2.449 Å is much longer than the usual values in lumazine derivatives complexes, ,, which allows us to define the geometry as tetrahedral with considerable trigonal planar distortion (“3 + 1”) with N(5), N(61), and S(63) in the basal plane and O(4) weakly coordinated in the apical position; in agreement with this, the sum of the angles S(63)−Cu−N(61), N(61)−Cu−N(5), and N(5)−Cu−S(63) (357.6°) is clearly closer to the expected value for a trigonal-planar configuration (360°) than the ideal value for a tetrahedron (328.5°). The Cu···Cu distance (2.876(2) Å) is almost equal to the sum of the van der Waals radius of copper (2.8 Å), indicating a minimum interaction between two copper atoms …”

“…The FT-IR spectrum shows bands of medium intensity in the 3400−3100 cm -1 range assignable to ν(N−H) of the amino and hydrazonic groups of the ligand. The characteristic bands of the lumazine derivative are two absorptions observed at 1720 and 1685 cm -1 assignable to the coupling of the ν(CO) of both carbonyl groups, the band at 1553 cm -1 attributed to ν(CN) of the pyrazine ring, and the two bands at 1450 and 1290 cm -1 assignable to ν(CC) + ν(C−N) vibrations . For the thiosemicarbazone moiety, thioamide bands I−IV are found at 1600, 1484, 1345, and 847 cm -1 .…”

“…The ligand crystallized as hemihydrate. The lumazine skeleton displays a roughly planar geometry like related ligands, , so the pyrimidine and pyrazine rings exhibit a dihedral angle of 1.6(1)°. The bond lengths of the carbonyl groups are slightly different (C(2)O(2), 1.210(3) Å; C(4)O(4), 1.222(3) Å) 5,21 whereas bond lengths at the thiosemicarbazone moiety indicate an extensive delocalization as usual on the thiosemicarbazone derivatives which is clearly reflected in the C−S distance at 1.673(3) Å intermediate between a single and double bond character (1.82 and 1.56 Å, respectively) and the N−N (1.375(3) Å) distance, less than the 1.44 Å accepted as typical of single bonds .…”

Isolation, Structural Elucidation, and Synthesis of Lepteridine From Ma̅nuka (Leptospermum scoparium) Honey

“…Since then it has been reported in several studies on related lumazines. Characterization data for lumazine 3 is limited to a melting point, elemental analysis, and UV/vis peaks; no NMR, MS, or IR data have been reported to date. − Similarly, characterization data for lumazine 4 is limited to a melting point, elemental analysis, and UV/vis. − To date, no reports detailing the isolation of lumazines 3 or 4 from natural materials have been published.…”

Interplay of thermochemistry and structural chemistry, the journal (volume 15, 2004) and the discipline

“…In the next paper, Acuña-Cueva et al [37] deal with halo derivatives of trivalent gold, in particular salts of AuBr 4 − . We recall recent studies on generic AuX 3 species and discussions of whether they are trivalent, gold-centered, or univalent gold-containing X 2 ·AuX species [38].…”