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

Abstract

The synthesis and characterization of the first thiosemicarbazone-lumazine (TSCLMH=the thiosemicarbazone of 6-acetyl-1,3,7-trimethyllumazine) hybrid ligand is reported. The influence of the conformation of this compound on its energy and the atomic contribution to the molecular orbitals have been theoretically investigated. Ni(II), Cu(I), Zn(II), and Cd(II) complexes of this ligand have been synthesized and characterized by elemental analysis, thermogravimetric studies, IR, 1H, 13C, and 15N NMR, and UV-vis-NIR spectroscopy, magnetic measurements, and X-ray crystallography. Four types of coordination modes for the ligand may be predicted: (a) double bidentate; (b) tetradentate; (c) tridentate; (d) bidentate. Structures of representative complexes of types a, b, and d have been determined by X-ray crystallography. In the [Cu(TSCLMH)]2(ClO4)2 complex, TSCLMH acts as a doubly bidentate bridging ligand forming a dimer with a Cu...Cu distance of 2.876 A. The geometry around the metal ion is trigonally distorted tetrahedral with a relatively long (four-atom) bridge between the metal centers instead of the shorter, mainly single atom, bridges present in other thiosemicarbazone derivatives complexes. In the [Cd(NO3)2(TSCLMH)(EtOH)] complex, the metal ion displays eight-coordinated geometry with the TSCLMH ligand acting in a tetradentate planar fashion and two nitrate anions, one monodentate and the other bidentate. The coordination polyhedron in [Cd(TSCLM)2(H2O)].MeOH.2H2O is a square pyramid with two monoanionic ligands acting as bidentate NS donors and a water molecule completing the coordination sphere. Fluorescence spectroscopic properties of TSCLMH have been studied as well as the changes in position and intensity of fluorescence bands caused by the complexation with different metal ions (Ni2+, Cu+, Zn2+, Cd2+).

Synthesis and chemical characterization of some transition metal complexes with a 6-acetyl-1,3,7-trimetyllumazine ligand

“…Single crystals of the complexes could not be isolated from any solutions, thus no definite structure could be described. However, according toliterature [25][26]29], there results and discussed through different techniques suggest below the proposed the possible coordination for behavior bidentate, tridentate and tetradentate ligand. shown in schema1-3.…”

“…In addition, the pyridine moiety plays a significant role in many biological processes like nicotinamide adenine dinucleotide phosphate NADP or vitamin B6 [17][18].Nowadays, the metal complexes of these heterocycles have recently been studied as models to mimic the reactivity of the metal site of some metalloenzymes and they carry out diverse biological functions, being present in a number of biological systems involving several biochemist reactions of physiological relevance [19][20][21][22][23][24]. Furthermore, the functionalized 6-acetyl-1,3,7-trimethyllumazine pro-ligand (lumazine:pteridine-2,4(1H,3H)-dione) has been already used as a precursor compound to build some thiosemicarbazone and hydrazone hybrid coordinative systems [25][26]. Thus, this work is aimed to describe the synthesis and chemical characterization of a new pteridine derivative, the pyridinehydrazone of 6-acetyl-1,3,7-trimetyllumazine (PZLMH) ( Figure. …”

Synthesis, Characterization of New Tungsten(IV)?Pterin Complexes and their Reactivity Studies towards Trimethylamine N-Oxide, Sodium Borohydride and Potassium Ferricyanide

“…Now the forgoing inference about the molecular structure of (3) (e.g., nonequivalent pterin/dedtc´ coordination as per Figure 6, as well as the energy information about its frontier orbitals ( Figure 9, Δ 1 =0.15 eV, Δ 2 =0.34 eV) may be utilized for understanding its reactivity data ( Figure 10 and Table 2) with a wide variety of substrates, affecting both the W(IV) and pterin centres [12][13][14][15]. They include an one-electron oxidant K 3 [Fe(CN) 6 ], an oxygen atom transfer agent (Me 3 N→O) and NaBH 4 which can affect the pyrazine part of the pterin ring [14]. Besides this, K 3 [Fe(CN) 6 ] and NaBH 4 fail to react with each other as evident from the absorption spectral studies (vide the supplementary information Figure S3).…”

“…In the above enzymes, this redox capability of the pterin moiety is matched by the ability of the metal centres to display multiple oxidation states [5]. This aspect has catalysed research work on the coordination chemistry of pteridines in general and pterins in particular [5][6][7][8]. Literature survey reveals the existence of only a limited amount of data on the synthetic tungstenpterin complexes [9] and provides with the impetus for the present endeavour using 2-pivaloylamino-6-acetonyl-isoxanthopterin (1, H 2 L) ( Figure 1).…”

Crystal Structure and DFT Calculation Studies of Ni (II) Cinnamaldehyde Thiosemicarbazone Complex

“…18 . The presence of multiple donor atoms within the same ligand multiplying coordination modes affects the properties of ligands and complexes 19,20 and in the same time thiosemicarbazones exist in equilibrium of various tautomers or conformers which greatly affects their chelating ability 21,22 . On the other hand Nickel can take up different coordination environments (such as octahedral, square-planar and tetrahedral).…”