Metal‐Controlled Anion‐Binding Tendencies of the Thiourea Unit of Thiosemicarbazones

Abstract

The terdentate ligand 3 (LH, 2-formylpyridine 4-thiosemicarbazone) forms with FeII and NiII 2:1 complexes of octahedral geometry of formula [MII(LH)2]2+. X-ray diffraction studies have shown that in both complexes the thiourea moieties of the coordinated thiosemicarbazones are exposed to the outside and are prone to establish hydrogen-bonding bifurcate interactions with oxoanions. However, spectrophotometric studies in CHCl3 solution have shown that only the poorly basic NO3 - ion is able to form authentic hydrogen-bond complexes with thiourea subunits, whereas all the other investigated anions (CH3COO-, NO2 -, F-) induce deprotonation of the N-H fragment. The extreme enhancement of the thiourea acidity is based on the coordinative interaction of the sulphur atom with the metal, which stabilises the thiolate form, and it is much higher than that exerted by any other covalently linked electron-withdrawing substituent, for example, --NO2.

Benzyl Dihydrazone versus Thiosemicarbazone Schiff Base: Effects on the Supramolecular Arrangement of Cobalt Thiocyanate Complexes and the Generation of CoN6 and CoN4S2 Coordination Spheres

“…Materials and Measurements: The Schiff bases were prepared by the previously reported methods and used without further purification . All other reagents and solvents for the synthesis and analysis were commercially available and used as received.…”

“…The second set of complexes, 4 and 5 , comprises the thiosemicarbazone derivatives [ N ‐phenylpyridine‐2‐carbaldehyde thiosemicarbazone (H L4 ) and pyridine‐2‐carbaldehyde thiosemicarbazone (H L5 ), respectively; see Scheme b], which are characterized by CoN 4 S 2 coordination spheres. As will be shown below, the structural differences and properties of the hydrogen‐bonded systems caused by substituent effects have been analyzed both qualitatively and quantitatively by the HS method, and DFT calculations suggested the presence of recently proposed antielectrostatic hydrogen bonding.…”

Enhanced Anion Binding from Unusual Coordination Modes of Bis(thiourea) Ligands in Platinum Group Metal Complexes

“…[7][8][9][10][11] We are particularly concerned with the understanding and use of structure, conformational aspects and supramolecular interactions to modulate the ability of the receptors to bind different anions. A particularly important class of anion receptors are those based on thiourea [2,[12][13][14][15][16][17][18][19][20][21] functionalities because of their ability to form strong hydrogen-bond complexes with anions, and their synthetic accessibility. Simple bis(thioureas) have been shown to bind glutarate, dihydrogenphosphate and acetate in DMSO [22][23][24][25][26] and have been incorporated into monolayers to mimic ion-channel sensing of hydrophilic anions.…”

Enhanced Sensitivity and Selectivity of Chemosensor for Malonate by Anchoring on Gold Nanoparticles

“…A bis-thiourea subunit can donate two hydrogen bonds according to a bifurcate mode and is therefore an ideal receptor for Y-shaped anions, just as dicarboxylate anions. 20 Shao and her co-workers 21 pointed out that the selectivity for special analyte of the host molecule would be rationalized on the basis of not only the guest basicity but also shape complementarity between the host and the anionic guests. Association constants of receptor 4 for dicarboxylate anions which is based on a 1∶1 (anion∶receptor) stoichiometric model of bis-anions were calculated by using EQNMR, a least squares fitting software package, and were displayed in Table 1 with a good correlation coefficient (R＞0.98).…”