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Metal‐Controlled Anion‐Binding Tendencies of the Thiourea Unit of Thiosemicarbazones
Author(s) -
Amendola Valeria,
Boiocchi Massimo,
Fabbrizzi Luigi,
Mosca Lorenzo
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200800801
Subject(s) - thiourea , chemistry , deprotonation , substituent , metal , hydrogen bond , covalent bond , ligand (biochemistry) , semicarbazone , crystallography , octahedron , inorganic chemistry , medicinal chemistry , ion , molecule , crystal structure , organic chemistry , biochemistry , receptor
The terdentate ligand 3 (LH, 2‐formylpyridine 4‐thiosemicarbazone) forms with Fe II and Ni II 2:1 complexes of octahedral geometry of formula [M II (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 CHCl 3 solution have shown that only the poorly basic NO 3 − ion is able to form authentic hydrogen‐bond complexes with thiourea subunits, whereas all the other investigated anions (CH 3 COO − , NO 2 − , 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, NO 2 .