Outer-sphere coordination, N-coordination and O-coordination of the deprotonated saccharin in copper(II) saccharinato complexes. Implications for thesaccharinato carbonyl stretching frequency

Tetraaquabis(o-sulfobenzimidato-N)copper(II) reacts with neutral N-heterocy cles to form complexes in which the o-sulfobenzimide (saccharin) entity int eracts directly with the copper atom (through either the endocyclic nitroge n atom or the exocyclic oxygen atom) or indirectly, through coordinated wat er molecules. With 4-aminopyridine, it yields diaquatetrakis(4-aminopyridin e)copper(II)di(o-sulfobenzimidate)dihydrate, whose metal atom shows trans-N 4O2 octahedral coordination. The o-sulfobenzimidate anions interact with th e copper atom through the coordinated water molecules, and they link with t he lattice water molecules to furnish three-dimensional network architectur e. The reagent when treated with pyrazole affords tetrakis(pyrazole)bis[1,2 -benzisothiazolyl-3-olato 1,1-dioxide]copper(II); in this neutral compound, the metal atom and the o-sulfobenzimidate moieties are linked by covalent copper-oxygen bonds. The aqua complex with di-2-pyridylamine has the copper atom in a square-pyramidal configuration: one of the o-sulfobenzimidate li gands binds through its nitrogen atom whereas the other binds through the e xocyclic oxygen atom in aqua(di-2-pyridylamine)[1,2-benzisothiazolyl-3-olat o 1,1-dioxide](o-sulfobenzimidato-N)copper(II), which adopts a linear hydro gen-bonded chain motif. When treated with nicotinamide, tetraaquabis(o-sulf obenzimidato-N)copper(II) affords a monohydrated di(nicotinic acid) adduct, the amide group being oxidized to a carboxylic group. Tn this square-pyram idal complex, the molecules are linked by hydrogen bonds involving the two carboxylic acid ends into a linear chain that propagates along the a-e diag onal of the unit cell. The coordination mode of the o-sulfobenzimidate enti ties in the complexes is reflected in the stretching frequencies of the car bonyl groups, the respective band(s) being blue-shifted for N-coordination and red-shifted for O-coordination relatively to the o-sulfobenzimidate ion s, leading to the frequency order N-coordinated > uncoordinated > O-coordin ated. These shifts should be considered in vibrational frequency versus bon d order correlations. (C) 2001 Elsevier Science B.V. All rights reserved.