Aqua bridge cleavage and metal ion extrusion by thiocyanate anions in a dicopper complex

Abstract

Reaction of the imidazolidinyl phenolate-based ligand, H 3L [(2-(2′-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine)] with Cu(ClO 4) 2·6H 2O produces an aqua-bridged cationic reactant complex [Cu 2(μ-H 2O)(μ-L)][ClO 4]·1.5H 2O ( 1·1.5H 2O). Solution phase interaction of 1·1.5H 2O with SCN − anions in 1:1 molar ratio leads to [Cu 2(μ-L)(NCS)]·2H 2O ( 2·2H 2O) that does not possess anymore the reactive aqua bridge but instead a terminal SCN − anion coordinated only to one Cu II ion. Whereas in 1:2 molar ratio, partial extrusion of the Cu II ions takes place to generate in situ [Cu(NCS) 3(OH 2)] − anions. These complex anions then quantitatively replace ClO 4 - anions in 1·1.5H 2O via ‘anion metathesis’ and concurrently remove the aqua bridge by coordination of linear MeCN to one of the Cu II ions to give [Cu 2(μ-L)(CH 3CN)][Cu(NCS) 3(OH 2)] ( 3). The literature unknown [Cu(NCS) 3(OH 2)] − anion forms an intimate H-bonded assembly with the cationic part of 3 to yield a novel [Cu 3] isosceles triangle. The precursor complex is known as antiferromagnetic whereas in 2·2H 2O, the Cu II ( S = 1/2) ions in a dinuclear entity exhibit ferromagnetic interactions ( J/k B = +15.0 K and g = 2.22) to yield an S T = 1 spin ground state in good agreement with the M versus H data below 8 K.