Pseudohalide complexation by manganese 12-metallacrowns-4 complexes

The reaction of manganese chloride, sodium or potassium thiocyanate and salicylhydroxamic acid in dimethyl form amide methanol solution leads to the formation of the 12-membered metallacrowns [Na(dmf)(2)](2)(SCN)(2){[12-MCMn(III)N(shi)-4](dmf)(4)} (1) and [K(dmf)(2)](2)(SCN)(2){[12-MCMn(III)N(shi)-4](dmf)(4)} (2). The crystal structure analyses of 1 and 2 show that pseudohalide ligands are bound to the ring manganese ions through the N atoms, while the alkaline ions, Na+ or K+ are accommodated at the cavity of the metallacrown ring. The alkali cations are bound to four oxygen atoms of the metallacrown ring and a single axial dmf. The binding of the pseudohalides (SCN-, OCN- and N-3(-)) to the manganese ions of the metallacrown ring is very similar to that observed previously for (NaBr)(2) and (KBr)(2) metallacrowns; however, unlike the previously described halide complexes, the thiocyante does not form a bridge between the ring and central metal ions. Furthermore, the pseudohalide ligands do not form a second bond to an adjacent metallacrown, thus, single metallacrowns are isolated rather than chains or columns. The affinity of thiocyanate for the metallacrown is approximately equal to chloride and significantly greater than bromide. (C) 2002 Elsevier Science B.V. All rights reserved.