CRYSTAL-STRUCTURE AND PROPERTIES OF THE NICKEL(II) COMPLEX OF A DIOXO[13]ANEN(4) LIGAND BEARING QUINOLINE PENDANTS - STRIKING DIFFERENCES BETWEEN THE NICKEL(II) AND COPPER(II) ANALOGS OF EN(4)=1,4,7,10-TETRAAZACYCLOTRIDECANE-11,13-DIONE)

The NL(II) complex of dioxo[13]aneN(4) ligand bearing two 8-methylquin oline as additional donor pendants (H(2)L) has been prepared and its c rystal structure and properties studied. The Ni-II atom is in square-p lanar coordination whilst the two 8-methylquinoline pendants are not c oordinated. In contrast, in the Cu(II) analogue CuL(2), the Cu(II) ato m is five coordinate and forms a distorted square-pyramidal configurat ion with one of the quinoline pendants coordinated. Electrochemical st udies of 1 in aqueous solution revealed that L can further stabilize t he trivalent state of nickel (E(1/2)(+2-->+3) = 0.60 V versus SCE] com pared with unsubstituted L degrees [E(1/2)(+2-->+3) = 0.92 V versus SC E]. This behaviour is also in contrast with that observed for CuL unde r the same conditions. An unusual red-shift was observed for the maxim um absorption band of the electronic spectrum of NiL in comparison to that of NiL degrees. Copyright (C) 1996 Elsevier Science Ltd