COMPLEXES WITH NEW CHELATE ANIONIC LIGANDS FORMED BY NUCLEOPHILIC ADDITION IN COPPER(II) COORDINATION SPHERE
Ivan Potocnak, Michal Dunaj-Jurco and Dusan Miklos
Department of Inorganic
Chemistry, Slovak Technical University, 81237 Bratislava,
Slovakia,
dunaj@cvtstu.cvt.stuba.sk
Keywords: crystal
structures, nucleophilic addition, carbon-activation, methanol,
water, nitrosodicyanomethanide, pseudohalogenide, copper(II)
Structures of four Cu(II) compounds with new chelate anionic ligands are presented. General formula of three compounds is [Cu(bipy)(mcoe)X], where bipy = 2,2'-bipyridine, X = NCO-, N(CN)2- [1] and ONC(CN)2- [2]; mcoe is the anionic chelate ligand methyl(2-cyano-2-imidoxy ethaneimidate), [(ON)(NC)C-C(NH)(OCH3)]- formed by a nucleophilic addition of the methanol molecule to the -carbon, which is coordination activated, of an ndcm anion (ndcm = nitrosodicyanomethanide, ONC(CN)2-):
Cu(NO3)2 + bipy + NaONC(CN)2 + KX + MeOH ---> [Cu(bipy)(mcoe)X] + NaNO3 + KNO3
The coordination polyhedra around the Cu atoms are distorted tetragonal pyramids. The Cu atoms are coordinated by four N atoms of bipy and mcoe ligands forming two five-membered metallocycles in the equatorial plane. Apical positions are occupied by the N atom of the anion X. The crystal structures are formed by discrete molecules.
The formula of the fourth compound is [Cu(bipy)(coe)], where coe is the anionic chelate ligand 2-cyano-2-imidoxy ethaneimidate, [(ON)(NC)C-C(NH)(O)]2-. It is formed by a nucleophilic addition of the hydroxo-anion from a water molecule to the -carbon, which is coordination activated, of the ndcm. The loss of a proton from the water molecule can be explained by hydrolysis of the C(CN)3- anion and succeeding liberation of HC(CN)3 from the reaction mixture:
Cu(NO3)2 + bipy + KC(CN)3 + NaONC(CN)2 + H2O --->
[Cu(bipy)(coe)] + NaNO3 + KNO3 + HC(CN)3
The coordination polyhedron around the Cu atom is a distorted square. The Cu atom is coordinated by four N atoms forming two five-membered metallocycles. The crystal structure consists of discrete molecules which are connected by weaker contacts between copper and oxygen atoms to infinite chains parallel with c (Cu-O1i = 2.503(3), Cu-O2ii = 2.801(3)A; i= -x, -y, -z+1; ii= -x+1, -y, -z+1). This way the coordination polyhedron is completed to an elongated tetragonal bipyramid with the {CuN4O*O*} chromophore; the angle O1i-Cu-O2ii being 167.9(1).
Inspection of the bond distances in mcoe and coe indicates a strongly delocalized p-bonding system. This is also supported by the fact that the anions are almost planar and the values of angles are close to 120o.
Calculated Wiberg (bond-order) indices show that due to the conjugation the bonds within metallocycles in mcoe and coe exhibit partially multiple character. The N-H bonds are polar and the hydrogen atoms are acidic what explains unusually short N-H bonds.