INFLUENCE OF THE BRIDGING GROUP OF CROSS-CONJUGATED NITROGENOUS BASESON THE SPECTRA AND STRUCTURE OF SOLVATOCHROMIC MIXED-LIGAND COPPER(II) CHELATES CONTAINING BETA-KETOENOLS

The concomitant reaction of copper(II) with a heterocyclic nitrogenous cross-conjugated Lewis base (2,2'-dipyridyl ketone, dpk, or 2,2'-dipy ridylamine, dpamH) and the anion of a 2-substituted 1,3-dione, beta(-) , e.g. X-acac(-) (X = H, Me, Cl, CN, NO2) affords mixed-ligand chelate s. The composition and structure of the chelates depend on the group l inking the pyridyl rings. Chelation renders the 2,2'-dipyridyl ketone susceptible to nucleophilic attack by protic molecules. It also depend s on the group attached to the beta-dionato moiety since electron attr acting substituents facilitate ligation of a water molecule when the 2 ,2'-dipyridylamine is present. Spectroscopic observations indicated sq uare pyramidal or distorted tetragonal stereochemistries of the ensuin g mixed-ligand chelates with the carbonyl oxygens and the pyridyl nitr ogens forming the basal plane. Confirmation was acquired by X-ray stru cture determination of representative chelates. The compound [Cu(NC-ac ac)dpamH(H2O) OClO3] crystallizes in the Pnma space group with Z = 8 ( i.e. four molecules per cell), a = 17.996(1) Angstrom, b = 13.972(1) A ngstrom,-c = 7.801(1) Angstrom. The copper atom is 2.401(3) Angstrom f rom the oxygen of the water molecule and 2.60(2) Angstrom from an oxyg en atom of the ClO4- group. The chelate [Cu(NC-acac)dpC(OH)OCH3(OClO3) , resulting from the addition of methanol to the carbon atom bridging the pyridyl rings, crystallizes in the P2(1)/n space group with a = 10 .661(1) Angstrom, b = 14.987(2) Angstrom, c = 13.963(1) Angstrom, beta = 110.57(3)degrees, Z = 4. An oxygen of the ClO4- group is in apical position, and it is 2.634(8) Angstrom from the copper atom. The etheri c oxygen is distanced 2.615(2) Angstrom from the copper atom, and the O-Cu-O angle of these weak bonds is only 154.4(2)degrees. In these che lates the nitrogenous bases adopt the boat conformation with the pyrid yl rings forming dihedral angles of approximately 33 degrees.