Three coordination modes of the pentadentate ligand 2,6-diacetylpyridinedisemicarbazone

The pentadentate ligand 2,6-diacetylpyridinedisemicarbazone, DAPSC, reacts with Cr(NO3)3·9H2O and forms two kinds of complexes. At pH=3, the ligand is singly-deprotonated and crystals of [Cr- (DAPSC---H)(H2O)2](NO3)2·H2O (Ia) are obtained. Evaporation of a solution at pH=0, yields crystals of [Cr(DAPSC)(H2O)2](NO3)3·2H2O (II) in which the ligand is fully protonated. The reaction of DAPSC with UO2(O2CCH3)2 in methanol, followed by crystallization of the product from DMSO yields crystals of [UO2(DAPSC---2H)(H2O)]·2DMSO (III) in which the ligand is fully deprotonated. Compound Ia is monoclinic, space group P21/n with a=11.746(1), b=14.752(2), c=11.866(1) Å,ß=105.53(2)°, V= 1981(1) Å3 and Z=4. Compound II is monoclinic, space group, P21/n with a=38.000(3), b= 14.939(2), c=8.233(1) Å, ß=96.12(2)°, V= 4647(1) Å and Z=8. Compound III is monoclinic, space group P21/n with a=18.048(2), b=15.207(2), c=8.842(1) Å,ß=97.72(2)°, V=2405(1) Å3 and Z=4. The structures were refined using 2084, 4169 and 2516 reflections to R values of 4.4%, 7.8% and 4.8% respectively.