Single and double deprotonated maleic acid in praseodymium hydrogenmaleateoctahydrate, Pr(C4O4H3)(3)(.)8H(2)O, and praseodymiummaleatechloride tetrahydrate, Pr(C4O4H2)Cl(.)4H(2)O

Single crystals of PT(C4O4H3)(3). 8H(2)O grew by slow evaporation of a solu tion which had been obtained by compound (P (1) over bar, Z = 2, a = 728.63 (3), b = 1040.23(3), c = 1676.05(8) pm, alpha = 72.108(2)degrees beta = 87. 774(2)degrees gamma = 70.851(2)degrees R-all = 0.0261) contains Pr3+ ions i n ninefold coordination of dissolving Pr(OH)3 in aqueous maleic acid. The t riclinic oxygen atoms which belong to two monodentate maleate ions and seve n H2O molecules. There is one further non-coordinating maleate ion and one crystal water molecule in the unit cell. Thermal treatment of Pr(C4O4H3)(3) . 8H(2)O leads first to the anhydrous compound which then decomposes to the respective oxide in two steps upon further heating. Evaporation of a solut ion of PT(C4O4H3)(3). 8H(2)O which contained additional Cl- ions yielded si ngle crystals of Pr(C4O4H2)Cl . 4H(2)O. In the crystal structure (monoclini c, P2(1)/c, Z=4, a=866.0(1), b=1344.3(1), c=896.9(l)pm, beta =94.48(2)degre es, R-all=0.0227), the Pr3+ ions are surrounded by nine oxygen atoms. The l atter belong to four H2O molecules and three maleate ions. Two of the latte r act as bidentate ligands.