Lanthanide(III) Methylsquarates: Synthesis and X-ray Structures

Abstract

Reaction of 3-methyl-4-hydroxycyclobut-3-ene-1,2-dione (methylsquarate) with LaCl3·7H2O and M(NO3)3·xH2O (M = Eu, Gd, and Tb) in alcoholic solutions afforded the polymeric complexes {La[μ3-(CH3C4O3)][(H2O)6][Cl2]·H2O}n (1), {Eu[μ-(CH3C4O3)3][(H2O)2]}n (3), {Gd[μ-(CH3C4O3)2][(H2O)4][NO3]·H2O}n (4), and {Tb[μ-(CH3C4O3)2][(H2O)4][NO3]·H2O}n (5), respectively and with La(NO3)3·6H2O, the monomer La(CH3C4O3)3(H2O)6·H2O (2). Complex 1 crystallizes in the orthorhombic space group Pca21, with a = 13.239(2) Å, b = 7.836(1) Å, c = 14.209(2) Å, and Z = 4. The lanthanum atom is nine-coordinate adopting a monocapped square antiprismatic geometry, being bonded to three μ3-bridging methylsquarate and six pendant aqua ligands and forming cationic polymer sheets which are intercalated by chloride ions and water of crystallization. Complex 3 is a 3-dimensional neutral network polymer in which the methylsquarate ligands are μ-1,3-bridging and the europium atoms adopt a bicapped trigonal prismatic geometry. 3 crystallizes in the orthorhombic space group Pbna with a = 8.713(1) Å, b = 13.115(1) Å, c = 15.253(1) Å, and Z = 4. The gadolinium and terbium complexes, 4 and 5, are isomorphous cationic sheet polymers with the methylsquarate ligand again adopting a μ-1,3-bridging role and with the metal having square antiprismatic geometry. Adjacent sheets are arranged so as to form channels within which the nitrate anions and water molecules are located. Complex 4 crystallizes in the monoclinic space group P21/c, with a = 14.543(2) Å, b = 8.396(1) Å, c = 15.251(2) Å, β = 109.37(1)°, and Z = 4. The monomer 2 crystallizes in the space group P21/c with a = 10.438(2) Å, b = 14.813(2) Å, c = 15.151(2) Å, β = 108.21(1)°, and Z = 4. The lanthanum atom is nine-coordinate adopting a monocapped square antiprismatic geometry with each metal atom being coordinated to three methylsquarate and six aqua ligands. In all of the polymeric species there is a pattern of delocalization which extends to include adjacent metal centers.