ic034922p_si_002.cif (198.24 kB)
Attempted Syntheses of Lanthanide(III) Complexes of the Anisole- and Anilinosquarate Ligands
dataset
posted on 2003-12-15, 00:00 authored by Patrice M. T. Piggot, Lincoln A. Hall, Andrew J. P. White, David J. WilliamsThe polymeric lanthanide complexes {Ln(μ-CH3OC6H5C4O3)(CH3OC6H5C4O3)2 (H2O)4·xH2O}n [Ln = La (1), Eu
(2), Gd (3)], formed from the reaction of aqueous solutions of anisolesquarate and Ln(NO3)3·xH2O, are all structurally
similar with only subtle differences between the lanthanum complex and the isomorphous pair of europium and
gadolinium analogues. The lanthanum atom in 1 has a square antiprismatic coordination geometry comprising two
pendant and two μ-1,3-bridging anisolesquarate groups and four aqua ligands. Complexes 2 and 3 have two
independent metal atoms in their asymmetric units compared to one for the lanthanum complex. However, the
gross structures of 1−3 are essentially the same. The asymmetric unit of the terbium complex {(CH3OC6H5C4O3)3Tb(H2O)4(μ-CH3OC6H5C4O3)(CH3OC6H5C4O3)2Tb(H2O)5}·H2O (4) contains two independent binuclear units which
hydrogen bond to form an extended structure very similar to those of 1−3. The ionic polymers {[Ln(μ2-C4O4)(H2O)6][C6H5NHC4O3]·4H2O}n [Ln = Eu (5), Gd (6), Tb (7)] result from the incomplete hydrolysis of the anilinosquarate
ion during the attempted synthesis of Eu(III), Gd(III), and Tb(III) anilinosquarate complexes. However, complete
hydrolysis of the substituent is accomplished by La(III) ions, and the neutral polymer {La2(μ2-C4O4)2(μ3-C4O4)(H2O)11·2H2O}n (8) is formed. In complexes 5−7, the central lanthanide atom has a square antiprismatic geometry,
being bonded to two μ-1,2-bridging squarate and six aqua ligands. Two anilinosquarate counteranions participate
in second-sphere coordination via direct hydrogen bonding to aqua ligands on each metal center. These counteranions,
and the included waters of crystallization, serve to link neighboring cationic polymer chains via an extensive array
of O−H···O hydrogen bonds to form a 3-dimensional network. The polymeric lanthanum complex 8 contains two
different metal environments, each having distorted monocapped square antiprismatic geometry. For one lanthanum
atom the coordination polyhedron comprises five aqua and four squarate ligands, while for the other the polyhedron
consists of six aqua and three squarate ligands; in each case one of the aqua ligands occupies the capping
position. The squarate ligand exhibits two coordination modes in 8 (μ-1,2- and μ-1,3-bridging), and neighboring
polymer chains are cross-linked by hydrogen bonds to form a 3-dimensional network.