A Proposal for Positive Cooperativity in Anion-Cation Binding in Yttrium and Lutetium Complexes Based on o-Amino-Substituted Phenolate Ligands. On the Way to Coordination Polymers by Self-Assembly. Molecular Structures of [ClLu(OAr)(3)Na] (X-ray) and [ClY(OAr')(3)Y(OAr')(3)Na] (X-ray and (89)Y-NMR).

Abstract

Unique hetero(poly)metallic complexes [ClM(OAr)(3)Na] (M = Lu (3a), Y (3b)) and [ClY(OAr')(3)Y(OAr')(3)Na] (4) containing the bis (OAr = OC(6)H(2)(CH(2)NMe(2))(2)-2,6-Me-4) and mono (OAr' = OC(6)H(4)(CH(2)NMe(2))-2) o-amino-substituted phenolate ligands have been synthesized and characterized by NMR ((1)H, (13)C, and (89)Y) and X-ray structure determinations (3a and 4). Crystals of 3a are triclinic, space group P&onemacr;, with unit cell dimensions a = 10.706(1) Å, b = 14.099(2) Å, c = 18.882(3) Å, alpha = 93.48(1) degrees, beta = 99.49(1) degrees, gamma = 108.72(11) degrees, and Z = 2. The chlorine, lutetium, and sodium atoms in 3a lie on a pseudo-3-fold axis ( angleCl-Lu.Na = 177.82(5) degrees ) around which the three phenolate ligands are arranged in such a way that a "propeller-like" molecule with screw-type chirality results. Crystals of 4 are triclinic, space group P1, with unit cell dimensions a = 11.411(4) Å, b = 13.325(4) Å, c = 13.599(4) Å, alpha = 88.91(3) degrees, beta = 65.44(2) degrees, gamma = 72.77(3) degrees, and Z = 1. In 4 the chlorine, the two yttrium and the sodium atoms lie on a pseudo-3-fold axis (Cl-Y(1).Y(2).Na: angleCl-Y.Y = 179.36(8) degrees and angleY.Y.Na = 178.38(10) degrees ) around which the six phenolate ligands are arranged in two shells of three ligands. One shell bridges the yttrium atoms in an asymmetric fashion, while the second shell bridges the second yttrium and the sodium atom, resulting in two shells of opposite screw-type chirality. (1)H, (13)C, and (89)Y (for 3b and 4) NMR confirmed that the structures found for 3a and 4 in the solid state are retained in solution. For 4 (89)Y NMR showed two separate resonances (202.4 and 132.4 ppm), with (2)J(YY) = 0.4 Hz. The formation of 3a and 3b is described as resulting from positive cooperativity in anion-cation bonding: coordination of chloride anion to a neutral metal tris(phenolate) leads to preorganization of available binding sites in the resulting anionic complex for the binding of the sodium cation. In 4 this cooperativity is the driving force for the self-assembly of an anionic bimetallic molecular structure with available, preorganized binding sites for the capture of the cation. A proposal is made to use these observations for the possible synthesis of new coordination polymers.