Alkali metal induced structural changes in complexes containing anionic lanthanum aryloxide moieties. X-ray crystal structures of (THF)La(OAr)(2)(mu-OAr)(2)Li(THF), (THF)La(OAr)(2)(mu-OAr)(2)Na(THF)(2), and CsLa(OAr)4 (Ar=2,6-i-Pr2C6H3)

Reaction of La-2(OAr)(6) (1, Ar = 2,6-i-Pr2C6H3) with 2 equiv of LiOAr in THF produces the lanthanum tetrakis(aryloxide) salt (THF)La(OAr)(2)(mu-OAr)(2)Li(THF) (2). A similar reaction employing NaOAr leads to isolation of the analogous sodium salt (THF)La(OAr)(2)(mu-OAr)(2)Na(THF)(2) (3). 1 reacts with 2 equiv of cesium aryloxide in THF to yield the base-free cesium salt CsLa(OAr)(4) (4). Compounds 2, 3, and 4 have been characterized by H-1 NMR and IR spectroscopy, microanalysis, and single-crystal X-ray diffraction studies. The overall molecular geometry of 2 comprises a five-coordinate La metal center coordinated by four aryloxide ligands and one THF ligand in a somewhat distorted trigonal bipyramidal geometry and a three-coordinate Li cation which is coordinated to the oxygen atoms of two aryloxide ligands as well as a single THF ligand. La-O bond lengths average 2.208(3) and 2.384(3) Angstrom for terminal and bridging aryloxide Ligands, respectively, while the average Li-O(aryloxide) bond distance is 1.866(10) Angstrom. The molecular geometry of 3 is similar to that observed in 2, with a five-coordinate La metal center displaying a distorted trigonal bipyramidal geometry in which a THF ligand and an aryloxide ligand occupy axial positions. Two of the aryloxide ligands on the La metal center bridge to a sodium cation, which completes its coordination sphere by coordination of two additional molecules of THF. La-O bond lengths average 2.227(6) and 2.333(5) Angstrom for terminal and bridging aryloxide ligands, respectively, while the average Na-OAr bond distance is 2.350(6) Angstrom. The ipso carbon atom of one of the bridging aryloxide ligands is directed toward the fifth coordination site of the sodium cation at a distance of 3.085(9) Angstrom. The solid state structure of CsLa(OAr)(4), (4) features alternating tetrahedral [La(OAr)(4)](-) anions (La-O = 2.241(6) Angstrom (ave.)) and Cs+ cations held in an extended structure by means of cesium-pi-arene interactions, resulting in the formation of a quasi one-dimensional infinite chain structure. The cesium environment in 4 consists exclusively of multihapto Cs-C interactions (Cs-C range 3.696(7)-3.847(7) Angstrom), with no Cs-O contacts of less than 4.649 Angstrom. Crystal data for 2 (at -100 degrees C): orthorhombic space group Pbca, a = 20.091(3) Angstrom, b = 19.983(2) Angstrom, c = 27.288(2) Angstrom, V = 10956 Angstrom(3), Z = 8, D-calc = 1.202 g cm(-3). Crystal data for 3 (at -100 degrees C): orthorhombic space group Pbca, a = 26.035(3) Angstrom, b = 20.771(4) Angstrom, c = 26.441(3) Angstrom, V = 14299 Angstrom(3), Z = 8, D-calc = 1.174 g cm(-3). Crystal data for 4 (at -100 degrees C): monoclinic space group C2/c, a = 21.261(2) Angstrom, b = 22.616(3) Angstrom, c = 20.740(2) Angstrom, beta = 108.126(7)degrees, V = 9478 Angstrom(3), Z = 8, D-calc = 1.465 g cm(-3).