The synthesis and characterization of several potentially heptadentate N4O3 Schiff bases and amine phenols, as well as a series of their mononuclear and dinuclear complexes with indium and the lanthanides are reported. Schiff bases containing imidazolidine rings were the products of the known condensation reaction of triethylenetetramine with 3 equiv of 5-substituted salicylaldehydes to form H(3)api (5-H-substituent), H(3)Clapi (5-Cl-substituent), or H(3)Brapi (5-Br-substituent); KBH4 reduction of these Schiff bases gave the appropriate isomeric N4O3 amine phenols H-3(1,2,4-btt) and H-3(1,1,4,-btt), as well as an acetone adduct, H-3(1,2,4-ahi). The Schiff bases reacted with 1 equiv of a lanthanide (Ln(3+)) nitrate to produce mononuclear nine-coordinated [Ln(H(3)Xapi)-(NO3)(3)] complex wherein the ligand adopts a tridentate capping coordination mode, whereas the amine phenols formed mononuclear seven-coordinate complexes with the lanthanides and indium; homodinuclear complexes [LnL]2 were also obtained with the Schiff bases. The X-ray structures of the Schiff bases H(3)api and H(3)Clapi, the mononuclear amine phenol complexes Yb(1,2,4-btt) . 0.5CH(3)OH and In(1,1,4-btt), and the homodinuclear Schiff base complex [La(Brapi)](2) . 2CHCl(3) have been determined. Crystals of H(3)api (C27H30N4O3) are monoclinic, space group P2(1)/a, a = 19.281(2) Angstrom, b = 5.774(3) Angstrom, c = 21.999(2) Angstrom, beta = 97.85(1)degrees, Z = 4; those of H(3)Clapi (C27H27Cl3N4O(3)) are orthorhombic, Pnmn, a = 11.398(4) Angstrom, b = 21.486(3) Angstrom, c = 10.942(4) Angstrom, Z = 4; those of [La(Brapi)]2 . 2CHCl(3)(C56H50Br6Cl6La2N8O6) are monoclinic, space group C2/c, a = 22.336(1) Angstrom, b = 14.770(2) Angstrom, c = 22.647(2) Angstrom, beta = 116.855(5)degrees, Z = 4; those of Yb(1,2,4-btt). 0.5CH3OH (C27.5H35N4O3.5Yb) are monoclinic, P2(1)/a, a = 12.798(2) Angstrom, b = 19.671(6) Angstrom, c = 21.129(2) Angstrom, beta = 91.895(9)degrees, Z = 8; and those of In(1,1,4-btt) (C27H33InN4O3) are triclinic, space group P (1) over bar, a = 12.771(3) Angstrom, b = 18.994(4) Angstrom, c = 11.450(2) Angstrom, alpha = 105.71(1)degrees, beta = 99.73(1)degrees, gamma = 89.21(2)degrees, Z = 4. The structures were solved by direct (organic compounds and La complex) or Patterson (Yb and In complexes) methods and were refined by full-matrix least-squares procedures to R = 0.034, 0.035, 0.042, 0.031, and 0.029 for 2386, 1444, 2800, 7570, and 8682 reflections with I greater than or equal to 3 sigma(I), respectively. Both amine phenol complexes Yb(1,2,4-btt) and In(1,1,4-btt) have pentagonal bipyramidal coordination geometry around the metal ions, which are each coordinated by N4O3 donor sets. The structure of [La(Brapi)](2) reveals that the two ligands bridge the two metal ions forming an LM(2)L sandwich structure. The dinuclear [LaBrapi](2) has a square antiprismatic geometry around each lanthanum atom. Each La atom is coordinated by an N4O4 donor set, N2O from each ligand and two bridging phenolate O atoms, one from each heptadentate ligand with a La-La separation of 4.023(1) Angstrom. Autoconversion of the Schiff base complexes wherein the ligand is tridentate to the sandwich structure dinuclear complexes, together with the evidence of variable-temperature H-1 NMR of [La(Clapi)](2) in DMSO-d(6) indicates that these new sandwich [LnL](2) complexes are quite stable and extremely rigid. ?