We present here the first examples of lanthanide ion complexes with only isophthalic acid or thiophenylisophthalic acid ligands. The complexes of isophthalic acid with Eu3+ (1) and Tb3+ (2) and the moderately soluble complexes of 5-thiophen-3-ylisophthalate with Eu3+ (3), Gd3+ (4), and Tb3+ (5) were isolated as single crystals through gel crystallization. X-ray diffraction studies confirm the cross-linking structure of these complexes, which, in case of the thiophenyl derivatives, results in low solubility in common solvents. The two-dimensional isophthalato complex of Eu3+ (1) crystallizes in the C2/c space group, with a = 22.154(4), b = 12.649(3), and c = 15.921(3) A, P = 112.34(3)degrees, and V=4126.7(14) angstrom(3), while the one-dimensional Tb3+ complex of the same ligand, 2, crystallizes in the space group P2(1)/c with a = 11.921(2), b = 10.838(2), and c = 17.499(4) angstrom, beta = 92.44(3)degrees, and V = 2258.9(8) angstrom(3). The thiophenylisophthalato complexes of Eu3+ (3) and Gd3+ (4) are two-dimensional and crystallize in the P2/n space group with parameters for 3 of a = 14.139(3), b = 10.684(2), and c = 15.138(3) angstrom, beta = 102.51(3)degrees, and V = 2232.3(8) angstrom(3) and parameters for 4 of a = 14.1195(13), b = 10.6594(10), and c = 15.1149(14) angstrom, beta = 102.529(2)degrees, and V = 2220.7(4) angstrom(3), while the Tb3+ complex, 5, also two-dimensional, crystallizes in the P (1) over bar space group with a = 11.051(2), b = 14.528(3), and c = 15.041(3) angstrom, alpha = 77.63(3), beta = 87.86(3), and gamma = 83.51(3)degrees, and V = 2343.48 angstrom(3). All complexes of Eu3+ and Tb3+ luminesce in aqueous solution, and the luminescence lifetimes and quantum yields are 123.8 +/- 7.4, 0.14% (1), 475.1 +/- 14.5, 3.58% (3), 129.3 +/- 3.5, 0.19% (4), and 213.9 +/- 2.2 mu s, 7.46% (5).