Compounds formed from the reaction of N,N,N,N-tetramethylsuccinamide (TMSA) with trivalent lanthanide salts possessing the poorly coordinating counteranions triflate (CF3SO3-) and perchlorate (ClO4-) have been prepared and examined. Structural features of these Ln-TMSA compounds have been studied in the solid phase by thermogravimetric analysis, infrared spectroscopy, and, in selected cases, by single-crystal X-ray diffraction and in solution by infrared spectroscopy. Eight-coordinate compounds, [Ln(TMSA)(4)](3+), derived from coordination of four succinamide ligands to the metal ion could be formed with all lanthanides examined (Ln = La,Pr,Nd, Eu, Yb, Lu). Structural analyses by single-crystal X-ray diffraction were performed for the lanthanide triflate salts Ln(C8H16N2O2)(4)(CF3SO3)(3): Ln = La, compound 1, monoclinic, P2(1)/n, a = 11.0952623 Angstrom, b = 19.2672(2) Angstrom, c = 24.9759(3) Angstrom, beta = 90.637(1)degrees Z = 4, D-calcd = 1.586 g cm(-3); Ln = Nd, compound 2, monoclinic, C2/c, a = 24.6586(10) Angstrom, b = 19.3078(7) Angstrom, c = 11.1429(4) Angstrom, beta = 90.450(1)degrees, Z = 4, D-calcd = 1.603 g cm(-3); Ln = Eu, compound 3, monoclinic, C2/c, a = 24.4934(2) Angstrom, b = 119.3702(1) Angstrom, c = 11.1542(1) Angstrom, beta = 90.229(1)degrees Z = 4, D-calcd = 1.617 g cm(-3); Ln = Lu, compound 5, monoclinic, C2/c, a = 24.2435(4) Angstrom, b = 19.6141(2) Angstrom, c ;= 11.2635(1) Angstrom, beta = 90.049(1)degrees Z = 4, D-calcd = 1.626 g cm(-3). X-ray analysis was also carried out for the perchlorate salt: Ln = Eu, compound 4, triclinic, P1, a = 10.9611(2) Angstrom. b = 14.6144(3) Angstrom, c = 15.7992(2) Angstrom, a = 106.594(1)degrees, beta = 91.538(1)degrees gamma = 90.311(1)degrees Z = 2, D-calcd = 1.561 g cm(-3). In the presence of significant amounts of water, 7-coordinate compounds with mixed aquo-TMSA cation structures [Ln(TMSA)(3)(H2O)(3+) (Ln = Yb)] and [Ln(TMSA)(2)(H2O)(3)](3+) (Ln = La, Pr, Nd, Eu, Yb) have been isolated with structural determinations by single-crystal X-ray diffraction obtained for the following species: Yb(C8H16N2O2)(3)(H2O)(CF3SO3)(3), compound 6, monoclinic, P2(1)/n, a = 8.9443(3) Angstrom, b = 11.1924(4) Angstrom, c = 44.2511(13) Angstrom, beta = 93.264(1)degrees, Z = 4, D-calcd = 1.735 g cm(-3); Yb(C8H16N2O2)(3)(H2O)(ClO4)(3), compound 7, monoclinic, Cc, a = 19.2312(6) Angstrom, b = 11.1552(3) Angstrom, c = 19.8016(4) Angstrom, beta = 111.4260(1)degrees, Z = 4, D-calcd = 1.690 g cm(-3); Yb(C8H16N2O2)(2)(H2O)(3)(CF3SO3)(3), compound 8, triclinic, P1, a = 8.6719(1) Angstrom, b = 12.2683(2) Angstrom, c = 19.8094(3) Angstrom, alpha = 75.815(1)degrees, beta = 86.805(1)degrees, gamma = 72.607(1)degrees Z = 2, D-calcd = 1.736 g cm(-3). Unlike in the analogous nitrate salts, only bidentate binding of the succinamide ligand to the lanthanide metal is observed. IR spectroscopy studies in anhydrous acetonitrile suggest that the solid-state structures of these Ln-TMSA compounds are maintained in solution.