The ligdnd N,N,N',N'-tetraethylpyridine- 2,6-dicarboxamide (Ly) reacts with trivalent lanthanide ions (Ln"') to give stable mononuclear triplestranded helical complexes [Ln(L9)J3 + (Ln = La to Lu).The crystal and molecular structures of [La(L9),](CI0,), 2.5C2H,CN (8) and [Eu(L9),](Tf0),. 2THF (9) show that the three ligand strands are each meridionally tricoordinated to produce a pseudo-tricapped trigonal prismatic arrangement of the nine donor atoms (six amide 0 and three pyridine N) around Ln"'. The distortions in the La"' coordination sphere of 8 are more significant than for Eu"' in 9, and the photophysical studies on Eu-doped (2 Yn) La, Gd, and Lu complexes confirm a better structural match of L9 for the heavy Ln"' ions. The separation of contact and pseudo-contact contributions to the induced lanthanide paramagnetic NMR shifts in [Ln(L9),13 + shows that the triple-helical structure is maintained in acetonitrile, buta minor structural change relative to that observed in the solid state occurs between Tb"' and Er"' leading to two distinct isostructural series for Ln = La-Tb and Ln = Er-Lu. The origin of this effect together with its consequences for the dynamic helical (P+M) interconversion and stability of [Ln(LY)J3+ in solution are discussed. A detailed investigation of the emission properties of [Ln(L9)J3 + (Ln = Eu, Tb) shows that mixed pyridinecarboxamide ligands can be used to simultaneously optimize the structural and photophysical properties in mononuclear triple-helical lanthanide building blocks.