The synthesis, structure, and characterization of a [Yb(Tren-Me3,2-HOPO)(H2O)(2)] complex are reported. As a result of its Yb-III emission in the near-infrared region, sensitized by the Me-3,2-HOPO chromophore, this complex can be utilized for the first time to determine the hydration state, q, via the luminescence lifetimes and hence the solution structure of these Me-3,2-HOPO-type ligands, which have attracted significant interest in complex with Gd-III as possible next-generation magnetic resonance imaging contrast agents.