Syntheses, lanthanide quantitative analyses, mass spectrometry and luminescence spectroscopy, and decay dynamics of crystals containing pentanuclear hetero-lanthanide(IH) nanoclusters [(Ln ' (5-x)Ln(x))(NO3)(6)(mu (5)-OH)(mu (4)-L)(2)] (0 less than or equal to x less than or equal to 5), Ln ' = Eu or Tb; Ln = La-Nd, Sm-Ho (hereafter Ln ' (5-x)Ln(x)) were undertaken in search of information on factors governing self-assembly processes by which the clusters are formed and electronic interactions within and between them. The data obtained are consistent with the self-assembly of Ln ' (5-x)Ln(x), nanoclusters being a concerted process featuring a profound expression of complementarity among mutually bridging [Ln(mu (4)-L](-) and [Ln(NO3)(2)](+) components. The energy transport regime in crystals of Eu(5-x)Ln(x) is in the dynamic regime when x = 0 or Ln = La and, at 293 K, Ln = Dy, despite the presence of two crystallographically different Eu3+ coordination environments which give rise to a doublet in the excitation and emission spectra of Eu3+(D-5(0)). The luminescence decay behavior of Eu3+(D-5(0)) in Eu(5-x)Ln(x) (Ln = Dy (for 77 K), Sm) is intermediate between the static and dynamic limits and reveals extensive electronic coupling among lanthanide ions, including many-body processes at relatively high Dy3+ or Sm3+ concentrations.