Two novel indium(III) phosphonates, [In-2(t-BuPO3H)(4)(phen)(2)Cl-2] (1) and [In-3(C5H9PO3)(2)(C5H9PO3H)(4)(phen)(3)]center dot NO3 center dot 3.5H(2)O (2) with phen = 1,10-phenanthroline, have been synthesized by solvothermal reactions involving indium(III) salts and organo-phosphonic acids. 1 is a dinudear compound where the two indium centers are bridged by a pair of isobidentate phosphonate ligands, [t-BuP(O)(2)OH](-), resulting in an eight-membered (In2P2O4) puckered ring. Compound 2 is trinuclear; the In-3 platform is held together by two bicapping tripodal phosphonate ligands from the top and bottom of the indium plane. In addition, two bridging monoanionic phosphonate ligands serve to bind two pairs of indium centers. Both 1 and 2 also contain monodentate, monoanionic phosphonate ligands. The solid-state MAS P-31 NMR spectrum of complex 1 shows two signals at 21.9 and 29.3 ppm. Compound 2 contains signal maxima at 25.8 and 28.9 ppm, with a shoulder at 31.5 ppm. Room temperature solid-state fluorescence spectra of 1 and 2 are characterized by strong emission bands at 385 um (lambda(ex) = 350 nm) and 395 nm (lambda(ex) = 350 nm), respectively, which are red-shifted with respect to the emission of free phenanthroline.