Electrospray ionization mass spectrometry (ESI MS) is a powerful technique for the study of coordination complexes because of its ability to analyze solution systems involving very low concentrations of metal complexes. In this work, the coordination chemistry of Be ions with a selection of well-known 1,3-diketone and related 1,2-diketone ligands has been investigated using ESI MS. With acetylacetone (Hacac), a range of acac-containing ions is observed, including [Be(acac)(2)H](+), [Be(acac)(MeOH)(n)](+) (n = 1, 2), and polynuclear species such as the dinuclear [Be-2(acac)(3)](+) and trinuclear [Be3O(acac)(3)](+). Density functional theory calculations indicate that the latter species has a central Be-3(mu(3)-O) core, with each Be chelated (as opposed to being bridged) by an acac ligand. The effect of changing the substituents on 1,3-diketone was explored by an investigation of mixtures of Be2+ with other 1,3-diketones such as dibenzoylmethane (Hdbm), where the [Be(dbm)(2)H](+) ion showed a lesser tendency to undergo fragmentation and aggregation processes. Comparisons with the corresponding aluminum acetylacetone system were also made. In contrast, mixtures of Be2+ and the 1,2-diketones diacetyl and phenanthrenequinone showed poor metal-ligand interactions. Be2+ interacted with the 1,2-diketone benzil [PhC(O)C(O)Ph], forming the [Be(benzil)(n)](2+) (n = 2-4) ions. The synthesis (from BeCl2) and X-ray structures of the dibenzoylmethanato (dbm) complex Be(dbm)(2) and the benzil complex [BeCl2(benzil)] are also reported.