kRecently, a new class of free stable gas-phase dianions with general formula Ben-1 O-n(2-) was discovered experimentally and, moreover, a CuBe2O42- dianion as well as an unidentified half-integral m/z signal at 53.5 tentatively assigned to MgBe2O42- were detected. Here, the structural and electronic properties of these dianions are investigated by means of high-level ab initio calculations. It is demonstrated that the Ben-1On2- (n >= 4), MgBe2O42- and CuBe(2)O(4)(2-)dianions exhibit linear geometries and represent electronically stable dianions in the gas phase. Relations of these dianions to other known free stable dianions are discussed. (c) 2005 Elsevier B.V. All rights reserved.