The reaction of 10-bromo-9-oxa-10-boraanthracene with the tetrakis(tetrahydrofuran) lithium salt of dimesityl-1,8-naphthalenediylborate in diethyl ether affords 1-(dimesitylboryl)-8-(10'-bora-9'-oxaanthryl) naphthalene (2). This diborane reacts with [Me3SiF2][S(NMe2)(3))] to afford the anionic complex [2-mu(2)-F](-), which has been isolated as a [S(NMe2)(3)](+) salt. The cyclic voltammograms of diborane 2 as well as 1-(dimesitylboryl)-8-(10'-bora-9'-thiaanthryl) naphthalene (1) exhibit two reversible reductions at E-1/2 = -2.200 and -2.566 V (vs FcH/FcH(+)) for 1 and E-1/2 = -2.248 and -2.620 V (vs FcH/FcH(+)) for 2 corresponding to the sequential reduction of the two boron centers. These two waves simultaneously disappear upon fluoride addition, thus indicating the formation of fluoride chelate complexes [1-mu(2)-F]-and [2-mu(2)-F](-). To identify the origin of the high fluoride affinity displayed by these diboranes, the structures of 2 and [2-mu 2-F]-have been studied experimentally and computationally. The crystallographic studies show that the structure of 2 is distorted, thus indicating the presence of important steric repulsions between the neighboring boryl moieties. By contrast, the structure of the anionic complex [2-mu 2-F]-is much more sterically relaxed than that of 2, as indicated by a reduction of the B-B distance from 3.279(4) angstrom in 2 to 2.922(7) angstrom in [2-mu(2)-F](-). The structural results suggest that the high fluoride affinity displayed by 2 results, at least in part, from the relief of steric repulsions induced by fluoride binding. Finally, the nature of the bonding as well as the strength of the interactions involved in the B-F-B bridge of [2-mu 2-F]-has been studied using density functional theory calculations and Atoms-In-Molecules analyses. These calculations indicate that the enthalpic gain associated with the formation of two B-F bonds in [2-mu 2-F]-only amounts to a fraction of the energy of a terminal B-F bond. These calculations also suggest that the relief of steric repulsions induced by fluoride binding in 2 may contribute to the high fluoride affinity of these types of molecules.