Hydrocarbon solutions of W2(O-t-Bu)6 react with pivalic acid, t-BuCOOH (6 equiv), to give W2(O2C-t-Bu)6 and t-BuOH. W2(O2C-t-Bu)6 crystallizes from hexane as yellow cubic crystals. (Crystal data at -156 °C: a = 16.730 (5) Å, b = 10.588 (2) Å, c = 22.860 (8) Å, β = 107.26 (1)°, Z = 4, dcalcd = 1.674 g cm-3, space group = P21/c.) Each tungsten atom is coordinated to five oxygen atoms that lie roughly in a pentagonal plane, to the other tungsten atom by a W=W bond (2.292 (1) Å), and weakly to an additional oxygen atom along an extension of the W-W axis (W-O (axial) = 2.54 Å (averaged)). The molecule has a pair of cis-bridging pivalate groups that impose a near-eclipsed geometry for the two WO5 pentagonal units. 1H NMR studies reveal that in toluene-d8 solution W2(O2C-t-Bu)6 exists as a mixture of two isomers, each having a C2 axis of symmetry. These observations are compared with previous findings and in particular with those for W2(O2CNMe2)6. It is proposed that most, if not all, compounds of formula W2(O2CX)6 will adopt a structure related to either W2(O2C-r-Bu)6 or W2(O2CNMe2)6, which are closely related, differing only in the arrangement of the chelate ligands about a common W2O10O'2 template.