Mixed valence (MV) chemistry can be used to model electron transfer reactions in large, complicated chemical and biological systems. Most mixed valent molecules consist of simple π-systems bridging two identical redox centres, although hydrogen-bonded bridges have also been reported. Such species are relatively rare and are not well understood. This thesis first presents the synthesis and characterisation of three novel quadruply bonded dimolybdenum paddlewheel complexes Mo2(O2CR)3(HL) (2–4, where O2CR is a carboxylate ligand, and L is a hydrogen-bearing pyrazine-type ligand) which, in non-donor solvent, self-assemble across self complimentary hydrogen bonds to form dimers-of-dimers [Mo2(O2CR)3(HL)]2 ([2]2–[4]2). MV states {[2a]2}+ {[4]2}+ are formed following one-electron reduction. The effects of small changes in the pyrazine-type ligands, and the identity of the carboxylate ancillary ligand, are examined. The novel cationic complex [Mo2(TiPB)3(H2Bim)][BF4] (5, where H2Bim is 2,2’-biimidazole) is also presented. The H2Bim moiety could not be deprotonated, and so this complex does not dimerise or form a stable MV state in solution. Precursors to the formation of new dimolybdenum MV species are explored. The synthesis and characterisation of the novel homoleptic species Mo2(TMB)4 (6), where TMB is 2,4,6-trimethylbenzoate, is presented. Methods of synthesis for the monocationic species [Mo2(TiPB)3(MeCN)4][BF4] (1b, where TiPB is 2,4,6-triisopropylbenzoate) are explored. The effects of relatively small structural changes in carboxylate ancillary ligands on the degree of electronic coupling are explored using oxalate-bridged MV complexes with the general formula [Mo2(O2CR)3]2(µ-ox) (7–12), where O2CR is either an aliphatic or aromatic carboxylate ligand and μ-ox is the oxalate bridge. MLCT transition energies evidence only a subtle effect of ligand choice on electronic coupling. Finally, three novel tetracationic dimolybdenum species [Mo2(L)2(MeCN)2][BF4]4, incorporating bipyridine type ligands L, are presented (13–15). The chelating binding modes of these ligands result in unique complex geometries, as shown by 1H-NMR spectroscopy and X-ray diffraction studies. Complexes 13–15 are therefore excellent candidates for building blocks of new dimolybdenum MV scaffolds. The single crystal structure of [Mo2(bipy)2(OAc)2][BF4]2 (16, where bipy is 2,2’-bipyridine and OAc is acetate), synthesised from reaction of the parent complex [Mo2(bipy)2(MeCN)4][BF4]4 (14), shows that the arrangement of chelating ligands is not disrupted by incorporation of target ligands. Reaction of 14 with oxalic acid does not form the expected building block [Mo2(bipy)2(oxH)2][BF4]2, but instead the covalently bridged molecular triangle [Mo2(bipy)2(µ ox)]3[BF4]6 (17), as shown by XRD. This species is the first reported example of an oxalate-bridged molecular triangle with Mo2(bipy)2 vertices. Attempts to synthesise the analogous terephthalate-bridged triangle result in a mixture, [Mo2(bipy)2(µ-TP)]n[BF4]2n, where n = 3 or 4 (18).