This thesis describes the synthesis and characterization of a number of polyborate compounds containing transition metal complex cations; most of these compounds contain 6-membered B3O3 boroxole rings within their structures. A total of twenty-six transition metal complex polyborate salts are reported: one contains the triborate monoanion, [B3O3(OH)4]-, three contain the tetraborate dianion [B4O5(OH)4]2-, twelve contain the pentaborate anion, [B5O6(OH)4]-, three contain the hexaborate dianion, [B6O7(OH)6]2- and five contain heptaborate anions (three of which are [B7O9(OH)5]2-, and two are [B7O9(OH)6]3-). Additionally, two compounds contain two isolated polyborate anion species (octaborate dianion [B8O10(OH)6]2- with pentaborate anion [B5O6(OH)4]-, and triborate anion [B3O3(OH)4]- with [B5O6(OH)4]-). The crystal structures of fifteen salts containing these polyborate anions are reported: [Co(en)3][B5O6(OH)4][B8O10(OH)6]∙5H2O (6), [Co(NH3)6]2[B4O5(OH)4]3∙11H2O (9), s-fac-[Co(dien)2][B7O9(OH)6]∙9H2O (11), [Co(diNOsar)]2[B3O3(OH)4]Cl5∙4.75H2O (12), [Cu(en)2][B5O6(OH)4]2∙2H2O (20), [Cu(pn)2{B5O6(OH)4}][B5O6(OH)4]∙4H2O (22), [Cu(TMEDA){B6O7(OH)6}]∙6H2O (23), [Cu(dac)2(H2O)2][Cu(dac)2][B7O9(OH)5]2∙4H2O (24), [Cu(N,N-dmen)2(H2O)][B5O6(OH)4]2·3H2O (27), [Cu(N,N-dmen){B6O7(OH)6}]·4H2O (28), [Ni(en){B6O7(OH)6}(H2O)2]∙H2O (37), [Ni(AEN)][B5O6(OH)4]∙H2O (38), [Ni(dac)2(H2O-)2][Ni(dac)2][B7O9(OH)5]2∙4H2O (39), [Ni(hn)2][B5O6(OH)4]2 (40), and s-fac-[Ni(dien)2][B5O6(OH)4]2 (41). All the synthesized compounds reported were characterized using spectroscopic (IR, multi-element NMR) and analytical (melting point, elemental analysis, magnetic susceptibility, thermal analysis, powder X-ray diffraction) techniques. The solid-state structures of transition metal complex polyborate salts all display multiple cation-anion H-bond interactions and these undoubtedly play a major role in the energetics of engineering these structures. For example, in compound [Co(NH3)6]2[B4O5(OH)4]3∙11H2O (9), fourteen of the 18 amino hydrogen atoms of the [Co(NH3)6]3+ cation are involved in secondary coordination to anions via H-bonds. Two unique polyborate anions, [B8O10(OH)6)]2- and [B7O9(OH)6]3- have been prepared and characterized in [Co(en)3][B5O6(OH)4][B8O10(OH)6]∙5H2O (6) and s-fac-[Co(dien)2][B7O9(OH)6]∙9H2O (11), respectively. vii The reaction of transition metal complex cations with boric acid in different ratios produced polyborate compounds with different polyborate anions e.g. reaction of [Cu(en)2]2+ with boric acid in 1:10 and 1:5 ratios produce polyborate compounds with pentaborate(1-) and tetraborate(2-) anions, respectively. New polyborate anion structural architectures are identified in this thesis: (i) the pentaborate(1-) anion in [Cu(pn)2{B5O6(OH)4}][B5O6(OH)4]∙4H2O (22) acts as a monodentate ligand coordinated to the Cu(II) cation, (ii) the hexaborate(2-) anion in [Cu(TMEDA){B6O7(OH)6}]∙6H2O (23) and [Cu(N,N-dmen){B6O7(OH)6}]·4H2O (28) coordinates as a tridentate ligand with the Cu(II) cations, and (iii) the hexaborate(2-) anion in [Ni(en){B6O7(OH)6}(H2O)2]∙H2O (37) coordinates as a bidentate ligand with the Ni(II) cation. This is the first time that such coordination mode (i) and (iii) have been observed.