To determine the influence of reaction conditions on the formation of metal−organic frameworks, a series of Co(II)/H2tbip/bpp complexes, {[Co2(tbip)2(H2O)6]·8H2O}n (1), {[Co(tbip)(bpp)(H2O)]2·4H2O}n (2), {[Co(tbip)(bpp)]·H2O}n (3), {[Co2(H2O)(tbip)(Htbip)2(bpp)2]·0.5(H2tbip)·0.5H2O}n (4), {[Co3(OH)(tbip)2(Htbip)(bpp)]}n (5) (H2tbip = 5-tert-butyl isophthalic acid, bpp = 1,3-bi(4-pyridyl)propane), have been synthesized through the hydrothermal reaction of cobalt(II) acetate, H2tbip, and bpp under different temperatures and pH conditions. The diverse product structures show the marked sensitivity of the structural chemistry of the aromatic carboxylate ligand to synthesis conditions. Polymer 1, which features a three-dimensional (3D) framework with CdSO4 topology, has carboxylate bridging polymeric chains spanning two different directions and bridging water molecules between these chains, and is formed at pH = 4 at 120 °C. At pH = 6, a one-dimensional tube-like structure of 2 is formed. Further increase of t...