A hydrothermal reaction of a mixture of Y(NO₃)₃, 1,2-benzenedicarboxylic acid (1,2-BDC) and NaOH gives rise to a new yttrium phthalate coordination polymer, [Y₄H₂O₂C₈H₄O₄)₆]_∞,I. The Y ions inI are present in four different coordination environments with respect to the oxygen atoms (CN6 = octahedral, CN7 = pentagonal bipyramid, CN8 = dodecahedron and CN9 = capped square anti-prism). The oxygen atoms of the 1,2-BDC are fully deprotonated, and show variations in their connectivity with Y atoms. The Y atoms themselves are connected through their vertices forming infinite Y-O-Y one-dimensional chains. The Y-O-Ychains are cross-linked by the 1,2-BDC anions forming a corrugated layer structure. The layers are supported by favourableπ…π interactions between the benzene rings of the 1,2-BDC anions. The variations in the coordination environment of the Y atoms and the presence of Y-O-Y interactions along with the favourableπ…π interactions between the benzene rings from different layers are noteworthy structural features. Crystal data: triclinic, space group =P−1 (no. 2),a = 12.6669 (2),b = 13.8538 (2),c = 16.0289 Å,α = 75.20 (1),β = 69.012 (1),γ= 65.529 (1)°,V = 2371.28 (7) ų,D_calc = 1.922 g cm⁻¹, μ(_MoKα) = 4.943 mm⁻¹. A total of 9745 reflections collected and merged to give 6566 unique reflections (R_int = 0.0292) of which 5252 withI>2σ(I) were considered to be observed. FinalR₂ = 0.0339,wR₂ = 0.0724 andS = 1.036 were obtained for 704 parameters.