A　2-D　oxalate-containing　bismuth(III)　compound　of　formula　(C3N2H12)[Bi(C2O4)2.5]·H2O　has　been　hydrothermally　synthesized　and　characterized　by　single　crystal　X-ray　diffraction.　The　Bi　atoms　and　oxalate　units　form　a　2-D　layered　structure　with　a　12-membered　aperture.　The　crystal　band　structure,　calculated　by　the　DFT　method,　shows　that　the　title　compound　is　an　insulator　with　a　band　gap　of　3.19　eV,　a　value　consistent　with　the　experimental　value　of　3.29　eV.　©　2007　Taylor　&　Francis.