The　interaction　of　neptunyl　ions　(NpO2+)　with　three　picolinic　type　ligands　(L),　including　the　deprotonated　picolinic　acid　anion　(PA−),　the　deprotonated　dipicolinic　acid　anion　(DPA2−)　and　the　1,10-phenanthroline-2,9-dicarboxylic　acid　anion　(PADA2−),　was　investigated　by　using　a　density　functional　theory　method　with　various　stoichiometric　ratios　of　Np : L　=　1 : 1,　1 : 2,　and　1 : 3.　The　coordination　modes,　the　influence　of　the　denticity　of　the　ligands,　and　the　stoichiometry　of　the　complexes　were　evaluated　in　terms　of　geometry,　electronic　structure,　and　thermodynamics.　The　calculations　show　that　the　coordination　of　NpO2+　to　tetradentate　ligands　is　more　stable　than　that　to　tridentate　and　bidentate　ones,　and　the　coordination　ability　of　the　three　deprotonated　ligands　follows　the　order:　PADA2−　>　DPA2−　>　PA−.　Quantum　theory　of　atoms-in-molecules　(QTAIM)　analysis,　charge　decomposition　analysis　(CDA)　and　natural　atomic　orbital　(NAO)　analysis　were　used　to　understand　the　bonding　nature　and　electronic　properties　of　the　complexes,　and　the　metal-ligand　dative　bond　was　identified　to　be　mainly　ionic.　In　view　of　the　favorable　coordination　modes　and　the　distinct　ability　of　the　ligands　in　binding　to　neptunyl,　we　conclude　that　the　denticity　of　the　ligands　and　the　combined　hard-soft　donor　strategy　work　cooperatively　in　the　coordination　of　NpO2+　with　ligands.　This　work　is　expected　to　contribute　to　the　rational　design　of　new　types　of　ligand　with　enhanced　ability　to　extract　neptunyl.　©　The　Royal　Society　of　Chemistry.