A　new　heterometallic　MOF,　namely　[Cd2K4(2,3-PDC)4]　(1)　(2,3-H2PDC　=　2,3-pyridine　dicarboxylic　acid),　has　been　successfully　synthesized　from　Cd2+　and　K+　salts　with　2,3-H2PDC　under　the　solvothermal　conditions.　Single　crystal　X-ray　diffraction　studies　reveal　that　1　is　a　three-dimensional,　highly　connected　trinodal　(5,5,18)-c　net.　Compound　1　features　a　rare　3D　diamondoid　Cd(ii)-K(i)　inorganic　connectivity　constructed　by　a　{Cd2K4}　cluster.　The　K+　ion　in　the　structure　functions　not　only　as　a　charge　balancer　but　also　as　a　connector　in　the　construction　of　MOF.　Tunable　blue-green　to　white　luminescence　of　1　was　achieved　by　variation　of　the　excitation　wavelength　and　the　inclusion　amount　of　Eu3+　ions　in　the　host　framework　of　1.　©　The　Royal　Society　of　Chemistry　2015.