LAUSR

Three heterometallic complexes including uranyl and either Co$^{III}$ or Mn$^{II}$ cations were crystallized under hydrothermal conditions. Complexes [Co(bipy)$_3$]$_2$[UO$_2$(NO$_3$)$_4$]$_2$[(UO$_2$)$_2$(NO$_3$)$_4$(OH)$_2$] (1) and [UO$_2$(NO$_3$)$_2$Co(bipy)$_2$(OH)$_2$]·NO$_3$·H$_2$O (2) (bipy = 2,2ʹ‐bipyridine) were obtained from the same solution. UO$_2{^{2+}}$ and Co$^{3+}$ are part of separate anions and cations, respectively, in complex 1, the uranyl ion being present in both a mononuclear dianion with two chelating and two monodentate nitrates in cis positions, and in a dinuclear, bis‐hydroxo‐bridged dianion. In contrast, both metal cations are part of a monocationic heterometallic bis‐hydroxo‐bridged complex in 2, UO$_2{^{2+}}$ retaining two nitrate and Co$^{III}$ two bipy ligands. This is the third example only of a hydroxo‐bridged heterometallic uranyl complex, and the first to involve Co$^{III}$. The complex [(UO$_2$)$_6$Mn(O)$_4$(OH)$_6$(H$_2$O)$_4$]·5H$_2$O (3), synthesized in the absence of any added ligand, crystallizes as a three‐dimensional framework in which anionic uranyl oxyhydroxide layers with the alpha‐U$_3$O$_8$‐type polyhedral arrangement are connected to one another by Mn(H$_2$O)$_4{^{2+}}$ cations axially bound to two uranyl oxo atoms. These very simple systems thus display a large range of possible intermetallic associations, that involving bis‐oxo‐bonding to uranyl enabling formation of a framework through pillaring of sheets