New layered oxuchalcogenide La$_{2}$O$_{2}$Mn$_{2}$OSe$_{2}$

We report a new La$_{2}$O$_{2}$Mn$_{2}$OSe$_{2}$ and investigate its physical properties. It is a member of Ln$_{2}$O$_{2}$Tm$_{2}$OCh$_{2}$ (Ln= rare earth, Tm=Fe, Co, and Ch=S, Se). The structure of these compounds can be described as an alternate stacking of fluorite type [Ln$_{2}$O$_{2}$]$^{2+}$ or [A$_{2}$F$_{2}$]$^{2+}$ layers and anti-CuO$_{2}$-type [Tm$_{2}$OCh$_{2}$]$^{2-}$ layers (anti-perovskite type). La$_{2}$O$_{2}$Mn$_{2}$OSe$_{2}$ is the first manganese-base compound with anti-CuO$_{2}$-type layers. It is a ferromagnetic (FM) Mott insulator exhibiting several successive magnetic transitions. The magnetic properties are different from other compounds with this structure.