CsMn(HCO2)3 crystallizes in the hexagonal P6_322 space group. Cs(1) is bonded in a 6-coordinate geometry to six equivalent O(1) atoms. All Cs(1)-O(1) bond lengths are 3.13 Å. Mn(1) is bonded in an octahedral geometry to six equivalent O(1) atoms. All Mn(1)-O(1) bond lengths are 2.20 Å. C(1) is bonded in a trigonal planar geometry to one H(1) and two equivalent O(1) atoms. The C(1)-H(1) bond length is 1.11 Å. Both C(1)-O(1) bond lengths are 1.27 Å. H(1) is bonded in a single-bond geometry to one C(1) atom. O(1) is bonded in a 3-coordinate geometry to one Cs(1), one Mn(1), and one C(1) atom. Linkers: 6 [O]C=O. Metal clusters: 2 [Cs] ,2 [Mn]. The MOF has largest included sphere 2.79 A, density 2.52 g/cm3, surface area 2570.92 m2/g, accessible volume 0.11 cm3/g