A novel water cluster [Mn(phen)2·H2O·Cl]·p-FBA·3H2O (p-FBA = p-fluorobenzoic acid and phen = 1,10-phenanthroline) was synthesized by the hydrothermal reaction of MnCl2 with p-FBA and phen at 150 ℃ and characterized by elemental analysis,IR spectra and TG. Its crystal structure was determined by X-ray single-crystal diffraction study. The crystal belongs to the triclinic system,space group P1,with a = 10.5768(1),b = 11.5960(1),c = 12.9916(2) ,α = 101.816(2),β = 95.397(2),γ = 103.052(2)o,V = 1502.8(3) 3,Z = 2,Dc = 1.463 g/cm3,R = 0.0399 and wR = 0.0997. The crystal structure shows that the manganese(Ⅱ ) ion is six-coordinated by four nitrogen atoms,one chloride ion and one oxygen atom forming a distorted octahedral coordination geometry. The structure includes three acyclically connected water molecules and one coordinated water molecule thus forming a (H2O)4 water cluster. This water pattern forms a cross-linked discrete ring. The steady (H2O)4 is further extended into a cage-like structure by the hydrogen-bonding interaction formed by dissociative aqua molecule and Cl-ligand. The dimer structure is further extended into a one-dimensional (1D) structure through C-H···O interaction. π···π Stacking interaction among adjacent phen aromatic rings further stabilizes the crystal structure. A novel water cluster [Mn (phen) 2 · H2O · Cl] · p-FBA · 3H2O (p-FBA = p-fluorobenzoic acid and phen = 1,10-phenanthroline was synthesized by the hydrothermal reaction of MnCl2 with p- FBA and phen at characterized by elemental analysis, IR spectra and TG. Its crystal structure was determined by X-ray single-crystal diffraction study. The crystal belongs to the triclinic system, space group P1, with a = 10.5768 (1 , b = 11.5960 (1), c = 12.9916 (2) , α = 101.816 (2), β = 95.397 (2), γ = 103.052 (2) o, 2, Dc = 1.463 g / cm3, R = 0.0399 and wR = 0.0997. The crystal structure shows that the manganese (II) ion is six- coordinated by four nitrogen atoms, one chloride ion and one oxygen atom forming a distorted octahedral coordination geometry The structure includes three acyclically connected water molecules and one coordinated water molecule thus forming a (H2O) 4 water cluster. This water pattern forms a cross-linked discrete ring. The steady (H2O) 4 is further extended into a cage-like structure by the hydrogen-bonding interaction formed by dissociative aqua molecule and Cl-ligand. The dimer structure is further extended into a one-dimensional (1D) structure through CH ··· O interaction. π ··· π Stacking interaction among adjacent phen further rings further stabilizes the crystal structure.