The fluorophosphate compounds A3Fe4(PO4)2F9 (A = K+ and NH4+) were found to exhibit a channel framework constructed from {Fe4O8F10} tetrahedral clusters and PO4 tetrahedra, featuring a tetramer chain structure along the a-axis. Here these two compounds were synthesized by a fluorine-rich hydrothermal method. The purity of the samples was characterized by single crystal and powder XRD, EDS, and FT-IR measurements. The results of magnetic and heat capacity measurements confirmed that both compounds possess an antiferromagnetic ordering at ∼10 K and ∼6 K with Weiss temperatures of −341.5(8) K and −334.3(5) K, respectively, indicating strong spin frustration in the systems due to large frustration factors of ∼34 and ∼56. The presence of spin frustration is suggested to arise from the competition of very close magnetic interactions within the tetrahedral Fe4 clusters.