Several synthetic pathways and characterization of silver(II) fluorosulfate are reported. The title compound crystallizes in the monoclinic space group, P2(1)/c, with a = 10.5130(4) angstrom, b = 7.7524(3) angstrom, c = 8.9366(4) angstrom, beta = 117.867(2)degrees [V = 643.88(5) angstrom(3), Z = 4, d(calcd). = 3.15 g cm(-3)] in a structure type related to that of AgF(2). Puckered [Ag(SO(3)F)(2)] sheets are present in the crystal structure with two oxygen atoms of the fluorosulfate anions utilized for bonding within the sheet; the third oxygen atom serves as a linker to the adjacent sheet. Terminal fluorine atoms form small cavities in the structure. The S-O stretching region of the vibrational (IR and Raman) spectra is rich in bands, thus confirming the structural complexity of Ag(SO(3)F)(2). Ag(SO(3)F)(2) is a soft ferromagnet with a Curie temperature of 24.8 K and it shows a single broad electron spin resonance (ESR) with g = 2.183 at T = 293 K. The intrasheet magnetic superexchange constant, J, derived from magnetization measurements, equals +1.0 meV per formula unit. Density functional theory calculations suggest that the superexchange occurs through the OO moiety of the Ag-O-S-O-Ag bridge while omitting the S atom, and the yield is J = +1.1 meV. The Coulomb-corrected local spin density approximation (LSDA+U) calculations predict a direct electronic band gap at the Fermi level of 1.05 eV. Large magnetic moments reside on O atoms attached to Ag(II); in consequence, Ag(SO(3)F)(2) is thermally unstable; at room temperature or in the presence of strong acids its dark brown crystals slowly decompose at the surface to a black mixed-valence Ag(3)(SO(3)F)(4). Very fast exothermic decomposition of Ag(SO(3)F)(2) with emission of a fluorosulfuryl radical (SO(3)F(center dot)) occurs above 120 degrees C as confirmed by simultaneous thermogravimetric, calorimetric and evolved gas analyses.