By reaction of iron(II) salts with 4-(p-methoxyphenyl)-1,2,4-triazole, hereafter abbreviated as p-MeOprtz, two compounds have been synthesized, namely [Fe-3(p-MeOptrz)(8)(H2O)4](BF4)(6) (1) and [Fe-3(p-MeOptrz)(6)(H2O)(6)](tos)(6) (tos = tosylate) (2a). The crystal structures have been solved at room temperature. Both compounds crystallize in the triclinic system, space group P (1) over bar. The lattice parameters are as follows : for 1.2H(2)O, a = 15.107(7) Angstrom, b = 14.678(7), c = 12.392(6) Angstrom, alpha = 112.14(6)degrees, beta = 95.85(5)degrees, gamma 104.40(6)degrees, Z = 1; for 2a.2CH(3)OH.8H2O, a = 12.983(5) Angstrom, b = 16.324(7) Angstrom, c = 17.362(8) Angstrom, alpha = 105.28(3)degrees, beta = 109.34(4)degrees, gamma = 106.94(4)degrees, Z = 1. Both structures consist of linear trinuclear cations with a +6 charge, and noncoordinated anions and solvent molecules. The central iron atom lies on an inversion center and is triply bridged to each of the external iron atoms by the p-MeOptrz ligands through the nitrogen atoms in the 1,2-positions. Each external iron atom completes its octahedral surroundings with one p-MeOptrz ligand and two water molecules in 1 and with three water molecules in 2a. The average value of the dihedral angle between triazole and phenyl rings of the bridging ligands is equal to 71.4 degrees in 1 and 33.2 degrees in 2a. Heating 2a at 100 degrees C affords a compound 2b of formula [Fe-3(p-MeOptrz)6(H2O)3]-(tos)6 The magnetic properties of 1, 2a.4H(2)O, and 2b have been investigated. For 1, the three iron(II) ions are high-spin in the whole temperature range. The temperature dependence of the molar magnetic susceptibility has beenquantitatively interpreted by full diagonalization of the spin Hamiltonian, taking into account the isotropic interaction between nearest neighbor spin carriers, and the local anisotropies. The interaction parameter between central and external iron(II) ions has been found at J = -5.7 cm(-1) (H = -JS(A).S-B). For 2a.4H(2)O and 2b the central iron(II) ion undergoes a gradual spin conversion centered at T-1/2 = 245 and 330 K, respectively. This spin conversion has also been studied by Mossbauer spectroscopy. The switching between high-spin and spinconversion situations when passing from 1 to 2a has been attributed to the variation of the dihedral angle within the p-MeOptrz bridging ligands, caused in this instance by the nature of the anion.