Synthesis, Structure, Magnetic Behavior, and Mössbauer Spectroscopy of Two New Iron(II) Spin-Transition Compounds with the Ligand 4-Isopropyl-1,2,4-triazole. X-ray Structure of [Fe3(4-isopropyl-1,2,4-triazole)6(H2O)6](tosylate)6·2H2O

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Abstract
Two new iron(II) compounds with the formula [Fe3(iptrz)6(H2O)6]X6·xH2O (with iptrz = 4-isopropyl-1,2,4-triazole and X = p-toluenesulfonate (Tos) or trifluoromethanesulfonate (Trifl)) were synthesized. The crystal structure of [Fe3(iptrz)6(H2O)6](Tos)6·2H2O (I) has been solved at room temperature. Crystals of I are triclinic, space group P1̄ with a = 12.8820(11) Å, b = 15.580(2) Å, c = 24.445(4) Å, α = 79.270(12)°, β = 86.688(11)°, γ = 83.007(8)°, Z = 2. The structure of I consists of linear trinuclear cations with a +6 charge and noncoordinated anions and lattice water molecules. The central iron ion is located on an inversion center and is coordinated by 6 nitrogen atoms of 6 iptrz molecules bridging via the nitrogen atoms in the 1,2-positions. Each external iron atom completes its coordination sphere with three coordinated water molecules. The temperature dependent magnetic measurements of compound I and [Fe3(iptrz)6(H2O)6](Trifl)6 (II) show that both compounds exhibit a gradual spin conversion of the central iron ion centered at T1/2 = 242 K for I and 187 K for II. Temperature dependent Mössbauer spectroscopy measurements on I show the behavior expected for a compound of this nature. The measurements on II indicate a strong influence of the spin conversion of the central iron ion on both external iron ions. The nature of this phenomenon is proposed to be connected to a very rigid lattice structure (ionic, H-bonding) connecting the trinuclear units.