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

Two new iron(II) compounds with the formula [Fe(3)(iptrz)(6)(H(2)O)(6)]X(6).xH(2)O (with iptrz = 4-isopropyl-1,2,4-triazole and X = p-toluenesulfonate (Tos) or trifluoromethanesulfonate (Trifl)) were synthesized. The crystal structure of [Fe(3)(iptrz)(6)(H(2)O)(6)](Tos)(6).2H(2)O (I) has been solved at room temperature. Crystals of I are triclinic, space group P with a = 12.8820(11) Å, b = 15.580(2) Å, c = 24.445(4) Å, alpha = 79.270(12) degrees, beta = 86.688(11) degrees, gamma = 83.007(8) degrees, 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 [Fe(3)(iptrz)(6)(H(2)O)(6)](Trifl)(6) (II) show that both compounds exhibit a gradual spin conversion of the central iron ion centered at T(1/2) = 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.