| Abstract
| - The use of orotic acid (H3L) in iron(III) chemistry has yielded a structurally, magnetically, and spectrochemicallyvery interesting complex. The 1:3:3 FeCl3·6H2O/H3L/aqueous NH3 reaction system in MeOH gives red (NH4)[Fe3(μ3-OH)(H2L)3(HL)3]·7.75H2O (1) in high yield. 1 crystallizes in the hexagonal space group P3̄ with (at 25°C) a = 14.813(7) Å, c = 15.084(7) Å, and Z = 2. There is a C3 axis passing through the central hydroxooxygen; thus, the three FeIII atoms form an equilateral triangle with an edge of 3.312 Å and the Fe3Ohydroxy coreis planar. The orotates present two novel coordination modes; each H2L- ligand bridges two FeIII atoms throughits syn,syn η1:η1:μ2 carboxylate group, while HL2- simultaneously chelates one FeIII atom through one carboxylateoxygen and the deprotonated amide nitrogen, and is bonded to a second metal ion through the adjacent carbonyloxygen. The three H2L- and the three HL2- ligands lie above and below the Fe3Ohydroxy plane, respectively.Hydrogen bonds between the orotates result in a 3D network. Magnetic measurements of 1 in the 1.8−300 Ktemperature range were fitted using a 2J model with mean-field corrections and show antiferromagnetic interactionsbetween the metal ions in the trinuclear moiety as well as between the trimers due to the 3D H-bonded network.The case of spin frustration is discussed extensively as well as the possible antisymmetric exchange interactions.The solid state X-band EPR spectrum of 1 at 4 K is consistent with the magnetic measurements showing that theS = 1/2 ground state is very close to the first excited S = 3/2, which is also populated at this temperature. Furthermore,the simulation of the EPR spectrum reveals the anisotropic character of the system.
- The first structurally characterized and studied orotato iron(III) complex (NH4)[Fe3(μ3-OH)(H2L)3(HL)3]·7.75H2O (1), exhibiting two novel metal-binding modes of H2L- and HL2-, is described. The three FeIII ions form an equilateral triangle due to the C3 axis passing through the central hydroxo oxygen. The trimers are H-bonded through the orotate ligands resulting in a 3D structure. Compound 1 exhibits antiferromagnetic interactions between the metal ions of the trinuclear moiety as well as between the trimers.
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