Manganese(iii) compounds with phenol–pyrazole based-ligands: impact of the co-ligand and the carboxylate ligand on the trinuclear core [Mn3(μ3-O)(phpzR)3(O2CR′)n]1−n

Abstract

The reaction of H₂phpzR (R = Me, Ph; H₂phpzMe = 3(5)-(2-hydroxyphenyl)-5(3)-methylpyrazole and H₂phpzPh = 3(5)-(2-hydroxyphenyl)-5(3)-phenylpyrazole) with Mn(O₂CR′)·nH₂O (R′ = Me and Ph) and (ⁿBu₄N)MnO₄ in ethanol (EtOH) affords three new manganese(III) compounds, [Mn₃(μ₃-O)(phpzMe)₃(O₂CMe)(EtOH)]·EtOH (1), (ⁿBu₄N)[Mn₃(μ₃-O)(phpzMe)₃(O₂CPh)₂] (2) and (ⁿBu₄N)[Mn₃(μ₃-O)(phpzPh)₃(O₂CPh)₂] (3). Their synthesis, crystal structure and magnetic properties are reported. Compounds 1–3 are μ₃-oxido-centered trinuclear manganese(III) compounds whose edges are bridged by phpzR²⁻ with average intracluster separations of 3.25 Å. The three Mn–O–Mn angles are distorted from the equilateral triangle with values in the range of 113° to 124°; 117° to 125°; and 117° to 126° for complexes 1–3, respectively. Hydrogen bonding interactions between the trinuclear units of 1 result in a one-dimensional chain structure. Compounds 2 and 3 have isolated trinuclear units, perhaps as a result of the presence of the bulky ⁿBu₄N⁺ cation. Temperature-dependent magnetic susceptibility studies indicate the presence of both antiferromagnetic and ferromagnetic interactions in compound 1 (J₁ = −10.3 cm⁻¹, J₂ = +10.9 cm⁻¹), while only antiferromagnetic interactions are present in compounds 2 and 3 (J₁ = −4.2 cm⁻¹, J₂ = −10.3 cm⁻¹ for 2; and J₁ = −4.8 cm⁻¹, J₂ = −10.2 cm⁻¹ for 3), with J₁ representing the similar Mn–O–Mn angles and J₂ representing the unique Mn–O–Mn angle (Mn(1)–O(1)–Mn(2)).