Manganese(III)Compounds of Phenol-Pyrazole-Based Ligands:Synthesis,Crystal Structure,Magnetic,and Thermal Properties

摘要

Reaction of H2phpzR(R=H,Me,Ph;H2phpzH=3(5)-(2-hydroxyphenyl)pyrazole,H2phpzMe=3(5)-(2-hydroxyphenyl)-5(3)-methylpyrazole,and H2phpzPh=3(5)-(2-hydroxyphenyl)-5(3)-phenylpyrazole))with MnCl2'2H2O or MnBr2·4H2O in an acetonitrile-methanol mixture and in the presence of a small quantity of triethylamine affords the compounds[Mn(HphpzR)2Cl](R=H(1),Me(3),and Ph(5)and[Mn(HphpzR)2Br](R=H(2),Me(4),and Ph(6)).This new family of compounds 1-6 with a library of phenol-pyrazole-based ligands was structurally characterized.All compounds are mononuclear manganese(III)coordination compounds in which the manganese(III)ion has a square-pyramidal geometry.In compounds 1-4 intermolecular hydrogen bonds are present between the N-H group of the pyrazole ring of a mononuclear entity and the halogen of a neighboring molecule,thus forming ladder-like chains.The presence of two crystallographically independent molecules in the unit cell of 5 and 6 precludes formation of 1D structure and instead gives rise to a 2D structure with the independent molecules aligned in a face-to-face manner.Low-temperature magnetization studies evidence the presence of antiferromagnetic interactions between the manganese(III)ions in all compounds.Detailed temperature-dependent susceptibility and magnetic specific heat measurements on compounds 1 and 2 show the presence of antiferromagnetic S-2 chains,the magnetic interaction being described by the anisotropic Heisenberg model with a predominantly planar(XY)type of crystal field anisotropy.In addition,the magnetic specific heat data evidence the occurrence of long-range magnetic ordering between chains in 1 and 2 below about 1.5 K.Compounds 3-6 show weaker antiferromagnetic interactions as compared with 1 and 2.