New single-molecule magnet based on Mn12 oxocarboxylate clusters with mixed carboxylate ligands, [Mn12O12(CN-o-C6H4CO2)12(CH3CO2)4(H2O)4]·8CH2Cl2: Synthesis, crystal and electronic structure, magnetic properties

Abstract

A new high symmetry Mn(12) oxocarboxylate cluster [Mn(12)O(12)(CN-o-C(6)H(4)CO(2))(12)(CH(3)CO(2))(4)(H(2)O)(4)]·8CH(2)Cl(2) (1) with mixed carboxylate ligands is reported. It was synthesized by the standard carboxylate substitution method. 1 crystallizes in the tetragonal space group I4(1)/a. Complex 1 contains a [Mn(12)O(12)] core with eight CN-o-C(6)H(4)CO(2) ligands in the axial positions, four CH(3)CO(2) and four CN-o-C(6)H(4)CO(2) in equatorial positions. Four H(2)O molecules are bonded to four Mn atoms in an alternating up, down, up, down arrangement indicating a 1 : 1 : 1 : 1 isomer. The Mn(12) molecules in 1 are self-assembled by complementary hydrogen C-H···N bonds formed with participation of the axial o-cyanobenzoate ligands of the adjacent Mn(12) clusters. The lattice solvent molecules (CH(2)Cl(2)) are weakly interacted with Mn(12) units that results in solvent loss immediately after removal of the crystals from the mother liquor. The electronic structure and the intramolecular exchange parameters have been calculated. Mn 3d bands of 1 are rather broad, and the center of gravity of the bands shifts down from the Fermi level. The overlap between Mn 3d bands and 2p ones of the oxygen atoms from the carboxylate bridges is higher than in the parent Mn(12)-acetate cluster. These changes in the electronic structure provide a significant difference in the exchange interactions in comparison to Mn(12)-acetate. The magnetic properties have been studied on a dried (solvent-free) polycrystalline sample of 1. The dc magnetic susceptibility measurements in the 2-300 K temperature range support a high-spin ground state (S = 10). A bifurcation of temperature dependencies of magnetization taken under zero field cooled and field cooled conditions observed below 4.5 K is due to slow magnetization relaxation. Magnetization versus applied dc field exhibited a stepwise hysteresis loop at 2 K. The ac magnetic susceptibility data revealed the frequency dependent out-of-phase (χ(M)'') signals characteristic of single-molecule magnets.

Nanoscopic molecular magnets

“…Numerous carboxylate bridged molecules are reported by various groups which are magnetically potent. 25 An important example is the (11) reported by Kushch et al 26 An interesting feature of the electronic structure of this complex is the higher overlap of the Mn 3d bands with the 2p bands of the O atoms as compared to the parent Mn 12 -acetate cage and that resulted in significant difference in the exchange interactions in comparison to the Mn 12 -acetate cage. ZFC and FC curves showed bifurcation below 4.5 K which gave evidence of slow relaxation of magnetization.…”

“…That was due to the fact that QTM was not approached even at 2 K and, accordingly, only the Orbach process involving the first excited state was measured in the AC susceptibility studies. 25 An important example is the Mn 12 oxocarboxylate complex [Mn 12 O 12 (CN-o-C 6 H 4 CO 2 ) 12 (CH 3 -CO 2 ) 4 (H 2 O) 4 ]·8CH 2 Cl 2 (11) reported by Kushch et al 26 An interesting feature of the electronic structure of this complex is the higher overlap of the Mn 3d bands with the 2p bands of the O atoms as compared to the parent Mn 12 -acetate cage and that resulted in significant difference in the exchange interactions in comparison to the Mn 12 -acetate cage. 17 The N 2 3− radical ligands possess diffuse spin orbitals which can penetrate the core electron density of the Tb III ions and thereby result in strong exchange coupling.…”

Synthesis, structure, and magnetic properties of a tetradecanuclear manganese complex

“…For an out-of-phase signal (v M 00 ) for the vacuum-dried sample of complex 1 (Fig. 8 4 ] clusters greatly influences the magnetization relaxation processes which have been elucidated by a JT isomerism [1,54,55]. The CH 2 Cl 2 solvated molecules may affect the orientation of the JT axes of Mn(III) ions of complex 1Á2CH 2 Cl 2 , which would be expected to affect the anisotropy energy.…”

Manganese, technetium and rhenium

“…34 Mn 12 oxocarboxylate single-molecule magnet clusters with mixed carboxylate ligands have also been prepared and their electronic structures and magnetic properties determined. 35 Different computational methods have been used to study the large antiferromagnetic coupling in the Mn IV -Mn IV bond in the Li 6 Ca 2 [Mn 2 N 6 ] and Li 6 Sr 2 [Mn 2 N 6 ] complexes. 36 Meanwhile, the electronic structure and magnetic properties of the tris(N,N 0 -diphenylhydrazido)manganese(IV) propeller complex Li 2 Mn(k 2 -PhN-NPh) 3 L 4 2 (L 4 = THF, diethyl ether) have been reported.…”