Abstract
A possibility of the intramolecular ferromagnetic (FM) interaction in pyrazole-bridged dinuclear Mn(II), Fe(II), Co(II), and Ni(II) complexes is examined by density functional theory (DFT) calculations. When azide is used for additional bridging ligand, the complexes indicate the strong antiferromagnetic (AFM) interaction, while the AFM interaction becomes very weak when acetate ligand is used. In the acetate-bridged complexes, an energy split of the frontier orbitals suggests the orbital counter-complementarity effect between the dxy orbital pair, which contributes to the FM interaction; however, a significant overlap of other d-orbital pairs also suggests an existence of the AFM interaction. From those results, the orbital counter-complementarity effect is considered to be canceled out by the overlap of other d-orbital pairs.
Highlights
Since the discovery of single-molecule magnets (SMMs) [1,2,3], a huge number of studies have been devoted to finding the compounds with a higher blocking temperature (TB)
In order to explain the AFM interaction of the acetate-bridged complexes, spin-unrestricted natural orbital (UNO) analysis is performed for the AFM state of each complex
We confirmed that the azide-bridged complexes indicate the strong AFM interaction, while the acetate-bridged complexes exhibit a very weak AFM interaction
Summary
Since the discovery of single-molecule magnets (SMMs) [1,2,3], a huge number of studies have been devoted to finding the compounds with a higher blocking temperature (TB). TThhee ooppttiimmiizzeedd CCaarrtteessiiaann ccoooorrddiinnaatteess ooff mmooddeell ssttrruuccttuurreess ffoorr bbootthh AAFFMM aanndd FFMM ssttaatteess aarree ssuummmmaarriizzeedd iinn TTaabbllee SS11 iinn SSuupppplleemmeennttaarryy MMaatteerriiaallss. All models show negative J values even at the optimized structures for the FM states, indicating that the AFM exchange interaction between the metal ions is dominant even in the acetate-bridged complexes, in contrast to the Cu(II) complexes [17]. −371 >8.9 a Calculated values in the work of [17]. b Experimental values in the work of [9]
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