Background: Studies of transition metal complexes containing cubane core were inspired by the discovery
of single-molecule magnetism in this family of compound. β-diketonates are quite often used for creation
of cubane complexes. β-Ketosulfones, compounds containing S(O)2CH2C(O) fragment, to certain extent
can be considered as analogues of β-diketones. It was intriguing to study the difference and similarities between
the coordination behavior of β-diketones and β-ketosulfones, as well as the difference between the properties of
3d metal complexes with these ligands.
Objectives: The aim of this work was to study the structure, magnetic and spectral properties of NiII and CoII
complexes with a representative of β-ketosulfone family - analog of well-known β-diketonates.
Methods: Crystallographic data were collected using Xcalibur Sapphire3 diffractometer with Mo-Kα radiation.
UV/vis spectra were obtained using a Cary 300 machine in 350-800 nm range. TG experiments were carried
our using Q1500 instrument in air. Reflectance spectra were measured on Beckman UV 5240 instrument. 1HNMR
spectra were measured at 300 MHz on Bruker WP 100 SY instrument. Magnetic susceptibility measurements
were carried out with Quantum Design PPMS-9 magnetometer operating in the range 300-2 K using
field of 5000 Oe. Measurements were performed on polycrystalline samples sealed in a polyethylene bag and
cover with mineral oil in order to prevent field-induced torquing of the crystals. The magnetic data were corrected
for the sample holder, the mineral oil and the diamagnetic contribution.
Results: The reaction of potassium salt of 2-(p-tolylsulfonyl)acetophenone (KL) with CoII and NiII nitrates resulted
in the formation of tetranuclear complexes [Ni4(µ3-OCH3)4(H2O)3(CH3OH)(L)4]·H2O (1·H2O) and
[Co4(µ3-OCH3)4(CH3OH)4(L)4]·4CH3OH·H2O (2·4CH3OH·H2O). Single crystal X-ray structure analysis
showed that both 1·H2O and 2·4CH3OH·H2O possessed [M4(µ3-OCH3)4] tetranuclear cubane cores. Exchange
coupling parameters were calculated for both NiII and CoII complexes by the analysis of temperature dependence
of magnetic susceptibility by full-matrix diagonalization using a model, which included zero-field splitting
(ZFS) of spin levels of metal ions and two (for 1) or one (for 2) different J parameters. All exchange interactions
in 1 were found to be ferromagnetic, while for 2 it was concluded that the contributions of ZFS and exchange
interactions were comparable.
Conclusion: It was shown that β-sulfoketonate formed NiII and CoII cubanes, similarly to β-diketonates. Two
new cubane-like polynuclear complexes were synthesized and characterized. For nickel complex all exchange
interactions were ferromagnetic. The values of J for NiII complex were consistent with the ones, expected from
the J vs. Ni-O-Ni angle correlation previously proposed for Ni4 β-diketonate cubanes. Magnetic properties of
CoII analogue could be fitted using a model, which took into account ZFS of CoII and one J value. It was found
that the contributions of ZFS and exchange interactions were comparable.