The metal–radical approach is a well-established synthetic way toward multi-spin systems that relies on the coordination of stable radical ligands with transition metal ions. The advantage offered by ...the use of paramagnetic ligands is that metal–radical magnetic exchange coupling is direct between the magnetic orbitals of the radical and metal ion. With the aim of further exploring this approach, crystals of four heterspin complexes, M(hfac)2LF2 {M = Mn, Co, or Ni and hfac = hexafluoroacetylacetonate} and Cu(hfac)2LFn, were obtained using a new fluorinated pyrazolyl-substituted nitronyl nitroxide radical, 4,4,5,5-tetramethyl-2-(5-fluoro-1-methyl-1H-pyrazol-4-yl)-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (LF) as a ligand. The newly synthesized complexes were fully characterized, including X-ray crystallography and magnetometry. XRD analysis revealed that complexes M(hfac)2LF2 have similar dimer structures in which a metal ion is in a six-coordinated environment with four O atoms from the two hfac ligands, one radical O atom, and one pyrazole N atom from ligand LF. Nonetheless, the packing patterns of the complexes were found to be considerably different. In Mn(hfac)2LF2, there are no magnetically important short contacts between manganese dimers. By contrast, in Co(hfac)2LF2 and Ni(hfac)2LF2, there are short contacts between non-coordinate O atoms of nitronyl nitroxide moieties. Magnetic behaviors of M(hfac)2LF2 showed that the M ions and the directly coordinated radicals are strongly antiferromagnetically coupled (JMn-ON = −84.1 ± 1.5 cm−1, JCo-ON = −134.3 ± 2.6 cm−1, and JNi-ON = −276.2 ± 2.1 cm−1; H^=−2JS⃑^MS⃑^NO). Notably, the magnetization of Mn(hfac)2LF2 having molecular structure proved to be accompanied by hysteresis. The Cu(hfac)2LFn complex has a chain-polymer structure with alternating magnetic fragments: three spin exchange clusters {ONO–Cu(II)–ONO} and {Cu(II)} ions. Despite the direct coordination of radicals, its magnetic properties are weakly ferromagnetic (JCu-ON = 14.8 ± 0.3 cm−1).
We consider the calculation of modulation power losses in a system "induction motor-inverter" for various pulse width modulation (PWM) methods of the supply voltage. Presented values of modulation ...power losses are the result of modeling a system "DC link - two-level three-phase voltage inverter - induction motor - load". In this study the power losses in a system "induction motor - inverter" are computed, as well as losses caused by higher harmonics of PWM supply voltage, followed by definition of active power consumed by the DC link for a specified value mechanical power on the induction motor shaft. Mechanical power was determined by the rotation speed and the torque on the motor shaft in various quasi-sinusoidal supply voltage PWM modes. These calculations reveal the best coefficient of performance (COP) in a system of a variable frequency drive (VFD) with independent voltage inverter controlled by induction motor PWM.
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