A series of MIICuII3stars (M = Mn, Ni, Cu, Zn) exhibiting unusual magnetic properties
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Inorg. Chem. 54 (1): 117–131 (2015)

The work in this report describes the syntheses, electrospray ionization mass spectrometry, structures, and exptl. and d. functional theor. (DFT) magnetic properties of four tetrametallic stars of compn. [MII(CuIIL)3](ClO4)2 (1, M = Mn; 2, M = Ni; 3, M = Cu; 4, M = Zn) derived from a single-compartment Schiff base ligand, N,N'-bis(salicylidene)-1,4-butanediamine (H₂L), which is the [2 + 1] condensation product of salicylaldehyde and 1,4-diaminobutane. The central metal ion (MnII, NiII, CuII, or ZnII) is linked with two μ2-phenoxo bridges of each of the three [CuIIL] moieties, and thus the central metal ion is encapsulated in between three [CuIIL] units. The title compds. are rare or sole examples of stars having these metal-ion combinations. In the cases of 1, 3, and 4, the four metal ions form a centered isosceles triangle, while the four metal ions in 2 form a centered equilateral triangle. Both the variable-temp. magnetic susceptibility and variable-field magnetization (at 2-10 K) of 1-3 were measured and simulated contemporaneously. While the MnIICuII3 compd. 1 exhibits ferromagnetic interaction with J = 1.02 cm-1, the NiIICuII3 compd. 2 and CuIICuII3 compd. 3 exhibit antiferromagnetic interaction with J = -3.53 and -35.5 cm-1, resp. Variable-temp. magnetic susceptibility data of the ZnIICuII3 compd. 4 indicate very weak antiferromagnetic interaction of -1.4 cm-1, as expected. On the basis of known correlations, the magnetic properties of 1-3 are unusual; it seems that ferromagnetic interaction in 1 and weak/moderate antiferromagnetic interaction in 2 and 3 are possibly related to the distorted coordination environment of the peripheral copper(II) centers (intermediate between square-planar and tetrahedral). DFT calcns. were done to elucidate the magnetic properties. The DFT-computed J values are quant. (for 1) or qual. (for 2 and 3) matched well with the exptl. values. Spin densities and magnetic orbitals (natural bond orbitals) correspond well with the trend of obsd./computed magnetic exchange interactions. [on SciFinder(R)]
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