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The novel tetranuclear copper (II) cluster namely (C 5 H 7 N 2 ) 2 [Cu 4 (µ 4 -O)(µ 3 -SO 4 ) 4 (C 5 H 6 N 2 ) 4 ] (1) was obtained by the hydrothermal reaction of copper (II) sulfate and the monodentate 4-aminopyridine ligand. Single-crystal X-ray diffraction indicated that compound 1 crystallizes in the monoclinic system, space group C2/c, a = 25.827 (5) Å, b = 10.657 (5) Å, c = 19.838 (5) Å, β = 121.195 (5)°, V = 4671 (3) Å 3 and Z = 4. The discrete [Cu 4 (µ 4 -O)(µ 3 -SO 4 ) 4 (C 5 H 6 N 2 ) 4 ] 2− anion present in (1) contains Cu 4 (µ 4 -O) tetrahedra with the copper centres held together by four sulfate groups in two different coordinated modes: η 1 .η 1 .η 1 .μ 3 :3.1110 and η 2 .η 1 .μ 3 :3.2100 (Harris notation). Again, the structural arrangement and the intermolecular interactions such as hydrogen-bonding are discussed from which supramolecular assembly was formed. The thermal behavior of the compound, studied by TG-DSC, showed that the successive decomposition stages of precursor lead to the formation of intermediate phases during heating giving rise to the copper oxide as a final product at 700 °C. Characteristic IR bands are discussed in terms of the known structure of (1). The magnetic properties of (1) have been studied by variable temperature dc magnetic susceptibility techniques. Using an idealized geometry of the tetranuclear cluster the magnitude of exchange coupling constants is examined. The calculations within the simplified model reveal a relatively strong superexchange interaction between the Cu(II) ions (on the order of a 100 cm −1 ) indicating a substantial anisotropy with the apical coupling being ferromagnetic while the equatorial coupling favoring an antiferromagnetic arrangement of the spin components. [ABSTRACT FROM AUTHOR]

Graphical abstract A combination of dinuclear Fe O Fe and tetranuclear Co CN Fe O Fe NC Co units with strong intramolecular antiferromagnetic coupling. Abstract The synthesis, characterization, structure and magnetic properties of a hexametallic mixed-metal iron(III)–cobalt(III) compound are described. The compound has been characterized by standard spectroscopic and analytical methods to determine its composition. Single-crystal X-ray diffraction has shown that the asymmetric unit consists of discrete dinuclear dicationic units of {(µ-oxido-µ-[sulfato- O1 , O2 ])bis[tris(2-pyridyl-methyl)amineiron(III)]}2+, herein designated as Fe12, and two half-dinuclear dianionic units of {(µ-oxido)bis[(µ-cyanido- κN -pentacyanidocobaltato(III))(tris(2-pyridyl-methyl)-amine)iron(III)]}2− units, herein designated as Fe33a and Fe44b, generating the overall composition Co 2 Fe 4 O 2 (CN) 12 (tpa) 4 , 1 , where tpa is tris(2-pyridyl-methyl)amine. X-ray structural results and thermogravimetric and differential scanning calorimetry measurements also indicate that the compound, depending upon its history, may contain up to nine interstitial waters of hydration, herein designated as 1 (H 2 O) 9. In the dinuclear dicationic unit, the bridging Fe O Fe bond in Fe12 is bent and there is also an Fe O S O Fe sulfato-based bridge with an angle of 132.8°. In contrast, in the two dinuclear dianionic units, Fe33a and Fe44b, the Fe O Fe bond angle is crystallographically constrained to be 180°. The Co CN Fe bonds are almost co-linear, with Co C N angles of 176° and C N Fe angles of 169°. In each species the tpa ligand is tripodal tetradentate with the tertiary amine trans to the sulfato ligand or to the cyanide ligand in the dianions or the bridged oxido ligand in the dications. Bond lengths and angles are all in the typical range for Fe(III) and Co(III) compounds. The magnetic behavior of 1 (H 2 O) 9 , obtained upon cooling from 300 to 2 K, reveals a strong antiferromagnetic interaction between the Fe(III) ions in each dinuclear unit. Attempts to discriminate between the two Fe(III) dinuclear units in 1 (H 2 O) 9 have in all cases led to two very different Heisenberg isotropic exchange coupling constants, namely J = −220(2) and −716(32) cm−1 for 1 (H 2 O) 9 ; i.e. one of the dinuclear units, probably the Fe12 unit, is so strongly antiferromagnetically coupled that it is close to diamagnetic between 2 and ca. 250 K and has a Heisenberg S = 0 ground state. [ABSTRACT FROM AUTHOR]