Mixed-valence polyoxovanadates(IV/V) have emerged as one of the most intricate class of supramolecular all-inorganic host species, able to encapsulate a wide variety of smaller guest templates during their self-assembly formation process. As showcased herein, the incorporation of guests, though governed solely by ultra-weak electrostatic and van der Waals interactions, can cause drastic effects on the electronic and magnetic characteristics of the shell complex of the polyoxovanadate. We address the question of methodology for the magnetochemical analysis of virtually isostructural {V^IV/V₂₂O₅₄}-type polyoxoanions of D_2d symmetry enclosing diamagnetic VO₂F₂⁻ (C_2v), SCN⁻ (C_∞v), or ClO₄⁻ (T_d) template anions. These induce different polarization effects related to differences in their geometric structures, symmetry, ion radii, and valence shells, eventually resulting in a supramolecular modulation of magnetic exchange between the V(3d) electrons that are partly delocalized over the {V₂₂O₅₄} shells. We also include the synthesis and characterization of the novel [V^VO₂F₂@HV^IV₈V^V₁₄O₅₄]⁶⁻ system that comprises the rarely encountered discrete difluorovanadate anion as a quasi-isolated guest species.

The reactions of lanthanide(III) nitrate salts (Dy^III, Tb^III, Gd^III, and Er^III) with the aroylhydrazone-based multidentate ligand 6-(hydroxymethyl)-N′-[1-(pyridin-2-yl)ethylidene]picolinohydrazide (LH₂) in the presence of Et₃N in a molar ratio of 1:1:4 afforded a series of homometallic tetranuclear lanthanide(III) complexes, [Ln₄(LH)₄(μ₂-OH)₃(μ₂-OMe)]4NO₃·xMeOH·yH₂O (1, Ln = Dy, x = 2, y = 4; 2, Ln = Tb, x = 2, y = 4; 3, Ln = Gd, x = 2, y = 5; and 4, Ln = Er, x = 3, y = 3). X-ray diffraction studies revealed that all of the complexes contain a tetracationic [2×2] square-grid-like [Ln₄(μ₂-OH)₃(μ₂-OMe)(μ₂-O)₄]⁴⁺ core, which is assembled by the concerted coordination action of four monoanionic [LH]^– ligands along with three μ₂-OH ligands and a μ₂-OMe ligand. All of the lanthanide centers are eight-coordinate and adopt distorted triangular-dodecahedral coordination geometries with two different types of coordination environments (6O,2N and 4O,4N). The magnetic susceptibility measurements of the complexes reveal both the presence of all-antiferromagnetic coupling interactions as well as both isotropic (3) and anisotropic (1, 2, 4) single-ion contributions, which do not result in slow relaxation characteristics typical of single-molecule magnets.

The emergence of increasingly complex molecular magnets, driven in particular by polyoxometalate chemistry, requires theoretical tools to accurately model and understand their magnetic phenomena. At the same time the unambiguous verification of model Hamiltonians remains a challenge, tied to factors ranging from available independent experimental data sets to available computation resources. Focusing on several recent examples for magnetically functionalized polyoxometalates and polynuclear coordination complexes, we demonstrate the recent developments of CONDON 2.0 that aim to address these issues, and suggest measurement protocols that will aid our multi-parameter computational approach.

The formation of a self-assembled multi-heterometal Keplerate polyoxomolybdate demonstrates compositional control of linker groups in spherical clusters. The resulting partially reduced {Mo^V/VI₇₂Fe^III₂₀V^IV₈Mo^V₂}-type cluster exhibits intramolecular ferrimagnetic ordering characteristic of such mixed-spin Keplerate systems. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Reaction of copper(II) salts with (S)-phenylethylaminodiacetate [(S)-peadaa] results in the 2D coordination network (S)-[Cu(peadaa)]_n (space group P2₁), which displays an unusual Cu···Cu connectivity mode. Solid-state circular dichroism (CD) indicates a strong interaction between the ligand chiral centre and the metal centres, whereas magnetic measurements show both antiferromagnetic coupling and strong ligand field effects. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

The linear trinuclear complex [Co₃(dpa)₂(Hdpa)₂(1-MeIm)₂(H₂O)₂] (1) and the two-dimensional coordination polymer [Co₂(dpa)₂(pyz)]_n (2; H₂dpa = diphenic acid, 1-MeIm = 1-methylimidazole, pyz = pyrazine) exemplify the versatile coordination chemistry of diphenic acid in conjunction with N-donor ligands. Complex 1 consists of a discrete arrangement of three Co^II atoms bridged by four diphenate ligands, whereas complex 2 contains a network of dinuclear Co^II units bridged by two diphenate ligands to form double-helical chains, which are further connected via pyrazine molecules into two-dimensional sheets. A magnetochemical analysis of these complexes reveals both strong ligand field effects on the Co^II4F free ion ground state and ferro- and antiferromagnetic exchange contributions mediated by the dpa ligands. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Recrystallization of freshly prepared Mn^II isobutyrate from PrOH or from EtOH/MeCN mixtures containing pyrazole (pyr) yields neutral mixed-valence decanuclear manganese(II/III) complexes, [Mn₁₀O₂(O₂CCHMe₂)₁₈(HO₂CCHMe₂)₂(PrOH)₂] (1) and [Mn₁₀O₂(O₂CCHMe₂)₁₈(pyr)₄] (2). The Mn₁₀ metal core of both 1 and 2 consists of eight Mn^II and two Mn^III centers and represents a new motif in the structural organization of polynuclear mixed-valence manganese clusters. Both, 1 and 2 exhibit a net antiferromagnetic exchange coupling resulting in singlet ground states. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)