Search

The construction of large and complex supramolecular architectures through self‐assembly is at the forefront of contemporary coordination chemistry. Notwithstanding great success in various systems using anionic bridges (e.g., O2− or S2−) or organic ligands (e.g., pyridine or carboxylate ligands), the assembly of large cyanide‐bridged clusters with increasing nuclearity remains a formidable synthetic challenge. In this study, it is achieved in preparing two heterometallic cyanometallate clusters with unprecedented complexity, [Fe20Co20] (1) and [Fe12Co15] (2), by creating the "flexibility" through a versatile ligand of bis((1H‐imidazol‐4‐yl)methylene)hydrazine (H2L) and low‐coordinate cobalt. Complex 1 features a super‐square array of four cyanide‐bridged [Fe4Co4] cube subunits as the corners that are interconnected by four additional [FeCo] units, resulting in a torus‐shaped architecture. Complex 2 contains a lantern‐like core‐shell cluster with a triple‐helix kernel of [Co3L3] enveloped by a [Fe12Co12] shell. The combined structure analysis and mass spectrometry study reveal a hierarchical assembly mechanism, which sheds new light on constructing cyanometallate nanoclusters with atomic precision. Moreover, complex 1 undergoes a thermally induced electron‐transfer‐coupled spin transition (ETCST) between the diamagnetic {FeIILS(µ‐CN)CoIIILS} and paramagnetic {FeIIILS(µ‐CN)CoIIHS} configurations (LS = low spin, HS = high spin) above room temperature, representing the largest molecule displaying electron transfer and spin transition characteristic. [ABSTRACT FROM AUTHOR]

The engineering of intermolecular interaction is challenging but critical for magnetically switchable molecules. Here, we prepared two cyanide‐bridged [Fe4Co4] cube complexes via the alkynyl‐ and alcohol‐functionalized trispyrazoyl capping ligands. The alkynyl‐functionalized complex 1 exhibited a thermally‐induced incomplete metal‐to‐metal electron transfer (MMET) behaviour at around 220 K, while the mixed alkynyl/alcohol‐functionalized cube of 2 showed a complete and abrupt MMET behaviour at 232 K. Remarkably, both compounds showed a long‐lived photo‐induced metastable state up to 200 K. The crystallographic study demonstrated that the incomplete transition of 1 was likely due to the possible elastic frustration originating from the competition between the anion‐propagated elastic interactions and inter‐cluster alkynyl‐alkynyl & CH‐alkynyl interactions, whereas the latter are eliminated in 2 as a result of the partial substitution by the alcohol‐functionalized ligand. Additionally, the introduction of chemically distinguishable cobalt centers within the cube unit of 2 did not lead to a two‐step but a one‐step transition, possibly because of the strong ferroelastic intramolecular interaction through the cyanide bridges. [ABSTRACT FROM AUTHOR]

The self-assembly of organic TCNQF- radicals (2-fluoro-7,7,8,8-tetracyano-p-quinodimethane) and the anisotropic [Tb(valpn)Cu]3+ dinuclear cations produced a singlechain magnet (SCM) involving stacking interactions of TCNQF- radicals (H2valpn is the Schiff base from the condensation of o-vanillin with 1,3-diaminopropane). Static and dynamic magnetic characterizations reveal that the effective energy barrier for the reversal of the magnetization in this hetero-tri-spin SCM is significantly larger than the barrier of the isolated single-molecule magnet based on the {TbCu} dinuclear core. [ABSTRACT FROM AUTHOR]

To shed light on magnetic properties of the magnetic exchange molecular cluster containing the constituent metal ion with unquenched orbital angular momentum, as representative examples two octahedrally coordinated high-spin Co(II)-cluster complexes were synthesized and characterized: complex (1) [Co3(Hbzp)6][ClO4]2· 2CH3OH·H2O (bzp = 2-benzoylpyridine) with a linear core Co(III)-Co(II)-Co(III) and complex (2) [Co4L(N3)4(CH3CN)4](ClO4)4·2H2O (L = Macrocyclic schiff base of tetra-2,6-pyridinedicarboxaldehyde-tetra-ethane-1,2-diamine) comprised by two nearly independent Co(II)-dimers. Following Lines' isotropic exchange approximation the magnetic interaction effective Hamiltonian was introduced, which includes the exchange interactions, the spin-orbit coupling, the low-symmetry crystal field, and the intercluster exchange interaction. On the basis of the irreducible tensor operator approach to solve Hamiltonian we have coded the software, BJMAG package, and performed the best-fit procedure for experimentally temperature variable magnetic susceptibilities for the complexes (1) and (2). The best-fit parameters were obtained as follows: λ = -126 cm-1, Δ = 432 cm-1, κ = 0.96, mJ′ = 2.7 cm-1 for the complex (1) and λ = -165 cm-1, Δ = 960 cm-1, κ = 0.95, J′ = 9 cm-1, mJ′ = -0.1 cm-1 for the complex (2). To further elucidate the individual role of each interaction in the employed model, the effects of the key factors governing the magnetic properties on temperature variable magnetic susceptibilities were examined in detail. The significance of the intercluster exchange interactions at low temperatures was briefly discussed and a self-consistent molecular field to calculate the thermally average spin of the nearest neighbor in the intercluster interaction was proposed. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [ABSTRACT FROM AUTHOR]