George E. Kostakis

Structural motifs and topological representation of Mn coordination clusters.

Polynuclear coordination clusters have become of particular interest in recent times as a result of their relevance to bioinorganic chemistry and to the special area of molecule-based magnetic materials where cluster compounds behave as single-molecule magnets (SMMs). In this review we have focused on describing Mn coordination cluster complexes. Adopting our topological approach for the description of coordination clusters we present a means of classifying the structural motifs found in manganese clusters which range in nuclearity from 5 to 84, as well as some representative heterometallic Mn-M (M = K, Na, Ca, Sr, Ln) cluster complexes that have been reported. This sheds new light on the classification of the types of core structure accessible which, in turn, provides a useful means for developing the so-far missing magneto-structural correlation algorithm for these finite 0-D systems (212 references).

Coexistence of Distinct Single‐Ion and Exchange‐Based Mechanisms for Blocking of Magnetization in a CoII2DyIII2 Single‐Molecule Magnet

Two ways to relax: A defect-dicubane Co2Dy2 single-molecule magnet (SMM) displays slow relaxation of magnetization with a blocking temperature of 22 K (at 1500 Hz), the highest reported for a 3d–4f-based SMM. Analysis of the relaxation reveals two distinct blocking regimes, one of which is intraionic, localized on the DyIII ions, while the other is exchange-based.

Defect-Dicubane Ni2Ln2 (Ln = Dy, Tb) Single Molecule Magnets

Two pairs of Ni(2)Dy(2) and Ni(2)Tb(2) complexes, [Ni(2)Ln(2)(L)(4)(NO(3))(2)(DMF)(2)] {Ln = Dy (1), Tb (2)} and [Ni(2)Ln(2)(L)(4)(NO(3))(2)(MeOH)(2)]·3MeOH {Ln = Dy (3), Tb (4)} (H(2)L is the Schiff base resulting from the condensation of o-vanillin and 2-aminophenol) possessing a defect-dicubane core topology were synthesized and characterized. All four complexes are ferromagnetically coupled, and the two Dy-analogues are found to be Single Molecule Magnets (SMMs) with energy barriers in the range 18-28 K. Compound 1 displays step-like hysteresis loops, confirming the SMM behavior. Although 1 and 3 show very similar structural topologies, the dynamic properties of 1 and 3 are different with blocking temperatures (3.2 and 4.2 K at a frequency of 1500 Hz) differing by 1 K. This appears to result from a change in orientation of the nitrate ligands on the Dy(III) ions, induced by changes in ligands on Ni(II).

A method for topological analysis of high nuclearity coordination clusters and its application to Mn coordination compounds

A novel method for the topological description of high nuclearity coordination clusters (CCs) was improved and applied to all compounds containing only manganese as a metal center, the data on which are collected in the CCDC (CCDC 5.33 Nov. 2011). Using the TOPOS program package that supports this method, we identified 539 CCs with five or more Mn centers adopting 159 topologically different graphs. In the present database all the Mn CCs are collected and illustrated in such a way that can be searched by cluster topological symbol and nuclearity, compound name and Refcode. The main principles for such an analysis are described herein as well as useful applications of this method.

Magnetic coordination clusters and networks: synthesis and topological description

With the discovery of the phenomenon of single-molecule magnetism, coordination chemists have turned their attention to synthesizing cluster aggregates of paramagnetic ions. This has led to a plethora of coordination clusters with various topologies and diverse magnetic properties. In this paper, we present ways of describing and understanding such compounds as well as outlining a new approach, which we have recently developed, to describing cluster topology. Our approach is based upon and pays tribute to the huge contribution made to coordination chemistry through the development of the Schläfli symbols for describing architectures. To illustrate the developments that are taking place in modern coordination chemistry, we start with some basic definitions of relevance to what follows. Then we describe approaches to discovering new magnetically interesting 3d/4f clusters, assigning their topological descriptions. Finally, we show how the concepts behind the construction of metal–organic frameworks can be extended to using clusters as nodes in the frameworks to give super metal–organic frameworks.

Spin-Canting and Metamagnetic Behavior in a New Species from the Hydrothermal Co(II)-trans-3-Pyridylacrylate System

Hydrothermal reaction of CoCl(2) with trans-3-pyridylacrylic acid (3-pycaH) and Et(3)N results in the formation of a new three-dimensional network formulated as [{Co(4)(mu-H(2)O)(2)(3-pyca)(8)}(0.94){Co(5)(mu(3)-OH)(2)(3-pyca)(8)}(0.06)]. Magnetic measurements reveal that spin-canting and metamagnetic behavior coexist in this compound with a critical temperature at 9.5 K.

A Strongly Blue-Emitting Heptametallic [DyIII7] Centered-Octahedral Single-Molecule Magnet

The employment of 2-(β-naphthalideneamino)-2-(hydroxymethyl)-1-propanol and 2-aminoisobutyric acid in dysprosium chemistry has led to the isolation of a novel heptanuclear [Dy(III)(7)] cluster displaying single-molecule-magnetism behavior and blue-emitting properties.

Heteronuclear 3 d/DyIII Coordination Clusters as Catalysts in a Domino Reaction

Three isoskeletal tetranuclear coordination clusters with general formula [M(II) 2 Dy(III) 2 L4 (EtOH)6 ](ClO4 )2 ⋅2 EtOH, (M=Co, 1; M=Ni, 2) and [Ni(II) 2 Dy(III) 2 L4 Cl2 (CH3 CN)2 ]⋅2 CH3 CN (3), have been synthesized and characterized. These air-stable compounds, and in particular 3, display efficient homogeneous catalytic behavior in the room-temperature synthesis of trans-4,5-diaminocyclopent-2-enones from 2-furaldehyde and primary or secondary amines under a non-inert atmosphere.

Ferromagnetic heteronuclear {Fe4(Er,Lu)2} cyclic coordination clusters based on ferric wheels

A new family of hexanuclear ferric-lanthanide [Fe(III)(4)Ln(III)(2)(Htea)(4)(Piv)(6)(N(3))(4)] clusters, where Ln(III) = Er(1) and Lu(2) is reported. Variable temperature solid-state magnetic susceptibility studies of 1 and 2 reveal the presence of ferromagnetic (1) or competing anti- and ferromagnetic exchange interactions (2) between the constituent Fe(III) ions.

RhII-catalyzed cycloadditions of carbomethoxy iodonium ylides ☆

Carbomethoxy iodonium ylides, generated from methyl acetoacetate and methyl malonate, respectively, are exploited in synthesis of cyclopropanes, cyclopropenes as well as various heterocycles.