Research efforts in the quest for new single-molecule magnets (SMMs) have increasingly focused on systems either based on or else incorporating 4f ions. [1] For most pure 3d systems, and especially those containing the Mn III ion such as the original Mn 12 -Ac coordination cluster, spin reorientation is blocked when the ground state spin (S) combines with uniaxial magnetic anisotropy (D) to give an energy barrier to magnetic relaxation with the superexchange interactions between the metal centers leading to a molecular spin ground state and a molecular anisotropy. [2,3] The resultant exchange-based blocking of magnetization can be analyzed using a giant spin model. [4] In systems incorporating highly anisotropic 4f ions [1] it has become clear that magnetic interactions between 4f ions are weak and generally dipolar in nature. Here the single-ion spin and anisotropy become of greater relevance. For example, recent calculations on a Dy 2 SMM showed that the blocking mechanism largely arises from the individual Dy III ions with exchange-based behavior only seen at very low temperatures. [5] In systems combining 3d and 4f ions the aim is to embed highly anisotropic 4f ions into an exchangecoupled molecular 3d system, since 3d-4f interactions can be intermediate in magnitude between 3d-3d and 4f-4f. How-ever, analysis of the origins of the blocking mechanism in such systems is not straightforward and can generally only be achieved through detailed ab initio calculations, such as we recently reported for a Cr 4 Dy 4 SMM. [6] We now present a SMM comprising two Co II and two Dy III ions for which we can demonstrate the novel situation of single-ion blocking of the Dy III ions at higher temperatures with a crossover to molecular exchanged-based blocking at low temperatures.Reaction of Dy(NO 3 ) 3 ·6 H 2 O, Co(NO 3 ) 2 ·6 H 2 O, H 2 L and Et 3 N in the molar ratio 1:1:2:4 in MeOH gives crystalline red powder which was recrystallized from THF giving pink crystals of [Co 2 Dy 2 (L) 4 (NO 3 ) 2 (THF) 2 ]·4 THF (1) in 75% yield. H 2 L is the Schiff-base we previously described [7] resulting from condensation of o-vanillin and 2-aminophenol to give a "pocket ligand" capable of binding two different types of metal ion (see Figure S1 in the Supporting Information).Compound 1 crystallizes in the triclinic space group P " 1 with Z = 1. Within the core of the centrosymmetric complex, the metal ions are linked by four (L) 2À ligands in the butterfly (or defect-dicubane) topology (Figure 1). One of the two crystallographically independent ligands chelates Dy(1) through its imine nitrogen and the two phenolate oxygens O(1) and O(3) (corresponding to pocket I, see Figure S1 in the Supporting Information). Co(1) and Co(1') are linked Figure 1. Molecular structure of the Co 2 Dy 2 complex in 1.

A series of five isostructural tetranuclear lanthanide complexes of formula [Ln(4)(mu(3)-OH)(2)(mdeaH)(2)(piv)(8)], (mdeaH(2) = N-methyldiethanolamine; piv = pivalate; Ln = Tb (1), Dy (2), Ho (3), Er (4), and Tm (5)) have been synthesized and characterized. These clusters have a planar "butterfly" Ln(4) core. Magnetically, the Ln(III) ions are weakly coupled in all cases; the Dy(4) compound 2 shows Single Molecule Magnet (SMM) behavior.

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).

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.

A c c e p t e d M a n u s c r i p t Research highlights We analyzed aspects of the synthetic, reactivity, structural and magnetic chemistry of Co CCs  We classified all the polynuclear Cobalt coordination clusters found in CCDC (CCDC 5.32 Nov. 2010) higher than 4.  All the known Co coordination clusters can be searched by cluster topological symbol and nuclearity, compound name, dimensionality and Refcode. Highlights

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).

Three isoskeletal tetranuclear coordination clusters with general formula [MII2DyIII2L4(EtOH)6](ClO4)2⋅2 EtOH, (M=Co, 1; M=Ni, 2) and [NiII2DyIII2L4Cl2(CH3CN)2]⋅2 CH3CN (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.

A series of custom-designed, high yield, isoskeletal tetranuclear Zn/4f coordination clusters showing high efficiency as catalysts with low catalytic loadings in Friedel-Crafts alkylation are described for the first time. The possibility of altering the 4f centers in these catalysts without altering the core topology allows us to further confirm their stability via EPR and NMR, as well to gain insights into the plausible reaction mechanism, showcasing the usefulness of these bimetallic systems as catalysts.