Dedicated to Professor Hansgeorg Schnöckel on the occasion of his 65th birthday.The first evidence of single molecule magnet (SMM) behavior was discovered in the mixed-valence compounds [Mn [1] In the quest to synthesize SMMs that show hysteresis at higher temperatures, it has been recognized that large ground-state spins and a uniaxial anisotropy (large negative D and small E considering the following Hamiltonian anisotropy term:It is thus of interest to discover how to obtain the largest-spin ground state possible for a given size of aggregate. As well as having four unpaired electrons in its high-spin state, the Mn III ion is particularly useful for introducing large anisotropies through the presence of Jahn-Teller distortions in this configuration and has been the most thoroughly studied candidate for synthesizing new SMMs. Amongst the large number of aggregates containing manganese(III) in the literature, a Mn 25 cluster has been reported as having a ground spin state of 51/2.[4] Herein we report on the realization of the maximum-spin ground state of 83/2 for the aggregate [Mn

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).

Anisotropy can be introduced into the [Mn(19)]-aggregate, which currently has the highest known spin ground state of S = 83/2, by the targeted replacement of the central Mn(II) cation with Dy(III) leading to a [Mn(18)Dy] complex with the same core topology showing slow relaxation of the magnetisation.

Dedicated to Professor Hansgeorg Schnöckel on the occasion of his 65th birthday.The first evidence of single molecule magnet (SMM) behavior was discovered in the mixed-valence compounds [Mn [1] In the quest to synthesize SMMs that show hysteresis at higher temperatures, it has been recognized that large ground-state spins and a uniaxial anisotropy (large negative D and small E considering the following Hamiltonian anisotropy term:It is thus of interest to discover how to obtain the largest-spin ground state possible for a given size of aggregate. As well as having four unpaired electrons in its high-spin state, the Mn III ion is particularly useful for introducing large anisotropies through the presence of Jahn-Teller distortions in this configuration and has been the most thoroughly studied candidate for synthesizing new SMMs. Amongst the large number of aggregates containing manganese(III) in the literature, a Mn 25 cluster has been reported as having a ground spin state of 51/2.[4] Herein we report on the realization of the maximum-spin ground state of 83/2 for the aggregate [Mn

The reaction of [Mn6O2(Piv)(10)(4-Me-py)(2.5)(PivH)(1.5)] (1) (py: pyridine, Piv: pivilate) with N-methyldiethanolamine (mdeaH2) and Ln(NO3)3 x 6 H2O in MeCN leads to a series of nonanuclear compounds [Mn5Ln4(O)6(mdea)2(mdeaH)2(Piv)6(NO3)4(H2O)2]2 MeCN (Ln=Tb(III) (2), Dy(III) (3), Ho(III) (4), Y(III) (5)). Single-crystal X-ray diffraction shows that compounds 2-5 are isostructural, with the central core composed of two distorted {Mn(IV)Mn(III)Ln2O4} cubanes sharing a Mn(IV) vertex, representing a new heterometallic 3d-4f motif for this class of ligand. The four new compounds display single-molecule magnet (SMM) behaviour, which is modulated by the lanthanide ion used. Moreover, the values found for Delta(eff) and tau(o) for 3 of 38.6 K and 3.0 x 10(-9) s respectively reveal that the complex 3 exhibits the highest energy barrier recorded so far for 3d-4f SMMs. The slow relaxation of the magnetisation for 3 was confirmed by mu-SQUID measurements on an oriented single crystal and the observation of M versus H hysteresis loops below 1.9 K.

The tridecanuclear heterovalent mixed-metal (Mn11Gd2) complex [MnIII 9MnII 2GdIII 2(O)8(OH)2(O2CR)17(NO3)2(H2O)] has been obtained from the reaction of the hexanuclear compound [Mn6O2(Piv)10(4-Me-py)2.5(PivH)1.5] with Gd(NO3)3·6H2O in CH3CN. The complex presents an unusual “bell”-shaped core with a high-spin ground state and is a new member of the high-nuclearity 3d-4f single-molecule magnets family.

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.

Three isostructural disklike heptanuclear FeIII compounds of the general formula [FeIII7(mu3-O)3(L)3(mu-O2CCMe3)6(eta1-O2CCMe3)3(H2O)3], where L represents a di- or triethanolamine moiety, display a three-blade propeller topology, with the central Fe atom representing the axle or axis of the propeller. This motif corresponds to the theoretical model of a frustrated Heisenberg star, which is one of the very few solvable models in the area of frustrated quantum-spin systems and can, furthermore, be converted to an octanuclear cage for the case where L is triethanolamine to give [FeIII8(mu4O)3(mu4-tea)(teaH)3(O2CCMe3)6(N3)3].1/2MeCN.1/2H2O or [FeIII8(mu4O)3(mu4-tea)(teaH)3(O2CCMe3)6(SCN)3].2MeCN when treated with excess NaN3 or NH4SCN, respectively. The core structure is formally derived from that of the heptanuclear compounds by the replacement of the three aqua ligands by an {Fe(tea)} moiety, so that the 3-fold axis of the propeller is now defined by two central FeIII atoms. Magnetic studies on two of the heptanulcear compounds established unequivocally S = 5/2 spin ground state for these complexes, consistent with overall antiferromagnetic interactions between the constituent FeIII ions.