In this review, aspects of the syntheses, structures and magnetic properties of giant 3d and 3d/4f paramagnetic metal clusters in moderate oxidation states are discussed. The term "giant clusters" is used herein to denote metal clusters with nuclearity of 30 or greater. Many synthetic strategies towards such species have been developed and are discussed in this paper. Attempts are made to categorize some of the most successful methods to giant clusters, but it will be pointed out that the characteristics of the crystal structures of such compounds including nuclearity, shape, architecture, etc. are unpredictable depending on the specific structural features of the included organic ligands, reaction conditions and other factors. The majority of the described compounds in this review are of special interest not only for their fascinating nanosized structures but also because they sometimes display interesting magnetic phenomena, such as ferromagnetic exchange interactions, large ground state spin values, single-molecule magnetism behaviour or impressively large magnetocaloric effects. In addition, they often possess the properties of both the quantum and the classical world, and thus their systematic study offers the potential for the discovery of new physical phenomena, as well as a better understanding of the existing ones. The research field of giant clusters is under continuous evolution and their intriguing structural characteristics and magnetism properties that attract the interest of synthetic Inorganic Chemists promise a brilliant future for this class of compounds.

The current intense interest in polynuclear clusters stems not only from their aesthetically pleasing structures, magnetic interactions, and magnetostructural correlations, but also from the discovery that some function as nanoscale magnetic particles, or single-molecule magnets (SMMs).[1] Below their blocking temperature (T B ), such molecules behave as magnets and exhibit hysteresis in scans of magnetization versus dc field. This behavior results from the combination of a large ground spin state (S) with a large and negative (easy-axis type) magnetoanisotropy. SMMs have several potential applications, including high-density information storage, in which each bit of information is stored as the magnetization orientation of an individual molecule, and quantum computation, in which the molecules can serve as qubits.Although there are many known species displaying SMM behavior, [1][2][3][4][5] most of which are manganese-carboxylate complexes, [3][4][5] there is a continuing need for new SMMs. One of the most successful synthetic approaches to new polynuclear clusters involves the use of chelating ligands containing alkoxide functions, since these are good bridging groups and, thus, favor the formation of polynuclear products.[4] Recently, we have been investigating the use of 1,3-propanediol (H 2 pd) and 2-methyl-1,3-propanediol (H 2 mpd) in manganese-carboxylate chemistry. Herein, we report the syntheses, crystal structures, and magnetic properties of two new 3D coordination polymers based on [Mn 19 Na(m 4 -O) 9 (m 3 -[*] Dr.

A [Mn(III)(11)Mn(II)(6)(mu(4)-O)(8)(mu(3)-L)(4)](25+) (L = N(3)(-) or OCN(-)) octahedral unit is reported, occurring within 1D (1)(infinity) and 2D (2)(infinity) coordination polymers, as well as the corresponding 0D discrete cluster 3. It possesses a giant ground-state spin value, determined in the case of 3 to be S = 37, the second largest to be reported to date. In addition, compound 3 displays single-molecule magnet (SMM) behavior, and is thus the largest-spin SMM.

The syntheses, crystal structures, and magnetic properties of a new family of heterometallic Mn(40)Na(4) and homometallic Mn(44) loop-of-loops aggregates are reported. The reactions of [Mn(3)O(O(2)CMe)(6)(py)(3)]·py with 1,3-propanediol (pdH(2)) and 2-methyl-1,3-propanediol (mpdH(2)) in the presence of NaN(3) afforded [Mn(10)Na(μ(3)-O)(2)(O(2)CMe)(13)(pd)(6)(py)(2)](4) (1)(4) and [Mn(10)Na(μ(3)-O)(2)(O(2)CMe)(13)(mpd)(6)(py)(H(2)O)](4) (2)(4), respectively. Mn(40)Na(4) complexes (1)(4) and (2)(4) consist of four Mn(10) loops linked through Na(+) ions to give a supramolecular aggregate with a saddle-like topology. Magnetic characterization of compound (1)(4) showed that each Mn(10) loop has an S = 4 ground-state spin and displays frequency-dependent in-phase and out-of-phase ac susceptibility signals. It also exhibits hysteresis loops that, however, are not typical of single-molecule magnets (SMMs) due to the existence of interloop interactions between the neighboring Mn(10) units of (1)(4) through the diamagnetic Na(+) ions, and also intermolecular interactions between different Mn(40)Na(4) aggregates. The magnetically discrete Mn(44) analogue was targeted with high priority and finally prepared from the reaction of [Mn(3)O(O(2)CMe)(6)(py)(3)]·py with pdH(2) in the presence of Mn(ClO(4))(2)·6H(2)O. The loop-of-loops structure of [Mn(44)(μ(3)-O)(8)(O(2)CMe)(52)(pd)(24)(py)(8)](ClO(4))(OH)(3) (3) is essentially identical to those of (1)(4) and (2)(4), with the most significant difference being that the four Na(+) ions of (1)(4) and (2)(4) have been replaced with Mn(2+) ions. Compound 3 is thus best described magnetically as a Mn(44) cluster. In accord with this description and the stronger exchange coupling between the four Mn(10) loops expected through the connecting Mn(2+) ions, magnetic susceptibility measurements revealed that 3 has an S = 6 ground-state spin and displays frequency-dependent in-phase and out-of-phase ac signals. Magnetization vs dc field sweeps on single-crystals of 3 displayed scan rate- and temperature-dependent hysteresis loops confirming that complex 3 is a new SMM, and is thus the second largest Mn cluster and SMM reported to date.