The magnet-like behavior can beobserved by slow relaxation of the magnetization below theblocking temperature. Since the discovery of SMMs in theearly 1990s, this assumption has formed the basis for theunderstanding of the origin of the anisotropic barrier.However, in recent years the development of novel lantha-nide-only SMMs that challenge and defy this theory pose anumber of questions:

A Polynuclear Lanthanide Single-Molecule Magnet with a Record

Homometallic titanium oxo clusters are one of the most important groups of metal oxo clusters, with more than 300 examples characterized by X-ray structure analyses. Most of them are uncharged and are obtained by partial hydrolysis and condensation of titanium alkoxo derivatives. The cluster cores, ranging from 3 to >50 titanium atoms, are stabilized by organic ligands. Apart from residual OR groups, carboxylato and phosphonato ligands are most frequent. The article critically reviews and categorizes the known structures and works out basic construction principles by comparing the different cluster types.

Titanium-Oxo Clusters with Bi- and Tridentate Organic Ligands: Gradual Evolution of the Structures from Small to Big.

The novel organophosphorus-containing lithium salt Li(THF)[(C(2)O(4))B(O(2)PPh(2))(2)] (1; THF = tetrahydrofuran) was synthesized and characterized using a variety of spectroscopic techniques. An X-ray structural analysis on crystals of 1 grown from THF reveals a dimeric structure [Li(THF)(C(2)O(4))B(O(2)PPh(2))(2)](2)·THF, whereby the two units of 1 are bridged via P-O···Li interactions. Compound 1 displays high air and water stability and is also thermally robust, properties needed of electrolytes for their possible use as electrolytes and/or additives in lithium-ion battery applications.

http://ma.ecsdl.org/content/MA2011-01/8/394.full.pdf

A Hybrid Lithium Oxalate-Phosphinate Salt

Metal-containing clusters have attracted increasing attention over the past 2-3 decades. This intense interest can be attributed to the fact that these discrete metal aggregates, whose atomically precise structures are resolved by single-crystal X-ray diffraction (SCXRD), often possess intriguing geometrical features (high symmetry, aesthetically pleasing shapes and architectures) and fascinating physical properties, providing invaluable opportunities for the intersection of different disciplines including chemistry, physics, mathematical geometry and materials science. In this review, we attempt to reinterpret and connect these fascinating clusters from the perspective of Platonic and Archimedean solid characteristics, focusing on highly symmetrical and complex metal-containing (metal = Al, Ti, V, Mo, W, U, Mn, Fe, Co, Ni, Pd, Pt, Cu, Ag, Au, lanthanoids (Ln), and actinoids) high-nuclearity clusters, including metal-oxo/hydroxide/chalcogenide clusters and metal clusters (with metal-metal binding) protected by surface organic ligands, such as thiolate, phosphine, alkynyl, carbonyl and nitrogen/oxygen donor ligands. Furthermore, we present the symmetrical beauty of metal cluster structures and the geometrical similarity of different types of clusters and provide a large number of examples to show how to accurately describe the metal clusters from the perspective of highly symmetrical polyhedra. Finally, knowledge and further insights into the design and synthesis of unknown metal clusters are put forward by summarizing these "star" molecules.

Platonic and Archimedean solids in discrete metal-containing clusters.

Arsenic, Antimony and Bismuth

The reaction of organobismuth precursors with trityl-H-phosphinic acid in varying reaction conditions afforded colorless crystals, whose single crystal X-ray characterization revealed the formation of monomer {(Ph3Bi)[(Ph3C)(H)PO2]2}·3/2(CH3CN)2.1/2H2O (1) and butterfly shaped tetranuclear cluster Bi4(μ3-O)2[(Ph3C)(H)(PO2)]8·2CH2Cl2·1/2CH3CN.2H2O (2). The reaction of titanium isopropoxide with two different phosphinic acids trityl-H-phosphinic acid and cycP(O)(OH) led to isolation of cubane type octahedral complex {Ti8(μ2-O)8(μ2-OH)4[(Ph3C)(H)PO2]12}[3C7H8] (3) and hexanuclear complex Ti6(μ2-cycPO2)9(μ2-O)6(μ2-OH)3·4CH3CN·4H2O (4) respectively.

Bismuth and Titanium Phosphinates: Isolation of Tetra-, Hexa- and Octanuclear Clusters

Isolation and structural characterization of novel organoantimony(V)-based oxo clusters are reported. (RSb)4(OH)4(t-BuPO3)6 and (RSb)2(O)(t-BuPO3H)6 independently in the presence of pyridine under solvothermal conditions afford the hexanuclear organoantimonate clusters [(RSb)6(μ3-O)2(μ2-O)6(t-BuPO3)4], where R = p-i-PrC6H4 (1), p-ClC6H4 (2). Further, reaction of organostibonate phosphonate with Ti(OiPr)4 in the presence of pyridine under solvothermal conditions afforded the mixed-metal titanium stibonate hexanuclear clusters [(RSb)2Ti4(μ3-O)2(μ2-O)2(t-BuPO3)4(μ-OCH3)4(OCH3)4], where R = p-i-PrC6H4 (3), p-ClC6H4 (4). Band gap measurements were performed on 1-4. They reveal a remarkable reduction in the band gap on moving from the heavier main-group-based oxo cages (1 and 2) to the titanium-incorporated oxo cages (3 and 4).

Assembling Homometallic Sb6 and Heterometallic Ti4Sb2 Oxo Clusters.

This paper investigates the reactivity and optical properties of transition metal-incorporated organoantimony(V) clusters prepared by a solvothermal route. The detailed structural characterization of novel heterometallic M2Sb4 oxo clusters is reported herein. Single crystal X-ray diffraction revealed the formation of hexanuclear organoantimony(V) based oxo clusters [(p-ClC6H4Sb)4V2(O)2(μ3-O)2(μ2-O)2(t-BuPO3)4(μ2-OCH3)4] (1), [M2(p-iPr-C6H4Sb)4(μ3-O)2(μ2-O)2(μ2-OCH3)4(t-BuPO3)4(py)2]·xCH3OH, where M = Mn, x = 2 (2), Co, x = 1 (3), Ni, x = 2 (4) and Cu, x = 2 (5). The magnetic behaviour of the clusters was probed by magnetic susceptibility measurements. Optical absorption studies showed that bandgap reduction can be achieved by incorporating an appropriate transition metal into the homometallic Sb6 oxo cluster.

Tunable bandgaps in self-assembled transition metal-incorporated heterometallic M2Sb4 (M = V, Mn, Co, Ni, and Cu) oxo clusters.

The reactions of [Zn3Cl2(3,5-Me2PzH)4(t-BuPO3)2] with organostibonic acid in varying reaction conditions have been investigated. Single-crystal X-ray diffraction studies reveal the formation of [Zn2(p-ClC6H4Sb)2(O)2(OCH3)2(t-BuPO3)3(py)2] (1), [Zn2(p-ClC6H4SbV)4(SbIII)2(O)8(t-BuPO3H)4(t-BuPO3)2(py)2Cl2] (2), and [Zn2(RSb)4(O)4(OCH3)4(t-BuPO3)4(py)2], where R = p-ClC6H4 (3) and R = p-iPrC6H4 (4), respectively. Interestingly, in the synthesis of 2, complete dearylation of organoantimony moieties followed by C-F bond formation, a reduction from Sb (V) to Sb (III), and Sb···Cl weak intermolecular interactions have been observed. ESI-MS studies suggested that clusters 1-4 maintained their structural integrity in the solution state also. Solution NMR studies (1H, 31P, and 13C) support well the observed solid-state structures. 1-4 were tested for antibacterial activity using a microdilution assay. 1 and 4 showed the best activity with lower MIC values (0.78-6.25 μg/mL) against all the tested pathogens. The total antioxidant activity of 1-4 was evaluated through the phosphomolybdenum assay, which showed a total antioxidant activity ranging from 28.96 to 86.46 mg AAE/g compound with the ascorbic acid standard.

Tokala Navaneetha

Papers

Bismuth and Titanium Phosphinates: Isolation of Tetra-, Hexa- and Octanuclear Clusters

Assembling Homometallic Sb6 and Heterometallic Ti4Sb2 Oxo Clusters.

Tunable bandgaps in self-assembled transition metal-incorporated heterometallic M2Sb4 (M = V, Mn, Co, Ni, and Cu) oxo clusters.

Discrete Molecular Aggregates Based on ZnII and SbIII/V Ions Displaying Efficient Antibacterial and Antioxidant Properties.