A family of dinuclear cobalt complexes with bridging bis(dioxolene) ligands derived from 3,3,3',3'-tetramethyl-1,1'-spirobis(indane-5,5',6,6'-tetrol) (spiroH4) and ancillary ligands based on tris(2-pyridylmethyl)amine (tpa) has been synthesized and characterized. The bis(dioxolene) bridging ligand is redox-active and accessible in the (spiro(cat-cat))(4-), (spiro(SQ-cat))(3-), and (spiro(SQ-SQ))(2-) forms, (cat = catecholate, SQ = semiquinonate). Variation of the ancillary ligand (Mentpa; n = 0-3) by successive methylation of the 6-position of the pyridine rings influences the redox state of the complex, governing the distribution of electrons between the cobalt centers and the bridging ligands. Pure samples of salts of the complexes [Co2(spiro)(tpa)2](2+) (1), [Co2(spiro)(Metpa)2](2+) (2), [Co2(spiro)(Me2tpa)2](2+) (3), [Co2(spiro)(Me3tpa)2](2+) (4), [Co2(spiro)(tpa)2](3+) (5), and [Co2(spiro)(tpa)2](4+) (6) have been isolated, and 1, 4, and 6 have been characterized by single crystal X-ray diffraction. Studies in the solid and solution states using multiple techniques reveal temperature invariant redox states for 1, 2, and 4-6 and provide clear evidence for four different charge distributions: 1 and 2 are Co(III)-(spiro(cat-cat))-Co(III), 4 is Co(II)-(spiro(SQ-SQ))-Co(II), 5 is Co(III)-(spiro(SQ-cat))-Co(III), and 6 is Co(III)-(spiro(SQ-SQ))-Co(III). Of the six complexes, only 3 shows evidence of temperature dependence of the charge distribution, displaying a rare thermally induced two-step valence tautomeric transition from the Co(III)-(spiro(cat-cat))-Co(III) form to Co(II)-(spiro(SQ-cat))-Co(III) and then to Co(II)-(spiro(SQ-SQ))-Co(II) in both solid and solution states. This is the first time a two-step valence tautomeric (VT) transition has been observed in solution. Partial photoinduction of the VT transition is also possible in the solid. Magnetic and spectroscopic studies of 5 and 6 reveal that spiroconjugation of the bis(dioxolene) ligand allows electronic interaction across the spiro bridge, suggesting that thermally activated vibronic coupling between the two cobalt-dioxolene moieties plays a key role in the two-step transition evident for 3.

The exchange of electric charges between a chemical reaction centre and an external electrical circuit is critical for many real-life technologies. This perspective explores the "wiring" of highly redox-active molecular metal oxide anions, so-called polyoxometalates (POMs) to conductive organic polymers (CPs). The major synthetic approaches to these organic-inorganic hybrid materials are reviewed. Typical applications are highlighted, emphasizing the current bottlenecks in materials development. Utilization of the composites in the fields of energy conversion, electrochemical energy storage, sensors and nanoparticle "wiring" into conductive materials are discussed. The outlook section presents the authors' views on emerging fields of research where the combination of POMs and CPs can be expected to provide novel materials for groundbreaking new technologies. These include light-weight energy storage, high-sensitivity toxin sensors, artificial muscles, photoelectrochemical devices and components for fuel cells.

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We report the spontaneous and rapid growth of micrometre-scale tubes from crystals of a metal oxide-based inorganic solid when they are immersed in an aqueous solution containing a low concentration of an organic cation. A membrane immediately forms around the crystal, and this membrane then forms micrometre-scale tubes that grow with vast aspect ratios at controllable rates along the surface on which the crystal is placed. The tubes are composed of an amorphous mixture of polyoxometalate-based anions and organic cations. It is possible for liquid to flow through the tubes, and for the direction of growth and the overall tube diameter to be controlled. We demonstrate that tube growth is driven by osmotic pressure within the membrane sack around the crystal, which ruptures to release the pressure. These robust, self-growing, micrometre-scale tubes offer opportunities in many areas, including the growth of microfluidic devices and the self-assembly of metal oxide-based semipermeable membranes for diverse applications.

Five members of a new family of polyoxometalate (POM)-ligated tetranuclear rare earth metal complexes have been synthesized and characterized. These compounds have the general formula (HDABCO)(8)H(5)Li(8)[Ln(4)As(5)W(40)O(144)(H(2)O)(10)(gly)(2)]·25H(2)O [Ln = Gd (1), Tb (2), Dy (3), Ho (4) and Y = (5), HDABCO = monoprotonated 1,4-diazabicyclooctane, gly = glycine] and were synthesized from the preformed POM precursor [As(2)W(19)O(67)(H(2)O)](14-). The structure is comprised of two {As(2)W(19)O(68)} building blocks linked by a unit containing four rare earth ions and two additional tungsten centers, with the two glycine ligands playing a key bridging role. Two crystallographically distinct rare earth ions are present in each complex, both of which possess axially compressed, approximate square antiprismatic coordination geometry. The variable-temperature magnetic susceptibility profiles for 2-4 are dominated by population/depopulation of the M(J) sublevels of the relevant ground terms, and fitting of the data has afforded the ligand field parameters in each case, from which the energies of the M(J) sublevels can be calculated. Alternating current magnetic susceptibility data have revealed the onset of slow magnetic relaxation for 3, with the energy barrier to magnetization reversal determined to be 3.9(1) K. As for other lanthanoid complexes that display slow magnetic relaxation, this energy barrier is due to the splitting of the M(J) sublevels of the Dy(3+) ions such that the ground sublevel has a relatively large |M(J)| value, thereby affording Ising-type magnetic anisotropy. This complex is thus the first POM-supported polynuclear lanthanoid-based SMM. Simulation of the W-band EPR spectrum of 1 has afforded the spin Hamiltonian parameters for this species, while the X-band EPR spectrum of 3 indicates the presence of a non-negligible fourth-order transverse component of the anisotropy, which is responsible for the small effective energy barrier observed for 3 and the absence of slow magnetic relaxation for 4.

The reaction of terbium and europium salts with the lacunary polyxometalate (POM) [As(2)W(19)O(67)(H(2)O)](14-) and 2-picolinic acid (picH) affords the ternary lanthanoid-organic-polyoxometalate (Ln-org-POM) complexes [Tb(2)(pic)(H(2)O)(2)(B-β-AsW(8)O(30))(2)(WO(2)(pic))(3)](10-) (1), [Tb(8)(pic)(6)(H(2)O)(22)(B-β-AsW(8)O(30))(4)(WO(2)(pic))(6)](12-) (2), and [Eu(8)(pic)(6)(H(2)O)(22)(B-β-AsW(8)O(30))(4)(WO(2)(pic))(6)](12-) (3). A detailed synthetic investigation has established the conditions required to isolate pure bulk samples of the three complexes as the mixed salts H(0.5)K(8.5)Na[1]·30H(2)O, K(4)Li(4)H(4)[2]·58H(2)O, and Eu(1.66)K(7)[3]·54H(2)O, each of which has been characterized by single crystal X-ray diffraction. Complexes 2 and 3 are isostructural and can be considered to be composed of two molecules of 1 linked through an inversion center with four additional picolinate-chelated lanthanoid centers. When irradiated with a laboratory UV lamp at room temperature, compounds K(4)Li(4)H(4)[2]·58H(2)O and Eu(1.66)K(7)[3]·54H(2)O visibly luminesce green and red, respectively, while compound H(0.5)K(8.5)Na[1]·30H(2)O is not luminescent. A variable temperature photophysical investigation of the three compounds has revealed that both the organic picolinate ligands and the inorganic POM ligands sensitize the lanthanoid(III) luminescence, following excitation with UV light. However, considerably different temperature dependencies are observed for Tb(III) versus Eu(III) through the two distinct sensitization pathways.

Extended modular frameworks that incorporate inorganic building blocks represent a new field of research where "active sites" can be engineered to respond to guest inclusion. [1][2] This process can initiate highly specific chemical reactions [3] that switch the overall nature of the framework, and it may even be developed to facilitate directed chemical reactions similar to those found in enzymatic systems. Achievement of this degree of sophistication requires the ability to control the framework assembly as precisely as in metal-organic frameworks, [1,[4][5][6] combined with the stability and functionality of inorganic zeolites and related systems. [7] Although progress has been made in fine-tuning the reactivity of framework materials, [8] reversible redox single-crystal to single-crystal (SC-SC) transformations that retain long-range order have not yet been observed.[9] Thus, it can be suggested that the best way to engineer redox-and electronically active frameworks would be to incorporate building blocks based on polyoxometalate (POM) clusters, [10][11][12] constructed from {MO x } units where M = Mo, W, V, Nb and x = 4-7. These clusters are attractive units for the construction of such frameworks since they are highly redox active and can incorporate a range of main-group-templating {XO n } units, as exemplified by the Keggin ion [M 12 nÀ . This ion can incorporate anions such as phosphate and silicate, and can bind transition metals within structural vacancies.[13]Herein we show that the directed assembly of a pure metal oxide framework, [(C 4 H 10 NO) 40 [14] based upon substituted Keggin-type POM building blocks, yields a material that can undergo a reversible redox process that involves the simultaneous inclusion of the redox reagent with a concerted and spatially ordered redox change of the framework. Compound 1 ox can also be repeatedly disassembled into its building blocks by dissolution in hot water; subsequent recrystallization results in the reassembly of unmodified 1 ox . These unique properties mean that this compound defines a new class of materials that bridges the gap between coordination compounds, metalorganic frameworks, and solid-state oxides. Furthermore, it has been shown that all the manganese(III) centers in 1 ox can be "switched" to manganese(II) using a suitable reducing agent to give the fully reduced framework 1 red . The redox process occurs with retention of long-range order by cooperative structural changes within the W-O-Mn linkages that connect the Keggin units. The nature of the redox process can be precisely deduced because of the SC-SC transformation between the oxidized and reduced states of the framework. This is important as, until now, covalently connected 3D polyoxometalate-based frameworks with large pockets (greater than 10 ) could be assembled only by the addition of "bridging" electrophiles. However, these solids typically have low stabilities and are not amenable to systematic design strategies, for instance the introduction of redox switchability.The approac...

Polyoxometalates (POMs), anionic oxide clusters of the early transition metals, [1] represent a vast class of inorganic materials with a virtually unmatched range of properties applicable to biology, [2] magnetism, [3] materials science, [4] or catalysis. [5] This unique span of properties qualifies POMbased materials as prime candidates for the designed construction of electronically interesting materials. Polyoxometalates possess enormous diversity in both size and structure [1b, 6] and thereby provide access to a huge library of readily available and controllable fragments, that is, secondary building units (SBUs) [7] that can be interconnected by electrophiles.The development of novel magnetic polyoxometalates [8] targets either the magnetic functionalization of the metal oxide fragment itself, which is mostly relevant for polyoxovanadates such as {V 15 As 6 }, [9] the interlinking of POM building blocks, as seen for {Mo 72 Fe 30 }, [10] [PMo 12 O 40 -(VO) 2 ] 5À , [11] or the use of lacunary POM fragments as multidentate ligands binding to polynuclear paramagnetic coordination clusters (e.g., {W 18 Cu 6 } [12] and {W 48 Cu 20 } [13] ). In particular, we reasoned that targeting the assembly of a mixed-valence manganese-based cluster [14][15] within a polyoxometalate ligand cage could offer many fantastic new possibilities for design and manipulation. For example, the POM "ligands" could be useful to "dilute" single-molecule magnets (SMMs) to remove unwanted dipolar interactions and also because of the intrinsic redox activity of the POM "ligands" that could allow additional routes to control magnetic-exchange pathways or introduce other functionality for device applications.[11] In addition, the POM shells are themselves surface compatible as well as being excellent ligands and SBUs that will allow a very high degree of reliable design and assembly that is not possible to achieve in SMMs based on first-row transition metals alone.One of the major limitations in the development of SMMs is that the underlying design strategies lie within the boundaries set by the serendipitous self-assembly of metal ions with bridging ligands of different connectivites and the controlled assembly of rigid building blocks typified by metallocyanide (Prussian blue-type) chemistry.[16] Within this scheme there have also been attempts to influence the primary SMM parameters (spin ground state and molecular anisotropy) deliberately through targeted structural and chemical modification.[17] However, despite the comparably precise structural control on the molecular level that characterizes POM chemistry, no single-molecule magnet has yet been derived from a polyoxometalate, as evidenced by hysteresis in magnetization versus field studies. Although several POM-based systems with high spin ground states or significant magnetic anisotropy are known, [18] (2). The cluster anions in 1 and 2 are structural analogues and differ only in the heteroatoms X that are central to the {XW 9 O 34 } fragments (X = Ge in 1, X = Si in 2), see Fig...