Polyoxometalate‐Mediated Self‐Assembly of Single‐Molecule Magnets: {[XW₉O₃₄]₂[Mn^III₄Mn^II₂O₄(H₂O)₄]}¹²⁻

Abstract

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...

Control of the modularity of {Mo2O2S2}-containing polyoxometalates. Synthesis, structure and characterization of tri- and tetra-modular assemblies based on the [β-B-AsW9O33]9− anion

“…Polyoxometalate compounds (POMs) constitute potentially attractive chemical systems able to generate large assemblies with targeted functionalities [1][2][3][4][5] and promising applications in diverse fields of science, such as catalysis [6][7][8][9], medicine [10][11][12][13][14], electrochemistry [15] and material sciences [16][17][18][19][20][21]. To this end, this class of compounds offers the possibility to use polyvacant anions as primary building blocks to step by step construct sophisticated well-designed multi-unit compounds.…”

Self‐Assembly of a Giant Tetrahedral 3 d–4 f Single‐Molecule Magnet within a Polyoxometalate System

“…[17,24] In another approach, 3d-substituted Weakley-type dimers were reacted in the presence of 4f ions to substitute the labile outer M(H 2 O) groups in sandwich-type POMs,( [M 4 (H 2 O) 2 -(GeW 9 O 34 ) 2 ] nÀ ;M= Mn II ,C u II ). Thef ield of POM-based SMMs is relatively new,w ith only af ew SMMs having been reported to date, [22,[33][34][35][36][37][38][39][40][41][42][43] and the [ErW 10 O 36 ] 9À polyanion is the first example (2008) of aP OM exhibiting SMM behavior. SMMs are molecules showing slow relaxation of their magnetization below ablocking temperature (T B ).…”

“…SMMs are molecules showing slow relaxation of their magnetization below ablocking temperature (T B ). Thef ield of POM-based SMMs is relatively new,w ith only af ew SMMs having been reported to date, [22,[33][34][35][36][37][38][39][40][41][42][43] and the [ErW 10 O 36 ] 9À polyanion is the first example (2008) of aP OM exhibiting SMM behavior. Thef ield of POM-based SMMs is relatively new,w ith only af ew SMMs having been reported to date, [22,[33][34][35][36][37][38][39][40][41][42][43] and the [ErW 10 O 36 ] 9À polyanion is the first example (2008) of aP OM exhibiting SMM behavior.…”

Modular Inorganic Polyoxometalate Frameworks Showing Emergent Properties: Redox Alloys

“…[9] The potential applications of such an approach are highly appealing, since the combination of coordination-compound-based building blocks, exhibiting different electronic properties, could allow the targeted tuning of frameworks with properties intermediate between A and B; and even the realization of "emergent" or unexpected properties for the alloy.In an attempt to develop an approach to this goal, we opted to use polyoxometalate (POM) building blocks, which are early-transition-metal oxide clusters that are well-known for the versatility of their physical and chemical properties. [10] Their applications cover a wide area of chemical research including, but not limited to, catalysis, [11] molecular magnetism, [12] and medicine. [13] However, more importantly in the current context, they exhibit a very diverse and susceptible redox chemistry and therewith offer the prospect to fine-tune their electronic properties.…”