Discrete, Cationic Palladium(II)-Oxo Clusters via f-Metal Ion Incorporation and their Macrocyclic Host-Guest Interactions with Sulfonatocalixarenes

We report on the discovery of the first two examples of cationic palladium(II)‐oxo clusters (POCs) containing f‐metal ions, [Pd^II₆O₁₂M₈{(CH₃)₂AsO₂}₁₆(H₂O)₈]⁴⁺ (M=Ce^IV, Th^IV), and their physicochemical characterization in the solid state, in solution and in the gas phase. The molecular structure of the two novel POCs comprises an octahedral {Pd₆O₁₂}¹²⁻ core that is capped by eight M^IV ions, resulting in a cationic, cubic assembly {Pd₆O₁₂M^IV₈}²⁰⁺, which is coordinated by a total of 16 terminal dimethylarsinate and eight water ligands, resulting in the mixed Pd^II‐Ce^IV/Th^IV oxo‐clusters [Pd^II₆O₁₂M₈{(CH₃)₂AsO₂}₁₆(H₂O)₈]⁴⁺ (M=Ce, Pd₆Ce₈; Th, Pd₆Th₈). We have also studied the formation of host‐guest inclusion complexes of Pd₆Ce₈ and Pd₆Th₈ with anionic 4‐sulfocalix[n]arenes (n=4, 6, 8), resulting in the first examples of discrete, enthalpically‐driven supramolecular assemblies between large metal‐oxo clusters and calixarene‐based macrocycles. The POCs were also found to be useful as pre‐catalysts for electrocatalytic CO₂‐reduction and HCOOH‐oxidation.

Discovery and Supramolecular Interactions of Neutral Palladium-Oxo Clusters Pd16 and Pd24

We report on the synthesis, structure, and physicochemical characterization of the first three examples of neutral palladium-oxo clusters (POCs). The 16-palladium(II)-oxo cluster [Pd16 O24 (OH)8 ((CH3 )2 As)8 ] (Pd16 ) comprises a cyclic palladium-oxo unit capped by eight dimethylarsinate groups. The chloro-derivative [Pd16 Na2 O26 (OH)3  Cl3  ((CH3 )2  As)8 ] (Pd16 Cl) was also prepared, which forms a highly stable 3D supramolecular lattice via strong intermolecular interactions. The 24-palladium(II)-oxo cluster [Pd24 O44 (OH)8 ((CH3 )2 As)16 ] (Pd24 ) can be considered as a bicapped derivative of Pd16 with a tetra-palladium-oxo unit grafted on either side. The three compounds were fully characterized 1) in the solid state by single-crystal and powder XRD, IR, TGA, and solid-state 1 H and 13 C NMR spectroscopy, 2) in solution by 1 H, 13 C NMR and 1 H DOSY spectroscopic methods, and 3) in the gas phase by electrospray ionization mass spectrometry (ESI-MS).

Soluble Hetero-Polyoxovanadates and Their Solution Chemistry Analyzed by Electrospray Ionization Mass Spectrometry

Polyoxometalates (POMs) are an intriguing class of compounds due to their tremendous structural variety and the wide spectrum of resulting properties, which make them interesting for applications in fields such as catalysis, material science or nanotechnology. Their ability to form large supramolecular architectures by self-assembly offers an entry to complex, functional systems. After an introduction into the structure and synthesis of POMs of the early transition metals, recently discovered water-soluble antimonato polyoxovanadates (Sb-POVs) and the investigation of their chemical reactivity are discussed. Electrospray ionization mass spectrometry (ESI-MS) is presented as an analytical technique suitable to investigate the structure of complex POM assemblies in solution and to probe the underlying reactivity and formation mechanisms. This Minireview highlights the first studies on the soluble Sb-POVs and how the knowledge of their reactivity obtained by ESI-MS has fostered the syntheses of numerous novel Sb-POV compounds.

Host-Guest-Induced Environment Tuning of 3d Ions in a Polyoxopalladate Matrix

A series of unprecedented supramolecular associates of phenylarsonate-capped {M^II Pd^II ₁₂ O₈ }-type (M=Co, Ni and Zn) polyoxopalladates with α-cyclodextrins (α-CD) was obtained and characterized in the solid state (single-crystal X-ray diffraction (XRD), FT-IR spectroscopy, elemental and thermogravimetric (TGA) analyses), in aqueous solution (¹ H and ¹³ C NMR) and in the gas phase (ESI-MS). The non-covalent host-guest interactions between the organopolyoxoanions and α-CD rings alter the O₈ coordination environment of a 3d transition metal ion (M^II ) situated at the center of a cuboid polyoxododecapalladate shell. This synthetically controlled "chemical pressure" effectively induces axial distortion of the otherwise cubic polyoxopalladate environment between two trans-positioned α-CD moieties. Its effect on the magnetic properties and the electronic structure of the Co^II derivative was assessed in a combined SQUID magnetometry, EPR, X-ray magnetic circular/linear dichroism (XMCD/XMLD), and X-ray absorption near-edge structure (XANES) spectroscopy study.

Rational Design of Organically Functionalized Polyoxopalladates and Their Supramolecular Properties

The Sr^II -centered 12-palladate(II) open-cube {SrPd₁₂ (OAc)₃ } has been systematically evolved by substitution of the three acetate ligands by a library of saturated carboxylic acids with increasing chain lengths leading to four novel polyoxopalladates(II) with the formula [SrPd₁₂ O₆ (OH)₃ (PhAsO₃ )₆ (L)₃ ]^4- (SrPd₁₂ L₃ , L=C_n H_2n+1 COO, n=2 to 5). These first examples of surfactant-type polyoxopalladates with a hydrophilic metal-oxo unit and three hydrophobic alkyl chains were characterized in the solid state (single-crystal XRD, FTIR, TGA), in solution (¹ H, ¹³ C NMR spectroscopy), and in the gas phase (ESI-MS). The two polyanions SrPd₁₂ L₃ with chain lengths of 5 and 6 are the first examples of polyoxopalladates that are soluble and stable in organic media. The Na salts of the amphiphilic polyoxopalladates SrPd₁₂ L₃ were shown to self-assemble into "blackberry"-type spherical supramolecular structures in dilute solutions, of which an unusual "volcano"-shaped trend of assembly size versus solvent polarity is chiefly influenced by directional hydrogen bonding interactions.