Dinuclear Palladium Complexes with Two Ligand‐Centered Radicals and a Single Bridging Ligand: Subtle Tuning of Magnetic Properties

The facile and tunable preparation of unique dinuclear [(L^?)Pd?X?Pd(L^?)] complexes (X=Cl or N₃), bearing a ligand radical on each Pd, is disclosed, as well as their magnetochemistry in solution and solid state is reported. Chloride abstraction from [PdCl( NNO^ISQ )] ( NNO^ISQ =iminosemiquinonato) with TlPF₆ results in an unusual monochlorido‐bridged dinuclear open‐shell diradical species, [{Pd( NNO ^ISQ)}₂(μ‐Cl)]⁺, with an unusually small Pd‐Cl‐Pd angle (ca. 93°, determined by X‐ray). This suggests an intramolecular d⁸–d⁸ interaction, which is supported by DFT calculations. SQUID measurements indicate moderate antiferromagnetic spin exchange between the two ligand radicals and an overall singlet ground state in the solid state. VT EPR spectroscopy shows a transient signal corresponding to a triplet state between 20 and 60 K. Complex 2 reacts with PPh₃ to generate [Pd(NNO^ISQ)(PPh₃)]⁺ and one equivalent of [PdCl( NNO^ISQ )]. Reacting an 1:1 mixture of [PdCl( NNO^ISQ )] and [Pd(N₃)( NNO^{I SQ})] furnishes the 1,1‐azido‐bridged dinuclear diradical [{Pd( NNO ^ISQ)}₂(κ¹‐N;μ‐N₃]⁺, with a Pd‐N‐Pd angle close to 127° (X‐ray). Magnetic and EPR measurements indicate two independent S=1/2 spin carriers and no magnetic interaction in the solid state. The two diradical species both show no spin exchange in solution, likely because of unhindered rotation around the Pd?X?Pd core. This work demonstrates that a single bridging atom can induce subtle and tunable changes in structural and magnetic properties of novel dinuclear Pd complexes featuring two ligand‐based radicals.     

O-acetyl galactoglucomannan esters for barrier coatings

A major enhancement of grease and water vapor barrier properties was accomplished with a 1–10 g/m² coating of O-acetyl galactoglucomannan (GGM) ester or with GGM coatings applied as water dispersions on cartonboard. GGMs were esterified with phthalic and benzoic anhydrides, respectively. The novel phthalic esters of GGM (GGM-Ph) were characterized with HPLC, NMR, and matrix-assisted laser desorption/ionization with mass spectrometry (MALDI-TOF-MS). The degree of substitution of GGM-Ph was obtained by ¹H NMR, ¹³C NMR, and HPLC. The GGM esters and GGM were coated onto cartonboard, and they demonstrated good moisture and very good grease resistance even with thin 1–3 g/m² coatings. The time for penetration of 0.1 % rapeseed oil was 54 h with the 2.4 g/m² coating thickness. The lowest water vapor transmission value was 39 g/m²/24 h with 9.7 g/m² coating. The GGM esters had clearly higher water resistance and slightly higher grease barrier values than native GGM. High-molar-mass-based GGM (50 kg/mol) and GGM-Ph rendered better water vapor and grease barrier properties than low-molar-mass GGM (9 kg/mol) and GGM-Ph. The GGM-based coatings can be safely used on an industrial scale as water was used as a solvent. As obtained from non-food-based side-stream wood-based resources, GGM and GGM esters project a sustainable and modern conception for barrier purposes in food packaging.     

Materials cohesion and interaction forces

The most important methods to determine the cohesive interactions of materials and adhesive interactions between different substances are reviewed. The term cohesion is generalized as representing the unifying interaction forces of a single material and adhesion forces between different substances due to attraction. The aim is to interlink a number of frequently used interaction parameters in order to promote the understanding of materials research executed within different scientific (Material, Colloid, Sol-Gel and Nano) communities. The modern interdisciplinary research requires a removal of the historical obstacles represented by widely differing nomenclature used for the same material properties. The interaction parameters of different models are reviewed and representative numerical values computed from tabulated thermodynamic and spectroscopic material constants. The results are compared with published values. The models are grouped to represent single and two component systems, respectively. The latter group includes models for films on substrates and work of adhesion between liquids and solids. In most cases rather rough approximations have been employed, mostly relating to van der Waals substances for which the gas state is common reference state. In order to improve the predictability of the key Hamaker constant, a novel model for interpreting the dielectric spectrum is presented. The interrelation between thermodynamic, electronic, spectroscopic and dielectric parameters is illustrated by model calculations on typical inorganic materials of current interest as model compounds. The ionic solids are represented by NaCl and KCl, while ZnO, FeO, Fe(2)O(3), Fe(3)O(4), Al(2)O(3), SiO(2), TiO(2), ZrO(2), SnO, SnO(2) represent ceramic oxides and semiconductors. The model compounds thus illustrate the effect of bond type (covalent or ionic) and valence (charge number and sign) of the constituent elements. However, since the focus is placed on a phenomenological analysis, the number of examples remains self-evidently incomplete.     

Localized Mixed‐Valence and Redox Activity within a Triazole‐Bridged Dinucleating Ligand upon Coordination to Palladium

The new dinucleating redox‐active ligand ( L^H4 ), bearing two redox‐active NNO‐binding pockets linked by a 1,2,3‐triazole unit, is synthetically readily accessible. Coordination to two equivalents of Pd^II resulted in the formation of paramagnetic (S= ) dinuclear Pd complexes with a κ²‐N,N′‐bridging triazole and a single bridging chlorido or azido ligand. A combined spectroscopic, spectroelectrochemical, and computational study confirmed Robin–Day Class II mixed‐valence within the redox‐active ligand, with little influence of the secondary bridging anionic ligand. Intervalence charge transfer was observed between the two ligand binding pockets. Selective one‐electron oxidation allowed for isolation of the corresponding cationic ligand‐based diradical species. SQUID (super‐conducting quantum interference device) measurements of these compounds revealed weak anti‐ferromagnetic spin coupling between the two ligand‐centered radicals and an overall singlet ground state in the solid state, which is supported by DFT calculations. The rigid and conjugated dinucleating redox‐active ligand framework thus allows for efficient electronic communication between the two binding pockets.     

Influence of aqueous aging on surface properties of plasma sprayed oxide coatings

The influence of aging in mild aqueous conditions (pH 4, 7 and 9) on surface properties of plasma sprayed oxide was studied using electrophoretic mobility studies and measuring concentrations of dissolved species from exposure liquids. In addition, required acid/base additions to maintain constant pH, redox potentials suspension conductivities were measured. The experiment time was two weeks. The plasma sprayed materials were based on Al(2)O(3), TiO(2) and Cr(2)O(3). Materials based on Al(2)O(3) dissolved easily at pH 4 due to presence of metastable gamma-Al(2)O(3) phase. In addition there was clear change in surface charging properties (zeta potential) of Al(2)O(3) surfaces so that the estimated IEP value drifted from >9 at the beginning of aging and dropped down to 8.5-8.7 after 2 weeks of treatment. Plasma sprayed TiO(2) did not dissolve under the experiment conditions. Even thought the surface charging (zeta potential) changed during the exposure, the estimated IEP remained close to the values reported for pure TiO(2) materials. Plasma sprayed Cr(2)O(3) based materials were also insoluble at the studied pH values. On the other hand, the estimated IEP values deviated radically from the reported PZC values of similar materials.     

Pincer ligands with an all-phosphorus donor set: subtle differences between rhodium and palladium

The synthesis of a new, all-phosphorus pincer PP(NEt2)P ligand L3(NEt2), which is derived from 2-indolylphosphine and features a central N(2)P(NEt(2)) core, is described. This 'PPP' species shows coordination toward Rh as a neutral trisphosphine ligand. Tridentate diphenylphosphine-derived PP(H)P ligands L1(H) and L2(H), featuring a secondary phosphine core, show 'ambivalent' coordination, acting as persistent neutral triphosphine ligands with Rh, and as easily-formed monoanionic phosphido(bisphosphine) pincer ligands toward Pd. These subtle differences, which might be more general for group 9 and 10 metal complexes with this ligand set, are explained by comparative DFT calculations (BP86; def2-TZVP level of theory) for the Rh and Pd species involved, including those with the structurally related PN(H)P ligands. The optimized structure for complex PdCl(L2) indicates minimal overlap of available Pd d-orbitals with the lone pair of the central, deprotonated phosphorus atom (formally a phosphido fragment), suggesting that it behaves predominantly like a bulky phosphine instead of a phosphido fragment.     

In situ solid-state NMR spectroscopy of protein in heterogeneous membranes: the baseplate antenna complex of Chlorobaculum tepidum

A clever combination: an in situ solid-state NMR analysis of CsmA proteins in the heterogeneous environment of the photoreceptor of Chlorobaculum tepidum is reported. Using different combinations of 2D and 3D solid-state NMR spectra, 90?% of the CsmA resonances are assigned and provide on the basis of chemical shift data information about the structure and conformation of CsmA in the CsmA-bacteriochlorophyll a complex.