Completing the triad: Synthesis and full characterization of homoleptic and heteroleptic carbonyl and nitrosyl complexes of the group VI metals

Oxidation of M(CO)$_{6}$ (M = Cr, Mo, W) with the synergistic oxidative system Ag[WCA]/0.5 I$_{2}$ yields the fully characterized metalloradical salts [M(CO)$_{6}$]+˙[WCA]− (weakly coordinating anion WCA = [F-{Al(OR$^{F}$)$_{3}$}$_{2}$]$^{-}$, R$^{F}$ = C(CF$_{3}$)$_{3}$). The new metalloradical cations with M = Mo and W showcase a similar structural fluxionality as the previously reported [Cr(CO)$_{6}$]$^{+}$˙. Their reactivity increases from M = Cr < Mo < W and their syntheses allow for in-depth insights into the properties of the group 6 carbonyl triad. Furthermore, the reaction of NO$^{+}$[WCA]$^{-}$ with neutral carbonyl complexes M(CO)$_{6}$ gives access to the heteroleptic carbonyl/nitrosyl cations [M(CO)$_{5}$(NO)]$^{+}$ as salts of the WCA [Al(ORF)$_{4}$]$^{-}$, the first complete transition metal triad of their kind

The dynamic nature of Cu sites in Cu-SSZ-13 and the origin of the seagull NOx conversion profile during NH3-SCR

Cu-Zeolites with chabazite structure show a peculiar dual-maxima NO conversion profile, also known as a seagull profile, during the selective catalytic reduction by ammonia. In order to understand the origin of this behavior, systematic catalytic tests and operando spectroscopy were applied to derive structure–performance relationships for Cu-SSZ-13 catalysts with low and high Cu loading. Operando X-ray absorption, X-ray emission and in situ electron paramagnetic resonance spectroscopy measurements, including novel photon-in/photon-out techniques, demonstrated the interconversion of isolated Cu sites and dimeric bis(μ-oxo) Cu species, the former occurring via formation of ammonia Cu2+/Cu+ complexes and the latter in an oxidizing gas mixture. The formation of dimeric Cu+–O2–Cu+ species by involving Cu sites in close vicinity was linked to the high activity at low temperatures of the highly loaded Cu-SSZ-13 sample. In contrast, the isolated Cu sites present at very low Cu loadings are strongly poisoned by adsorbed NH3. The activity decrease around 350 °C that gives rise to the seagull shaped NO conversion profile could be attributed to a more localized structure of mono(μ-oxo)dicopper complexes. Above this temperature, which corresponds to partial NH3 desorption from Cu sites, the isolated Cu sites migrate to form additional dimeric entities thus recovering the SCR activity

The dynamic nature of Cu sites in Cu-SSZ-13 and the origin of the seagull NOx conversion profile during NH₃-SCR

Cu-Zeolites with chabazite structure show a peculiar dual-maxima NO conversion profile, also known as a seagull profile, during the selective catalytic reduction by ammonia. In order to understand the origin of this behavior, systematic catalytic tests and operando spectroscopy were applied to derive structure–performance relationships for Cu-SSZ-13 catalysts with low and high Cu loading. Operando X-ray absorption, X-ray emission and in situ electron paramagnetic resonance spectroscopy measurements, including novel photon-in/photon-out techniques, demonstrated the interconversion of isolated Cu sites and dimeric bis(μ-oxo) Cu species, the former occurring via formation of ammonia Cu2+/Cu+ complexes and the latter in an oxidizing gas mixture. The formation of dimeric Cu+–O2–Cu+ species by involving Cu sites in close vicinity was linked to the high activity at low temperatures of the highly loaded Cu-SSZ-13 sample. In contrast, the isolated Cu sites present at very low Cu loadings are strongly poisoned by adsorbed NH3. The activity decrease around 350 °C that gives rise to the seagull shaped NO conversion profile could be attributed to a more localized structure of mono(μ-oxo)dicopper complexes. Above this temperature, which corresponds to partial NH3 desorption from Cu sites, the isolated Cu sites migrate to form additional dimeric entities thus recovering the SCR activity

In-depth exploration of the photophysics of a trinuclear palladium complex

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K⊂{[FeII^{II}(Tp)(CN)3_{3}]4_{4}[CoIII^{III}(pz^{pz}Tp)]3_{3}[CoII^{II}(pz^{pz}Tp)]}: a neutral soluble model complex of photomagnetic Prussian blue analogues

Straightforward access to a new cyanide-bridged {Fe$_{4}$Co$_{4}$} “molecular box” containing a potassium ion, namely K⊂{[Fe$^{II}$(Tp)(CN)$_{3}$]$_{4}$[Co$^{III}$($^{pz}$Tp)]$_{3}$[Co$^{II}$($^{pz}$Tp)]} (1) (with Tp and $^{pz}$Tp = tris- and tetrakis(pyrazolyl)borate, respectively), is provided, alongside its full characterisation. A detailed analysis of the molecular structure (X-ray diffraction, mass spectrometry, NMR spectroscopy) and electronic properties (EPR spectroscopy, SQUID magnetometry, UV/Vis spectroscopy, cyclic voltammetry) reveals that 1 shows slow magnetic relaxation and a remarkable photomagnetic effect at low temperature which is reminiscent of some FeCo Prussian Blue Analogues (PBAs), and is ascribed to a photo-induced electron transfer. However, in contrast with these inorganic polymers, the overall neutral compound 1 is soluble and remarkably stable in organic solvents such as CH2Cl2. Moreover, 1 shows interesting redox versatility, with electrochemical experiments revealing the possible access to six stable redox states

Comparative studies of substitution reactions of rhenium(I) dicarbonyl-nitrosyl and tricarbonyl complexes in aqueous media

The ligand substitution behavior of ReBr3(CO)(3)](NEt4)(2) (1) and ReBr3(CO)(2)(NO)]NEt4 (2) in aqueous media was compared. Ligand exchange reactions were performed with multiclentate chelating systems such as picolylaminediacetic acid (L-1; N,N',O,O'), nitrilotriacetic acid (L-2; N,O,O',O''), iminodiacetic acid (L-3; N,O,O'), and bis(2-pyridyl)methane (L-4; N,N'). The products of the substitution reactions were isolated and characterized by means of IR, NMR, MS, and X-ray structure analysis. NIVIR and crystallographic analyses confirmed the formation of single structural isomers in all cases with a ligand-to-metal ratio of 1:1. With ligands L-1 and L 2 and precursor 1 the tridentately coordinated complexes Re(L-1)(CO)(3)] (7) and Re(L-2)(CO)(3)](2-) (8) were formed. With precursor 2 the same ligands unexpectedly coordinated tetradentately after displacing a CO ligand, yielding complexes Re(L1)(CO)(NO)] (3) and Re(L 2) (CO)(NO)](-) (4). In both complexes NO was found to be coordinated trans to the carboxylate group. Time-dependent IR spectra of the reaction of 2 with ligand L-1 and L 2 confirmed the loss of one CO during the reaction. The product of the reaction of 2 with L 3 was identified as the neutral complex Re(L-3)(CO)(2)NO)] (5), again, with the nitrosyl coordinated trans to the carboxylate. With 1, ligand L-3 formed the anionic complex Re(L-3)(CO)(3)](-) (9). Finally the reactions with L-4 yielded the complexes ReBr(L-4)(CO)(2)(NO)]Br (6) and ReBr(L1)(CO)3] (10), in which bromide was found to be coordinated trans to the NO and CO, respectively. The X-ray structures of 3, 5-7, and 10 are discussed: 3, monoclinic P2(1)/n, with a = 14.6071(6) angstrom, b = 8.0573(3) angstrom, c = 24.7210(111) angstrom, beta = 107.117(5)degrees, and Z = 4; 5, triclinic P1, with a = 6.9091(5) angstrom, b = 9.8828(7) angstrom, c = 14.2834(10) angstrom, alpha = 89,246(9)degrees, beta = 89.420(9)degrees, gamma = 86.196(9)degrees, and Z = 4; 6, triclinic P1, with a = 9.8236(8) angstrom, b = 10.0949(8) angstrom, c 12.5346(10) angstrom, alpha = 108.679(9)degrees, beta = 111.992(9)degrees, gamma = 95.426(10)degrees, and Z = 2; 10, monoclinic P2(1)/c, with a 12.7491(12) angstrom, b = 13.3015(13) angstrom, c = 9.0112(g) angstrom, beta = 107.195(2)degrees, and Z = 7

NMR, PGSE diffusion, and X-ray diffraction studies of lithium and potassium salts derived from diphenylphosphino(o-cyanophenyl)aniline and their crown ether complexes

H-1, P-31, and Li-7 pulsed-gradient spin-echo (PGSE) diffusion and variable-temperature NMR results for THF solutions of the lithium and potassium salts derived from diphenylphosphino(o-cyanophenyl)aniline are reported and compared to the solid-state results obtained via X-ray diffraction studies. The solution results favor mononuclear salts, sometimes strongly ion paired, whereas the solid-state data reveal dinuclear species. The structures of the products from reactions of these salts with crown ethers are determined via PGSE and H-1 Overhauser NMR methods