The surprising lability of bis(2,2’:6’,2’’-terpyridine)- chromium(III) complexes

The complex [Cr(tpy)(O3SCF3)3] (tpy = 2,2′:6′,2′′-terpyridine) is readily made from [Cr(tpy)Cl3] and is a convenient precursor to [Cr(tpy)2][PF6]3 and to [Cr(tpy)(4′-(4-tolyl)tpy)][PF6]3 and [Cr(tpy)(5,5′′-Me2tpy)][PF6]3 (4′-(4-tolyl)tpy = 4′-(4-tolyl)-2,2′:6′,2′′-terpyridine; 5,5′′-Me2tpy = 5,5′′-dimethyl-2,2′:6′,2′′-terpyridine); these are the first examples of heteroleptic bis(tpy) chromium(III) complexes. The single crystal structures of 2{[Cr(tpy)2][PF6]3}·5MeCN, [Cr(tpy)(4′-(4-tolyl)tpy)][PF6]3·3MeCN and [Cr(tpy)(5,5′′-Me2tpy)][PF6]3·3MeCN have been determined. Each cation contains the expected octahedral {Cr(tpy)2}3+ unit; in all three structures, the need to accommodate three anions per cation and the solvent molecules prevents the formation of a grid-like array of cations that is typical of many lattices containing {M(tpy)2}2+ motifs. Three reversible electrochemical processes are observed for [Cr(tpy)(4′-(4-tolyl)tpy)][PF6]3 and [Cr(tpy)(5,5′′-Me2tpy)][PF6]3, consistent with those documented for [Cr(tpy)2]3+. At pH 6.36, aqueous solutions of [Cr(tpy)2][PF6]3 are stable for at least two months. However, contrary to the expectations of the d3 Cr3+ ion being a kinetically inert metal centre, the tpy ligands in [Cr(tpy)2]3+are labile in the presence of base; absorption and 1H NMR spectroscopies have been used to monitor the effects of adding NaOH to aqueous and CD3OD solutions, respectively, of the homo- and heteroleptic complexes. Ligand dissociation is also observed when [Bu4N]F is added to CD3OD solutions of the complexes, but in aqueous solution, [Cr(tpy)2][PF6]3 is stable in the presence of fluoride ion

Pyrrolizidines for direct air capture and CO2 conversion

Greenhouse gases such as CO2 strongly contribute to the rising temperatures of our planet, but as long as our society is dependent on fossil fuels, this trend will even increase in the near future. Therefore, CO2 capture and subsequent utilization constitute an approach for decarbonization and CO2 mitigation, and for this purpose, amine scrubbing remains the industrially most established process. In this article, we describe the CO2 capture-ability of pyrrolizidine-based diamines, a scaffold with remarkably good properties to fulfill this challenge. We observed fast equimolar CO2-uptake, as well as high stability of these compounds during multiple capture and release-cycles. In addition, the amines could be utilized for direct air capture. Finally, we demonstrate the utility of the pyrrolizidine absorbents in the reduction of CO2 and for the formation of oxazolidinones

Heteroleptic chromium(III) tris(diimine) [Cr(N^N)2(N'^N')]3+ complexes

A series of heteroleptic tris(diimine) complexes of chromium(III) is reported and the crystal structures of {4[Cr(bpy)2(phen)][PF6]3}·11MeCN and 4[Cr(4,4′-Me2bpy)2(bpy)][PF6]3}·12MeCN·H2O are described. The combined effects of a 1:3 cation: anion ratio and lattice solvent molecules are discussed, in particular in the context of the influence on intercation embraces. The presence of the methyl substituents in {4[Cr(4,4′-Me2bpy)2(bpy)][PF6]3}·12MeCN·H2O results in Me–πbpy contacts becoming the dominant packing interactions and in the assembly of motifs distinct from those in {4[Cr(bpy)2(phen)][PF6]3}·11MeCN

Redox cycling of iridium(III) complexes gives versatile materials for photonics applications

The cyclometallated iridium(III) complex [Me4N][Ir(ppy)2(cat)] (Hppy = 2-phenylpyridine; H2cat = benzene-1,2-diol) has been prepared under inert atmosphere and has been structurally characterized by single crystal X-ray diffraction. Under ambient conditions, the fully reduced complex (as formulated) undergoes rapid one-electron oxidation both in solution and in the solid state to a species containing a semiquinone ligand. The resultant neutral complex [Ir(ppy)2(sq)] (sq = o-semiquinone) was also prepared by exposing the reaction mixture to O2 during the course of the reaction. Electron paramagnetic resonance (EPR) spectroscopy confirms the diamagnetic nature of the complex [Me4N][Ir(ppy)2(cat)] and indicates that the unpaired electron in [Ir(ppy)2(sq)] resides primarily on the sq ligand. The photophysical, electrochemical, and spectroelectrochemical properties of [Ir(ppy)2(sq)] were investigated and reveal the changes in absorption as the complex is converted into the catecholate and quinone forms

Regioisomerism in cationic sulfonyl-substituted [Ir(C^N)2(N^N)]+ complexes: its influence on photophysical properties and LEC performance

In a series of regioisomeric [Ir(C^N) 2 (bpy)] + complexes containing methylsulfonyl groups on the cyclometallating ligands, the influence of the substitution position on photophysical, electrochemical and LEC device properties is investigated

Cardiac risk factors and risk scores vs cardiac computed tomography angiography: a prospective cohort study for triage of ED patients with acute chest pain.

OBJECTIVE: The objective of the study is to evaluate cardiac risk factors and risk scores for prediction of coronary artery disease (CAD) and adverse outcomes in an emergency department (ED) population judged to be at low to intermediate risk for acute coronary syndrome. METHODS: Informed consent was obtained from consecutive ED patients who presented with chest pain and were evaluated with coronary computed tomography angiography (cCTA). Cardiac risk factors, clinical presentation, electrocardiogram, and laboratory studies were recorded; the Thrombolysis in Myocardial Infarction (TIMI) and Global Registry of Acute Coronary Events (GRACE) scores were tabulated. Coronary computed tomography angiography findings were rated on a 6-level plaque burden scale and classified for significant CAD (stenosis ≥50%). Adverse cardiovascular outcomes were recorded at 30 days. RESULTS: Among 250 patients evaluated by cCTA, 143 (57%) had no CAD, 64 (26%) demonstrated minimal plaque (70% stenosis). Six patients developed adverse cardiovascular outcomes. Among traditional cardiac risk factors, only age (older) and sex (male) were significant independent predictors of CAD. Correlation with CAD was poor for the TIMI (r = 0.12) and GRACE (r = 0.09-0.23) scores. The TIMI and GRACE scores were not useful to predict adverse outcomes. Coronary computed tomography angiography identified severe CAD in all subjects with adverse outcomes. CONCLUSION: Among ED patients who present with chest pain judged to be at low to intermediate risk for acute coronary syndrome, traditional risk factors are not useful to stratify risk for CAD and adverse outcomes. Coronary computed tomography angiography is an excellent predictor of CAD and outcome