Slow relaxation of magnetization in a bis-mer-tridentate octahedral Co(II) complex

Reaction of a rigid tridentate ligand o-[(1H-imidazol-2-yl)methylideneamino]phenol (2-H(2)imap) with Co(ClO4) in the presence of NaN3, or Co(NO3)(2) without a base yields [Co-II(2-Himap)(2)] 1 and [Co-III(2-Himap) (2)]NO3 center dot MeOH2, respectively. Both complexes exhibit a mer-octahedral geometry with the cobalt centre being distorted along an octahedral-trigonal prismatic pathway. The packing in 1 and 2 is dominated by H-bonding forming 2D sheets and 1D chains, respectively. Detailed dc and ac magnetic studies indicate that 1 is a field-induced single-ion magnet (SIM) with D = 36.7 cm(-1) and E = 2.0 cm(-1). Extensive ab initio calculations support these conclusions and suggest that relaxation of the magnetization occurs principally through direct quantum tunnelling in the ground state, with the Raman process dominant in an applied field. This contrasts with the recently reported series of mer-[Co(L)(2)] (L = monoanionic NNO donor ligand; Inorg. Chem., 2017, 56, 6056-6066) complexes where D is negative, as these compounds have a more ambiguous geometry, and highlights the importance of supramolecular interactions in subtly altering the coordination sphere thereby impacting the magnetic behaviour

Case Reports1. A Late Presentation of Loeys-Dietz Syndrome: Beware of TGFβ Receptor Mutations in Benign Joint Hypermobility

Background: Thoracic aortic aneurysms (TAA) and dissections are not uncommon causes of sudden death in young adults. Loeys-Dietz syndrome (LDS) is a rare, recently described, autosomal dominant, connective tissue disease characterized by aggressive arterial aneurysms, resulting from mutations in the transforming growth factor beta (TGFβ) receptor genes TGFBR1 and TGFBR2. Mean age at death is 26.1 years, most often due to aortic dissection. We report an unusually late presentation of LDS, diagnosed following elective surgery in a female with a long history of joint hypermobility. Methods: A 51-year-old Caucasian lady complained of chest pain and headache following a dural leak from spinal anaesthesia for an elective ankle arthroscopy. CT scan and echocardiography demonstrated a dilated aortic root and significant aortic regurgitation. MRA demonstrated aortic tortuosity, an infrarenal aortic aneurysm and aneurysms in the left renal and right internal mammary arteries. She underwent aortic root repair and aortic valve replacement. She had a background of long-standing joint pains secondary to hypermobility, easy bruising, unusual fracture susceptibility and mild bronchiectasis. She had one healthy child age 32, after which she suffered a uterine prolapse. Examination revealed mild Marfanoid features. Uvula, skin and ophthalmological examination was normal. Results: Fibrillin-1 testing for Marfan syndrome (MFS) was negative. Detection of a c.1270G > C (p.Gly424Arg) TGFBR2 mutation confirmed the diagnosis of LDS. Losartan was started for vascular protection. Conclusions: LDS is a severe inherited vasculopathy that usually presents in childhood. It is characterized by aortic root dilatation and ascending aneurysms. There is a higher risk of aortic dissection compared with MFS. Clinical features overlap with MFS and Ehlers Danlos syndrome Type IV, but differentiating dysmorphogenic features include ocular hypertelorism, bifid uvula and cleft palate. Echocardiography and MRA or CT scanning from head to pelvis is recommended to establish the extent of vascular involvement. Management involves early surgical intervention, including early valve-sparing aortic root replacement, genetic counselling and close monitoring in pregnancy. Despite being caused by loss of function mutations in either TGFβ receptor, paradoxical activation of TGFβ signalling is seen, suggesting that TGFβ antagonism may confer disease modifying effects similar to those observed in MFS. TGFβ antagonism can be achieved with angiotensin antagonists, such as Losartan, which is able to delay aortic aneurysm development in preclinical models and in patients with MFS. Our case emphasizes the importance of timely recognition of vasculopathy syndromes in patients with hypermobility and the need for early surgical intervention. It also highlights their heterogeneity and the potential for late presentation. Disclosures: The authors have declared no conflicts of interes

The photochemistry of cobalt(III)-aminoacidato complexes

The photodecarboxylation reaction of Co(III)-aminocarboxylato complexes has been examined from several angles. Firstly, the currently accepted mechanism for the formation of [Co(bpy)(CHâ‚‚NHâ‚‚)]2+, following the UV photolysis of [Co(bpy)2(gly)]2+ (bpy = 2,2'-bipyridine, gly = glycinate), has been tested. A Co(II)-bound aminocyclopropylmethyl radical, with a lifetime of around 10^-4s, has been proposed as a reaction intermediate. This assertion was tested with the use of a radical clock, derived from chelated cyclopropylglycine. If a Co(II)-bound aminocyclopropylmethyl radical is formed, it will ring-open with rate constant k >= 10^7 s^-1 (298 K). This rate constant has been estimated on the basis of transition-state theoretical calculations and published data for related radicals. The cyclopropyl group actually survived photolysis, and was found as cyclopropanecarboxaldehyde. This result implies that either the rate determining step has been wrongly assigned, or the proposed mechanism is incorrect. Carbonyl compounds were also detected following the photolysis of [Co(bpy)2(aa)]^2+complexes, where aa = alaninate, valinate, phenylglycinate, and aminoisobutyrate. It was proposed that a Co-C-N metallacycle is formed briefly, but decomposes to give a Co(I) complex and an iminium ion. Hydrolysis of the latter fragment would account for the carbonyl compounds. Secondly, some novel Co-C-N metallacycles have been prepared via the photodecarboxylation reaction. Cobalt(III) complexes with N,N-bis(2- pyridylmethyl)aminoacidate (amino acid = glycine, alanine, and cyclopropylglycine) ligands with 1,10-phenanthroline (phen) filling the remaining coordination sites, were prepared. Upon UV photolysis in aqueous solution, all three complexes yielded Co-CN metallacycles which were sufficiently stable to allow characterisation by conventional ^1H NMR, ^13C NMR, and UV-vis techniques. The solid state structure of the photolysis product of the glycinate derivative was determined by X-ray crystallography. These organometallic products eventually decompose, giving carbonyl compounds, free bis(2- pyridylmethyl)amine (bpa), free phen and the Co(II) ion. A peroxo-bridged Co(III) dimer, [Co(phen)(bpa)(02)Co(phen)(bpa)]^4+, crystallised from this mixture, and was characterised by X-ray crystallography. Thirdly, the UV photolysis reactions of a series of [Co(bpy)2(aa)]^2+in DMSO solution were investigated. Carbonyl compounds are also produced in this solvent. The formation of trans(N)-[Co(aa)2(bpy)]+ complexes was also observed. This was ascribed to secondary (thermal) chemistry between dissolved molecular oxygen and some of the photolysis products: free amino acid, free phen, and Co(II). This same mixture gave rise to the [Co(bpy)3]3+ ion in aqueous solution. This difference was rationalised on the basis of the equilibria of the various [CoII(aa)x(bpy)y]^(2-x)+ complexes in the different solvents, and the potentials at which they are oxidised

Selective Capture of Carbon Dioxide from Hydrocarbons Using a Metal-Organic Framework: Relevance to the Purification of Natural Gas and Acetylene

Efficient and sustainable methods for carbon dioxide (CO2) capture are highly sought after. Mature technologies involve chemical reactions that absorb CO2, but they have many drawbacks. Energy-efficient alternatives may be realized by porous physisorbents with void spaces that are complementary in size and electrostatic potential to molecular CO2. Here, we present a robust, recyclable and inexpensive adsorbent termed MUF-16 (MUF = Massey University Framework). This metal-organic framework captures CO2 with a high affinity in its one-dimensional channels. The position of the CO2 molecules sequestered in the framework pores, as determined by X-ray crystallography, illustrate how complementary noncovalent interactions envelop the CO2 while repelling other guest molecules. The low affinity of the MUF-16 pores for these competing gases underpins new benchmarks for the adsorption of CO2 over methane, acetylene, ethylene, ethane, propylene and propane. IAST calculations show that for 50/50 mixtures at 293 K and 1 bar, the CO2/CH4 selectivity is 6690 and the CO2/C2H2 selectivity is 510, for example. Breakthrough gas separations under dynamic conditions benefit from short time lags in the elution of the weakly-adsorbed component to deliver high-purity hydrocarbon products. Ultimately, MUF-16 may be applicable to the removal of CO2 from sources such as natural gas and chemical feedstocks.</p

Systematic Ligand Modulation Enhances the Moisture Stability and Gas Sorption Characteristics of Quaternary Metal–Organic Frameworks

Complex metal–organic frameworks (MOFs) that maintain high structural order promise sophisticated and tunable properties. Here, we build on our strategy of using combinations of structurally distinct ligands to generate a new isoreticular series of ordered quaternary Zn₄O–carboxylate MOFs. Rational design of the framework components steers the system toward multicomponent MOFs and away from competing phases during synthesis. Systematic ligand modulation led to the identification of a set of frameworks with unusually high stability toward water vapor. These frameworks lose no porosity after 100 days’ exposure to ambient air or 20 adsorption–desorption cycles up to 70% relative humidity. Across this series of frameworks, a counterintuitive relationship between the length of pendant alkyl groups and framework stability toward water vapor emerges. This phenomenon was probed via a series of gas and vapor adsorption experiments together with Grand Canonical Monte Carlo (GCMC) simulations, and could be rationalized on the basis of the propensity of the frameworks to adsorb water vapor and the proximity of the adsorbed water molecules to the water-sensitive metal clusters. Systematic variation of the pore volume and topography also tunes the CO₂ and CH₄ gas adsorption behavior. Certain of these materials display increases in their adsorption capacities of 237% (CO₂) and 172% (CH₄) compared to the parent framework