Heisenberg Spin Chains via Chalcogen Bonding: Noncovalent S···O Contacts Enable Long-Range Magnetic Order.

The new radical ligand 5,8-dimethyl-1,4-dioxonaphtho[2,3-d][1,2,3]dithiazolyl (1) is reported. Two crystal polymorphs, 1α and 1ß, differing in their pancake-bonded dimerization motif and S···O contact network, are identified. The self-assembly of Mn(II) metal ions with 1 leads to the formation of [Mn(hfac)2]3(1)2 that exhibits a Mn(II)-radical-Mn(II)-radical-Mn(II) linear arrangement of three Mn(hfac)2 units bridged by two radical ligands (hfac = 1,1,1,5,5,5-hexafluoroacetylacetonato-). Characterization by single-crystal X-ray diffraction of this Mn(II) complex packing structure reveals close noncovalent S···O contacts between the [Mn(hfac)2]3(1)2 units in one dimension along the b-c direction. The magnetic properties of the coordination complex are characterized by dc and ac susceptibility measurements on a microcrystalline solid. The magnetic data down to 4.8 K indicate the presence of effective ferromagnetic interactions (J/kB = +0.16 K) between the molecular ST = 13/2 units along the supramolecular chain involving noncovalent S···O contacts. Below 2.9 K, a non-zero out-of-phase component appears in the ac susceptibility, indicating the presence of a three-dimensional magnetic phase transition.

Coordination Complexes of a Neutral 1,2,4-Benzotriazinyl Radical Ligand: Synthesis, Molecular and Electronic Structures, and Magnetic Properties.

A series of d-block metal complexes of the recently reported coordinating neutral radical ligand 1-phenyl-3-(pyrid-2-yl)-1,4-dihydro-1,2,4-benzotriazin-4-yl (1) was synthesized. The investigated systems contain the benzotriazinyl radical 1 coordinated to a divalent metal cation, Mn(II) , Fe(II) , Co(II) , or Ni(II) , with 1,1,1,5,5,5-hexafluoroacetylacetonato (hfac) as the auxiliary ligand of choice. The synthesized complexes were fully characterized by single-crystal X-ray diffraction, magnetic susceptibility measurements, and electronic structure calculations. The complexes [Mn(1)(hfac)2 ] and [Fe(1)(hfac)2 ] displayed antiferromagnetic coupling between the unpaired electrons of the ligand and the metal cation, whereas the interaction was found to be ferromagnetic in the analogous Ni(II) complex [Ni(1)(hfac)2 ]. The magnetic properties of the complex [Co(1)(hfac)2 ] were difficult to interpret owing to significant spin-orbit coupling inherent to octahedral high-spin Co(II) metal ion. As a whole, the reported data clearly demonstrated the favorable coordinating properties of the radical 1, which, together with its stability and structural tunability, make it an excellent new building block for establishing more complex metal-radical architectures with interesting magnetic properties.

Comment on "crystallographic snapshot of an arrested intermediate in the biomimetic activation of CO2 ".

Out of focus: A recent Communication published in this journal describes the synthesis of [nBu4 N]HCO3 . The authors performed a single-crystal X-ray study that revealed a putative species described as an incipient hydroxide ion engaging in a long, and presumably weak, interaction with CO2 . Our recent exploration of the coordination chemistry of CO2 with small ions leads us to believe that such an exceptional bonding situation is unlikely. Instead, we argue that the crystal structure is that of [nBu4 N]O2 CCH3 and therefore not representative of the bulk powder from the synthesis.

1-Phenyl-3-(pyrid-2-yl)benzo[e][1,2,4]triazinyl: the first "Blatter radical" for coordination chemistry.

A neutral air- and moisture-stable N,N'-chelating radical ligand, 1-phenyl-3-(pyrid-2-yl)benzo[e][1,2,4]triazinyl (1) was synthesized and characterized by electron paramagnetic resonance spectroscopy, X-ray crystallography, and magnetic measurements. Subsequent reaction of 1 with Cu(hfac)2·2H2O (hfac = hexafluoroacetylacetonate) under ambient conditions afforded the coordination complex Cu(1)(hfac)2 in which the radical binds to the metal in a bidentate fashion. Magnetic susceptibility data collected from 1.8 to 300 K indicate a strong ferromagnetic metal-radical interaction in the complex and weak antiferromagnetic radical···radical interactions between the Cu(1)(hfac)2 units. Detailed computational investigations support this assignment. Radical 1 is a new addition to the growing library of 1,2,4-triazinyl radicals and the first member of this family of paramagnetic species synthesized specifically for coordination purposes.

A second arterial conduit to the circumflex circulation significantly improves survival after coronary artery bypass surgery.

OBJECTIVES: Conventional coronary artery bypass surgery involves the use of a single left internal mammary artery to the left anterior descending artery and saphenous vein grafts reserved for other sites. This retrospective propensity-matched study investigated the impact of a second arterial conduit to the left-sided circulation on early and long-term survival after coronary artery bypass surgery. METHODS: Data were retrospectively collected from 2004 to 2014 for all revascularizations with at least 1 arterial and/or 1 venous graft to the circumflex circulation, in addition to an internal mammary artery to the left anterior descending artery. Propensity-matched groups were created based on baseline characteristics. Hazard functions were estimated using Cox multivariable regression, and the Kaplan-Meier survival curves were compared between the matched cohorts. RESULTS: A total of 1226 patients with a venous conduit to the left-sided circulation were successfully matched to an equal number of patients with an arterial conduit. Regression analysis identified a second arterial conduit, logistic European System for Cardiac Operative Risk Evaluation score (EuroSCORE), pulmonary disease, left ventricular ejection fraction, New York Heart Association (NYHA) Class and previous myocardial infarction as significant predictors of survival. A second arterial graft to the left circumflex circulation was a predictor of improved survival (hazard ratio 0.64, 95% confidence interval 0.51-0.80; P < 0.001). There were significant early and late survival benefits (arterial vs venous: 98.2% vs 96.3%, P = 0.003 at 1 year; 82.4% vs 62.2%, P < 0.001 at 10 years) from a second arterial conduit to the circumflex circulation. CONCLUSIONS: There are significant early and late incremental survival benefits from a second arterial conduit to the circumflex circulation.

Does a third arterial conduit to the right coronary circulation improve survival?

BACKGROUND: The long-term benefits of a third arterial conduit to the right circulation in triple-vessel disease remain debatable. This retrospective, single-center, propensity-matched study investigates the impact of a third arterial conduit to the right circulation on early and intermediate survival after coronary artery bypass grafting. METHODS: Data were retrospectively collected from 2004 to 2014 for all surgical revascularizations for triple-vessel disease with at least 2 arterial conduits to the left circulation and a third arterial or venous conduit to the right circulation. A total of 167 pairs were propensity matched to arterial versus venous third conduit to right circulation. Hazard functions were obtained with Cox multivariate regression and Kaplan-Meier survival curves were compared between the matched cohorts. RESULTS: Extracardiac arteriopathy, logistic euroSCORE, and left main stem disease were significant predictors of adverse survival. A third arterial conduit to the right circulation was not a significant predictor of improved survival in multivariate analysis (HR, 0.72; 95% CI, 0.34-1.55; P = .411). 30-day mortality was 0.6% in both groups. There was no significant difference in early or intermediate survival in the propensity-matched groups (venous vs arterial, 99.2% vs 99.2%; P = 1.000 at 1 year; 85.2% vs 88.8%; P = .248 at 5 years and 69.2% vs 88.8%; P = .297 at 7 years) CONCLUSIONS: The use of a third arterial versus a venous conduit to the right circulation does not improve early or intermediate survival up to 7 years in triple-vessel coronary artery disease in this study. Longer follow-up and larger cohorts may be needed for differences to emerge.

Coexistence of long-range antiferromagnetic order and slow relaxation of the magnetization in the first lanthanide complex of a 1,2,4-benzotriazinyl radical.

The first lanthanide complex of a 1,2,4-benzotriazinyl radical (1), Dy(1)(tbacac)3 (2, tbacac = 2,2,6,6-tetramethyl-3,5-heptane-dionato), was synthesised and found to have an antiferromagnetically ordered ground state with a metamagnetic phase diagram and a critical field of 0.91 T at 1.85 K. The application of a small dc field revealed the single-molecule magnet behaviour of 2, illustrating the coexistence of long-range antiferromagnetic order and slow relaxation of the magnetization.

Synthesis and characterisation of p-block complexes of biquinoline at different ligand charge states.

The first examples of p-block coordination complexes of biquinoline, namely [(biq)BCl2]Cl and [(biq)BCl2]˙, were synthesized and structurally characterized. The acquired data allowed the estimation of the ligand charge state based on its metrical parameters. The subsequent use of this protocol, augmented with theoretical calculations, revealed ambiguities in the published data for transition metal complexes of biquinoline.

Synthesis of a labile sulfur-centred ligand, [S(H)C(PPh2S)2](-): structural diversity in lithium(i), zinc(ii) and nickel(ii) complexes.

A high-yield synthesis of [Li{S(H)C(PPh2S)2}]2 [Li2·(3)2] was developed and this reagent was used in metathesis with ZnCl2 and NiCl2 to produce homoleptic complexes 4 and 5b in 85 and 93% yields, respectively. The solid-state structure of the octahedral complex [Zn{S(H)C(PPh2S)2}2] (4) reveals notable inequivalence between the Zn-S(C) and Zn-S(P) contacts (2.274(1) Å vs. 2.842(1) and 2.884(1) Å, respectively). Two structural isomers of the homoleptic complex [Ni{S(H)C(PPh2S)2}2] were isolated after prolonged crystallization processes. The octahedral green Ni(ii) isomer 5a exhibits the two monoprotonated ligands bonded in a tridentate (S,S',S'') mode to the Ni(ii) centre with three distinctly different Ni-S bond lengths (2.3487(8), 2.4500(9) and 2.5953(10) Å). By contrast, in the red-brown square-planar complex 5b the two ligands are S,S'-chelated to Ni(ii) (d(Ni-S) = 2.165(2) and 2.195(2) Å) with one pendant PPh2S group. DFT calculations revealed that the energetic difference between singlet and triplet state octahedral and square-planar isomers of the Ni(ii) complex is essentially indistinguishable. Consistently, VT and (31)P CP/MAS NMR spectroscopic investigations indicated that a mixture of isomers exists in solution at room temperature, while the singlet state square-planar isomer 5b becomes favoured at -40 °C.

Off-pump repair of a post-infarct ventricular septal defect: the 'Hamburger procedure'.

We report a novel off-pump technique for the surgical closure of post-infarct ventricular septal defects (VSDs). The case report describes the peri-operative management of a 76 year old lady who underwent the 'Hamburger procedure' for closure of her apical VSD. Refractory cardiogenic shock meant that traditional patch repairs requiring cardiopulmonary bypass would be poorly tolerated. We show that echocardiography guided off-pump posterior-anterior septal plication is a safe, effective method for closing post-infarct VSDs in unstable patients. More experience is required to ascertain whether this technique will become an accepted alternative to patch repairs.