Synthesis, magnetism, <SUP>1</SUP>H NMR and redox activity of dicopper(II) complexes having a discrete {Cu<SUB>2</SUB>(&#956;-phenoxide)<SUB>2</SUB>}<SUP>2+</SUP> unit supported by a non-macrocyclic ligand environment. Crystal structure of [Cu<SUB>2</SUB>(L)<SUB>2</SUB>(OClO<SUB>3</SUB>)<SUB>2</SUB>] [HL = 4-methyl-2,6-bis(pyrazol-1-ylmethyl)phenol]

Reaction between 4-methyl-2,6-bis(pyrazol-1-ylmethyl)phenol (HL) or its 3,5-dimethylpyrazole derivative (HL') and Cu(ClO4)2&#183;6H2O afforded [CuII2(L/L')2(OClO3)2] 1 and 2. Complex 1 has been structurally characterized showing that each copper(II) centre is square pyramidal with two bridging phenoxide oxygens and two terminal pyrazole nitrogens in the equatorial plane and a perchlorate oxygen atom axially co-ordinated. Variable-temperature magnetic susceptibility measurements revealed that the dicopper(II) centres are strongly antiferromagnetically coupled [singlet-triplet energy separation, 2J (in cm-1): -1204 for 1 and -798 for 2]. The complexes exhibit 1H NMR spectra within &#948; 0-10 due to their S = 0 ground state. In MeCN solution they exhibit ligand field transitions in the range 14 300-16 600 cm-1 and phenolate-to-copper(II) charge-transfer transition at &#8776;22 700 cm-1. In MeCN solution each complex displays three consecutive irreversible responses (scan rate of 50 mV s-1) with Epc values (V vs. SCE) at -0.02, -0.54 and -0.86 (1) and 0.00, -0.42 and -0.80 (2). The first two responses are due to CuII-CuI and the most cathodic response to CuI-Cu0 redox processes, respectively

Synthesis, spectra and redox properties of mononuclear five-co-ordinate copper(II) complexes with non-communicable pyrazole/pyridyl containing ligands: X-ray structure of [2,6-bis(3,5-dimethyl-pyrazol-1-ylmethyl)pyridine][2-(3,5-dimethylpyrazol-1-ylmethyl)pyridine]copper(II) diperchlorate

Synthesis and characterization of a series of five-co-ordinate mononuclear copper(II) compounds (1-8) have been achieved using 1 tridentate / bidentate heterocyclic nitrogen donor ligands with mixed hard-soft donor sets [L1 = 2,6-bis(pyrazol-1-ylmethyl)pyridine; L2 = 2,6-bis(3,5-dimethylpyrazol-1-ylmethyl)pyridine; L3 = 2-(pyrazol-1-ylmethyl)pyridine; L4 = 2-(3,5-dimethylpyrazol-1-ylmethyl)- pyridine]. Two types of complexes have been synthesized: (i) the anion bound complexes [Cu(L1/L2 )X2] (X=Cl- 1and 2; N-3 3 and 4; SCN- 5 and 6) and (ii) mixed-ligand complexes [Cu(L1/L2)(L3/L4)](ClO4)2 7 and 8. Complexes 1-8 belong to only a handful of copper(II) complexes with this class of non-planar ligands where pyrazole and pyridine rings are separated by methylene spacer(s). A representative complex [Cu(L2)(L4)](ClO4)2 8, having CuN5 co-ordination sphere, has been structurally characterized, to reveal square pyramidal stereochemistry at the copper(II) centre. Conductivity measurements revealed that one of the co-ordinated anions in 3, 5 and 6 is dissociated in solution, with the vacant site occupied by solvent molecule. Absorption and EPR spectral features of 1-8 represent that these copper(II) complexes adopt essentially a square pyramidal geometry. However, for 1 both in the solid state as well as in solution and for 2 in solution we propose that the copper(II) centre could be six-co-ordinate. Cyclic voltammetric measurements reveal the following trends in their E&#189; values (CuII -CuI redox process): (i) relative stabilization of CuII state by anionic ligands (N-3, Cl- or NCS- ) and a strongly co-ordinating solvent like DMF and (ii) predominance of steric over electronic effect (L1 vs. L2)

A tetragonal core with asymmetric iron environments supported solely by bis(μ-OH){μ-(O-H···O)} bridging and terminal pyridine amide (N, O) coordination: a new member of the tetrairon(III) family

Room-temperature aerobic reaction of [Fe(MeCN)4][ClO4]2 with 1,3-bis(2-pyridinecarboxamido)propane (H2bpp) yields the tetrairon(III) complex [Fe4(H2bpp)4(&#956;-OH)2(&#956;-OHO)][ClO4]7&#183;2H2O&#183;xMeCN (1&#183;xMeCN, 0&#8804;x&#8804;3). Crystal structure determination reveals that 1&#183;3MeCN is a new member of the tetrairon(III) family, bridged solely by two hydroxido ligands and a localized {O-H&#183;&#183;&#183;O}3- bridging unit. The properties of the "tetragonal" core [Fe4(&#956;-OH)2{&#956;-(O-H&#183;&#183;&#183;O)}]7+ have been investigated by variable-temperature magnetic and Mossbauer spectroscopic measurements. Successful modeling of the data has revealed asymmetric iron environments and three types of magnetic exchange interactions [through &#956;-OH and &#956;-O/&#956;-OH of &#956;-(O-H&#183;&#183;&#183;O) bridges]. This tetragonal core is a valuable addition to the tetrairon(III) cluster family from inorganic and bioinorganic perspectives

Reaction behaviour of dinuclear copper(I) complexes with m-xylyl-based ligands towards dioxygen

Intramolecular ligand hydroxylation was observed during the reactions of dioxygen with the dicopper(I) complexes of the ligands L1 (L1 = &#945;,&#945;'-bis[(2-pyridylethyl)amino]-m-xylene) and L3 (L3 = &#945;,&#945;'-bis[N-(2-pyridylethyl)-N-(2-pyridylmethyl)amino]-m-xylene). The dinuclear copper(I) complex [Cu2L3](ClO4)2 (3) and the dicopper(II) complex [Cu2(L1-O)(OH)(ClO4)]ClO4 (1) were characterized by single-crystal X-ray structure analysis. Furthermore, phenolate-bridged complexes were synthesized with the ligand L2-OH (structurally characterized [Cu2(L2-O)Cl3] (7) with L2 = &#945;,&#945;'-bis[N-methyl-N-(2-pyridylethyl)amino]-m-xylene; synthesized from the reaction between [Cu2(L2-O)(OH)](ClO4)2 (2) and Cl-) and Me-L3-OH: [Cu2(Me-L3-O)(&#956; -X)](ClO4)2&#183;nH2O (Me-L3-OH = 2,6-bis[N-(2-pyridylethyl)-N-(2-pyridylmethyl)amino]-4-methylphenol and X = C3H3N2- (prz) (4), MeCO2- (5) and N3- (6)). The magnetochemical characteristics of compounds 4-7 were determined by temperature-dependent magnetic studies, revealing their antiferromagnetic behaviour [-2J (in cm-1) values: -92 for 4, -86 for 5 and -88 for 6; -374 for 7]

Mortality and pulmonary complications in patients undergoing surgery with perioperative SARS-CoV-2 infection: an international cohort study

Background: The impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on postoperative recovery needs to be understood to inform clinical decision making during and after the COVID-19 pandemic. This study reports 30-day mortality and pulmonary complication rates in patients with perioperative SARS-CoV-2 infection. Methods: This international, multicentre, cohort study at 235 hospitals in 24 countries included all patients undergoing surgery who had SARS-CoV-2 infection confirmed within 7 days before or 30 days after surgery. The primary outcome measure was 30-day postoperative mortality and was assessed in all enrolled patients. The main secondary outcome measure was pulmonary complications, defined as pneumonia, acute respiratory distress syndrome, or unexpected postoperative ventilation. Findings: This analysis includes 1128 patients who had surgery between Jan 1 and March 31, 2020, of whom 835 (74·0%) had emergency surgery and 280 (24·8%) had elective surgery. SARS-CoV-2 infection was confirmed preoperatively in 294 (26·1%) patients. 30-day mortality was 23·8% (268 of 1128). Pulmonary complications occurred in 577 (51·2%) of 1128 patients; 30-day mortality in these patients was 38·0% (219 of 577), accounting for 81·7% (219 of 268) of all deaths. In adjusted analyses, 30-day mortality was associated with male sex (odds ratio 1·75 [95% CI 1·28–2·40], p\textless0·0001), age 70 years or older versus younger than 70 years (2·30 [1·65–3·22], p\textless0·0001), American Society of Anesthesiologists grades 3–5 versus grades 1–2 (2·35 [1·57–3·53], p\textless0·0001), malignant versus benign or obstetric diagnosis (1·55 [1·01–2·39], p=0·046), emergency versus elective surgery (1·67 [1·06–2·63], p=0·026), and major versus minor surgery (1·52 [1·01–2·31], p=0·047). Interpretation: Postoperative pulmonary complications occur in half of patients with perioperative SARS-CoV-2 infection and are associated with high mortality. Thresholds for surgery during the COVID-19 pandemic should be higher than during normal practice, particularly in men aged 70 years and older. Consideration should be given for postponing non-urgent procedures and promoting non-operative treatment to delay or avoid the need for surgery. Funding: National Institute for Health Research (NIHR), Association of Coloproctology of Great Britain and Ireland, Bowel and Cancer Research, Bowel Disease Research Foundation, Association of Upper Gastrointestinal Surgeons, British Association of Surgical Oncology, British Gynaecological Cancer Society, European Society of Coloproctology, NIHR Academy, Sarcoma UK, Vascular Society for Great Britain and Ireland, and Yorkshire Cancer Research

Coordination chemistry with pyrazole-based chelating ligands: molecular structural aspects

Pyrazole-based chelating ligands form a variety of coordination complexes with a number of metal ions, providing varying coordination geometry and nuclearity. Recent years have seen considerable interest in the designing of various pyrazole-based ligands and to study their structural properties to serve specific stereochemical requirement of a particular metal-binding site. Using over 120 pyrazole-based chelating ligands, the stereochemical properties of over 110 discrete coordination complexes, studied by single-crystal X-ray crystallography were analysed. Various bonding modes for a given chelating ligand are involved, and are reviewed with reference to ligand structure and the resulting coordination complexes. It is shown that the metal coordination number of the resulting complexes varies from two to eight. The ligands are introduced systematically as a function of their denticity, making easy access to information on specific type of ligands and coordination complexes thereof. X-ray crystallographically-determined bond lengths of various donor atoms/groups are collected in a table, thus providing an accessible source for reference purposes. Source material for the review amounts to about 130 references

Synthesis, structure, and properties of monomeric Fe(II), Co(II), and Ni(II) complexes of neutral N-(aryl)-2-pyridinecarboxamides

We have prepared and structurally characterized six-coordinate Fe(II), Co(II), and Ni(II) complexes of types [MII(HL1)2(H2O)2][ClO4]2 (M = Fe, 1; Co, 3; and Ni, 5) and [MII(HL2)3][ClO4]2&#183;MeCN (M = Fe, 2 and Co, 4) of bidentate pyridine amide ligands, N-(phenyl)-2-pyridinecarboxamide (HL1) and N-(4-methylphenyl)-2-pyridinecarboxamide (HL2). The metal centers in bis(ligand)-diaqua complexes 1, 3 and 5 are coordinated by two pyridyl N and two amide O atoms from two HL1 ligands and six-coordination is completed by coordination of two water molecules. The complexes are isomorphous and possess trans-octahedral geometry. The metal centers in isomorphous tris(ligand) complexes 2 and 4 are coordinated by three pyridyl N and three amide O atoms from three HL2 ligands. The relative dispositions of the pyridine N and amide O atoms reveal that the pseudo-octahedral geometry have the meridional stereochemistry. To the best of our knowledge, this work provides the first examples of structurally characterized six-coordinate iron(II) complexes in which the coordination is solely by neutral pyridine amide ligands providing pyridine N and amide O donor atoms, with or without water coordination. Careful analyses of structural parameters of 1-5 along with that reported in the literature [MII(HL1)2(H2O)2][ClO4]2 (M = Cu and Zn) and [CoIII(L2)3] have allowed us to arrive at a number of structural correlations/generalizations. The complexes are uniformly high-spin. Spectroscopic (IR and UV/Vis) and redox properties of the complexes have also been investigated

Stereotactic Radiosurgery for Treatment of Brain Metastases

Synthesis and crystal structure of two coordination polymers of composition [MnII(H2bpbn)1.5][ClO4]2&#183;2MeOH&#183;2H2O (1) and [CoII(H2bpbn)(H2O)2]Cl2&#183;H2O (2) [H2bpbn = N,N'-bis(2-pyridinecarboxamido)-1,4-butane], formed from the reaction between [Mn(H2O)6][ClO4]2/CoCl2&#183;4H2O with H2bpbn in MeCN, are described. In 1 each MnII ion is surrounded by three pyridine amide units, providing three pyridine nitrogen and three amide oxygen donors. Each MnII center in 1 has distorted MnN3O3 coordination. In 2 each CoII ion is coordinated by two pyridine amide moieties in the equatorial plane and two water molecules provide coordination in the axial positions. Thus, the metal center in 2 has trans-octahedral geometry. In both 1 and 2, the existence of 1D zigzag network structure has been revealed. Owing to &#960;-&#960; stacking of pyridine rings from adjacent layers 1 forms 2D network; 2 forms 2D and 3D network assemblies via N-H&#183;&#183;&#183;Cl and O-H&#183;&#183;&#183;Cl secondary interactions. Both the metal centers are high-spin

Modeling tyrosinase monooxygenase activity. Spectroscopic and magnetic investigations of products due to reactions between copper(I) complexes of xylyl-based dinucleating ligands and dioxygen: aromatic ring hydroxylation and irreversible oxidation products

A full account of a chemical system possessing features that mimic the reactivity aspects of tyrosinase is presented. Using dinucleating ligands with a m-xylyl spacer three new dicopper(I) complexes have been synthesized and their reactivity with dioxygen investigated. The six-membered chelate ring forming ligands provide only two nitrogen coordinations to each copper. The complexes [CuI2L(CH3CN)2]X2 (X = ClO4- (1a), SbF6- (1b)) and [CuI2(L-NO2)(CH3CN)2][SbF6]2 (1c) [L = &#945;,&#945;'-bis[N-methyl-N-(2-pyridylethyl)amino]-m-xylene; L-NO2 = para-nitro derivative of L] have been characterized by IR and 1H NMR spectroscopy. The reaction of O2 with 1a-c in CH2Cl2 or THF is instantaneous and causes stoichiometric xylyl hydroxylation reactions producing phenol products. Thus 1a produces phenoxo-/hydroxo-bridged product [CuII2(L-O)(OH)][ClO4]2 (2a). The existence of putative peroxo-dicopper(II) species could not be detected even at -80 &#176;C. A trend is observed for the extent of aromatic ring hydroxylation (298 K): CH3CN ~DMF &gt; CH3OH &#187; CH2Cl2. Cyclic voltammetric experiment of 1a in DMF reveals an appreciably low redox potential (E&#189; = -0.26 V vs SCE) for the CuII2/CuI2 redox process. Variable-temperature (25-300 K) magnetic susceptibility measurements establish that the copper(II) centers in 2a and the dihydroxo-bridged complex [CuII2L'(OH)2][ClO4]2 (2b) [formed due to an impurity (L') present during the synthesis of L following Method A; L' = bis[&#945;,&#945;'-bis(N-methyl-N-(2-pyridylethyl)amino)-m-xylene]methylamine] are antiferromagnetically coupled, with 2a considerably more coupled than 2b. Reaction of 1a with O2 in CH2Cl2 (298 K) produces an additional unhydroxylated product of composition [CuII2L(OH)(OH2)][ClO4]3&#183;2H2O&#183;0.5HCl (3a). In agreement with its proposed hydroxo-/aquo-bridged structure, 3a is weakly antiferromagnetically coupled. In CH3CN solution, 3a rearranges to generate a doubly hydroxo-bridged species [CuII2L(OH)2]2+. Using a solution-generated dicopper(I) complex of a closely similar ligand (L' ') providing five-membered chelate ring, the reactivity toward dioxygen was also investigated. It produces only an irreversibly oxidized product of composition CuII2L' '(OH)(ClO4)3(H2O)2 (3b) (L' ' = &#945;,&#945;'-bis[N-methyl-N-(2-pyridylmethyl)amino]-m-xylene). For 3b the copper(II) centers are almost uncoupled