A new Fe-II quaterpyridyl M4L6 tetrahedron exhibiting selective anion binding

A rigid linear bis-bidentate quaterpyridine undergoes metal directed self-assembly with iron(II) salts yielding M4L6 host–guest complexes; selective anion binding for PF6− over BF4− is observed

A family of discrete magnetaically switchable nanoballs

The thermal and light-induced magnetic properties of a family of discrete magnetically switchable "nanoball" species (3 nm in diameter) is reported. The self-assembly of these materials is accomplished by the use of the metallo building block, [Cu([Tp4-py])(NCCH3)] ([Tp4-py]=tris-[3-(4'-pyridyl)pyrazol-1-yl]hydroborate), combined with a [Fe(NCX)2] (X=S, Se and BH3) species. We previously showed that the thiocyanate analogue (Fe(NCS)-nano) undergoes a thermal and light-induced spin crossover (SCO)--the largest such discrete SCO material reported. Now included in this family are the Se and BH3 analogues, Fe(NCSe)-nano and Fe(NCBH3)-nano, which show increased thermal transition temperatures (T1/2=124 K, 162 and 173 K). This variation in transition temperature over the series

Single-crystal to single-crystal structural transformation and photomagnetic properties of a porous iron(II) spin-crossover framework

The porous coordination framework material, Fe(NCS)2(bped)2·3EtOH, SCOF-3(Et) (where bped is DL-1,2-bis(4'-pyridyl)-1,2-ethanediol), displays a spin-crossover (SCO) transition that has been stimulated both thermally and by light irradiation. The one-step thermal SCO (70-180 K) is sensitive to the presence of molecular guests, with a more gradual transition (70-225 K) apparent following the desorption of ethanol molecules that hydrogen bond to the spin centers. Additional intraframework hydrogen-bonding interactions stabilize the vacant one-dimensional pore structure of the apohost, SCOF-3, despite a dramatic single-crystal to single-crystal (SC-SC) structural change upon removal of the guests. Comprehensive structural analyses throughout this transformation, from primitive orthorhombic (Pccn) to body-centered tetragonal (I4/mcm), reveal a flexing of the framework and a dilation of the channels, with an accompanying subtle distortion of the iron(II) coordination geometry. Photomagnetic measurements of the light-induced excited spin state trapping (LIESST) effect have been used to assess the degree of cooperativity in this system

Single-crystal to single-crystal structural transformation and photomagnetic properties of a porous iron(II) spin-crossover framework

The porous coordination framework material, Fe(NCS)2(bped)2·3EtOH, SCOF-3(Et) (where bped is DL-1,2-bis(4'-pyridyl)-1,2-ethanediol), displays a spin-crossover (SCO) transition that has been stimulated both thermally and by light irradiation. The one-step thermal SCO (70-180 K) is sensitive to the presence of molecular guests, with a more gradual transition (70-225 K) apparent following the desorption of ethanol molecules that hydrogen bond to the spin centers. Additional intraframework hydrogen-bonding interactions stabilize the vacant one-dimensional pore structure of the apohost, SCOF-3, despite a dramatic single-crystal to single-crystal (SC-SC) structural change upon removal of the guests. Comprehensive structural analyses throughout this transformation, from primitive orthorhombic (Pccn) to body-centered tetragonal (I4/mcm), reveal a flexing of the framework and a dilation of the channels, with an accompanying subtle distortion of the iron(II) coordination geometry. Photomagnetic measurements of the light-induced excited spin state trapping (LIESST) effect have been used to assess the degree of cooperativity in this system

Formation of Zinc-Containing Nanoparticles from Zn²⁺ Ions in Cell Culture Media: Implications for the Nanotoxicology of ZnO

Zinc ions generate a range of poorly soluble Zn-containing nanoparticles when added to commonly used mammalian cell culture media. The formation of these nanoparticles confounds the use of soluble Zn salts as positive controls during cytotoxicity testing of other Zn-containing nanoparticles, such as ZnO. These nanoprecipitates can either be crystalline or amorphous and vary in composition depending upon the concentration of Zn­(II) within the medium. The cytotoxicity and immune system response of these nanoparticles in situ are similar to those of 30 nm ZnO nanoparticles. The low residual level of truly soluble Zn species (taken as species passing through a 2 kDa membrane) in cell culture media with serum is insufficient to elicit any appreciable cytotoxicity. These observations highlight the importance of employing appropriate controls when studying ZnO nanoparticle toxicity and suggest a re-evaluation of the conclusions drawn in some previous cytotoxicity studies

New bis-, tris- and tetrakis(pyrazolyl)borate ligands with 3-pyridyl and 4-pyridyl substituents: synthesis and coordination chemistry

The new ligands dihydrobis[3-(4-pyridyl)pyrazol-1-yl]borate [Bp(4py)](-), hydrotris[3-(4-pyridyl)pyrazol-1-yl]borate [Tp(4py)](-), tetrakis[3-(4-pyridyl)pyrazol-1-yl]borate [Tkp(3py)](-), dihydrobis[3-(3-pyridyl)pyrazol-1-yl]borate [Bp(3py)](-), hydrotris[3-(3-pyridyl)pyrazol-1-yl]borate [Tp(3py)](-) and tetrakis[3-(3-pyridyl)pyrazol-1-yl]borate [Tkp(4py)](-) are derivatives of the well known bis-, tris- and tetrakis-(pyrazolyl)borate cores, bearing 4-pyridyl or 3-pyridyl substituents attached to the pyrazolyl C-3 positions. These pyridyl groups cannot chelate to the metal ions in the poly(pyrazolyl) cavity but are externally directed. Structural studies on a range of metal complexes show how, in many cases, coordination of these pendant pyridyl groups to the M(pyrazolyl), core of an adjacent metal complex fragment results in formation of coordination oligomers or polymeric networks. [Tl(B-3py)], [TlBp4y] and [Tl(Tp(4py))] form one-dimensional polymeric chains via coordination of one of their pendant pyridyl units to the Tl(I) centre of an adjacent complex fragment; in contrast, in [Tl(Tp(3py))] coordination of all three pendant pyridyl units to separate Tl(I) neighbours results in formation of a two-dimensional polymeric sheet. In [Tl(Tkp(3py))] and [Tl(Tkp(4py))] the Tl(I) is coordinated by two or three of the four pyrazolyl arms, respectively; bridging interactions of pendant 4-pyridyl groups with adjacent Tl(I) centres result in a two-dimensional sheet forming in each case. In Ag(Tkp(4py)) each Ag(I) ion is coordinated by two pyrazolyl rings, and two bridging pyridyl ligands from other complex units, resulting in a one-dimensional chain consisting of pairs of cross-linked zigzag chains. In contrast to these polymeric coordination networks, the structures of [Cu(Tp(4py))] and [(Tp(3py))Cd(CH3CO2)] are dimers, with a pendant pyridyl residue from the first metal centre attaching to a vacant coordination site on the second, and vice versa; these dimers are stabilised by pi-stacking interactions between sections of the two ligands. [Ni(Tp(3py)),] is monomeric, with an octahedral coordination geometry arising from two tris(pyrazolyl)borate chelates; the array of pendant 3-pyridyl groups is involved only in intramolecular hydrogen-bonding. [(Tp(4pY))Re(CO)(3)] is also monomeric, with a facial arrangement of three pyrazolyl ligands and three carbonyls, with the pendant 4-pyridyl groups not further coordinated. [(Tp(2py))Re(CO)(3)], based on the related ligand hydrotris[3-(2-pyridyl)pyrazol-1-yl]borate, has a similar fac-(CO)(3)(pyrazolyl)(2) coordination geometry

New members of the [Ru(diimine)(CN)(4)](2-) family : structural, electrochemical and photophysical properties

A series of complexes of the type K2[Ru(NN)(CN)4] has been prepared, in which NN is a diimine ligand, and were investigated for both their structural and photophysical properties. The ligands used (and the abbreviations for the resulting complexes) are 3-(2-pyridyl)pyrazole (Ru-pypz), 2,2′-bipyrimidine (Ru-bpym), 5,5′-dimethyl-2,2′-bipyridine (Ru-dmb), 1-ethyl-2-(2-pyridyl)benzimidazole (Ru-pbe), bidentate 2,2′:6′,2[triple prime]-terpyridine (Ru-tpy). The known complexes with NN = 2,2′-bipyridine (Ru-bpy) and 1,10-phenathroline (Ru-phen) were also included in this work. A series of crystallographic studies showed that the [Ru(NN)(CN)4]2− complex anions form a range of elaborate coordination networks when crystallised with either K+ or Ln3+ cations. The K+ salts are characterised by a combination of near-linear Ru–CN–K bridges, with the cyanides coordinating to K+ in the usual ‘end-on’ mode, and unusual side-on π-type coordination of cyanide ligands to K+ ions. With Ln3+ cations in contrast only Ru–CN–Ln near-linear bridges occurred, affording 1-dimensional helical or diamondoid chains, and 2-dimensional sheets constituted from linked metallamacrocyclic rings. All of the K2[Ru(NN)(CN)4] complexes show a reversible Ru(II)/Ru(III) couple (ca. +0.9 V vs. Ag/AgCl in water), the exception being Ru-tpy whose oxidation is completely irreversible. Luminescence studies in water showed the presence of 3MLCT-based emission in all cases apart from Ru-bpym with lifetimes of tens/hundreds of nanoseconds. Time-resolved infrared studies showed that in the 3MLCT excited state the principal C–N stretching vibration shifts to positive energy by ca. 50 cm−1 as a consequence of the transient oxidation of the metal centre to Ru(III) and the reduction in back-bonding to the cyanide ligands; measurement of transient decay rates allowed measurements of 3MLCT lifetimes for those complexes which could not be characterised by luminescence spectroscopy. A few complexes were also examined in different solvents (MeCN, dmf) and showed much weaker emission and shorter excited-state lifetimes in these solvents compared to water