We report the synthesis and characterization for several gold(III) complexes involving a series of cyclometallating ligands. These cyclometallating ligands (CN) are: 2-phenylpyridine (ppy), 2-(p-tolyl) pyridine (tpy), 2-(2'-benzothienyl)pyridine (btp) and 7,8-benzoquinoline (bzq). With the assistance of TGA data, we have developed solventless reactions to prepare the neutral cyclometallated Au(III) dichloro complexes. Reaction of these with the crown trithioether [9]aneS(3) (1,4,7-trithiacyclononane), followed by metathesis with NH4PF6, yields the heteroleptic complexes [Au([9]aneS(3))(CN)](PF6)(2). The X-ray structures of the gold(III) [9]aneS(3) complexes display axial Au-S interactions formed by the endodentate conformation of the thiacrown, resulting in elongated square pyramidal geometries. The Au-S axial distance correlates with the electron-donating properties of the CN ligand with the better donating btp showing the longest distance (2.855(1) angstrom) while the ppy shows the shortest (2.818(1) angstrom). The coordinated 9]aneS(3) ligand shows fluxional behavior by its NMR spectroscopy, resulting in a single C-13 NMR resonance despite the asymmetric coordination environment of the cyclometallating ligand. Electrochemical studies of the [9]aneS(3) complexes reveal irreversible one-electron reductions which are assigned as a Au(III)/Au(II) couple. The ease of reduction correlates with the axial Au-S distances with the btp being the easiest to reduce and the ppy the most difficult. In addition, we report the crystal structures for three intermediate complexes: [Au(H-tpy)Cl-3], [Au(H-btp)Cl-3], and [Au(btp)Cl-2]. The [Au(H-btp)Cl-3] complex shows an interesting Au-S axial interaction at 3.139(2) angstrom which alters the physicochemical properties of the complex. (C) 2014 Elsevier B. V. All rights reserved.

Botulinum neurotoxin (BoNT) is produced by Clostridium botulinum and associates with nontoxic neurotoxin-associated proteins to form high-molecular weight progenitor complexes (PCs). The PCs are required for the oral toxicity of BoNT in the context of food-borne botulism and are thought to protect BoNT from destruction in the gastrointestinal tract and aid in absorption from the gut lumen. The PC can differ in size and protein content depending on the C. botulinum strain. The oral toxicity of the BoNT PC increases as the size of the PC increases, but the molecular architecture of these large complexes and how they contribute to BoNT toxicity have not been elucidated. We have generated 2D images of PCs from strains producing BoNT serotypes A1, B, and E using negative stain electron microscopy and single-particle averaging. The BoNT/A1 and BoNT/B PCs were observed as ovoid-shaped bodies with three appendages, whereas the BoNT/E PC was observed as an ovoid body. Both the BoNT/A1 and BoNT/B PCs showed significant flexibility, and the BoNT/B PC was documented as a heterogeneous population of assembly/disassembly intermediates. We have also determined 3D structures for each serotype using the random conical tilt approach. Crystal structures of the individual proteins were placed into the BoNT/A1 and BoNT/B PC electron density maps to generate unique detailed models of the BoNT PCs. The structures highlight an effective platform that can be engineered for the development of mucosal vaccines and the intestinal absorption of oral biologics.

We wish to report the crystal structure for a solid-state solution, {[Pt(9S3)Cl-2](2)[Pt(9S3)(2)]}Cl-2 center dot 4H(2)O (1), which contains two different complexes of Pt(II) with the trithiacrown 9S3 (1,4,7-trithiacyclononane). One complex [Pt(9S3)Cl-2] is neutral and contains a Pt(II) center with a single 9S3 ligand and two coordinated chloro ligands. The second Pt(II) complex is a dication and contains two coordinated 9S3 ligands and two non-coordinating chloride anions. There are two crystallographically equivalent [Pt(9S3)Cl-2] complexes present for every single [Pt(9S3)(2)](2+) cation. Four water solvent molecules are also present. In the neutral complex ([Pt(9S3)Cl-2], the Pt(II) center is surrounded by a cis-[S2Cl2 + S-1] ligand environment formed by the two chloro ligands and two of the three sulfur atoms from the 9S3 ligand. These two sulfurs are positioned 2.225(2) and 2.242(2) angstrom from the Pt(II), but the third sulfur shows a long distance interaction at 3.311(2) angstrom to form an elongated square pyramidal structure. This axial Pt-S distance is the longest observed in 57 crystal structures of Pt(II) 9S3 complexes. The cation [Pt(9S3)(2)](2+) displays two centrosymmetrically coordinated 9S3 ligands forming a [S-4 + S-2] environment with an elongated octahedral shape. In the dication, the two equatorial Pt-S distances are 2.297(2) and 2.306(2) angstrom with the axial sulfur at 3.065(2) angstrom. The most interesting intermolecular aspects of the structure are hydrogen bonding interactions between two of the water molecules and two chloride counter-ions, resulting in a nearly square O2Cl2 ring. This ring shares an edge with a six-membered ring formed by four waters and two chlorides which are hydrogen bonded. The hydrogen bonding interactions, which result from the presence of water in the crystal, appear to be an important component in stabilizing the lattice for the unusual solid-state solution structure. Crystal Data for (1): P2(1)/n, a = 7.8327(10) angstrom, b = 25.152(4) angstrom, c = 12.382(2) angstrom, V = 2314.3(6) angstrom(3), Z = 2. We also report an improved synthetic procedure for the preparation of two thiacrown complexes [Pt(9S3)Cl-2] and [Pt(10S3)Cl-2], which are commonly used as precursors for other heteroleptic thioether complexes. The new syntheses proceed at room temperature without the need for long reflux times and produce large crystals which are easily isolable without filtration. The simplicity of these new preparations results in improved yields over previously employed methods.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

We wish to report the crystal structure for a solid-state solution, {[Pt(9S3)Cl2]2[Pt(9S3)2]}Cl2·4H2O (1), which contains two different complexes of Pt(II) with the trithiacrown 9S3 (1,4,7-trithiacyclononane). One complex [Pt(9S3)Cl2] is neutral and contains a Pt(II) center with a single 9S3 ligand and two coordinated chloro ligands. The second Pt(II) complex is a dication and contains two coordinated 9S3 ligands and two non-coordinating chloride anions. There are two crystallographically equivalent [Pt(9S3)Cl2] complexes present for every single [Pt(9S3)2]2+ cation. Four water solvent molecules are also present. In the neutral complex ([Pt(9S3)Cl2], the Pt(II) center is surrounded by a cis-[S2Cl2 + S1] ligand environment formed by the two chloro ligands and two of the three sulfur atoms from the 9S3 ligand. These two sulfurs are positioned 2.225(2) and 2.242(2) Å from the Pt(II), but the third sulfur shows a long distance interaction at 3.311(2) Å to form an elongated square pyramidal structure. This axial Pt–S distance is the longest observed in 57 crystal structures of Pt(II) 9S3 complexes. The cation [Pt(9S3)2]2+ displays two centrosymmetrically coordinated 9S3 ligands forming a [S4 + S2] environment with an elongated octahedral shape. In the dication, the two equatorial Pt–S distances are 2.297(2) and 2.306(2) Å with the axial sulfur at 3.065(2) Å. The most interesting intermolecular aspects of the structure are hydrogen bonding interactions between two of the water molecules and two chloride counter-ions, resulting in a nearly square O2Cl2 ring. This ring shares an edge with a six-membered ring formed by four waters and two chlorides which are hydrogen bonded. The hydrogen bonding interactions, which result from the presence of water in the crystal, appear to be an important component in stabilizing the lattice for the unusual solid-state solution structure. Crystal Data for (1): P2 1 /n, a = 7.8327(10) Å, b = 25.152(4) Å, c = 12.382(2) Å, V = 2314.3(6) Å3, Z = 2. We also report an improved synthetic procedure for the preparation of two thiacrown complexes [Pt(9S3)Cl2] and [Pt(10S3)Cl2], which are commonly used as precursors for other heteroleptic thioether complexes. The new syntheses proceed at room temperature without the need for long reflux times and produce large crystals which are easily isolable without filtration. The simplicity of these new preparations results in improved yields over previously employed methods.

Botulinum neurotoxin (BoNT) binds peripheral neurons at the neuromuscular junction through a dual-receptor mechanism that includes interactions with ganglioside and protein receptors. The receptor identities vary depending on BoNT serotype (A-G). BoNT/B and BoNT/G bind the luminal domains of synaptotagmin I and II, homologous synaptic vesicle proteins. We observe conditions under which BoNT/B binds both Syt isoforms, but BoNT/G binds only SytI. Both serotypes bind ganglioside G(T1b). The BoNT/G receptor-binding domain crystal structure provides a context for examining these binding interactions and a platform for understanding the physiological relevance of different Syt receptor isoforms in vivo.

We report that our previously published molecular square, [{Pt([9]aneS(3))(bipy)}(4)](OTf)(8), although quite stable in nitromethane, slowly establishes an equilibrium with another coordination polymer, most likely a triangle, in acetonitrile. Multinuclear measurements on the square precursor complex, [Pt([9]aneS(3))Cl-2], show acetonitrile coordination upon dechlorination in that solvent, and acetonitrile coordination is additionally confirmed by the solid-state structure of [Pt([9]aneS(3))(MeCN)(2)](2+). We form the complex through the reaction of [Pt([9]aneS(3))Cl-2] with excess AgPF6 in refluxing MeCN to produce a solid- state solution containing two complex cations with exclusive hexafluorophosphate counterions. Besides [Pt([9]aneS(3))(MeCN)(2)](2+), a second cation is obtained, [Pt([9]aneS(3))(2)](2+), which shows disorder between a double endo and a rare double exo conformation for the two [9]aneS(3) ligands. We also report the structures of two Rh(III) thiacrown complexes, cis-[Rh([12]aneS(4))Cl-2](PF6), which involves cis chloro ligands and an asymmetric binding of the two equatorial sulphur donors, as well as trans-[Rh([16]aneS(4))(H2O)(Cl)](OTf)(2) with adjacent rather than alternating chair and twist-boat conformations. Lastly, the crystal structure of [{Pd([9]aneS(3))(Cl)}(2)(pyrazine)](OTf)(2) displays a pyrazine ligand bridging two [Pd([9]aneS(3))Cl](+) moieties with cis stereochemistry of the two chloro ligands. Distortion of the pyrazine ligand is observed, which alleviates strain from bridging the two Pd centres. The extended structure of the complex consists of chains of dimers running parallel to the b- axis of the crystal.

The complex [Pt(9S3)(SbPh3)(Ph)](PF6) forms directly from [Pt(9S3)(SbPh3)(2)](PF6)(2) during the room temperature crystallization of the latter in nitromethane. The crystal structure shows a five-coordinate Pt(II) center containing the tridentate thiacrown ligand, a Sb donor from the triphenylstibine ligand, and a sigma-coordinating phenyl group. The phenyl group forms via Sb-C bond cleavage from one of the SbPh3 ligands in the bis complex. (C) 2009 Elsevier B.V. All rights reserved.

We report the synthesis and full characterization for a series of thiacrown complexes of Pt(II) incorporating the fluxional trithiacrown ligand 1,4,7-trithiacyclononane ([9]aneS3) and several group 15 donors ligands. Reaction of [Pt([9]aneS3)Cl2] with a full stoichiometric equivalent of the group 15 donor (L = 2 x AsPh3, SbPh3 or 1,2-bis(diphenylarsenio) ethane (dpae) followed by metathesis with NH4PF6 yields [Pt([9]aneS3)L](PF6)2. We also report the analogous Pd(II) complex with dpae. Similar reactions of the starting Pt complex with one equivalent of XPh3 (X = As or Sb) result in complexes of the formula [Pt([9]aneS3)(XPh3)(Cl)](PF6). All six new complexes have been fully characterized by multinuclear NMR, IR, and UV-Vis spectroscopies in addition to elemental analysis and single crystal structural determinations. The X-ray structures of each complex indicate an axial M-S interaction formed by the endodentate conformation of the [9]aneS3 ligand. The axial M-S distance is highly dependent upon the ancillary donor set. The axial M-S distance shortens with the identity of the group 15 donor ligand according to the trend, Sb < As < P, due to their increasingly poorer donor qualities. The two bis pnictogen complexes, [Pt([9]aneS3)(AsPh3)2](PF6)2 and [Pt([9]aneS3)(SbPh3)2](PF6)2 form unusual five-coordinate distorted trigonal bipyramids in contrast to the pseudo-five coordinate, elongated square pyramidal structures typically observed in Pt(II) complexes of [9]aneS3. The distortion arises from intramolecular pi-pi interactions between the phenyl rings on the two different triphenyl ligands. Chemical shifts in the 195Pt NMR also show similar periodic relationships which trend progressively upfield as the donor atom becomes larger. As expected, the coordinated [9]aneS3 ligand shows fluxional behavior in its NMR spectra, resulting in a single 13C NMR resonance, despite the asymmetric coordination environment found in both chloro complexes. The line width for the carbon NMR resonance as well as for the 195Pt NMR peak is highly sensitive to the nature of the group 15 donor, with poorer donors such as SbPh3 showing significant line broadening. Measurements from the electronic spectra support that the ligand field strength of the pnictogen donor decreases with its increasing size.