Synthesis, Characterization, and Computational Studies on Gallium(III) and Iron(III) Complexes with a Pentadentate Macrocyclic bis-Phosphinate Chelator and Their Investigation As Molecular Scaffolds for 18F Binding.

With the aim of obtaining improved molecular scaffolds for 18F binding to use in PET imaging, gallium(III) and iron(III) complexes with a macrocyclic bis-phosphinate chelator have been synthesized and their properties, including their fluoride binding ability, investigated. Reaction of Bn-tacn (1-benzyl-1,4,7-triazacyclononane) with paraformaldehyde and PhP(OR)2 (R = Me or Et) in refluxing THF, followed by acid hydrolysis, yields the macrocyclic bis(phosphinic acid) derivative, H2(Bn-NODP) (1-benzyl-4,7-phenylphosphinic acid-1,4,7-triazacyclononane), which is isolated as its protonated form, H2(Bn-NODP)·2HCl·4H2O, at low pH (HClaq), its disodium salt, Na2(Bn-NODP)·5H2O at pH 12 (NaOHaq), or the neutral H2(Bn-NODP) under mildly basic conditions (Et3N). A crystal structure of H2(Bn-NODP)·2HCl·H2O confirmed the ligand's identity. The mononuclear [GaCl(Bn-NODP)] complex was prepared by treatment of either the HCl or sodium salt with Ga(NO3)3·9H2O or GaCl3, while treatment of H2(Bn-NODP)·2HCl·4H2O with FeCl3 in aqueous HCl gives [FeCl(Bn-NODP)]. The addition of 1 mol. equiv of aqueous KF to these chloro complexes readily forms the [MF(Bn-NODP)] analogues. Spectroscopic analysis on these complexes confirms pentadentate coordination of the doubly deprotonated (bis-phosphinate) macrocycle via its N3O2 donor set, with the halide ligand completing a distorted octahedral geometry; this is further confirmed through a crystal structure analysis on [GaF(Bn-NODP)]·4H2O. The complex adopts the geometric isomer in which the phosphinate arms are coordinated unsymmetrically (isomer 1) and with the stereochemistry of the three N atoms of the tacn ring in the RRS configuration, denoted (N)RRS, and the phosphinate groups in the RR stereochemistry, denoted (P)RR, (isomer 1/RR), together with its (N)SSR (P)SS enantiomer. The greater thermodynamic stability of isomer 1/RR over the other possible isomers is also indicated by density functional theory (DFT) calculations. Radiofluorination experiments on the [MCl(Bn-NODP)] complexes in partially aqueous MeCN/NaOAcaq (Ga) or EtOH (Ga or Fe; i.e. without buffer) with 18F- target water at 80 °C/10 min lead to high radiochemical incorporation (radiochemical yields 60-80% at 1 mg/mL, or ∼1.5 µM, concentration of the precursor). While the [Fe18F(n-NODP)] is unstable (loss of 18F-) in both H2O/EtOH and PBS/EtOH (PBS = phosphate buffered saline), the [Ga18F(Bn-NODP)] radioproduct shows excellent stability, RCP = 99% at t = 4 h (RCP = radiochemical purity) when formulated in 90%:10% H2O/EtOH and ca. 95% RCP over 4 h when formulated in 90%:10% PBS/EtOH. This indicates that the new "GaIII(Bn-NODP)" moiety is a considerably superior fluoride binding scaffold than the previously reported [Ga18F(Bn-NODA)] (Bn-NODA = 1-benzyl-4,7-dicarboxylate-1,4,7-triazacyclononane), which undergoes rapid and complete hydrolysis in PBS/EtOH (refer to Chem. Eur. J. 2015, 21, 4688-4694).

Pyramidal Dicationic Ge(II) Complexes with Homoleptic Neutral Pnictine Coordination: A Combined Experimental and Density Functional Theory Study.

An unusual series of Ge(II) dicationic species with homoleptic phosphine and arsine coordination, [Ge(L)][OTf]2, L = 3 × PMe3, triphos (MeC(CH2PPh2)3), triars (MeC(CH2AsMe2)3), or κ3-tetraphos (P(CH2CH2PPh2)3) (OTf- = O3SCF3-) have been prepared by reaction of [GeCl2(dioxane)] with L and 2 mol equiv of Me3SiOTf in anhydrous CH2Cl2 (or MeCN for L = triars, triphos). X-ray crystal structures are reported for [Ge(PMe3)3][OTf]2, [Ge(triars)][OTf]2, and [Ge(κ3-tetraphos)][OTf]2, confirming homoleptic P3- or As3-coordination at Ge(II) in each case and with the discrete OTf- anions providing a charge balance. The Ge-P/As bond lengths are significantly shorter than those in neutral germanium(II) dihalide complexes with diphosphine or diarsine coordination. Solution NMR spectroscopic data indicate that the complexes are labile in solution. Using excess AsMe3 and [GeCl2(dioxane)] gives only the neutral product, [Ge(AsMe2)2(OTf)2], the crystal structure of which shows four coordination at Ge(II), via two As donor atoms and an O atom from two κ1-OTf- ligands; further weak, long-range intermolecular interactions give a chain polymer. The electronic structure of the [Ge(PMe3)3]2+ dication has been investigated using density functional theory (DFT) calculations. The computed geometrical parameters for this dication are in good agreement with the experimental X-ray crystallographic values in [Ge(PMe3)3][OTf]2. The results also indicate that the pyramidal arrangement of the [Ge(PMe3)3]2+ (computed P-Ge-P angle 96.8° at the B3LYP-D3 level) arises from a balance between electronic energy (Eelec) contributions, which favor a lower P-Ge-P angle, and nuclear-nuclear contributions (Enn), which favor a higher P-Ge-P angle, to the total energy (ETOT). An Atoms in Molecules (AIM) analysis reveals that one reason why Eelec decreases as the P-Ge-P angle decreases is because of C···H and H···H interactions between atoms on different CH3 groups. The stability of the [Ge(PMe3)3]2+ dication is enhanced by the distribution of a significant part of the positive charge on Ge2+ to the atomic centers of the PMe3 ligands. Similar results were obtained for [Ge(AsMe3)3][OTf]2, showing the tris-AsMe3 complex to be less stable compared to the PMe3 analogue. Related calculations were also performed for the neutral [Ge(PMe3)2(OTf)2] and [Ge(AsMe3)2(OTf)2] complexes.

Tertiary Phosphine and Arsine Complexes of Phosphorus Pentafluoride: Synthesis, Properties, and Electronic Structures.

The reaction of PMe3 or PPh3 with PF5 in anhydrous CH2Cl2 or hexane forms the white, moisture-sensitive complexes [PF5(PR3)] (R = Me, Ph). Similar reactions involving the diphosphines o-C6H4(PR2)2 afford the complexes [PF4{o-C6H4(PR2)2}][PF6]. The X-ray structures of [PF5(PR3)] and [PF4{o-C6H4(PMe2)2}][PF6] show pseudo-octahedral fluorophosphorus centers. Multinuclear NMR spectra (1H, 19F{1H}, 31P{1H}) show that in solution in CH2Cl2/CD2Cl2 the structures determined crystallographically are the only species present for [PF5(PMe3)] and [PF4{o-C6H4(PMe2)2}][PF6] but that [PF5(PPh3)] and [PF4{o-C6H4(PPh2)2}][PF6] exhibit reversible dissociation of the phosphine at ambient temperatures, although exchange slows at low temperatures. The complex 19F{1H} and 31P{1H} NMR spectra have been analyzed, including those of the cation [PF4{o-C6H4(PMe2)2}]+, which is a second-order AA'XX'B2M spin system. The unstable [PF5(AsMe3)], which decomposes in a few hours at ambient temperatures, has also been isolated and spectroscopically characterized; neither AsPh3 nor SbEt3 forms similar complexes. The electronic structures of the PF5 complexes have been explored by DFT calculations. The DFT optimized geometries for [PF5(PMe3)], [PF5(PPh3)], and [PF4{o-C6H4(PMe2)2}]+ are in good agreement with their respective crystal structure geometries. DFT calculations on the PF5-L complexes reveal the P-L bond strength falls with L in the order PMe3 > PPh3 > AsMe3, consistent with the experimentally observed stabilities, and in the PF5-L complexes, electron transfer from L to PF5 on forming these complexes also follows the order PMe3 > PPh3 ≈ AsMe3.

Tungsten(VI) selenide tetrachloride, WSeCl4 - synthesis, properties, coordination complexes and application of [WSeCl4(SenBu2)] for CVD growth of WSe2 thin films.

WSeCl4 was obtained in good yield by heating WCl6 and Sb2Se3in vacuo. Green crystals grown by sublimation were shown by single crystal X-ray structure analysis to contain square pyramidal monomers with apical WSe, and powder X-ray diffraction (PXRD) analysis confirmed this to be the only form present in the bulk sample. Density functional theory (DFT) calculations using the B3LYP-D3 functional replicated the structure, identified the key bonding orbitals, and were used to aid assignment of the IR spectrum of WSeCl4. Reaction of WSeCl4 with ligands L gave [WSeCl4(L)] (L = MeCN, DMF, thf, py, OPPh3, 2,2'-bipy, SeMe2, SenBu2), whilst the dimers [(WSeCl4)2(µ-L-L)] were formed with L-L = Ph2P(O)CH2P(O)Ph2, 1,4-dioxane and 4,4'-bipyridyl. The complexes were characterised by microanalysis, IR and 1H NMR spectroscopy, and single crystal X-ray structures determined for [WSeCl4(L)] (L = OPPh3, MeCN, DMF) and [(WSeCl4)2(µ-L-L)] (L-L = 1,4-dioxane, 4,4'-bipyridyl). All except the 2,2'-bipy complex, which is probably seven-coordinate, contain six-coordinate tungsten with the neutral donor trans to WSe. Alkylphosphines, including PMe3 and PEt3, decompose WSeCl4 upon contact, forming phosphine selenides (SePR3). In contrast, the selenoether complexes [WSeCl4(SeMe2)] and [WSeCl4(SenBu2)] were isolated and characterised. The crystal structure of the minor W(VI) by-product, [(WSeCl4)2(µ-SeMe2)], was determined and using SMe2, a few crystals of the W(V) species, [{WCl3(SMe2)}2(µ-Se)(µ-Se2)], were obtained and structurally characterised. The isolated W(VI) complexes are compared with those of WOCl4 and WSCl4 and the combination of experimental and computational data are consistent with WSeCl4 being a weaker Lewis acid and its complexes significantly less stable than those of the lighter analogues, especially in solution. Low pressure chemical vapour deposition (LPCVD) using [WSeCl4(SenBu2)] in the range 660-700 °C (0.1 mmHg) produced highly reflective thin films, which were identified to be WSe2 by grazing incidence X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. XRD analysis of the thinner films revealed them to be highly oriented in the <00l> direction.

Tungsten disulfide thin films via electrodeposition from a single source precursor.

We report a simple process for the electrodeposition of tungsten disulfide thin films from a CH2Cl2-based electrolyte using a tailored single source precursor, [NEt4]2[WS2Cl4]. This new precursor incorporates the 1 : 2 W : S ratio required for formation of WS2, and eliminates the need for an additional proton source in the electrolyte to remove excess sulfide. The electrochemical behaviour of [NEt4]2[WS2Cl4] is studied by cyclic voltammetry and electrochemical quartz crystal microbalance techniques, and the WS2 thin films are grown by potentiostatic electrodeposition.

Thioether complexes of WSCl4, WOCl4 and WSCl3 and evaluation of thiochloride complexes as CVD precursors for WS2 thin films.

The red-brown [(WSCl4)2{µ-RS(CH2)2SR}] (R = Me, Ph, iPr) and [(WSCl4)2{µ-MeS(CH2)3SMe}] have been made by reaction of WSCl4 with the thioether in a 2 : 1 molar ratio, in anhydrous CH2Cl2 solution, and characterised by microanalysis, IR, UV/Vis and 1H NMR spectroscopy. The X-ray structures of the four dithioether complexes reveal square pyramidal WSCl4 units and bridging dithioethers with W[double bond, length as m-dash]S trans to thioether sulfur. Paramagnetic W(v) complexes, [WSCl3{RS(CH2)2SR}] (R = Me, iPr), have been made similarly using a 1 : ≥1 ratio of reactants or longer reaction times. The W(vi) complexes, [WSCl4(SMe2)] and [WSCl4(SeMe2)], are also described. Analogous complexes of WOCl4, [(WOCl4)2{RS(CH2)2SR}] (R = Ph, iPr), have been made similarly from WOCl4, but reactions using MeS(CH2)nSMe (n = 2, 3) led to reduction to W(v), forming [WOCl3{MeS(CH2)nSMe], both of which were identified crystallographically. Curiously, they are geometric isomers: [WOCl3{MeS(CH2)3SMe}] has the dithioether trans Cl/Cl whereas in [WOCl3{MeS(CH2)2SMe}] it is trans O/Cl. Remarkably, low pressure chemical vapour deposition (CVD) experiments using the dinuclear W(vi) species, [(WSCl4)2{iPrS(CH2)2SiPr}], as a single source precursor produced thin films of 4H-WS2, identified by grazing incidence X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy; the tungsten thiochloride complex is the first single source low pressure CVD precursor for WS2. In contrast, the mononuclear W(v) complex, [WSCl3{iPrS(CH2)2SiPr}], does not deposit WS2 under similar conditions.

Neutral and cationic phosphine and arsine complexes of tin(iv) halides: synthesis, properties, structures and anion influence.

The reaction of trans-[SnCl4(PR3)2] (R = Me or Et) with trimethylsilyltriflate (TMSOTf) in CH2Cl2 solution substitutes one chloride to form [SnCl3(PR3)2(OTf)]; addition of excess TMSOTf does not substitute further chlorides. The complexes have been fully characterised by microanalysis, IR and multinuclear NMR (1H, 13C{1H}, 19F{1H}, 31P{1H}, 119Sn) spectroscopy. The crystal structure of [SnCl3(PMe3)2(OTf)] revealed mer-chlorines and trans-phosphines. In contrast, trans-[SnBr4(PR3)2], [SnCl4{Et2P(CH2)2PEt2}], [SnCl4{o-C6H4(PMe2)2}] and [SnCl4{o-C6H4(AsMe2)2}] did not react with TMSOTf in CH2Cl2 solution even after 3 days. The arsine complexes, [SnX4(AsEt3)2] (X = Cl, Br), were confirmed as trans-isomers by similar spectroscopic and structural studies, while attempts to isolate [SnI4(AsEt3)2] were unsuccessful and reaction of SnX4 with SbR3 (R = Et, iPr) resulted in reduction to SnX2 and formation of R3SbX2. trans-[SnCl4(AsEt3)2] is converted by TMSOTf into [SnCl3(AsEt3)2(OTf)], whose X-ray structure reveals the same geometry found in the phosphine analogues, with the triflate coordinated. The salts, [SnCl3(PEt3)2][AlCl4] and [SnCl2(PEt3)2][AlCl4]2 were made by treatment of [SnCl4(PEt3)2] with one and two mol. equivalents, respectively, of AlCl3 in anhydrous CH2Cl2, whereas reaction of [SnCl4(AsEt3)2] with AlCl3 produced a mixture including Et3AsCl2 and [Et3AsCl][Sn(AsEt3)Cl5] (the latter identified crystallographically). In contrast, using Na[BArF] (BArF = [B{3,5-(CF3)2C6H3}4]-) produced [SnCl3(PEt3)2][BArF] and also allowed clean isolation of the arsine analogue, [SnCl3(AsEt3)2][BArF]. [SnCl4{o-C6H4(PMe2)2}] also reacts with AlCl3 in CH2Cl2 to form [SnCl3{o-C6H4(PMe2)2}][AlCl4] and [SnCl2{o-C6H4(PMe2)2}][AlCl4]2. Multinuclear NMR spectroscopy on the [AlCl4]- salts show that δ31P and δ119Sn move progressively to high frequency on conversion from the neutral complex to the mono- and the di-cations, whilst 1J(119Sn-31P) follow the trend: [SnCl3{o-C6H4(PMe2)2}]+ > [SnCl4{o-C6H4(PMe2)2}] > [SnCl2{o-C6H4(PMe2)2}]2+. DFT studies on selected complexes show only small changes in ligand geometries and bond lengths between the halide and triflate complexes, consistent with the X-ray crystallographic data reported and the HOMO and LUMO energies are relatively unperturbed upon the introduction of (coordinated) triflate, whereas the energies of both are ca. 4 eV lower in the cationic species and reveal significant hybridisation across the pnictine ligands.

Synthesis and electronic structure of the first cyaphide-alkynyl complexes.

The novel complexes trans-[Ru(dppe)2(C≡CR)(C≡P)] (R = CO2Me, C6H4OMe), the first to incorporate cyaphide as part of a conjugated system, are obtained in facile manner. The electronic structure of these compounds is probed by X-ray, DFT and UV/Vis studies.