[Tc(NO)(Cp)(PPh3)Cl] and [Tc(NO)(Cp)(PPh3)(NCCH3)](PF6), and Their Reactions with Pyridine and Chalcogen Donors.

Reactions of the technetium(I) nitrosyl complex [Tc(NO)(Cp)(PPh3)Cl] with triphenylphosphine chalcogenides EPPh3 (E = O, S, Se), and Ag(PF6) in a CH2Cl2/MeOH mixture (v/v, 2/1) result in an exchange of the chlorido ligand and the formation of [Tc(NO)(Cp)(PPh3)(EPPh3)](PF6) compounds. The cationic acetonitrile complex [Tc(NO)(Cp)(PPh3)(NCCH3)]+ is formed when the reaction is conducted in NCCH3 without additional ligands. During the isolation of the corresponding PF6- salt a gradual decomposition of the anion was detected in the solvent mixture applied. The yields and the purity of the product increase when the BF4- salt is used instead. The acetonitrile ligand is bound remarkably strongly to technetium and exchange reactions readily proceed only with strong donors, such as pyridine or ligands with 'soft' donor atoms, such as the thioether thioxane. Substitutions on the cyclopentadienyl ring do not significantly influence the ligand exchange behavior of the starting material. 99Tc NMR spectroscopy is a valuable tool for the evaluation of reactions of the complexes of the present study. The extremely large chemical shift range of this method allows the ready detection of corresponding ligand exchange reactions. The observed 99Tc chemical shifts depend on the donor properties of the ligands. DFT calculations support the discussions about the experimental results and provide explanations for some of the unusual findings.

Gold-Based Coronands as Hosts for M3+ Metal Ions: Ring Size Matters.

The controlled, self-assembled synthesis of multinuclear coordination compounds can be performed via different approaches. Frequently, steric, geometric and/or electronic factors located at the ligand systems predefine the way in which metal ions can assemble them to large aggregates. For the compounds in the present paper, also the Pearson's acidities and preferred coordination geometries of the metal ions were used as organization principles. The ligand under study, 2,6-dipicolinoylbis(N,N-diethylthiourea), H2L1ethyl, possesses 'soft' sulfur and 'hard' nitrogen and oxygen donors. One-pot reactions of this compound with [AuCl(tht)] (tht = tetrahydrothiophene) and M3+ salts (M = Sc, Y, La, Ln, Ga, In) give products with gold-based {Au3(L1ethyl)3}3+ or {Au2(L1ethyl)2}2+ coronands, which host central M3+ ions. The formation of such units is templated by the M3+ ions and the individual size of the coronand rings is dependent on the ionic radii of the central ions in a way that small ions such as Ga3+ form a [Ga⊂{Au2(L1ethyl)2}]+ assembly, while larger ions (starting from Sc3+/In3+) establish neutral [M⊂{Au3(L1ethyl)3}] units with nine-coordinate central ions.

Technetium Complexes with an Isocyano-alkyne Ligand and Its Reaction Products.

The attachment of an ethyne substituent in the para position of phenylisocyanide, CNPhpC≡CH, enables the isocyanide to replace carbonyl ligands in the coordination sphere of common technetium(I) starting materials such as (NBu4)[Tc2(µ-Cl)3(CO)6]. The ligand exchange proceeds under thermal conditions and finally forms the corresponding hexakis(isocyanide)technetium(I) complex. The product undergoes a copper-catalyzed cycloaddition ("Click" reaction), e.g., with benzyl azide, which gives the [Tc(CNPhazole)6]+ cation. The free, uncoordinated "Click" product is obtained from a reaction of the corresponding tetrakis(CNPhazole)copper(I) complex and NaCN. It readily reacts with mer-[Tc(CO)3(tht)(PPh3)2](BF4) (tht = tetrahydrothiophene) under exchange of the thioether ligand. Alternatively, [Cu(CNPhazole)4]+ can be used as a transmetalation reagent for the synthesis of the hexakis(isocyanide)technetium(I) complex, which is the preferable approach for the synthesis of the technetium complex with the short-lived nuclear isomer 99mTc, and a corresponding protocol for [99mTc(CNPhazole)6]+ is reported. The 99Tc and copper complexes have been studied by single-crystal X-ray diffraction and/or spectroscopic methods including IR and multinuclear NMR spectroscopy.

A Complete Triad of Zero-Valent 17-Electron Monoradicals of Group 7 Elements Stabilized by m-Terphenyl Isocyanides.

The first consistent series of mononuclear 17-electron complexes of three Group 7 elements has been isolated in crystalline form and studied by X-ray diffraction and spectroscopic methods. The paramagnetic compounds have a composition of [M0 (CO)(CNp-F-ArDArF2 )4 ] (M=Mn, Tc, Re; ArDArF2 =2,6-(3,5-(CF3 )2 C6 H3 )2 C6 H2 F) and are stabilized by four sterically encumbering isocyanides, which prevent the metalloradicals from dimerization. They have a square pyramidal structure with the carbonyl ligands as apexes. The frozen-solution EPR spectra of the rhenium and technetium compounds are clearly anisotropic with large 99 Tc and 185,187 Re hyperfine interactions for one component. High-field EPR (Q band and W band) has been applied for the elucidation of the EPR parameters of the manganese(0) complex.

Na[Tc(CO)(CNp-F-ArDArF2)4]: an isocyanide analogue of the elusive Na[Tc(CO)5].

The first crystalline technetium complex in a negative oxidation state, [Tc-I(CO)(CNp-F-ArDArF2)4]-, was isolated and structurally characterized as its [Na(Crypt-2.2.2)]+ salt. It mirrors the properties of the textbook organometallic compound Na[Tc(CO)5], which has eluded isolation and structural characterization until today. [Na(Crypt-2.2.2)][Tc-I(CO)(CNp-F-ArDArF2)4] reacts expectedly as a nucleophile, which is demonstrated by reactions with HCl and ClSnMe3. They give the unprecedented monohydrido and trimethylstannyl complexes of technetium.

Phenylimido complexes of rhenium: fluorine substituents provide protection, reactivity, and solubility.

Reactions of [Re(NPhF)Cl3(PPh3)2] ({NPhF}2- = p-fluorophenylimide) with a variety of alkyl and aryl isocyanides have been studied. Different reactivity patterns and products have been obtained depending on the steric and electronic properties of the individual ligands. This involves the formation of 1 : 1 and 1 : 2 exchange products of Re(V) with the general formulae mer-[Re(NPhF)Cl3(PPh3)(isocyanide)] and cis- or trans-[Re(NPhF)Cl3(isocyanide)2]. The stability of the obtained products is correlated with the substitution pattern of the isocyanide ligands. The products have been studied by single-crystal X-ray diffraction and spectroscopic methods, including IR and multinuclear NMR spectroscopy as well as mass spectrometry. The use of partially fluorinated starting materials and ligands allows the modulation of the solubilities of the starting materials and the products as well as the monitoring of the reactions by means of 19F NMR. The attachment of the CF3 or F substituent on the isocyanides gives control over the steric bulk and the electronic properties of the ligands and, thus, their reactivity.

The Chemistry of Phenylimidotechnetium(V) Complexes with Isocyanides: Steric and Electronic Factors.

Organometallic approaches are of ongoing interest for the development of novel functional 99mTc radiopharmaceuticals, while the basic organotechnetium chemistry seems frequently to be little explored. Thus, structural and reactivity studies with the long-lived isotope 99Tc are of permanent interest as the foundation for further progress in the related radiopharmaceutical research with this artificial element. Particularly the knowledge about the organometallic chemistry of high-valent technetium compounds is scarcely developed. Here, phenylimido complexes of technetium(V) with different isocyanides are introduced. They have been synthesized by ligand-exchange procedures starting from [Tc(NPh)Cl3(PPh3)2]. Different reactivity patterns and products have been obtained depending on the steric and electronic properties of the individual ligands. This involves the formation of 1:1 and 1:2 exchange products of Tc(V) with the general formulae [Tc(NPh)Cl3(PPh3)(isocyanide)], cis- or trans-[Tc(NPh)Cl3(isocyanide)2], but also the reduction in the metal and the formation of cationic technetium(I) complex of the formula [Tc(isocyanide)6]+ when p-fluorophenyl isocyanide is used. The products have been studied by single-crystal X-ray diffraction and spectroscopic methods, including IR and multinuclear NMR spectroscopy. DFT calculations on the different isocyanides allow the prediction of their reactivity towards electron-rich and electron-deficient metal centers by means of the empirical SADAP parameter, which has been derived from the potential energy surface of the electron density on their potentially coordinating carbon atoms.

Mixed-Isocyanide Complexes of Technetium under Steric and Electronic Control.

Reactions of the alkyl isocyanide fac-[Tc(CO)3(CNR)2Cl] complexes (2) (CNR = CNnBu or CNtBu) with the sterically encumbered isocyanide CNp-FArDarF2 [DArF = 3,5-(CF3)2C6H3] allow a selective exchange of the carbonyl ligands of 2 and the isolation of the mixed-isocyanide complexes mer,trans-[Tc(CNp-FArDarF2)3(CNR)2Cl] (3). Depending on the steric requirements of the residues R, the remaining chlorido ligand can be replaced by another isocyanide ligand. Cationic complexes such as mer-[Tc(CNp-FArDarF2)3(CNnBu)3]+ (4a) or mer,trans-[Tc(CNp-FArDarF2)3(CNnBu)2(CNtBu)]+ (6) have been prepared in this way and isolated as their PF6- salts. mer,trans-[Tc(CNp-FArDarF2)3(CNnBu)2(CNtBu)](PF6) represents to the best of our knowledge the first transition-metal complex with three different isocyanides in its coordination sphere. Since the degree of the ligand exchange seems to be controlled both by the electronic and steric measures of the incoming isocyanides, we undertook similar reactions with the sterically less demanding p-fluorophenyl isocyanide, CNPhpF, which indeed readily led to the hexakis(isocyanide)technetium(I) cation through an exchange of all ligands in the staring materials [Tc2(CO)6(µ-Cl)3]- or fac-[Tc(CO)3(CNR)2Cl]. The influence of the substituents at the isocyanide ligands in such reactions has been reasoned with the density functional theory-derived electrostatic potential at the accessible surface of the corresponding isocyanide carbon atoms.

Large Telluroxane Bowls Connected by a Layer of Iodine Ions.

Phenyltelluroxane clusters of the composition [{(PhTe)19 O24 }2 I18 (solv)] (1) are formed during the hydrolysis of [PhTeI3 ]2 or the oxidation of various phenyltellurium(II) compounds with iodine under hydrolytic conditions. The compounds consist of two half-spheres with a {(PhTe)19 O24 }9+ network, which are connected by 18 iodine atoms. The spherical clusters can accommodate solvent molecules such as pyridine or methanol in the center of two rings formed by iodine atoms. The presence of other metal ions during the cluster formation results in a selective replacement of the central {PhTe}3+ units of each half-sphere as has been demonstrated with the isolation of [{(PhTe)18 ({Ca(H2 O)2 }O24 }2 I16 ] (2) and [{(PhTe)18 ({Y(NO3 )(H2 O)}O24 }2 I16 ] (3). A crownether-like coordination by six oxygen atoms of the telluroxane network is found for the {Ca(H2 O}2 }2+ and {Y(NO3 )(H2 O)}2+ building blocks. Mass spectrometric studies show that considerable amounts of the intact clusters are transferred to the gas phase without dissociation.

One Ligand, One Metal, Seven Oxidation States: Stable Technetium Complexes with the "Kläui Ligand".

A series of technetium complexes with (η5-cyclopentadienyl)tris(dimethyl phosphito-P)cobaltate(III), also known as the "Kläui ligand" {LOMe}-, has been prepared. The products span seven different oxidation states (+1 to +7) of the radioactive transition metal and comprise nitrosyl, halide, oxido and nitrido complexes. All members of this series ([TcI(NO)Cl(PPh3)(LOMe)], [TcII(NO)Cl2(LOMe)], [TcIIICl2(PPh3)(LOMe)], [TcIVCl3(LOMe)], [TcVOCl2(LOMe)], [TcVNCl(PPh3)(LOMe)], [TcVINCl2(LOMe)], and [TcVIIO3(LOMe)] are air- and water-stable compounds, which recommends this class of technetium complexes as potential candidates for nuclear medical imaging procedures.

A closed-shell monomeric rhenium(1-) anion provided by m-terphenyl isocyanide ligation.

The mixed isocyanide/carbonyl complexes cis- and trans-[Re(CO)3Br(CNArDipp2)2] (ArDipp2 = 2,6-(2,6-(i-Pr)2C6H3)2C6H3) can be synthesized from reactions of [Re(CO)5Br] and CNArDipp2 depending on the conditions applied. Reduction of the neutral Re(i) species gives the monoanionic complex [Re(CO)3(CNArDipp2)2]- or the neutral [Re(CO)3(CNArDipp2)2], which contain rhenium in the formal oxidation states "-1" and "0", respectively.

Trinuclear CoIILnIIICoII Complexes (Ln = La, Ce, Nd, Sm, Gd, Dy, Er, and Yb) with 2,6-Dipicolinoylbis(N,N-diethylthiourea): Synthesis, Structures, and Magnetism.

One-pot reactions of 2,6-dipicolinoylbis(N,N-diethylthiourea) (H2L) with Co(CH3COO)2·4H2O and LnCl3, where Ln = La, Ce, Nd, Sm, Gd, Dy, Er, and Yb, in warm methanol in the presence of Et3N, give stable trinuclear complexes of the composition [LnCo2(L)2(µ1,3-OOCCH3)2X] ("CoLnCo" complexes), where X- = κ2-CH3COO- or Cl-. X-ray structure determinations reveal symmetric trinuclear complexes containing two organic ligands (L2-), two terminal CoII ions, and one central LnIII ion. The organic ligands coordinate equatorially to the two CoII ions via two bidentate (O,S) N-acylthiourea moieties and tridentate to the central Ln ion via the (O,N,O) 2,6-dipicolinoyl moieties. Two acetate bridges established between each of the terminal Co and central Ln ions complete the square-pyramidal coordination spheres of CoII. All products possess an additional chlorido ligand axially coordinated to the lanthanide except the gadolinium(III) and lanthanum(III) complexes, where bidentate acetato ligands are coordinated. Fitting the χmT versus T data of the "CoLaCo" complex gives the axial and rhombic zero-field-splitting parameters D = 24.3(4) cm-1 and E = -1.0(2) cm-1, respectively, and anisotropic Landé values gx,y = 2.81(1) and gz = 2.00 as well as weak antiferromagnetic interactions between two high-spin CoII centers with J = -0.49(2) cm-1. The nature of the magnetic interactions between the LnIII ions and the CoII ions in the "CoLnCo" complexes is deduced by comparing their χMT values to the sum of χMT values of the analogous "CoLaCo" and related "ZnLnZn" complexes. The "CoDyCo" complex reveals an antiferromagnetic interaction, while the remaining "CoLnCo" complexes show ferromagnetic interactions.

An unexpected rhenium(IV)-rhenium(VII) salt: [Co(NH3)6]3[ReVIIO4][ReIVF6]4·6H2O.

The title hydrated salt, tris-[hexa-amminecobalt(III)] tetraoxidorhenate(VII) tetra-kis-[hexa-fluorido-rhenate(IV)] hexa-hydrate, arose unexpectedly due to possible contamination of the K2ReF6 starting material with KReO4. It consists of octa-hedral [Co(NH3)6]3+ cation (Co1 site symmetry 1), tetra-hedral [ReVIIO4]- anions (Re site symmetry 1) and octa-hedral [ReIVF6]2- anions (Re site symmetries 1and ). The [ReF6]2- octa-hedral anions (mean Re-F = 1.834 Å), [Co(NH3)6]3+ octa-hedral cations (mean Co-N = 1.962 Å), and the [ReO4]- tetra-hedral anion (mean Re-O = 1.719 Å) are slightly distorted. A network of N-H⋯F hydrogen bonds consolidates the structure. The crystal studied was refined as a two-component twin.

Effect of Fluorination on the Structure and Anti-Trypanosoma cruzy Activity of Oxorhenium(V) Complexes with S,N,S-Tridentate Thiosemicarbazones and Benzoylthioureas. Synthesis and Structures of Technetium(V) Analogues.

A series of 16 "3 + 2" mixed-ligand complexes of the general composition [ReO(L1)(L2)] (H2L1a-H2L1d = tridentate thiosemicarbazones having a phenyl group with 4-H, 4-F, 3,5-di-F, and 4-CF3 substituents; HL2a-HL2d = bidentate N,N-diethyl-N'-benzoylthioureas with 4-H, 4-F, 3,5-di-F, and 4-CF3 substituents at the benzoyl groups) have been synthesized and characterized by spectroscopic methods and X-ray diffraction. Irrespective of the individual fluorine substitution, the complexes are stable and possess the same general structure. Some systematic electronic effects of the fluorine-substitution patterns of the ligands have been found on the 13C NMR chemical shifts of the N-C═N carbon atoms of the {L1}2- and the C═O carbon atoms of the {L2}- ligands. Antiparasitic properties of the rhenium complexes have been tested against epimastigotes and trypomastigotes forms of two Trypanosoma cruzi strains and the amastigotes form of one of them. The results of this study indicate that the activity of the rhenium complexes can clearly be modulated by fluorine substitution of their ligands. Some of the fluorinated compounds show a high activity against epimastigotes and trypomastigotes forms of the parasites. Reactions between (NBu4)[TcOCl4] and two representatives of the fluorinated ligands (H2L1b, 4-F-substituted, and H2L1c, 4-CF3-substituted) form stable complexes of the composition [TcOCl(L1b)] and [TcOCl(L1c)]. Subsequent reactions of these products with HL2b (4-F-substituted) give the corresponding [TcO(L1)(L2)] mixed-ligand complexes. Also, the technetium compounds are stable as solids and in solutions and have structures corresponding to those of their rhenium analogues.

The Formation of Rhenium(V) Complexes with Dihydroxyphosphoranes and Diarylphosphinic Acid Derivatives Generated from Tris(1,2,3-triazolyl)phosphine Oxides.

Tris(1-phenyl-1 H-1,2,3-triazol-4-yl)phosphine oxide (OP(1,2,3Tz1-Ph)3) and tris(1-benzyl-1 H-1,2,3-triazol-4-yl)phosphine oxide (OP(1,2,3Tz1-benz)3) react with (NBu4)[ReOCl4] under partial hydrolysis and formation of rhenium(V) complexes with unprecedented dihydroxyphosphoranato or diarylphosphinato ligands. Anionic, binuclear complexes of the compositions [Cl3(O)Re{O2P(1,2,3Tz1-Ph)3}Re(O)Cl2]- and [Cl3(O)Re{O2P(1,2,3Tz1-benz)3}Re(O)Cl2]- are formed as the result of a first hydrolysis step of the phosphine oxides, which has been proven by an experiment with H218O. Two more metal-containing products of these reactions, [ReOCl3{O2P(1,2,3Tz1-Ph)2}]- and [Cl3(O)Re{O2P(1,2,3Tz1-benz)2}Re(O)Cl3]-, could also be isolated and studied by X-ray diffraction. Their structures confirm a metal-mediated P-C bond cleavage and the formation of arylphosphinic acids, which finally act as ligands in the products.

Complexes of Technetium(V) and Rhenium(V) with ß-Diketonates.

Reactions of (NBu4)[MOCl4] complexes (M = Tc or Re) with an excess of hexafluoroacetylacetone (Hhfac) give products with a composition of (NBu4)[MOCl3(hfac)] as bright yellow (Tc) or red (Re) solids. The products are stable as solids but rapidly decompose in solution. A number of related phenylimidorhenium(V) complexes were synthesized starting from [Re(NPhF)Cl3(PPh3)2], where (NPhF)2- is a para-fluorinated phenylimido ligand. Products with compositions of [Re(NPhF)Cl2(PPh3)(acac)], [Re(NPhF)Cl2(PPh3)(hfac)], [Re(NPhF)Cl2(PPh3)(tfac)], [Re(NPhF)Cl2(PPh3)(naphtfac)], and [Re(NPhF)Cl2(PPh3)(tbutfac)] (Hacac = acetylacetone, Htfac = trifluoroacetylacetone, Hnaphtfac = naphthoyltrifluoroacetylmethane, and Htbutfac = tert-butyroyltrifluoroacetylmethane) were isolated from reactions of the quite soluble [Re(NPhF)Cl3(PPh3)2] with the corresponding ß-diketones and studied spectroscopically and by X-ray diffraction. The ß-diketonates are coordinated in a meridional arrangement with the phenylimide. The formation of two isomers was detected for nonsymmetric ß-diketones with a preference for the "equatorial" position for the more bulky substituents. Products with more than one chelating ligand were not obtained. The technetium complexes [Tc(NPhX)Cl3(PPh3)2] (X = p-F or p-CF3) were prepared from reactions of pertechnetate, PPh3, HCl, and substituted arylacetylhydrazines and isolated as green solids. They are sufficiently stable as solid but rapidly decompose in moist solvents upon hydrolysis of the Tc-N bonds. From reactions of [Tc(NPh)Cl3(PPh3)2] or [Tc(NPhF)Cl3(PPh3)2] in dry solvents, the complexes [Tc(NPh)Cl2(PPh3)(hfac)] and [Tc(NPhF)Cl2(PPh3)(hfac)] were prepared and isolated in crystalline form. An X-ray diffraction study shows that fluorination of the para position of the phenylimido ligand results in a slight lengthening of all bonds in the coordination sphere of technetium.

Uranyl Complexes with Aroylbis( N, N-dialkylthioureas).

The reaction of isophthaloylbis( N, N-diethylthiourea), H2L1, with UO2(CH3COO)2·2H2O and NEt3 as a supporting base gives a tetranuclear, anionic complex of the composition [{UO2(L1)}4(OAc)2]2-, in which the uranyl ions are S, O-chelate bonded. Each two of them are additionally linked by an acetato ligand. Similar reactions of various uranyl starting materials (uranyl acetate, uranyl nitrate, (NBu4)2[UO2Cl4]) with corresponding pyridine-centered ligands (pyridine-2,6-dicarbonylbis( N, N-dialkylthioureas), H2L2) yield mononuclear, neutral compounds, in which the thiourea derivatives are coordinated as S, N, N, N, S-five-dentate chelators. The equatorial coordination spheres of the formed hexagonal bipyramidal complexes [UO2(L2)(solv)] are completed by solvent ligands (H2O, MeOH, or DMF). Attempted reactions without a supporting base result in decomposition of the organic ligands and the formation of hexanuclear uranyl complexes with pyridine-2,6-dicarboxylato ligands, while the use of an excess of base results in condensation and the formation of dinuclear [{UO2(L2)(µ-OMe)}2]2- complexes. A stable complex of the composition [UO2(L3)] results from reactions of common uranyl starting materials with 2,2'-bipyridine-6,6'-dicarbonylbis( N, N-diethylthiourea) (H2L3). The equatorial coordination sphere of the neutral, hexagonal bipyramidal complex is occupied by an SN4S donor atom set, which is provided by the hexadentate organic ligand. While the uranium complexes with {L1}2- and {L2}2- are labile and rapidly decompose in acidic solutions, [UO2(L3)] is stable over a wide pH range, and the ligand readily extracts uranyl ions from aqueous solutions into organic solvents.

Expanding the Chemistry of Rhenium Metal-Metal Bonded Fluoro Complexes: Facile Preparation and Characterization of Paddlewheel Complexes.

Quadruply bonded rhenium(III) dimers with the stoichiometry Re2L4F2 (1, L = hexahydro-2H-pyrimido[1,2a]pyrimidinate (hpp-); 2, L = diphenyl formamidinate (dpf-)) were prepared from the solid-state melt reactions (SSMRs) between (NH4)2[Re2F8]·2H2O and HL. Those compounds were characterized in the solid state by single-crystal X-ray diffraction and in solution by UV-visible spectroscopy and cyclic voltammetry. The compound [Re2(hpp)4F2]PF6 (3) was prepared from the one-electron oxidation of Re2(hpp)4F2 with [Cp2Fe]PF6. Compounds 1-3 are isostructural with the corresponding chloro derivatives. In solution, compound 1 undergoes two one-electron oxidations. Comparison with its higher halogen homologues reveals that Re2(hpp)4F2 (1) is more easily oxidized than its chloro and bromo analogues.

Iron(III) Metallacryptand and Metallacryptate Assemblies Derived from Aroylbis(N,N-diethylthioureas).

The reaction of isophthaloylbis(N,N-diethylthiourea), H2L1, with FeCl3·6H2O gives the dinuclear tris-complex [Fe2(L1)3] (5), possessing a cryptand-like structure. A similar reaction with the ligand 2,6-dipicolinoylbis(N,N-diethylthiourea), H2L2, however, results in the formation of the anionic, mononuclear Fe(III) complex [Fe(L2)2]- (6), which could be isolated as its "Tl+ salt" by the subsequent addition of Tl(NO3). A tighter view to the solid state structure of the obtained product, however, characterizes compound 6 as a one-dimensional coordination polymer, in which four-coordinate Tl+ ions connect the {[Fe(L2)2]-} units to infinite chains. When Fe3+ ions and Tl+ ions are added to H2L2 simultaneously in a one-pot reaction, a different product is obtained: a cationic trinuclear complex of the composition {M⊂[Fe2(L2)3]}+. It has been isolated as a PF6- salt and represents a {2}-metallacryptate with a nine-coordinate Tl+ ion in the central void. Structurally related products of the compositions {M⊂[Fe2(L2)3]}(PF6) (M = Na+, K+, Rb+) (8(PF6)) could be isolated from analogous reactions with alkaline salts instead of Tl(NO3). {2}-Metallacryptates with larger central voids were synthesized with the ether-spaced aroylbis(N,N-diethylthiourea) H2L3. The compounds {M⊂[Fe2(L3)3]}(PF6) (M = K+, Rb+, Tl+ or Cs+) (9(PF6)) were prepared by a similar protocol like those with H2L2 with the simultaneous addition of the metal ions to a solution of H2L3. Due to the larger spacer between the aroylthiourea units, the coordination number of the central M+ ions is 12 by six carbonyl and six ether oxygen atoms. All products were characterized by elemental analysis, IR spectroscopy, and X-ray structure analysis. Cyclic voltammetric studies were carried out with the three representative complexes [Fe2(L1)3], {K⊂[Fe2(L2)3]}(PF6), and {K⊂[Fe2(L3)3]}(PF6). The obtained voltammograms indicate the dependence of the redox properties of the oligonuclear systems on the conjugation in the organic backbones of the ligands.

Functional polyoxometalates from solvothermal reactions of VOSO4 with tripodal alkoxides - a study on the reactivity of different "tris" derivatives.

We report a study on the structure directing effects of functional groups and counterions. The aim was to find a facile and high yielding synthetic procedure to obtain polyoxometalate (POM) building blocks for post-functionalisation. Therefore, solvothermal reactions of VOSO4 with various tris(hydroxymethyl)methane derivatives in alkaline methanolic solutions were investigated. In doing so, new POM fragments were isolated and characterised. The binding modes of the functionalised tripodal alkoxides turned out to be surprisingly different.