A 1 : 1 crystalline complex of lead(IV) tetraacetate and pyridine (LTA-py) has been prepared. The single-crystal X-ray structure, at 296 and 150 K, establishes the presence of a relatively short Pb-N bond (2.307 A) within an intriguing seven-coordinate lead inner sphere consisting of the pyridine ligand and two bidentate and two monodentate acetate ligands. The pyridine occupies a surprising amount of the available coordination space and has induced a dramatic change in coordination compared to the four chelating acetate ligands found in lead tetraacetate (LTA). Thermal measurements (TGA/DSC) indicate the de-coordination of pyridine and its loss from the solid between 360 and 380 K. (207)Pb CP/MAS NMR spectroscopy also demonstrates the existence of the Pb-N bond through observation of (1)J((207)Pb,(14)N)= 63 Hz and a (207)Pb-(14)N dipolar coupling constant, of 149 Hz. The solid-state (207)Pb NMR parameters are used to give insight into the coordination environment of Pb(iv) in LTA-py. In solution, ligand exchange is rapid on chemical shift and J-coupling time scales. A (207)Pb NMR study of the titration of an LTA solution by pyridine yields a stability constant for LTA-py of K = 1.5 M(-1) and predicts it to have a (207)Pb NMR chemical shift essentially identical to that observed by CP/MAS NMR in the solid state. This correlation between the solid state and solution indicates that the seven-coordinate LTA-py structure found in the crystalline state does persist in solution, and this could further explain why the addition of pyridine has such profound effects on lead(IV) carboxylate-mediated organic reactions. Simulations of exchange-broadened line shapes of (13)C CP/MAS NMR spectra in the temperature regime above 280 K indicate local motion of the pyridine rings in the form of 180 degrees jumps (activation energy 72.5 kJ mol(-1)); these are first such ring flips reported for a coordinated pyridine ligand.

Diastereoselective conjugate addition of homochiral lithium (R)-N-allyl-N-alpha-methylbenzylamide to methyl (2E,5E)-hepatadienoate, followed by protecting group manipulation and subsequent iodocyclocarbamation allows a concise route to the core fragment, methyl (3R,5R,6R)-3,6-diamino-5-hydroxyheptanoate, of sperabillins B and D. Differentiation between the C-3 and C-6 primary amino groups of this core amino acid was readily achieved by treatment with acetone, giving the 5,6-isopropylidene and C-3-imine protected diamine, with subsequent regioselective acylation of the C-6-nitrogen facilitating the total synthesis of sperabillin D in 10.8% overall yield, and the first asymmetric synthesis of sperabillin B in 5.8% overall yield.

The structure of Tl2SeO4 at 293, 100 and 30K has been determined. Space group at 293 and 100K is Pmcn, Z=4, lattice parameters at 293K are a=6.0838(12)(100K: 6.0336(19)), b=10.965(3) (100K: 10.903(5)) and c=7.9385(15)Å(100K: 7.921(2)). At 30K space group is P212121, Z=4, with lattice parameters a=6.2333(17), b=10.533(3) and c=7.828(2). Measurement was carried out with a Stoe IPDS (293K) and a Nonius CCD using an Oxford He-cryostat for cooling (100 and 30K). Final agreement factors at 293K after refinement with the program SHELXL97 are R(F)=0.061 (100K: 0.097), wR(F∗∗2)=0.051 (100K: 0.156) for 566(100K: 678) unique reflections and R(F)=0.039, wR(F∗∗2)=0.097 for 1162 unique reflections at 30K. The high-temperature phase is isotypical to the β-K2SO4 structure, characterized by isolated selenate tetrahedra and two different cation sites with coordination number 9 and 11. In the low-temperature phase, the tetrahedra are rotated and the coordination numbers of the Tl+ ions are reduced to 8 and 10, respectively. Structural changes are similar to the ones observed in high- and low-temperature phases of Tl2MoO4. A comparison to other Tl2TX4 compounds shows that the structural instabilities are closely connected to shortest Tl–O distances.

Crystals of the title compound (1) contain two independent, centrosymmetric half-molecules per asymmetric unit. While both of these show Jahn-Teller elongated six-coordinate geometries, the lengths of the elongated Cu-N bonds in the two molecules differ by 0.117(2) A at 30 K. The structure of one of these molecules (molecule A) does not vary with temperature below 350 K. The other molecule (molecule B) shows Cu-N bond lengths that are temperature-dependent between 225 and 375 K, but do not vary further at lower temperature. This indicates a fluxional axis of Jahn-Teller elongation in this molecule at these higher temperatures. Consideration of the thermal parameters in these structures implies that the fluxionality in molecule B is frozen out near 150 K. This conclusion is supported by a Q-band powder EPR study. The d-d transition energies of molecules A and B have been calculated by several density function (DF) methods, including a time-dependent DF calculation. The crystallographic data have been reproduced using the vibronic coupling model of Burgi and Hitchman. This has shown that the different fluxionality regimes for molecules A and B are not a consequence of their different static molecular structures, but rather reflect their different local environments in the crystal.

Ungewöhnliche Wasserstoffbrücken wurden bei den Addukten beobachtet, die aus einem sterisch anspruchsvollen N-heterocyclischen Carben mit einem Phenol und einem Diarylamin erhalten wurden. Im ersten Fall – hier wird das Carben protoniert – enthält das Addukt 1 die bislang kürzeste C−H⋅⋅⋅O-Brücke; im zweiten Fall entsteht kein Ionenpaar, sondern das neutrale Carben-Amin-Addukt 2 mit einer einzigartigen N−H⋅⋅⋅C-Brücke.

This paper reports a crystallographic and EPR study of pseudo-Jahn–Teller fluxionality in [Cu(L1)2][BF4]2 (1; L1 = 2,6-dipyrazol-1-ylpyridine). For 50 ≤ T ≤ 350 K, the Cu(II) ion in crystalline 1 is fluxional, with its axis of pseudo-Jahn–Teller elongation being disordered about the two N{pyrazole}–Cu–N{pyrazole} axes. The crystallographic data for 1 at these temperatures are well reproduced by a two-state model that neglects intermolecular interactions, but which yields an unusually small pseudo-Jahn–Teller radius (SpJT) for the compound. This was confirmed by measuring SpJT independently from the mean-square displacement amplitudes (MSDAs) in 1 and [Zn(L1)2][BF4]2 (2). At 41 K, 1 undergoes a phase transformation to a new polymorph containing three molecules per asymmetric unit, which have static structures and exhibit more normal SpJT values. Q-band EPR data show that the proportion of static spins in a powdered sample of 1 grows in relatively slowly as the temperature is lowered below 40 K.

A series of new complexes of some bis-bidentate N-4 ligands [picolinamide azine (pahap), 2-pyrazinecarboxamide azine (pzhpz) and butanedione-monoxime picolinamide hydrazone (pahox)], based on a rotationally flexible N-N bridging unit, with Mn(II), Ni(II), Cu(II), Zn(II) and Cd(II) is reported. 2 : 2 (M : L) ratio complexes with Mn(II) and Cd(II), in which anionic ligands (Cl-, NO3-) are bonded to the metals, have large > 80 degrees M-N-N-M torsional angles, indicating `open' dinuclear structures. With weakly or non-coordinating anions (e.g. ClO4-, ZnBr42-) 2 : 3 complexes are formed with smaller torsional angles (39-43 degrees) in keeping with the presence of three N-N bridges and `closed' spiral structures. Antiferromagnetic exchange is observed bewteen Mn(II) and Ni(II) centres in both types of complex, whereas with Cu(II) small Cu-N-N-Cu angles lead to dominant ferromagnetic exchange coupling. Structural and magnetic data are discussed.

In order to evaluate the potential for side reactions when using B-chlorocatechol borane (ClBcat) in stoichiometric or catalytic transformations involving metal phosphine complexes, we examined the interaction between ClBcat and a series of PR3 compounds. Reactions of ClBcat with the basic phosphines PMe3, PEt3, PMe2Ph and PBu3t, in exactly 1 & ratio;1 stoichiometry, all afforded crystalline adducts of the form R3P . ClBcat, which have been characterised spectroscopically. All display broad singlets at room temperature in both B-11{H-1} and P-31{H-1} NMR spectra with no B-P coupling observed. The low temperature B-11{H-1} and P-31{H-1} NMR spectra, however, do show B-P coupling, suggesting rapid dissociation at room temperature. The compounds ClBcat, BrBcat, and the adducts between ClBcat and PMe3, PEt3 and PBu3t have been characterised by single crystal X-ray diffraction. In ClBcat and BrBcat, the halogen contributes little pi -bonding to boron as the B-O bond lengths are identical in both compounds. The reaction of ClBcat with a small excess of PCy3 yielded Cy3P . ClBcat, which has also been characterised by single crystal X-ray diffraction and shows considerable distortion. The reaction between ClBcat and the less basic phosphines PPh3 and PPh2Me yielded only the redistribution products R3P . BCl3 and B(2)cat(3). In fact, reaction of all of the phosphines with an excess of ClBcat gave only redistribution products, although there was evidence for an intermediate in the B-11{H-1} NMR spectra, with PMe3 and PEt3. The isolated R3P . ClBcat adducts proved unstable, even at low temperature in the solid state, eventually leading to R3P . BCl3 and B(2)cat(3). Reaction of ClBcat with NEt3 afforded Et3N . ClBcat, which was characterised spectroscopically and by single crystal X-ray diffraction. This adduct is stable both in solution and in the solid state.

Reaction of the niobium diphosphine compound [NbCp(NAr)(PMe3)2] (Ar = 2,6-C6H3Pri2) with HSiMe2Cl gives the formally d2 silylamido derivative [NbCp{η3-N(Ar)SiMe2-H}Cl(PMe3)] 6. X-Ray diffraction and NMR studies of this compound show that it has a stretched β-agostic Si–H → Nb interaction. Reaction of the related precursor [NbCp(NAr′)(PMe3)2] (Ar′ = 2,6-C6H3Me2) with HSiMe2Cl gives an isomeric structure [NbCp{η3-N(Ar′)SiMe2-H}(PMe3)(Cl)] 7 differing from 6 in that the phosphine rather than chloride lies trans to the co-ordinated Si–H bond. A preliminary X-ray study and large 1J(Si–H) coupling constant of 116 Hz suggest that this compound is best described as an unstretched β-agostic (Si–H⋯M) d2 silylamide complex. Reaction of the tantalum diphosphine compound [TaCp(NAr)(PMe3)2] with HSiMe2Cl affords the d0 silylhydride derivative [TaCp(NAr)(H)(SiMe2Cl)(PMe3)] 8 which, according to an X-ray diffraction study and NMR data, has an interligand hypervalent interaction (IHI) between the silyl and hydride ligands. Reactions of 6 and 8 with Me3SiX (X = I, OTf) lead to the corresponding iodido and triflate derivatives [NbCp{η3-N(Ar)SiMe2-H}X(PMe3)] (X = OTf 11 or I 12) and [TaCp(NAr)(H)(SiMe2X)(PMe3)] (X = OTf 14 or I 15). Reaction of 8 with AgOTf gives [TaCp(NAr)(PMe3)2Cl]OTf 13, the crystal structure of which has been determined. Density functional theory calculations on models of the compounds 6 and 7 showed that the experimental geometries are only correctly reproduced when the phosphine ligands are adequately modelled. The extent of oxidative addition of the Si–H bond to the metal in 6 mainly depends on the basicity of the phosphine ligand. With PH3 in place of PMe3 the calculated structures are better described as silanimine-hydrido derivatives. The formation of isomeric type 6versus7 is determined by an interplay of the steric and electronic effects of the ligand environment.

The single-crystal structures and magnetic properties of a series of self-assembled cluster complexes of Mn(II), Co(II), Co(II)/Co(III), and Cu(II), with a group of alkoxy-diazine ligands, which have square and rectangular primary architectures, are reported. In one novel case a secondary coordination sphere of metal ions can be built up on a square core, due to the presence of vacant extra-core coordination sites. [Mn4(poapz-H)4(H2O)4](NO3)4·H2O (1); monoclinic, C2/c, a=21.7120(4) Å, b=17.421(4) Å, c=17.273(4) Å, β=109.34(3)°. [Co4(poap-H)2(poap-2H)2](NO3)4·7H2O (3); triclinic, P1, a=9.6855(6) Å, b=12.9462(7) Å, c=13.7383(8) Å, α=106.5730(10), β=99.0400(10) Å, γ=95.737(10)°. [Co4(poapz-H)4(H2O)4](NO3)4·2H2O (4); monoclinic, C2/c, a=21.160(2) Å, 17.808(2) Å, c=17.000(2) Å, β=106.904(9)°. [Co4(pzoapz-H)4(H2O)4](ClO4)4·3H2O (5); monoclinic, P21/a, a=23.24(1) Å, b=13.681(3) Å, c=23.37(2) Å, β=118.17(4)°. [Cu4(poap-H)4](ClO4)4·CH3CN·4.75H2O (6); triclinic, P1, a=13.966(1) Å, b=14.195(1) Å, c=19.452(2) Å, α=83.435(2)°, β=80.727(1)°, γ=63.023(1)°. [Cu5(3poap-H)3(3poap-3H)] (ClO4)4·7.5H2O (7); triclinic, P1, a=11.8316(12) Å, b=14.7017(16) Å, c=21.1527(23) Å, α=92.401(2)°, β=104.690(2)°, γ=104.586(2)°. Magnetic properties are interpreted in relation to the structures. The Mn(II) complexes (1, 2) and the Co(II) complexes (4, 5) exhibit intramolecular antiferromagnetic coupling associated with large M–O–M angles, the Cu(II)4 complex 6 exhibits intramolecular ferromagnetic coupling due to magnetic orbital orthogonality, while the Cu(II)5 complex 7 is best described as a combination of a ferromagnetic trinuclear subunit and an antiferromagnetic dinuclear subunit.

4-Aminopyridine (4AP) and 2,5-dihydroxybenzonquinone (DHBQ) crystallize in a 2:1 ratio as a molecular salt with two molecules of water, i.e. 2C(5)H(7)N(2)(+).C6H2O42-. 2H(2)O in space group P2(1)/c. The 4AP molecules and the DHBQ molecules pack to form infinite one-dimensional hydrogen-bonded chains mediated by the water molecules, which themselves act as tetrahedral centres and link the chains in three dimensions.

2,5-Dihydroxy-1,4-benzoquinone (DHBQ) and 4,4'-bipyridine (BPY) crystallize in a 1:1 ratio as a neutral molecular adduct, C(6)H(4)O(4).C(10)H(8)N(2), in space group C2/c, with half of each molecule in the asymmetric unit. The molecules are linked by a strong O--H...N hydrogen bond [O...N 2.6323 (15) A] and a weak C--H...O hydrogen bond [C...O 3.2082 (17) A] to form infinite stacks of parallel one-dimensional hydrogen-bonded ribbons. The two rings of the bipyridine are twisted at 28.3 degrees with respect to each other, and the benzoquinone ring is inclined at an angle of 18.3 degrees with respect to the plane of the neighbouring pyridine ring. The 4,4'-bipyridine molecule lies on a twofold axis and the benzoquinone molecule lies across an inversion centre.

Two flexible `polytopic' ligands take part in self assembly reactions with Ni(II) salts to produce helical structures, with `incomplete' metal ion coordination, and the occupancy of empty coordination pockets by a water molecule and a putative fluoride ion. [Ni3(pd2am-H)3(H2O)](NO3)3·2H2O 1 consists of a localized Ni2(N–N)3 dinuclear centre with three N–N single bond bridges, and a distant mono-nuclear Ni(II) centre, within the same molecular ion, and [Ni2(2pzoap)3F](BF4)3·8.5H2O 2 has a dinuclear stucture with two well separated octahedral Ni(II) sites. In both cases a single entity (H2O 1, F−2) occupies a potential coordination pocket. Antiferromagnetic coupling is observed between the adjacent Ni(II) centres in 1, associated with the N–N bridging interactions, but the distant metal centres in 2 are uncoupled.

4,4'-Bipyridine (BPY) and 2,3,5,6-tetrahydroxy-1,4-benzoquinone (THBQ) crystallize in a 3:2 ratio as a neutral molecular adduct, 3C(10)H(8)N(2).2C(6)H(4)O(6), in space group P1. There are two independent and centrosymmetric THBQ molecules and two different BPY molecules in the asymmetric unit, one of which lies about an inversion centre. The molecules link together through O-H...O and O-H...N hydrogen bonds to form three interpenetrating networks which create a 'superlattice' of three times the volume of the primitive cell.

2,2'-Bipyridine (2BPY) and hexahydroxybenzene (HHB) crystallize in a 2:1 ratio as a neutral molecular adduct, C(6)H(6)O(6).2C(10)H(8)N(2), in space group P1 with Z = 1 and with the HHB molecule lying on an inversion centre. HHB, of which this is the first single-crystal X-ray structure determination, forms O-H...O hydrogen-bonded chains parallel to the a axis, with O...O distances of 2.761 (1) and 2.782 (1) A. O-H...N hydrogen bonds to the 2BPY molecules crosslink these chains, with O...N distances of 2.707 (1) and 2.735 (1) A.

A series of bi(tetrathiafulvalenyl) derivatives has been prepared from iodo-TTF precursors by Ullmann coupling (copper in refluxing N,N-dimethylformamide) or by reaction with copper(I) thiophene-2-carboxylate (CuTC) in 1-methylpyrrolidin-2-one at 20 degrees C. Solution electrochemical and UV-VIS spectroscopic studies suggest that there is no significant through-bond interaction between the two TTF units in these systems. The X-ray crystal structures are reported for 4,5,5',5 ",4''',5'''-hexakis(methylsulfanyl)-4',4 "-bitetrathiafulvalene and a semiconducting 1:1 perchlorate salt of 4,5:4''',5'''-bis(ethylenedithio)-5',5 "-dimethyl-4',4 "-bitetrathiafulvalene 8(+.). ClO4-. The torsion angle around the central bond is 89 degrees in and 77 degrees in 8(+.). ClO4-. The crystal packing of 8(+.). ClO4- is characterised by puckered layers, parallel to the (001) plane, of cations contacting via their sulfur atoms; the anions occupy infinite channels, parallel to the z-axis and running through the cation motif.

Reaction of [CpM(NAr)(PMe3)(2)] (M = Nb, Ta; Ar = 2,6-C(6)H(3)iPr(2)) With HSiClMe2 gives two remarkably different nonclassical Si...H...M products depending only on the identity of M; [CpTa(NAr)(H)(SiMe2Cl)(PMe3)] possesses an unusual electron-rich M-H Si interligand hypervalent interaction while [CpNb{eta(3)-N(Ar)SiMe2-H}Cl(PMe3)] is the first example of a beta-agostic silylamine Si-H...M interaction showing a "stretched" Si-H bond.

The compound tetraphenylphosphonium tetrachlorooxo-S,S-diphenylsulfiliminatouranium, [Ph4P][UOCl4(NSPh2)], has been prepared in high yield from [Ph4P][UOCl5] and [Ph2S=NSiMe3]. An X-ray structure of this compound shows that the uranium atom has a pseudooctahedral geometry with oxygen and nitrogen atoms in trans positions. The structure of the analogous phosphoriminato complex [Ph4P][UOCl4(NPPh3)] has been determined for comparison. Derivatization of the sulfide group shows that only a limited range of functionalization confers stability toward reduction. The emission spectrum of the first electronic excited state reveals a greatly reduced energy compared with that of the uranyl ion. This red shift in the transition is consistent with the weakening of the U-N bond relative to the U-O bond.

The new compounds [Nb{(eta-C5H4)X(eta-C5H4)}Cl-2] (X = CEt2 1a, C(C5H10) 1b, C2Me4 1c), [Nb{(eta-(C5H3Bu)-Bu-t)C2Me4(eta-(C5H3Bu)-Bu-t)}Cl-2] 1d, [Nb{(eta-C5H4)X(eta-C5H4)}(eta(2)-BH4)] (X = CEt2 2a*, C(C5H10) 2b, C2Me4 2c*, SiMe2 2e*), [Nb((eta-(C5H3Bu)-Bu-t)C2Me4(eta-(C5H3Bu)-Bu-t)}(eta(2)-BH4)] (2d*), [Nb{(eta-C5H4)X(eta-C5H4)}(eta(2)-BD4)] (X = C2Me4 3c, CMe2 4), and [V{(eta-C5H4)C2Me4(eta-C5H4)}(eta(2)-BH4)} (5*) have been prepared. The asterisk indicates the crystal structure has been determined. The hydrogen scrambling processes in the tetrahydroborate complexes 2a-e, 3c, 4, 5, and [Nb{(eta-C5H4)CMe2(eta-C5H4)}(eta(2)-BH4)] have been studied. The free energy barrier Delta G(double dagger) td bridge-terminal hydrogen exchange is considerably reduced when the bridging unit imposes significant structural changes in the metallocene.