Karen L. V. Mann

Anion-Templated Assembly of a Supramolecular Cage Complex

The templating effect of the tetrafluoroborate ion leads to assembly of four CoII ions and six bridging ligands around this anion to give a tetrahedral complex with a bridging ligand along each edge and the anion trapped in the central cavity (shown below). Surprisingly under identical conditions but with NiII a simpler dinuclear complex forms.

Anionengesteuerter Aufbau eines supramolekularen Käfigkomplexes

Der Templateffekt eines Tetrafluoroborat-Ions fuhrt dazu, das sich vier CoII-Ionen und sechs zweifach zweizahnige Liganden um dieses Ion zusammenlagern, wobei ein tetraedrischer Vierkernkomplex mit einem verbruckenden Liganden entlang jeder Kante entsteht und das Anion im zentralen Hohlraum eingeschlossen ist (siehe unten). Uberraschenderweise wird mit NiII unter gleichen Bedingungen ein einfacherer Zweikernkomplex erhalten.

COMPLEXES OF A NEW BIDENTATE CHELATING PYRIDYL/SULFONAMIDE LIGAND WITH COPPER(II), COBALT(II) AND PALLADIUM(II): CRYSTAL STRUCTURES AND SPECTROSCOPIC PROPERTIES

Abstract Reaction of the bidentate ligand 2-(2-aminophenyl)pyridine with p -toluenesulfonyl chloride afforded the new bidentate ligand HL which contains potentially chelating pyridyl and (protonated) sulfonamide N-donor binding sites. The crystal structure of the ligand shows that the sulfonamide NH proton is involved in a hydrogen-bonding interaction with the pyridyl N atom, resulting in a near-coplanar arrangement of the pyridyl and phenyl rings. Reaction of HL with various metal(II) acetates (M = Cu, Co, Pd) affords the neutral complexes [ML 2 ] in each case in which the sulfonamide is deprotonated. All of these have been crystallographically characterised; the Cu(II) and Pd(II) complexes are planar, whereas the Co(II) complexes is pseudo-tetrahedral with the two CoN 2 planes at 85° to one another. Appropriate spectroscopic and electrochemical studies on the complexes are described.

Complexes of main-group elements containing stereochemically active lone pairs: the crystal structures of [Tl(TpAn)] {TpAn=tris[3-(2-methoxyphenyl)pyrazol-1-yl]hydroborate} and [Pb(TpPy)(NO3)]·0.5Et2O {TpPy = tris[3,-(2-pyrdyl)pyrazol-1-yl]hydroborate}

Abstract The new podand ligand tris[3-(2-methoxyphenyl)pyrazol-1-yl]hydroborate (TpAn) has been prepared and the crystal structure of [Tl(TpAn)] determined. The metal ion is in a trigonal pyramidal geometry arising from the three pyrazolyl N-donors, with the lone pair of the TlI ion in the fourth position of the tetrahedron of electron pairs. There is also a weak but significant interaction with one of the anisyl oxygen atoms ( Tl · O = 3.018 A ), and the displacement of the metal ion towards this oxygen atom results in a noticeable lengthening of the TlN(pyrazolyl) bond which lies approximately trans to it (2.70 A, compared with 2.54 A for the other two TlN bonds). The crystal structure of [Pb(TpPy)(NO3)]·0.5Et2O shows that the PbII ion has four strong interactions (with the pyrazolyl nitrogen atoms and one of the nitrate oxygen atoms; range of bond lengths 2.49–2.67 A) and four weak ones (with the pyridyl nitrogen atoms and the other nitrate oxygen atom; range of bond lengths 2.80–2.99 A). If only the four stronger interactions are considered, the irregular coordination sphere of the PbII ion has an obvious gap in it which is the site of the stereochemically active long pair.

Copper(II) complexes of new potentially hexadentate N3S3- or N6-donor podand ligands based on the tris(pyrazolyl)borate or tris(pyrazolyl)methane core

The mononuclear copper(II) complexes of the following potentially hexadentate podand ligands have been prepared and crystallographically characterised: tris[3-{2-(methylsulfanyl)phenyl}pyrazol-1-yl]hydroborate [L1]-, phenyltris[3-(2-pyridyl)pyrazol-1-yl]methane (L2), and tris[3-{(6-methyl)-pyrid-2-yl}pyrazol-1-yl]hydroborate [L3]-. Of these, [L1]- [a potentially N3S3 donor with three pyrazolyl and three thioether groups, based on a tris(pyrazolyl)borate core] and L2 [a potentially N6 donor with three pyrazolyl and three pyridyl groups, based on a tris(pyrazolyl)methane core] have been prepared for the first time. In [Cu(L1)][PF6] the Cu(II) centre is in a five-coordinate N3S2 coordination environment which is approximately square pyramidal; the pendant thioether group has a weak, long-range interaction with the sixth coordination site of Cu(II). [Cu(L1)][PF6] undergoes a reversible Cu(I)–Cu(II) redox conversion. In [Cu(L2)(MeOH)][PF6]2 the ligand is four-coordinate via two bidentate pyridyl/pyrazolyl arms, with the third arm pendant; an axial methanol ligand completes the square-pyramidal coordination. In [Cu(L3)(H2O)][PF6], which is five coordinate and approximately trigonal bipyramidal, [L3]- acts as an N4 donor via all three pyrazolyl groups but only one pyridyl group; the two pendant pyridyl groups are involved in O–H···N hydrogen-bonding interactions with the coordinated water molecule. This ‘second-sphere’ stabilisation of a coordinated ligand is strongly reminiscent of the cooperative interactions by which substrates are bound to the active sites of metalloproteins. The EPR spectra of this complex are solvent-dependent, showing a change from a dz2 ground state in non-donor solvents to a dx2-y2 ground state in donor solvents.

Preparation of the new podand ligand SP(pzpy)3 [pzpy = 3-(2-pyridyl)-pyrazol-1-yl], and the syntheses and crystal structures of copper(II) and copper(I) complexes of its hydrolysis product [OSP(pzpy)2]−, and a double helical copper(I) complex of [O2P(pzpy)2]−

Abstract The new podand ligand SP(pzpy)3 [L1; pzypy = 3-(2-pyridyl)-pyrazol-1-yl], containing three bidentate pyrazolyl-pyridine arms linked to an apical PS group via the pyrazolyl N1 atoms, was prepared and crystallographically characterised. Reaction with Cu(II) or Cu(I) resulted in complexes of the partially-hydrolysed ligand [OSP(pzpy)2]− (L2), containing two bidentate chelating arms linked by a thiophosphinate fragment. [Cu2(L2)2(μ-pzpy)2] contains a planar dinuclear copper(II) core with two pyrazolate bridges linking the metal centres, and one L2 ligand attached to each metal by one bidentate arm with the other arm pendant. In [Cu2(L2)2] each ligand L2 acts as an N,N-donor to one metal ion and an N,S-donor to the other with a non-coordinated pyridyl group, such that each metal ion has an N3S donor set; this complex is achiral with a “side-by-side” disposition of bridging ligands. For comparison purposes we also crystallographically characterised [Cu2(L3)2], where L3 is [O2P(pzpy)2]−, an analogue of L2 but with a phosphinate rather than thiophosphinate group. This complex is a dinuclear double helicate in which each ligand acts as an N,N-bidentate chelate to each metal ion. Comparison of this with the structure of [Cu2(L2)2] shows that it is the involvement of the thiophosphinate S atom of L2 in coordination that prevents helication from occurring.

Synthesis of the new ligand bis[3-(2-pyrazinyl-pyrazol-1-yl) dihydroborate, and the crystal structures of its complexes with thallium(I) and lead(II)

Abstract Reaction of 3-(2-pyrazinyl)pyrazole with KBH4 in a 21:1 ratio afforded the new ligand bis 3 , 2 , 1 dihydroborate [L]−a bis(pyrazolyl)borate in which each pyrazolyl ring is functionalised with a pyrazin-2-yl group at the C3 position[L]− is therefore a potentially chelating tetradentate ligand with two externally-directed N atoms (the pyrazinyl N4 atoms) which are available for additional metal–ion bindingleading to eg coordination polymers The crystal structure of [TlL] shows it to be a simple mononuclear complex with the Tl(I) ion coordinated in the N4 binding pocket of the ligandand the externally-directed N atoms involved only in intermolecular N H–C hydrogen-bonding interactions The two Tl–N bonds to the pyrazolyl N2 atoms (average length 270 A) are much shorter than the bonds to the pyrazinyl N1 atoms (average length 305 A) also there is an obvious gap in the apical position of the metal–ion coordination sphere characteristic of a stereochemically active lone pair The crystal structure of [PbL2] Et2O shows that the Pb(II) centre is nine-coordinate with two tetradentate chelating ligands and the ninth donor being a pyrazinyl N4 atom from an adjacent complex unit The molecules therefore form infinite one-dimensional chains in the crystal via bridging pyrazinyl groups The coordination geometry about the Pb(II) ions is approximately capped square antiprismatic with no obvious gap in the coordination sphere suggesting that the lone pair is stereochemically inactive.

Copper(II)-templated assembly of tetranuclear grid-like complexes from simple pyridine–pyrazole ligands

Reaction of Cu(O 2 CMe) 2 ·H 2 O with HL 1 [3-(2-pyridyl)pyrazole] or HL 2 [6-(3-pyrazolyl)-2,2′-bipyridine] and NH 4 PF 6 followed by crystallisation of the crude products from dmf–ether affords [Cu 4 L 1 6 (dmf) 2 ][PF 6 ] 2 1 and [Cu 4 L 2 4 (dmf) 4 ]- [PF 6 ] 4 2 respectively, in which the deprotonated pyrazolyl groups act as bridging ligands and the 2 × 2 grid–like architectures are a result of the preference of the Cu II ions for elongated square-pyramidal coordination geometries.

Double-helical dinuclear copper(I) and mononuclear copper(II) complexes of a compartmental tetradentate bridging ligand: crystal structures and spectroscopic properties

Reaction of 3-(2-pyridyl)pyrazole with α,α′-dibromoxylene affords a new tetradentate ligand L having two bidentate pyridyl-pyrazole compartments linked by an o-CH2C6H4CH2 spacer. With CuI, L forms a dinuclear double helicate [Cu2L2][PF6]2 in which both ligands are bridging both pseudo-tetrahedral metal ions, which are 5.05 A apart. However L does not support a double helical architecture with CuII. Reaction of L with CuCl2 affords [CuLCl][BF4] which is trigonal bipyramidal both in the solid state (by X-ray crystallography) and in solution (by EPR spectroscopy). Reaction of L with Cu(MeCO2)2·H2O affords [Cu2L3][BF4]4 which was characterised by mass spectroscopy and elemental analysis. By analogy with the (known) nickel(II) analogue, this complex has one ligand acting as a bis-bidentate bridge between two {CuL}2+ fragments in which L acts as a terminal tetradentate chelating ligand. Recrystallisation of this afforded a few crystals of the decomposition product [CuL(MeOH)][CuL(SiF6)][BF4]2, which contains trigonal-bipyramidal [CuL(MeOH)]2+ and six-co-ordinate [CuL(SiF6)] fragments, the latter displaying the first known example of the hexafluorosilicate anion acting as a bidentate chelating F,F-donor.