John C. Jeffery

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.

Coordination and supramolecular chemistry of multinucleating ligands containing two or more pyrazolyl-pyridine ‘arms’

Abstract A wide variety of new ligands has been prepared in which two or three bidentate or terdentate chelating units, based on pyrazolyl-pyridine (bidentate) or pyrazolyl-bipyridine (terdentate) fragments, have been attached to a central spacer. This may be a borohydride unit to give bis- or tris(pyrazolyl)borate derivatives, or an aromatic (phenyl or biphenyl) unit. A general characteristic of these ligands is that they can coordinate all of their binding ‘arms’ to a single metal ion, giving mononuclear complexes, or they can coordinate each separate ‘arm’ to a different metal ion to give assembly of polynuclear species of occasionally quite unexpected structural complexity. We have observed self-assembly of helicates, helical rings, and tetrahedral cages, in some cases with non-coordinated anions playing a crucial templating role in the assembly process. The tetrahedral cages in particular, which have been prepared with both M4(μ3-L)4 and M4(μ2-L)6 stoichiometries, provide elegant examples of how high-symmetry structures can assemble from simple components.

Studies of the construction of coordination polymers using linear pyridyl-donor ligands

The synthesis and structural characterisation of [Cu(4,4%-bipyridine)X], X Br (1), I (2), [Cu(bpe)2](BF4)·MeCN (3), bpe1,2bis(4-pyridyl)ethene, [Ag(bpp)](NO3 )( 4), bpp1,3-bis(4-pyridyl)propane, and [H2bpeb](NO3)2 (5), bpeb 1,4-bis[2-(4pyridyl)ethenyl]benzene, are reported. Compounds 1 and 2 contain Cu2X2 dimers bridged by 4,4%-bipyridine ligands into (6,3) sheets which display inclined 2D interpenetration. Five interpenetrating diamondoid networks are seen in the structure of 3, while 4 is composed of sinusoidal Ag(bpp) chains and NO3 counterions. Compound 5 contains protonated bpeb molecules hydrogen bonding to NO3 counterions.

Anion-templated self-assembly of tetrahedral cage complexes of cobalt(II) with bridging ligands containing two bidentate pyrazolyl-pyridine binding sites

The bridging ligands L1 and L2 contain two N,N-bidentate pyrazolyl-pyridine units linked to a central aromatic spacer unit (1,2-phenyl or 2,3-naphthyl, respectively). Reaction with Ni(II) salts and treatment with the anions tetrafluoroborate or perchlorate result in formation of dinuclear complexes having a 2:3 metal:ligand ratio, with one bridging and two terminal tetradentate ligands. In contrast, reaction of L1 and L2 with Co(II) salts, followed by treatment with tetrafluoroborate or perchlorate, results in assembly of cage complexes having a 4:6 metal:ligand ratio; these complexes have a metal ion at each corner of an approximate tetrahedron, and a bis-bidentate bridging ligand spanning each edge. The central cavity is occupied by a tetrahedral counterion that forms multiple hydrogen-bonding interactions with the methylene protons of the bridging ligands. The anionic guest fits tightly into the central cavity of the cage to which it is ideally complementary in terms of shape, size, and charge. Solution NMR experiments show that the central anion acts as a template for cage formation, with a mixture of Co(II) and the appropriate bridging ligand alone giving no assembly into a cage until the tetrahedral anion is added, at which point cage assembly is fast and quantitative. The difference between the structures of the complexes with Ni(II) and Co(II) illustrate how the uncoordinated anions can exert a profound influence on the course of the assembly process.

Synthesis of the new tripodal ligand tris-[3-(2′-pyridyl)pyrazol-1-yl]hydroborate, and the crystal structure of its europium(III) complex

The new tripodal ligand tris-[3-(2′-pyridyl)pyrazol-1-yl]hydroborate (L–), comprising three N,N-bidentate chelating arms linked by the apical boron atom, has been synthesized; the crystal structure of [EuL(MeOH)2F][PF6] reveals the nine-coordinate metal lying within the hexadentate ligand cavity.

Structural and near-IR photophysical studies on ternary lanthanide complexes containing poly(pyrazolyl)borate and 1,3-diketonate ligands

The ligands tris[3-(2-pyridyl)pyrazol-1-yl]hydroborate (L1, potentially hexadentate) and bis[3-(2-pyridyl)pyrazol-1-yl]dihydroborate (L2, potentially tetradentate) have been used to prepare ternary lanthanide complexes in which the remaining ligands are dibenzoylmethane anions (dbm). [Eu(L1)(dbm)2] is eight-coordinate, with L1 acting only as a tetradentate chelate (with one potentially bidentate arm pendant) and two bidentate dbm ligands. [Nd(L1)(dbm)2] was also prepared but on recrystallization some of it rearranged to [Nd(L1)2][Nd(dbm)4], which contains a twelve-coordinate [Nd(L1)2]+ cation (two interleaved hexadentate podand ligands) and the eight-coordinate anion [Nd(dbm)4]- which, uniquely amongst eight-coordinate complexes having four diketonate ligands, has a square prismatic structure with near-perfect O8 cubic coordination. Formation of this sterically unfavourable geometry is assumed to arise from favourable packing with the pseudo-spherical cation. The isostructural series of complexes [Ln(L2)(dbm)2](Ln = Pr, Nd, Eu, Gd, Tb, Er, Yb) was also prepared and all members structurally characterised; again the metal ions are eight-coordinate, from one tetradentate ligand L2 and two bidentate dbm ligands. Photophysical studies on the complexes with Ln = Pr, Nd, Er, and Yb were carried out; all show the near-IR luminescence characteristic of these metal ions, with longer lifetimes in CD3OD than in CH3OH. For [Yb(L2)(dbm)2], two species with different luminescence lifetimes were observed in CH3OH solution, corresponding to species with zero or one coordinated solvent molecules, in slow exchange on the luminescence timescale. For [Nd(L2)(dbm)2] a single average solvation number of 0.7 was observed in MeOH. For [Pr(L2)(dbm)2] a range of emission lines in the visible and NIR regions was detected; time-resolved measurements show a particularly high susceptibility to quenching by solvent CH and OH oscillators.

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.

Dinuclear ruthenium(II) complexes [{(L)ClRuII}2(μ-tppz)]2+ (L = an arylazopyridine ligand) incorporating tetrakis(2-pyridyl)pyrazine (tppz) bridging ligand: synthesis, structure and spectroelectrochemical properties

A series of dinuclear complexes [{(L1–4)ClRuII}2(μ-tppz)][ClO4]2 {[1](ClO4)2 to [4](ClO4)2} has been prepared, in which two {RuII(L1–4)Cl}+ fragments [L = a 2-arylazopyridine ligand of the type 2-(C5H4N)–NN–C6H4R; for L1, R = H; L2, R = p-Me; L3, R = p-Cl; L4, R = m-Me] are linked by the bridging ligand tppz [2,3,5,6-tetrakis(2-pyridyl)pyrazine]. A single isomer forms during the synthesis in each case, and the crystal structure of [4](ClO4)2 shows it to be a twofold-symmetric isomer with each ligand L arranged such that its pyridine donor is on the long axis of the molecule (trans to the pyrazine ring of tppz) and the azo donor is trans to one of the pyridyl donors of tppz. This allows the peripheral aryl ring attached to the azo unit of each ligand L to be oriented over either face of the bridging ligand giving a three-layer π-stacked (aryl–pyrazine–aryl) sandwich. Electrochemical studies revealed (i) separations of 190–250 mV (depending on the aryl substituent of L) between the successive Ru(II)/Ru(III) couples, indicative of a significant inter-metallic electronic coupling, and (ii) several ligand-based reductions of the π-acceptor pyrazine and arylazopyridine ligands. A UV/Vis/NIR spectroelectrochemical study showed the presence of an IVCT transition at ca. 1900 nm in MeCN for the Ru(II)–Ru(III) mixed-valence states, whose narrowness is indicative of borderline class III behaviour. Several reduced forms of the complexes were also spectroscopically characterised.

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.

Proton-induced dimerisation and related reactions of mononuclear tungsten carbyne complexes. Crystal structures of the compounds [W{C(H)(C6H4Me-4)}(I)(CO)2(η-C5H5)] and [W{η2-C2(OH)(C6H4Me-4)}(CO)(PMe3)(η-C5H5)] [BF4]· (Me2CO)

Protonation of the compounds [W( 6;CR)(CO) 2 (η-C 5 H 5 )] R = C 6 H 4 Me-4 or Me) with ca. 0.5 mol equivalents of the reagent HBF 4 ·Et 2 O affords the ditungsten salts [W 2 (η-H)(η-RC 2 R)(CO) 4 (η-C 5 H 5 ) 2 ] [BF 4 ] formed via a coupling of the carbyne groups in the precursors. These compounds are readily deprotonated to give the bridged alkyne complexes [W 2 (η-RC 2 R)(CO) 4 (η-C 5 H 5 ) 2 ], a process which is reversed with acid. Aqueous HI with [W( CR)(CO) 2 (η-C 5 H 5 )] affords the iodo carbene complexes [W( CHR)(I)(CO) 2 (η-C 5 H 5 )]. The structure of the species with R = C 6 H 4 Me-4 has been established by X-ray diffraction [W C 2.05(2)A]. The tolyl substituent on the alkylidene carbon atom is transoid to the ηC 5 H 5 ligand, and the alkylidene group is transoid to the iodine atom. Protonation of the ketenyl-tungsten complexes (R = C 6 H 4 Me-4, PR′ 3 = PMe 3 , PPr 3 i or PMePh 2 ; R = Me, PR′ 3 = PMe 3 ) affords the salts [W{η 2 C 2 (OH)(R)}(CO)(PR′ 3 )(η-C 5 H 5 )][BF 4 ] containing hydroxy-alkyne ligands. The structure of the species with R = C 6 H 4 Me-4 and PR′ 3 - PMe 3 has been established by X-ray diffraction. It contains an acetone molecule of crystallisation which is hydrogen bonded to the proton of the hydroxyl group on the alkyne. The 1 H and 13 C-{ 1 H} NMR spectra of the new compounds are reported and discussed.