Graham M. Davies

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.

Chiral coordination polymers based on thallium(I) complexes of new bis- and tris(pyrazolyl)borate ligands with externally-directed 4-pyridyl groups

The new ligands dihydro-bis[3-(4-pyridyl)pyrazol-1-yl]borate (Bp4py) and hydro-tris[3-(4-pyridyl)pyrazol-1-yl]borate (Tp4py) are derivatives of the well known bis- and tris(pyrazolyl)borate cores, bearing 4-pyridyl substituents attached to the pyrazolyl C3 positions; crystal structures of the Tl(I) complexes show that both are infinite one-dimensional polymeric chains, in which the Tl(I) centre within each bis-pyrazolyl or tris-pyrazolyl cavity is also connected to a pendant 4-pyridyl residue from an adjacent complex unit to build up the chain.

Dichloro­tetra­kis[3-(4-pyrid­yl)-1H-pyrazole]cobalt(II) acetonitrile tetra­solvate: an infinite hydrogen-bonded network, in an instant

Reaction of 3-(4-pyridyl)pyrazole (4pypz) with cobalt(II) chloride in acetonitrile affords the title complex, [CoCl(2)(C(8)H(7)N(3))(4)].4CH(3)CN, within seconds of addition, as purple X-ray quality crystals. The molecule has C4 symmetry. The metal ion exhibits a trans-N(4)Cl(2) octahedral geometry, with the four 3-(4-pyridyl)-1H-pyrazole ligands coordinating through their pyridyl N-atom donors; one coordinated chloride ion forms hydrogen bonds with the pyrazole rings from four separate units. This configuration creates an infinite three-dimensional coordination network containing channels that are filled with acetonitrile solvent molecules.

Bis(1,3-diphen­ylpropane-1,3-dionato-κ2O,O′){hydro­tris[3-(2-pyrid­yl)pyrazol-1-yl]borato}praseodymium(III): another member of an unpredicta­ble series

Reaction of praseodymium(III) chloride with stoichometric quantities of dibenzoylmethane (Hdbm) and hydrotris[3-(2-pyridyl)pyrazol-1-yl]borate (Tp 2py) affords the title complex, [Pr(C24H19BN9)(C15H11O4)2]. The lanthanide ion in this ternary complex exhibits an N6O4 ten-coordinate geometry arising from the five bidentate arms found on the anionic ligands. The structure is entirely different from those found in other lanthanide complexes with the same ligand set.