No abstract

Lanthanide(III) complexes have been prepared with [L 1 ] -[the tetradentate chelating ligand bis{3-(2-pyridyl)-pyrazolyl}dihydroborate], [L 2 ] -[the tetradentate chelating ligand bis{3-(2-pyrazinyl)pyrazolyl}dihydroborate], [L 3 ] -[the hexadentate chelating ligand bis[3-{6′-(2,2′-bipyridyl)}pyrazol-1-yl]dihydroborate], and [L 4 ] 2-[the 12-dentate compartmental ligand hexakis{3-(2-pyridyl)pyrazol-1-yl}diboran(IV)ate, which has two hexadentate tris-(pyrazolyl)borate-based cavities linked "back-to-back" by a B-B bond]. [Ln(L 1 ) 2 (NO) 3 ] are 10-coordinate with two tetradentate N-donor ligands and one bidentate nitrate. [Ln(L 2 ) 2 (NO) 3 ] have 10-coordinate structures similar to those of the [L 1 ] -complexes except that the coordinated N 1 of the pyrazine rings is not such a good donor as the pyridine rings in the [L 1 ] -complexes, leading to marked lengthening of these Ln-N bonds. [Ln(L 3 )(NO 3 ) 2 ] are also 10-coordinate from one hexadentate chelating ligand which has a pseudoequatorial coordination mode and two pseudoaxial bidentate nitrate ligands; the hexadentate ligand has a shallow helical twist to prevent steric interference between its ends. Finally [{Ln(NO 3 ) 2 (L 4 )] are dinuclear, with each metal center being 10-coordinate from a tripodal hexadentate ligand cavity and two bidentate nitrates. Five complexes were structurally characterized: [Tb(L 2 ) 2 (NO 3 )]‚dmf is monoclinic (P2 1 /c) with a ) 14.881(3) Å, b ) 15.5199(12) Å, c ) 15.845(2) Å, ) 92.387(12)°, and Z ) 4. [Gd(L 2 ) 2 (NO 3 )]‚dmf is monoclinic (P2 1 /c) with a ) 14.926(2) Å, b ) 15.465(2) Å, c ) 15.878(2) Å, ) 92.698(11)°, and Z ) 4. [Eu(L 3 )(NO 3 ) 2 ]‚dmf‚0.5Et 2 O is triclinic (P1 h) with a ) 10.020(3) Å, b ) 13.036(3) Å, c ) 14.740(3) Å, R ) 70.114(14)°, ) 71.55(2)°, γ ) 79.66(2)°, and Z ) 2. [{La(NO 3 )-(dmf) 2 } 2 (L 4 )](NO 3 ) 2 ‚dmf is orthorhombic (Pbca) with a ) 18.813(2) Å, b ) 15.241(2) Å, c ) 27.322(2), and Z ) 4. [{Gd(NO 3 ) 2 } 2 (L 4 )]‚2.4dmf is tetragonal (P4 2 /n) with a ) 16.622(6), c ) 24.19(5) Å, and Z ) 4. Detailed photophysical studies have been performed on the free ligands and their complexes with Gd(III), Eu(III), and Tb(III) in several solvents. The results show a wide range in the emission properties of the complexes which can be rationalized in terms of subtle variations in the steric and electronic properties of the ligands. In particular the dinuclear Tb(III) complex of [L 4 ] 2-has an emission quantum yield of ca. 0.5 in D 2 O and MeOD.

The synthesis and magnetic properties are reported of two new clusters [Mn(10)O(4)(OH)(2)(O(2)CMe)(8)(hmp)(8)](ClO(4))(4) (1) and [Mn(7)(OH)(3)(hmp)(9)Cl(3)](Cl)(ClO(4)) (2). Complex 1 was prepared by treatment of [Mn(3)O(O(2)CMe)(6)(py)(3)](ClO(4)) with 2-(hydroxymethyl)pyridine (hmpH) in CH(2)Cl(2), whereas 2 was obtained from the reaction of MnCl(2).4H(2)O, hmpH, and NBu(n)(4)MnO(4) in MeCN followed by recrystallization in the presence of NBu(n)(4)ClO(4). Complex 1.2py.10CH(2)Cl(2).2H(2)O crystallizes in the triclinic space group P1. The cation consists of 10 Mn(III) ions, 8 mu(3)-O(2)(-) ions, 2 mu(3)-OH(-) ions, 8 bridging acetates, and 8 bridging and chelating hmp(-) ligands. The hmp(-) ligands bridge through their O atoms in two ways: two with mu(3)-O atoms and six with mu(2)-O atoms. Complex 2.3CH(2)Cl(2).H(2)O crystallizes in the triclinic space group P1. The cation consists of four Mn(II) and three Mn(III) ions, arranged as a Mn(6) hexagon of alternating Mn(II) and Mn(III) ions surrounding a central Mn(II) ion. The remaining ligation is by three mu(3)-OH(-) ions, three terminal chloride ions, and nine bridging and chelating hmp(-) ligands. Six hmp(-) ligands contain mu(2)-O atoms and three contain mu(3)-O atoms. The Cl(-) anion is hydrogen-bonded to the three mu(3)-OH(-) ions. Variable-temperature direct current (dc) magnetic susceptibility data were collected for complex 1 in the 5.00-300 K range in a 5 kG applied field. The chi(M)T value gradually decreases from 17.87 cm(3) mol(-1) K at 300 K to 1.14 cm(3) mol(-1) K at 5.00 K, indicating an S = 0 ground state. The ground-state spin of complex 2 was established by magnetization measurements in the 0.5-3.0 T and 1.80-4.00 K ranges. Fitting of the data by matrix diagonalization, incorporating only axial anisotropy (DS(z)(2)), gave equally good fits with S = 10, g = 2.13, D = -0.14 cm(-1) and S = 11, g = 1.94, D = -0.11 cm(-1). Magnetization versus dc field scans down to 0.04 K reveal no hysteresis attributable to single-molecule magnetism behavior, only weak intermolecular interactions.