Luminescence tuning of imidazole-based lanthanide(III) complexes [Ln = Sm, Eu, Gd, Tb, Dy

To tune the lanthanide luminescence in related molecular structures, we synthesized and characterized a series of lanthanide complexes with imidazole-based ligands: two tripodal ligands, tris{[2-{(1-methylimidazol-2-yl)methylidene}amino]ethyl}amine (Me(3)L), and tris{[2-{(imidazol-4-yl)methylidene}amino]ethyl}amine (H(3)L), and the dipodal ligand bis{[2-{(imidazol-4-yl)methylidene}amino]ethyl}amine (H(2)L). The general formulas are [Ln(Me(3)L)(H(2)O)(2)](NO(3))(3)·3H(2)O (Ln = 3+ lanthanide ion: Sm (1), Eu (2), Gd (3), Tb (4), and Dy (5)), [Ln(H(3)L)(NO(3))](NO(3))(2)·MeOH (Ln(3+) = Sm (6), Eu (7), Gd (8), Tb (9), and Dy (10)), and [Ln(H(2)L)(NO(3))(2)(MeOH)](NO(3))·MeOH (Ln(3+) = Sm (11), Eu (12), Gd (13), Tb (14), and Dy (15)). Each lanthanide ion is 9-coordinate in the complexes with the Me(3)L and H(3)L ligands and 10-coordinate in the complexes with the H(2)L ligand, in which counter anion and solvent molecules are also coordinated. The complexes show a screw arrangement of ligands around the lanthanide ions, and their enantiomorphs form racemate crystals. Luminescence studies have been carried out on the solid and solution-state samples. The triplet energy levels of Me(3)L, H(3)L, and H(2)L are 21?000, 22?700, and 23?000 cm(-1), respectively, which were determined from the phosphorescence spectra of their Gd(3+) complexes. The Me(3)L ligand is an effective sensitizer for Sm(3+) and Eu(3+) ions. Efficient luminescence of Sm(3+), Eu(3+), Tb(3+), and Dy(3+) ions was observed in complexes with the H(3)L and H(2)L ligands. Ligand modification by changing imidazole groups alters their triplet energy, and results in different sensitizing ability towards lanthanide ions.     

Rhenium(V) oxo complexes with N-heterocyclic carbenes

Air-stable rhenium(V) oxo complexes are formed when [ReOCl(3)(PPh(3))(2)] is treated with N-heterocyclic carbenes of the 1,3-dialkyl-4,5-dimethylimidazol-2-ylidene type, L(R) (R = Me, Et, i-Pr). Complexes of the compositions [ReO(2)(L(R))(4)](+), [ReOCl(L(R))(4)](2+), or [ReO(OMe)(L(R))(4)](2+) can be isolated depending on the alkyl substituents at the nitrogen atoms of the ligands and the reaction conditions applied. Despite the steric overcrowding of the equatorial coordination spheres of the metal atoms by each of the four carbene ligands, stable complexes with six-coordinate rhenium atoms are obtained. Steric demands of the alkyl groups allow control of the stability of the mono-oxo intermediates. Air-stable cationic complexes of the compositions [ReOCl(L(Me))(4)](2+), [ReOCl(L(Et))(4)](2+), and [ReO(OMe)(L(Me))(4)](2+) have been isolated, whereas reactions of [ReOCl(3)(PPh(3))(2)] or other rhenium(V) precursors with the more bulky 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (L(i)(-)(Pr)) directly yield the dioxo complex [ReO(2)(L(i)(-)(Pr))(4)](+). X-ray structures of [ReO(2)(L(i)(-)(Pr))(4)][ReO(4)], [ReO(2)(L(i)(-)(Pr))(4)][PF(6)], [ReO(2)(L(Me))(4)][ReO(4)](0.45)[PF(6)](0.55), [ReO(MeOH)(L(Me))(4)][PF(6)](2), and [ReOCl(L(Et))(4)][PF(6)](2) show that the equatorial coordination spheres of the rhenium atoms are essentially planar irrespective of the steric demands of the individual carbene ligands.     

Facially coordinating triamine ligands with a cyclic backbone: some structure-stability correlations

Metal complex formation of the two cyclic triamines 6-methyl-1,4-diazepan-6-amine (MeL(a)) and all-cis-2,4,6-trimethylcyclohexane-1,3,5-triamine (Me(3)tach) was studied. The structure of the free ligands (H(x)MeL(a))(x+) and H(x)Me(3)tach(x+) (0 ≤ x ≤ 3) was investigated by pH-dependent NMR spectroscopy and X-ray diffraction experiments. The crystal structure of (H(2)Me(3)tach)(p-O(3)S-C(6)H(4)-CH(3))(2) showed a chair conformation with axial nitrogen atoms for the doubly protonated species. In contrast to a previous report, Me(3)tach was found to be a stronger base than the parent cis-cyclohexane-1,3,5-triamine (tach); pK(a)-values of H(3)Me(3)tach(3+) (25 °C, 0.1 M KCl): 5.2, 7.4, 11.2. The crystal structures of (H(3)MeL(a))(BiCl(6))·2H(2)O and (H(3)MeL(a))(ClO(4))Cl(2) exhibited two distinct twisted chair conformations of the seven membered diazepane ring. [Co(MeL(a))(2)](3+) (cis: 1(3+), trans: 2(3+)), trans-[Fe(MeL(a))(2)](3+) (3(3+)), [(MeL(a))ClCd(μ(2)-Cl)](2) (4), trans-[Cu(MeL(a))(2)](2+) (5(2+)), and [Cu(HMeL(a))Br(3)] (6) were characterized by single crystal X-ray analysis of 1(ClO(4))(3)·H(2)O, 2Br(3)·H(2)O, 3(ClO(4))(3)·0.8MeCN·0.2MeOH, 4, 5Br(2)·0.5MeOH, and 6·H(2)O. Formation constants and redox potentials of MeL(a) complexes were determined by potentiometric, spectrophotometric, and cyclovoltammetric measurements. The stability of [M(II)(MeL(a))](2+)-complexes is low. In comparison to the parent 1,4-diazepan-6-amine (L(a)), it is only slightly enhanced. In analogy to L(a), MeL(a) exhibited a pronounced tendency for forming protonated species such as [M(II)(HMeL(a))](3+) or [M(II)(MeL(a))(HMeL(a))](3+) (see 6 as an example). In contrast to MeL(a), Me(3)tach forms [M(II)L](2+) complexes (M = Cu, Zn) of very high stability, and the coordination behavior corresponds mainly to an "all-or-nothing" process. Molecular mechanics calculations showed that the low stability of L(a) and MeL(a) complexes is mainly due to a large amount of torsional strain within the pure chair conformation of the diazepane ring, required for tridentate coordination. This behavior is quite contrary to Me(3)tach and tacn (tacn =1,4,7-triazacyclononane), where the main portion of strain is already preformed in the free ligand, and the amount, generated upon complex formation, is comparably low.     

Tetranuclear manganese complexes with dimer-of-dimer and ladder structures from the use of a bis-bipyridyl ligand

The reaction of the bis-chelating ligand 1,2-bis(2,2'-bipyridine-6-yl)ethane (L) with the trinuclear species of formula [Mn(3)O(O(2)CR)(6)(py)(3)](ClO(4)) (R = Me (1); R = Et (2); R = Ph (3)) has afforded the new tetranuclear mixed-valent complexes [Mn(4)O(2)(O(2)CR)(4)L(2)](ClO(4))(2) (R = Me (4); R = Et (5); R = Ph (6)) and [Mn(4)O(2)(OMe)(3)(O(2)CR)(2)L(2)(MeOH)](ClO(4))(2) (R = Me (7); R = Et (8); R = Ph (9)). Complexes 4-6 were obtained in yields of 20%, 44%, and 37%, respectively. They are mixed-valent, with an average Mn oxidation state of +2.5. Complexes 7-9 were obtained in yields of 57%, 65%, and 70%, respectively. They are also mixed-valent, but with an average Mn oxidation state of +2.75. Complexes 4 x 2THF and 9 x 3MeOH x H(2)O crystallize in the triclinic space group P1 macro and contain [Mn(4)(mu(3)-O)(2)](6+) and [Mn(4)(mu(3)-O)(2)(mu-OMe)(2)](5+) cores, respectively, the latter being a new structural type in the family of Mn(4) complexes. Reactivity studies of 4-9 have shown that 4-6 can be converted into 7-9, respectively, and vice versa. The magnetic properties of 5 and 9 have been studied by dc and ac magnetic susceptibility techniques. Complex 5 displays antiferromagnetic coupling between its Mn ions resulting in a spin ground state of S = 0. Complex 9 also displays antiferromagnetic coupling, but the resulting ground state is S = (7)/(2), as confirmed by fitting magnetization versus field data collected for 9 at low temperatures, which gave S = (7)/(2), D = -0.77 cm(-1), and g = 1.79. Complex 9 exhibits a frequency-dependent out-of-phase ac susceptibility peak, indicative of the slow magnetization relaxation that is diagnostic of single-molecule magnetism behavior.     

o-Iminobenzosemiquinonato(1-) and o-amidophenolato(2-) complexes of palladium(II) and platinum(II): a combined experimental and density functional theoretical study

From the reaction mixture of [M(II)(bpy)Cl(2)], the ligand 2-anilino-4,6-di-tert-butylphenol, H[L(AP)], and 2 equiv of a base (NaOCH(3)) in CH(3)CN under anaerobic conditions were obtained the blue-green neutral complexes [M(II)(L(AP)-H)(bpy)] (M = Pd (1), Pt (2)). (L(AP)-H)(2)(-) represents the o-amidophenolato dianion, (L(AP))(1)(-) is the o-aminophenolate(1-), (L(ISQ))(1)(-) is its one-electron-oxidized, pi-radical o-iminobenzosemiquinonate(1-), and (L(IBQ))(0) is the neutral quinone. Complexes 1 and 2 can be oxidized by ferrocenium hexafluorophosphate, yielding the paramagnetic salts [M(II)(L(ISQ))(bpy)]PF(6) (S = (1)/(2)) (M = Pd (1a), Pt (2a)). The reaction of PtCl(2), 2 equiv of H[L(AP)], and 4 equiv of base in CH(3)CN in the presence of air yields diamagnetic [Pt(L(ISQ))(2)] (3), which is shown to possess an electronic structure that is best described as a singlet diradical. Complexes 1, 1a, 2, 2a, and 3 have been structurally characterized by X-ray crystallography at 100 K. It is clearly established that O,N-coordinated (L(AP)-H)(2)(-) ligands have a distinctly different structure than the corresponding O,N-coordinated (L(ISQ))(1)(-) radicals. It is therefore possible to unambiguously assign the protonation and oxidation level of o-aminophenol derived ligands in coordination compounds. All complexes have been investigated by cyclic voltammetry, spectroelectrochemistry, EPR, and UV-vis spectroscopy. Complexes 1 and 2 can be reversibly oxidized to the [M(II)(L(ISQ))(bpy)](+) and [M(II)(L(IBQ))(pby)](2+) mono- and dications, respectively, and reduced to the [M(L(AP)-H)(bpy(*))](-) anion, where (bpy(*))(1)(-) is the radical anion of 2,2'-bipyridine. Complex 3 exhibits four reversible one-electron-transfer waves (two oxidations and two reductions) which are all shown to be ligand centered. The EPR spectra of the one-electron-reduced species [Pt(L(AP)-H)(L(ISQ))](-) (S = (1)/(2)) and of the one-electron-oxidized species [Pt(L(ISQ))(L(IBQ))](+) (S = (1)/(2)) in CH(2)Cl(2) solutions have been recorded. To gain a better understanding of the electronic structure of 3 and its monooxidized and reduced forms, relativistic DFT calculations have been carried out. Magnetic coupling parameters and hyperfine couplings were calculated and found to be in very good agreement with experiment. It is shown that both the one-electron oxidation and reduction of 3 are ligand centered. A simple MO model is developed in order to understand the EPR properties of the monocation and monoanion of 3.     

Syntheses and crystal structures of a series of alkaline earth vanadium selenites and tellurites

Six new novel alkaline-earth metal vanadium(V) or vanadium(IV) selenites and tellurites, namely, Sr(2)(VO)(3)(SeO(3))(5), Sr(V(2)O(5))(TeO(3)), Sr(2)(V(2)O(5))(2)(TeO(3))(2)(H(2)O), Ba(3)(VO(2))(2)(SeO(3))(4), Ba(2)(VO(3))Te(4)O(9)(OH), and Ba(2)V(2)O(5)(Te(2)O(6)), have been prepared and structurally characterized by single crystal X-ray diffraction analyses. These compounds exhibit six different anionic structures ranging from zero-dimensional (0D) cluster to three-dimensional (3D) network. Sr(2)(VO)(3)(SeO(3))(5) features a 3D anionic framework composed of VO(6) octahedra that are bridged by SeO(3) polyhedra. The oxidation state of the vanadium cation is +4 because of the partial reduction of V(2)O(5) by SeO(2) at high temperature. Ba(3)(VO(2))(2)(SeO(3))(4) features a 0D [(VO(2))(SeO(3))(2)](3-) anion. Sr(V(2)O(5))(TeO(3)) displays a unique 1D vanadium(V) tellurite chain composed of V(2)O(8) and V(2)O(7) units connected by tellurite groups, forming 4- and 10-MRs, whereas Sr(2)(V(2)O(5))(2)(TeO(3))(2)(H(2)O) exhibits a 2D layer consisting of [V(4)O(14)] tetramers interconnected by bridging TeO(3)(2-) anions with the Sr(2+) and water molecules located at the interlayer space. Ba(2)(VO(3))Te(4)O(9)(OH) exhibits a one-dimensional (1D) vanadium tellurite chain composed of a novel 1D [Te(4)O(9)(OH)](3-) chain further decorated by VO(4) tetrahedra. Ba(2)V(2)O(5)(Te(2)O(6)) also features a 1D vanadium(V) tellurites chain in which neighboring VO(4) tetrahedra are bridged by [Te(2)O(6)](4-) dimers. The existence of V(4+) ions in Sr(2)(VO)(3)(SeO(3))(5) is also confirmed by magnetic measurements. The results of optical diffuse-reflectance spectrum measurements and electronic structure calculations based on density functional theory (DFT) methods indicate that all six compounds are wide-band gap semiconductors.     

Synthesis and reactivity of bis(imido) uranium(VI) cyclopentadienyl complexes

The bis(imido) uranium(VI)-C(5)H(5) and -C(5)Me(5) complexes (C(5)H(5))(2)U(N(t)Bu)(2), (C(5)Me(5))(2)U(N(t)Bu)(2), (C(5)H(5))U(N(t)Bu)(2)(I)(dmpe), and (C(5)H(5))(2)U(N(t)Bu)(2)(dmpe) can be synthesized from reactions between U(N(t)Bu)(2)(I)(2)(L)(x) (L=THF, x=2; L=dmpe, x=1) and Na(C(5)R(5)) (R=H, Me); these complexes represent the first structurally characterized C(5)H(5)-compounds of uranium(VI) and they further highlight the differences between UO(2)(2+) and the bis(imido) fragment.     

Contribution of disulfide S2(2-) anions to the crystal and electronic structures in ternary sulfides, Ba12In4S19, Ba4M2S8 (M=Ga, In)

Three semiconducting ternary sulfides have been synthesized from the mixture of elements with about 20% excess of sulfur (to establish oxidant rich conditions) by solid-state reactions at high temperature. Ba(12)In(4)S(19) ≡ (Ba(2+))(12)(In(3+))(4)(S(2-))(17)(S(2))(2-), 1, crystallizes in the trigonal space group R ?3 with a = 9.6182(5) ?, b = 9.6182(5) ?, c = 75.393(7) ?, and Z = 6, with a unique long period-stacking structure of a combination of monometallic InS(4) tetrahedra, linear dimeric In(2)S(7) tetrahedra, disulfide S(2)(2-) anions, and isolated sulfide S(2-) anions that is further enveloped by Ba(2+) cations. Ba(4)In(2)S(8) ≡ (Ba(2+))(4)(In(3+))(2)(S(2-))(6)(S(2))(2-), 2, crystallizes in the triclinic space group P ?1? with a = 6.236(2) ?, b = 10.014(4) ?, c = 13.033(5) ?, α = 104.236(6)°, β = 90.412(4)°, γ = 91.052(6)°, and Z = 2. Ba(4)Ga(2)S(8) ≡ (Ba(2+))(4)(Ga(3+))(2)(S(2-))(6)(S(2))(2-), 3, crystallizes in the monoclinic P2(1)/c with a = 12.739(5) ?, b = 6.201(2) ?, c = 19.830(8) ?, β = 104.254(6)° and Z = 4. Compounds 2 and 3 represent the first one-dimensional (1D) chain structure in ternary Ba/M/S (M = In, Ga) systems. The optical band gaps of 1 and 3 are measured to be around 2.55 eV, which agrees with their yellow color and the calculation results. The CASTEP calculations also reveal that the disulfide S(2)(2-) anions in 1-3 contribute mainly to the bottom of the conduction bands and the top of valence bands, and thus determine the band gaps.     

Scandium and yttrium metallocene borohydride complexes: comparisons of (BH4)1- vs. (BPh4)1- coordination and reactivity

The synthetically accessible borohydride complexes (C(5)Me(4)H)(2)Ln(THF)(BH(4)) and (C(5)Me(5))(2)Ln(THF)(BH(4)) (Ln = Sc, Y) were examined as precursors alternative to the heavily-used tetraphenylborate analogs, [(C(5)Me(4)H)(2)Ln][BPh(4)] and [(C(5)Me(5))(2)Ln][BPh(4)], employed in LnA(2)A'/M reduction reactions (A = anion; M = alkali metal) that generate "LnA(2)" reactivity and form reduced dinitrogen complexes [(C(5)R(5))(2)(THF)(x)Ln](2)(μ-η(2):η(2)-N(2)) (x = 0, 1). The crystal structures of the yttrium borohydrides, (C(5)Me(4)H)(2)Y(THF)(μ-H)(3)BH, 1, and (C(5)Me(5))(2)Y(THF)(μ-H)(2)BH(2), 2, were determined for comparison with those of the yttrium tetraphenylborates, [(C(5)Me(4)H)(2)Y][(μ-Ph)(2)BPh(2)], 3, and [(C(5)Me(5))(2)Y][(μ-Ph)(2)BPh(2)], 4. The complex (C(5)Me(4)H)(2)Sc(μ-H)(2)BH(2), 5, was synthesized and structurally characterized for comparison with (C(5)Me(5))(2)Sc(μ-H)(2)BH(2), 6, [(C(5)Me(4)H)(2)Sc][(μ-Ph)BPh(3)], 7, and [(C(5)Me(5))(2)Sc][(μ-Ph)BPh(3)], 8. Structural information was also obtained on the borohydride derivatives, (C(5)Me(4)H)(2)Sc(μ-H)(2)BC(8)H(14), 9, and (C(5)Me(5))(2)Sc(μ-H)(2)BC(8)H(14), 10, obtained from 9-borabicyclo(3.3.1)nonane (9-BBN) and (C(5)Me(4)R)(2)Sc(η(3)-C(3)H(5)), where R = H, 11; Me, 12. The preference of the metals for borohydride over tetraphenylborate binding was shown by the facile displacement of (BPh(4))(1-) in 3, 4, 7, and 8 by (BH(4))(1-) to make the respective borohydride complexes 1, 2, 5, and 6. These results are consistent with the fact that the borohydrides are not as useful as precursors in A(2)LnA'/M reductions of N(2). An unusual structural isomer of [(C(5)Me(4)H)(2)Sc](2)(μ-η(2):η(2)-N(2)), 13', was isolated from this study that shows the variations in ligand orientation that can occur in the solid state.     

Raman microscopy of synthetic goudeyite (YCu6(AsO4)2(OH)6 x 3H2O)

Raman microscopy has been used to study the molecular structure of a synthetic goudeyite (YCu(6)(AsO(4))(3)(OH)(6) x 3H(2)O). These types of minerals have a porous framework similar to that of zeolites with a structure based upon (A(3+))(1-x)(A(2+))(x)Cu(6)(OH)(6)(AsO(4))(3-x)(AsO(3)OH)(x). Two sets of AsO stretching vibrations were found and assigned to the vibrational modes of AsO(4) and HAsO(4) units. Two Raman bands are observed in the region 885-915 and 867-870 cm(-1) region and are assigned to the AsO stretching vibrations of (HAsO(4))(2-) and (H(2)AsO(4))(-) units. The position of the bands indicates a C(2v) symmetry of the (H(2)AsO(4))(-) anion. Two bands are found at around 800 and 835 cm(-1) and are assigned to the stretching vibrations of uncomplexed (AsO(4))(3-) units. Bands are observed at around 435, 403 and 395 cm(-1) and are assigned to the nu(2) bending modes of the HAsO(4) (434 and 400 cm(-1)) and the AsO(4) groups (324 cm(-1)).     

Osazone anion radical complex of rhodium(III)

One electron paramagnetic parent osazone complex of rhodium of type trans-Rh(L(NHPh)H(2))(PPh(3))(2)Cl(2) (1), defined as an osazone anion radical complex of rhodium(III), trans-Rh(III)(L(NHPh)H(2)(?-))(PPh(3))(2)Cl(2), 1((t-RhL?)), with a minor contribution (～2%) of rhodium(II) electromer, trans-Rh(II)(L(NHPh)H(2))(PPh(3))(2)Cl(2), 1((t-Rh?L)), and their nonradical congener, trans-[Rh(III)(L(NHPh)H(2))(PPh(3))(2)Cl(2)]I(3) ([t-1](+)I(3)(-)), have been isolated and are substantiated by spectra, bond parameters, and DFT calculations on equivalent soft complexes [Rh(L(NHPh)H(2))(PMe(3))(2)Cl(2)] (3) and [Rh(L(NHPh)H(2))(PMe(3))(2)Cl(2)](+) (3(+)). 1 is not stable in solution and decomposes to [t-1](+) and a new rhodium(I) osazone complex, [Rh(I)(L(NHPh)H(2))(PPh(3))Cl] (2). 1 absorbs strongly at 351 nm due to MLCT and LLCT, while [t-1](+) and 2 absorb moderately in the range of 300-450 nm, respectively, due to LMCT and MLCT elucidated by TD-DFT calculations on 3((t-RhL?)), [t-3](+), and Rh(I)(L(NHPh)H(2))(PMe(3))Cl (4). EPR spectra of solids at 295 and 77 K, and dichloromethane-toluene frozen glass at 77 K of 1 are similar with g = 1.991, while g = 2.002 for the solid at 25 K. The EPR signal of 1 in dichloromethane solution is weaker (g = 1.992). In cyclic voltammetry, 1 displays two irreversible one electron transfer waves at +0.13 and -1.22 V, with respect to Fc(+)/Fc coupling, due to oxidation of 1((t-RhL?)) to [t-1](+) at the anode and reduction of rhodium(III) to rhodium(II), i.e., [t-1](+) to electromeric 1((t-Rh?L)) at the cathode.     

Novel supramolecular isomerism in coordination polymer synthesis from unsymmetrical bridging ligands: solvent influence on the ligand placement orientation and final network structure

The assembly of Co(NCS)(2) with 1-methyl-1'-(3-pyridyl)-2-(4-pyridyl)ethene (L(1)) exhibits a novel supramolecular isomerism of [Co(L(1))(2)(NCS)(2)](infinity) caused by different placement orientation of L(1) around metal centers. The reaction in MeOH/H(2)O and EtOH/H(2)O resulted in a double chain structure of 1, and that in EtOH/CH(3)NO(2) led to an open framework structure of 2. The reaction in MeOH/CH(3)NO(2) solvent system concomitantly afforded 1 and 2. The assemblies of 1-(3-pyridyl)-2-(4-pyrimidyl)ethene (L(2)) with Co(NCS)(2) created the water-coordinated complexes of Co(L(2))(2)(H(2)O)(2)(NCS)(2) (3 and 4), an MeOH coordinated complex of Co(L(2))(2)(H(2)O)(2)(NCS)(2) (5), and an open framework coordination polymer of [Co(L(1))(2)(NCS)(2)](infinity) (6) depending on the reaction solvent system. From these observations, it is suggested that in the formation of 1, the solvent-coordinated intermediate species would be generated first and its trans coordination configuration should define the placement orientation of L(1) in the resulting polymer of 1. On the other hand, it is presumed that the solvent-coordinated intermediate would not be produced during the formation of 2 due to the weaker coordination ability of EtOH and CH(3)NO(2) molecules. The open framework coordination polymers of 2 and 6 are converted in the solid state into the isomeric coordination polymer of 1 and hydrogen bonded network structure of 3, respectively.     

Thermochromism of metal ion complexes of semiquinone radical anions. Control of equilibria between diamagnetic and paramagnetic species by Lewis acids

Metal ion complexes of semiquinone radical anions exhibit different types of thermochromism depending on metal ions and quinones. Metal ion complexes of 1,10-phenanthroline-5,6-dione radical anion (PTQ(.-)) produced by the electron-transfer reduction of PTQ by 1,1'-dimethylferrocene (Me(2)Fc) in the presence of metal ions (Mg(2+) and Sc(3+)) exhibit the color change depending on temperature, accompanied by the concomitant change in the ESR signal intensity. In the case of Mg(2+), electron transfer from Me(2)Fc to PTQ is in equilibrium, when the concentration of the PTQ(.-)-Mg(2+) complex (lambda(max) = 486 nm) increases with increasing temperature because of the positive enthalpy for the electron-transfer equilibrium. In contrast to the case of Mg(2+), electron transfer from Me(2)Fc to PTQ is complete in the presence of Sc(3+), which is a much stronger Lewis acid than Mg(2+), to produce the PTQ(.-)-Sc(3+) complex (lambda(max) = 631 nm). This complex is in disproportionation equilibrium and the concentration of the PTQ(.-)-Sc(3+) complex increases with decreasing temperature because of the negative enthalpy for the proportionation direction, resulting in the remarkable color change in the visible region. On the other hand, the p-benzosemiquinone radical anion (Q(.-)) forms a 2:2 pi-dimer radical anion complex [Q(.-)-(Sc(3+))(2)-Q] with Q and Sc(3+) ions at 298 K (yellow color), which is converted to a 2:3 pi-dimer radical anion complex [Q(.-)-(Sc(3+))(3)-Q] with a strong absorption band at lambda(max) = 604 nm (blue color) when the temperature is lowered to 203 K. The change in the number of binding Sc(3+) ions depending on temperature also results in the remarkable color change, associated with the change in the ESR spectra.     

Synthesis and structures of the [benzamidinato]3- complexes Li3(tmeda)(L1)]2 and [Li(thf)4][Li5(L2)(OEt2)2] [L1 = N(SiMe3)C(Ph)N(SiMe3) and L2 = N(SiMe3)C(C6H4-4)NPh

Reduction at ambient temperature of each of the lithium benzamidinates [Li(L(1))(tmeda)] or [{Li(L(2))(OEt(2))(2)}(2)] with four equivalents of lithium metal in diethyl ether or thf furnished the brown crystalline [Li(3)(L(1))(tmeda)] (1) or [Li(thf)(4)][Li(5)(L(2))(2)(OEt(2))(2)] (2), respectively. Their structures show that in each the [N(R(1))C(R(3))NR(2)](3-) moiety has the three negative charges largely localised on each of N, N' and R = Aryl); a consequence is that the "aromatic" 2,3- and 5,6-CC bonds of R(3) approximate to being double bonds. Multinuclear NMR spectra in C(6)D(6) and C(7)D(8) show that 1 and 2 exhibit dynamic behaviour. [The following abbreviations are used: L(1) = N(SiMe(3))C(Ph)N(SiMe(3)); L(2) = N(SiMe(3))C(C(6)H(4)Me-4)N(Ph); tmeda = (Me(2)NCH(2)-)(2); thf = tetrahydrofuran.] This reduction is further supported by a DFT analysis.     

First isolation of fully delocalized mixed-valent imido-bridged [Ti2]7+ complexes by one-electron reduction of [(C5R5)TiCl]2(μ-NAr)2

Mixed-valent imido-bridged dinuclear titanium complexes, [Cp(2)Co][{(C(5)R(5))TiCl}(2)(μ-NAr)(2)] (R = H, Me; Ar = 3,5-(CF(3))(2)C(6)H(3)), were prepared by one-electron reduction of the corresponding [(C(5)R(5))TiCl](2)(μ-NAr)(2). One unpaired electron is delocalized in the central Ti(μ-NR)(2)Ti core as the first example of a fully delocalized mixed-valent imido-bridged [Ti(2)](7+) species.     

Isolation of (CO)1- and (CO2)1- radical complexes of rare earths via Ln(NR2)3/K reduction and [K2(18-crown-6)2]2+ oligomerization

Deep-blue solutions of Y(2+) formed from Y(NR(2))(3) (R = SiMe(3)) and excess potassium in the presence of 18-crown-6 at -45 °C under vacuum in diethyl ether react with CO at -78 °C to form colorless crystals of the (CO)(1-) radical complex, {[(R(2)N)(3)Y(μ-CO)(2)][K(2)(18-crown-6)(2)]}(n), 1. The polymeric structure contains trigonal bipyramidal [(R(2)N)(3)Y(μ-CO)(2)](2-) units with axial (CO)(1-) ligands linked by [K(2)(18-crown-6)(2)](2+) dications. Byproducts such as the ynediolate, [(R(2)N)(3)Y](2)(μ-OC≡CO){[K(18-crown-6)](2)(18-crown-6)}, 2, in which two (CO)(1-) anions are coupled to form (OC≡CO)(2-), and the insertion/rearrangement product, {(R(2)N)(2)Y[OC(═CH(2))Si(Me(2))NSiMe(3)]}[K(18-crown-6)], 3, are common in these reactions that give variable results depending on the specific reaction conditions. The CO reduction in the presence of THF forms a solvated variant of 2, the ynediolate [(R(2)N)(3)Y](2)(μ-OC≡CO)[K(18-crown-6)(THF)(2)](2), 2a. CO(2) reacts analogously with Y(2+) to form the (CO(2))(1-) radical complex, {[(R(2)N)(3)Y(μ-CO(2))(2)][K(2)(18-crown-6)(2)]}(n), 4, that has a structure similar to that of 1. Analogous (CO)(1-) and (OC≡CO)(2-) complexes of lutetium were isolated using Lu(NR(2))(3)/K/18-crown-6: {[(R(2)N)(3)Lu(μ-CO)(2)][K(2)(18-crown-6)(2)]}(n), 5, [(R(2)N)(3)Lu](2)(μ-OC≡CO){[K(18-crown-6)](2)(18-crown-6)}, 6, and [(R(2)N)(3)Lu](2)(μ-OC≡CO)[K(18-crown-6)(Et(2)O)(2)](2), 6a.     

Carboxylate and alkyl carbonate coordination at the hydrophobic binding site of redox-active dicobalt amine thiophenolate complexes

A series of new dicobalt complexes of the permethylated macrocyclic hexaamine dithiophenolate ligand H(2)L(Me) have been prepared and investigated in the context of ligand binding and oxidation state changes. The octadentate ligand is an effective dinucleating ligand that supports the formation of bioctahedral complexes with a central N(3)Co(mu-SR)(2)(mu-X)CoN(3) core structure, leaving a free bridging position X for the coordination of the substrates. The acetato- and cinnamato-bridged complexes [(L(Me))Co(II)(2)(mu-O(2)CMe)](+) (2) and [(L(Me))Co(II)(2)(mu-O(2)CCH=CHPh)](+) (5) were prepared by reaction of the mu-Cl complex [(L(Me))Co(II)(2)(mu-Cl)](+) (1) with the corresponding sodium carboxylates in methanol. The electrochemical properties of these and of the methyl carbonate complex [(L(Me))Co(II)(2)(mu-O(2)COMe)](+) (8) were also investigated. All complexes undergo two stepwise oxidations at ca. E(1)(1/2) = +0.22 and at E(2)(1/2) = ca. +0.60 V vs SCE, affording the mixed-valent complexes [(L(Me))Co(II)Co(III)(mu-O(2)CR)](2+) (3, 6, 9) and the fully oxidized Co(III)Co(III) forms [(L(Me))Co(III)(2)(mu-O(2)CR)](3+) (4, 7, 10), respectively. Compounds 3, 6, 9 and 4, 7, 10 refer to acetato-, cinnamato-, and methylcarbonato species, respectively. The Co(II)Co(III) compounds were prepared by comproportionation of the respective Co(II)(2) and Co(III)(2) compounds. The Co(III)Co(III) species were prepared by bromine oxidation of the Co(II)Co(II) forms. The crystal structures of complexes 2.BPh(4).MeCN, 3.(I(3))(2), 5.BPh(4).2MeCN, 6.(ClO(4))(2).EtOH, 7.(ClO(4))(3).MeCN.(H(2)O)(3), and 9.(ClO(4))(2).(MeOH)(2).H(2)O were determined by single-crystal X-ray crystallography at 210 K. The oxidations occur without gross structural changes of the parent complexes. The Co(II)Co(III) complexes are composed of high-spin Co(II) (d(7)) and low-spin Co(III) (d(6)) ions. The Co(III)Co(III) complexes are diamagnetic. The oxidation reactions affect the binding mode of the substrates. In the Co(II)(2) and Co(II)Co(III) forms the carboxylates bridge the two Co(2+) ions in a symmetric mu-1,3 fashion with uniform C-O bond distances, whereas asymmetric bridging modes, with one short C=O and one long C-O distance, are adopted in the fully oxidized species. This is consistent with the observed shifts in vibrational frequencies for nu(as)(C-O) and nu(s)(C-O) across the series.     

Synthesis and reactivity of rare earth metal alkyl complexes stabilized by anilido phosphinimine and amino phosphine ligands

Anilido phosphinimino ancillary ligand H(2)L(1) reacted with one equivalent of rare earth metal trialkyl [Ln{CH(2)Si(CH(3))(3)}(3)(thf)(2)] (Ln=Y, Lu) to afford rare earth metal monoalkyl complexes [L(1)LnCH(2)Si(CH(3))(3)(THF)] (1 a: Ln=Y; 1 b: Ln=Lu). In this process, deprotonation of H(2)L(1) by one metal alkyl species was followed by intramolecular C--H activation of the phenyl group of the phosphine moiety to generate dianionic species L(1) with release of two equivalnts of tetramethylsilane. Ligand L(1) coordinates to Ln(3+) ions in a rare C,N,N tridentate mode. Complex l a reacted readily with two equivalents of 2,6-diisopropylaniline to give the corresponding bis-amido complex [(HL(1))LnY(NHC(6)H(3)iPr(2)-2,6)(2)] (2) selectively, that is, the C--H activation of the phenyl group is reversible. When 1 a was exposed to moisture, the hydrolyzed dimeric complex [{(HL(1))Y(OH)}(2)](OH)(2) (3) was isolated. Treatment of [Ln{CH(2)Si(CH(3))(3)}(3)(thf)(2)] with amino phosphine ligands HL(2-R) gave stable rare earth metal bis-alkyl complexes [(L(2-R))Ln{CH(2)Si(CH(3))(3)}(2)(thf)] (4 a: Ln=Y, R=Me; 4 b: Ln=Lu, R=Me; 4 c: Ln=Y, R=iPr; 4 d: Ln=Y, R=iPr) in high yields. No proton abstraction from the ligand was observed. Amination of 4 a and 4 c with 2,6-diisopropylaniline afforded the bis-amido counterparts [(L(2-R))Y(NHC(6)H(3)iPr(2)-2,6)(2)(thf)] (5 a: R=Me; 5 b: R=iPr). Complexes 1 a,b and 4 a-d initiated the ring-opening polymerization of d,l-lactide with high activity to give atactic polylactides.     

Synthesis of the (N2)3- radical from Y2+ and its protonolysis reactivity to form (N2H2)2- via the Y[N(SiMe3)2]3/KC8 reduction system

Examination of the Y[N(SiMe(3))(2)](3)/KC(8) reduction system that allowed isolation of the (N(2))(3-) radical has led to the first evidence of Y(2+) in solution. The deep-blue solutions obtained from Y[N(SiMe(3))(2)](3) and KC(8) in THF at -35 °C under argon have EPR spectra containing a doublet at g(iso) = 1.976 with a 110 G hyperfine coupling constant. The solutions react with N(2) to generate (N(2))(2-) and (N(2))(3-) complexes {[(Me(3)Si)(2)N](2)(THF)Y}(2)(μ-η(2):η(2)-N(2)) (1) and {[(Me(3)Si)(2)N](2)(THF)Y}(2)(μ-η(2):η(2)-N(2))[K(THF)(6)] (2), respectively, and demonstrate that the Y[N(SiMe(3))(2)](3)/KC(8) reaction can proceed through an Y(2+) intermediate. The reactivity of (N(2))(3-) radical with proton sources was probed for the first time for comparison with the (N(2))(2-) and (N(2))(4-) chemistry. Complex 2 reacts with [Et(3)NH][BPh(4)] to form {[(Me(3)Si)(2)N](2)(THF)Y}(2)(μ-N(2)H(2)), the first lanthanide (N(2)H(2))(2-) complex derived from dinitrogen, as well as 1 as a byproduct, consistent with radical disproportionation reactivity.     

Molybdenum(VI) dioxo and oxo-imido complexes of fluorinated β-ketiminato ligands and their use in OAT reactions

Substitution of a methyl by a trifluoromethyl moiety in well-known β-ketimines afforded the ligands (Ar)NC(Me)CH(2)CO(CF(3)) (HL(H), Ar = C(6)H(5); HL(Me), A r= 2,6-Me(2)C(6)H(3); HL(iPr), Ar = 2,6-(i)Pr(2)C(6)H(3)). Subsequent complexation to the [MoO(2)](2+) core leads to the formation of novel complexes of general formula [MoO(2)(L(R))(2)] (R = H, 1; R = Me, 2; R = iPr, 3). For reasons of comparison the oxo-imido complex [MoO(N(t)Bu)(L(Me))(2)] (4) has also been synthesized. Complexes 1-4 were investigated in oxygen atom transfer (OAT) reactions using the substrate trimethylphosphine. The respective products after OAT, the reduced Mo(IV) complexes [MoO(PMe(3))(L(R))(2)] (R = H, 5; R = Me, 6; R = iPr, 7) and [Mo(N(t)Bu)(PMe(3))(L(Me))(2)] (8), were isolated. All complexes have been characterized by NMR spectroscopy, and 1-4 also by cyclic voltammetry. A positive shift of the Mo(VI)-Mo(V) reduction wave upon fluorination was observed. Furthermore, molecular structures of complexes 2, 4, 5, and 8 have been determined via single crystal X-ray diffraction analysis. Complex 8 represents a rare example of a Mo(IV) phosphino-imido complex. Kinetic measurements by UV-vis spectroscopy of the OAT reactions from complexes 1-4 to PMe(3) showed them to be more efficient than previously reported nonfluorinated ones, with ligand L' = (Ar)NC(Me)CH(2)CO(CH(3)) [MoO(2)(L')(2)] (9) and [MoO(N(t)Bu)(L')(2)] (10), respectively. Thermodynamic activation parameters ΔH(?) and ΔS(?) of the OAT reactions for complexes 2 and 4 have been determined. The activation enthalpy for the reaction employing 2 is significantly smaller (12.3 kJ/mol) compared to the reaction with the nonfluorinated complex 9 (60.8 kJ/mol). The change of the entropic term ΔS(?) is small. The reaction of the oxo-imido complex 4 to 8 revealed a significant electron-donating contribution of the imido substituent.