Structures of the solvated organic-based ferromagnet decamethylferrocenium tetracyanoethenide, [FeCp*2](*+)[TCNE]*- x yRCN (R = Me, Et, n-Pr).

The ferromagnet [FeCp*(2)][TCNE] (T(c) = 4.80 K) has two structural phase transitions at 249 and 282 K that has thwarted the determination of its structure by single crystal X-ray diffraction; however, its structure at 100 K is reported [P2(1)/c, a = 9.710(1) A, b = 14.214(2) A, c = 18.753(2) A, beta = 113.207(2) degrees, V = 2378.7(5) A(3), Z = 4, T = 100 K]. Because of the facile loss of solvent, the ferromagnetic solvates, [FeCp*(2)][TCNE] x yS {S = MeCN [y = 1, P, a = 9.556(2) A, b = 9.781(2) A, c = 16.152(2) A, alpha = 74.860(2) degrees, beta = 84.333(3) degrees, gamma = 65.030(4) degrees, V = 1321.0(4) A3, Z = 2, T = 100 K], EtCN [y = 1/2, Pnma, a = 14.750(5) A, b = 10.577(5) A, c = 33.972(10) A, V = 5301(3) A3, Z = 8, T = 100 K], n-PrCN [y = 1/2, C2/m, a = 35.902(6) A, b = 10.488(2) A, c = 14.302(2) A, beta = 101.396(3) degrees, V = 5279(1) A(3), Z = 8, T = 173 K]} have also been difficult to crystallographically characterize, but have been determined from single crystal X-ray diffraction data. These structures consist of parallel chains of alternating [FeCp*(2)](*+) and [TCNE](*-) ions, with an intrachain Fe...Fe distance of 10.54 +/- 0.09 A. The solvates additionally possess chains of solvent that separate the alternating chains of [FeCp*(2)](*+) and [TCNE](*-) ions. The MeCN solvate forms layers of chains that separate two rows of chains, while the EtCN and n-PrCN solvates form chains surrounded by six chains, and have fewer nonmagnetic coupling pathways that result in higher ordering temperature with respect to the MeCN solvate.

Disorder and intermolecular interactions in a family of tetranuclear Ni(II) complexes probed by high-frequency electron paramagnetic resonance.

High-frequency electron paramagnetic resonance (HFEPR) data are presented for four closely related tetranuclear Ni(II) complexes, [Ni(hmp)(MeOH)Cl]4.H2O (1a), [Ni(hmp)(MeOH)Br]4.H2O (1b), [Ni(hmp)(EtOH)Cl]4.H2O (2), and [Ni(hmp)(dmb)Cl]4 (3) (where hmp(-) is the anion of 2-hydroxymethylpyridine and dmb is 3,3'-dimethyl-1-butanol), which exhibit magnetic bistability (hysteresis) and fast magnetization tunneling at low temperatures, properties which suggest they are single-molecule magnets (SMMs). The HFEPR spectra confirm spin S = 4 ground states and dominant uniaxial anisotropy (DSz(2), D < 0) for all four complexes, which are the essential ingredients for a SMM. The individual fine structure peaks (due to zero-field splitting) for complexes 1a, 1b, and 2 are rather broad. They also exhibit further (significant) splitting, which can be explained by the fact that there exists two crystallographically distinct Ni 4 sites in the lattices for these complexes, with associated differences in metal-ligand bond lengths and different zero-field splitting (ZFS) parameters. The broad EPR lines, meanwhile, may be attributed to ligand and solvent disorder, which results in additional distributions of microenvironments. In the case of complex 3, there are no solvate molecules in the structure, and only one distinct Ni 4 molecule in the lattice. Consequently, the HFEPR data for complex 3 are extremely sharp. As the temperature of a crystal of complex 3 is decreased, the HFEPR spectrum splits abruptly at approximately 46 K into two patterns with very slightly different ZFS parameters. Heat capacity data suggest that this is caused by a structural transition at 46.6 K. A single-crystal X-ray structure at 12(2) K indicates large thermal parameters on the terminal methyl groups of the dmb (3,3-dimethyl-1-butanol) ligand. Most likely there exists dynamic disorder of parts of the dmb ligand above 46.6 K; an order-disorder structural phase transition at 46.6 K then removes some of the motion. A further decrease in temperature (<6 K) leads to further fine structure splittings for complex 3. This behavior is thought to be due to the onset of short-range magnetic correlations/coherences between molecules caused by weak intermolecular magnetic exchange interactions.

Hydrocarbation chemistry proceeding from nickel carbenes.

Nickel carbene complex 2 [Ni(triphos)C(H)N(H)xylyl]2+(BF4-)2 reacts with alkenes quantitatively and regiospecifically to give the anti-Markovnikov hydrocarbation products. X-ray crystallography shows significant iminium alkyl character of the hydrocarbation products, similar to that observed in parent carbene 2. Mechanistic studies suggest the importance of a "hydride" pathway over "alkene" (metallocycle formation or carbocation) pathways.

Sesquiterpenes from Omphalotus illudens.

Three sesquiterpenes, illudosone hemiacetal (1a), isoomphadione (2) and illudiolone (3) were isolated from the liquid culture extract of Omphalotus illudens. Their structures were elucidated by spectroscopic techniques as well as by X-ray crystallographic analysis.

Effects of Sterics and Electronic Delocalization on the Photophysical, Structural, and Electrochemical Properties of 2,9-Disubstituted 1,10-Phenanthroline Copper(I) Complexes.

The syntheses, crystal structures, electronic absorption spectra, electrochemical properties, and photophysical properties of a series of copper(I) bis(phenanthroline) complexes are reported. The phenanthroline ligands that have been prepared and investigated are the following: dop (2,9-di-(2-methylphenyl)-1,10-phenanthroline), xop (2-(2-methylphenyl)-9-(2,6-dimethylphenyl)-1,10-phenanthroline), dpep (2,9-diphenylethynyl-1,10-phenanthroline), and dmesp (2,9-dimesityl-1,10-phenanthroline). The complex [Cu(dop)(2)](PF(6)).Et(2)O crystallizes in space group P&onemacr;with a = 11.854(3) Å, b = 14.705(3) Å, c = 15.866(4) Å, alpha = 107.81(2) degrees, beta = 106.72(2) degrees, gamma = 97.56(2) degrees, V = 2447.6(10) Å(3), and Z = 2. For 5739 unique data with F > 4.0sigma(F), R = 7.52%. The complex [Cu(xop)(2)](PF(6)).(3)/(2)CH(3)OH crystallizes in space group C2/c with a = 23.096(6) Å, b = 23.387(6) Å, c = 17.873(7) Å, beta = 100.08(3) degrees, V = 9505(5) Å(3), and Z = 8. For 5631 unique data with F > 4.0sigma(F), R = 6.02%. The complex [Cu(dpep)(2)](PF(6)) crystallizes in space group P&onemacr; with a = 13.327(7) Å, b = 14.114(7) Å, c = 15.175(5) Å, alpha = 87.23(4) degrees, beta = 66.48(3) degrees, gamma = 61.84(4) degrees, V = 2273(2) Å(3), and Z = 2. For 4851 unique data with F > 4.0sigma(F), R = 5.47%. The complex [Cu(dmesp)(dpep)](PF(6)) crystallizes in space group Pbca with a = 14.547(6) Å, b = 22.868(6) Å, c = 30.659(10) Å, V = 10199(6) Å(3), and Z = 8. For 2281 unique data with F > 4.0sigma(F), R = 9.43%. The electrochemical, spectral, and structural properties of [Cu(dop)(2)](+) and [Cu(xop)(2)](+) demonstrate that the copper coordination environment is more sterically encumbered and more rigid in these two complexes than the coordination environment in the comparison molecule [Cu(dpp)(2)](+) (dpp = 2,9-diphenyl-1,10-phenanthroline). A larger energy gap is predicted for [Cu(dop)(2)](+) and [Cu(xop)(2)](+) based on these data, and consequently, a blue-shifted emission is observed relative to [Cu(dpp)(2)](+). The room-temperature excited-state lifetimes in dichloromethane and methanol of the dop and xop complexes are shown to be shorter than the dpp complex, and these results are interpreted as due to a reduction in ligand pi-electron delocalization in the former two complexes. The complexes [Cu(dpep)(2)](+) and [Cu(dmesp)(dpep)](+) are shown to have increased ligand pi-electron delocalization relative to [Cu(dpp)(2)](+); however, neither complex displays room-temperature steady-state emission in dichloromethane.

Structures of the Copper(I) and Copper(II) Complexes of 2,9-Diphenyl-1,10-phenanthroline: Implications for Excited-State Structural Distortion.

The syntheses, crystal structures, and electronic absorption spectra of the copper(I) and copper(II) complexes of 2,9-diphenyl-1,10-phenanthroline (dpp) are reported. The complex [Cu(dpp)(2)](PF(6)) (1) crystallizes in space group P2(1)/c with a = 11.081(4) Å, b = 25.491(8) Å, c = 14.263(5) Å, beta = 92.84(3) degrees, Z = 4, and V = 4024(2) Å(3). For 4813 unique data with F > 4.0sigma(F), R = 5.41% and R(w) = 6.43%. The coordination geometry about the copper(I) center in [Cu(dpp)(2)](+) is best described as distorted tetrahedral with approximate C(2) symmetry. The structure of [Cu(dpp)(2)](+) is largely determined by interligand pi-stacking interactions that occur between the phenyl groups of one ligand and the phenanthroline moiety of the other ligand. Solution-state absorption and (1)H NMR spectra indicate that the [Cu(dpp)(2)](+) complex is fluxional in solution, rocking between two enantiomeric structures of C(2) molecular symmetry through an intermediate of C(s)() symmetry. The complex [Cu(dpp)(2)](ClO(4))(2) (2) crystallizes in space group P&onemacr; with a = 7.809(3) Å, b = 13.027(6) Å, c = 20.344(10) Å, alpha = 87.68(4) degrees, beta = 89.16(4) degrees, gamma = 79.26(4) degrees, Z = 2, and V = 2032(1) Å(3). For 4943 unique data with F > 4.0sigma(F), R = 5.22% and R(w) = 5.37%. The coordination geometry about the copper(II) center in [Cu(dpp)(2)](2+) is best described as flattened tetrahedral with approximate D(2) symmetry. There are no interligand pi-stacking interactions in the structure of [Cu(dpp)(2)](2+). The four-coordinate geometry in [Cu(dpp)(2)](2+) persists in solution on the basis of solution-state and solid-state absorption spectroscopy. Structural distortion in the metal-to-ligand charge-transfer excited state of [Cu(dpp)(2)](+) is discussed on the basis of the structures of 1 and 2.

A Photoluminescent Copper(I) Complex with an Exceptionally High CuII /CuI Redox Potential: [Cu(bfp)2 ]+ (bfp=2,9-bis(trifluoromethyl)-1,10-phenanthroline).

Unprecedented stabilization of the copper(I) oxidation state is demonstrated for the complex cation [Cu(bfp)2 ]+ (1) due to the steric and electronic effects of the CF3 groups (E1/2 (CuII /CuI )=+1.55 V vs. SCE). The redox existence range of the copper(I) species is remarkably high at 2.77 V. It is emissive in solution at room temperature and shows great potential as a photocatalyst; in the excited state it is a very potent photooxidant.

Electron Transfer in Mixed-Valence [Fe(III)(2)Fe(II)O(O(2)CCH(3))(6)(3-Cl-py)(3)].3-Cl-py: Effects of a Crystallographic Phase Transition and Conversion of Solvate and Ligand Molecules from Statically Disordered to Dynamically Disordered on the Valence Detrapping.

A crystallographic phase transition involving changes in the solvate molecule has been found for mixed-valence [Fe(3)O(O(2)CCH(3))(6)(3-Cl-py)(3)].3-Cl-py (1), where 3-Cl-py is 3-chloropyridine. Single-crystal X-ray structures were determined at 300, 228, 200, 169, and 122 K for complex 1. At 300, 228, and 200 K the crystal is monoclinic, space group P2(1)/c, whereas at 169 and 122 K it is triclinic, space group P&onemacr;. Determinations of the unit cell parameters at several temperatures shows that a reversible crystallographic phase transition between the monoclinic and triclinic forms occurs at approximately 200 K. Complex 1 crystallizes in the monoclinic space group P2(1)/c at 300 K, having a unit cell with a = 21.212(8) Å, b = 8.434(2) Å, c = 23.676(3) Å, and Z = 4. Refinement with 5702 observed [F(o) > 4sigma(F(o))] reflections gave R = 0.0542 and R(w) = 0.0937. Complex 1 crystallizes in the triclinic space group P&onemacr; at 122 K, having a unit cell with a = 20.983(11) Å, b = 8.360(4) Å, c = 23.293(10) Å, and Z = 4. At 300 K there is one somewhat asymmetric Fe(3)O complex in the structure. The core dimensions in the Fe(3)O complex at 300 K indicate that the complex is becoming almost valence-detrapped. At 122 K there are two different Fe(3)O complexes in the unit cell, both of which are similar in dimensions. As the temperature is decreased from 300 to 122 K, each Fe(3)O complex becomes more and more distorted in an equilateral triangle. At 122 K one iron ion in each Fe(3)O complex clearly is a high-spin Fe(II) ion and the other two are high-spin Fe(III) ions. There are significant changes in the nature of the 3-Cl-py solvate molecules above and below the phase transition that are likely important in controlling the valence detrapping. At 122 K there are two different Fe(3)O complexes, each with their nearby 3-Cl-py solvate molecules in one position. There are three different phases: a monoclinic one with all solvate molecules disordered, a second triclinic phase at 169 K with half of the solvate molecules disordered, and a third triclinic phase at 122 K with all solvate molecules statically ordered. (57)Fe Mössbauer spectra taken in the 110-293 K range show that complex 1 converts from valence-trapped at 110 K to become detrapped by 293 K, where a single quadrupole-split doublet is seen. Throughout the 140-230 K range it was necessary to employ one Fe(III) doublet and two Fe(II) doublets to fit each Mössbauer spectrum. It is shown that the two Fe(II) doublets likely arise from Fe(3)O complexes experiencing the different disordered solvate environments described above. Thus, while the approximately 200 K structural phase transition involving the solvate molecules does not precipitously lead to an increase in the rate of electron transfer in Fe(3)O complexes in 1, it is clear that the changes seen in the solvate molecules from X-ray structures do play a major role in the valence detrapping in complex 1.