Showing papers by "Louis J. Farrugia published in 2006"
TL;DR: High-resolution X-ray diffraction data, in conjunction with DFT(B3LYP) quantum calculations, have been used in a QTAIM analysis of the charge density in the trimethylenemethane (TMM) complex Fe(eta(4)-C[CH(2)](3))(CO)(3).
Abstract: High-resolution X-ray diffraction data, in conjunction with DFT(B3LYP) quantum calculations, have been used in a QTAIM analysis of the charge density in the trimethylenemethane (TMM) complex Fe(η4-C{CH2}3)(CO)3. The agreement between the theoretical and experimental topological properties is excellent. Only one bond path is observed between the TMM ligand and the Fe atom, from the central Cα atom. However, much evidence, including from the delocalization indices and the source function, suggests that there is a strong chemical interaction between the Fe and Cβ atoms, despite the formal lack of chemical bonding according to QTAIM.
148 citations
TL;DR: The synthesis of four new oxo-centered Fe clusters (1 a-c, 2) of the form [Fe(III)3(mu3-O)(CH2=CHCOO)6] with acrylate as the bridging ligand gives rise to potentially intrinsically chiral oxe-centered {M3} trimers that show a tendency to spontaneously resolve upon crystallization.
Abstract: The synthesis of four new oxo-centered Fe clusters (1 a-c, 2) of the form [Fe(III)3(mu3-O)(CH2=CHCOO)6] with acrylate as the bridging ligand gives rise to potentially intrinsically chiral oxo-centered {M3} trimers that show a tendency to spontaneously resolve upon crystallization. For instance, 1 a, [Fe(III)3(mu3-O)(CH2=CHCOO)6-(H2O)3]+, crystallizes in the chiral space group P3(1) as a chloride salt. Crystallization of 1 b, [Fe3(mu3-O)(C2H3CO2)6(H2O)3]NO3 x 4.5 H2O, from aqueous solution followed by recrystallization from acetonitrile also gives rise to spontaneous resolution to yield the homochiral salt [Fe3(mu3-O)(C2H3CO2)6-(H2O)3]NO3 x CH3CN of 1 c (space group P2(1)2(1)2(1)). Furthermore, the reaction of 1 a with hexamolybdate in acetonitrile gives the helical coordination polymer {[(Fe3(mu3-O)L6(H2O))(MoO4)-(Fe3(mu3-O)L6(H2O)2)] x 2 CH3CN x H2O}infinity 2 (L: H2C=CHCOO), which crystallizes in the space group P2(1). The nature of the ligand geometry allows the formation of atropisomers in both the discrete (1 a-c) and linked {Fe3} clusters (2), which is described along with a magnetic analysis of 1 a and 2.
52 citations
TL;DR: The ESP, EF and EFG values at the nuclear positions in formamide are in very good agreement with those directly evaluated from density-functional PBE calculations with 6-31G**, aug-CC-pVDZ and aug-cc-pVTZ basis sets.
Abstract: Accurate, yet simple and efficient, formulae are presented for calculation of the electrostatic potential (ESP), electric field (EF) and electric field gradient (EFG) from the aspherical Hansen–Coppens pseudoatom model of electron density [Hansen & Coppens (1978). Acta Cryst. A34, 909–921]. They are based on the expansion of |r′ − r|−1 in spherical harmonics and the incomplete gamma function for a Slater-type function of the form Rl(r) = rn exp(−αr). The formulae are valid for 0 ≤ r ≤ ∞ and are easily extended to higher values of l. Special treatment of integrals is needed only for functions with n = l and n = l + 1 at r = 0. The method is tested using theoretical pseudoatom parameters of the formamide molecule obtained via reciprocal-space fitting of PBE/6-31G** densities and experimental X-ray data of Fe(CO)5. The ESP, EF and EFG values at the nuclear positions in formamide are in very good agreement with those directly evaluated from density-functional PBE calculations with 6-31G**, aug-cc-pVDZ and aug-cc-pVTZ basis sets. The small observed discrepancies are attributed to the different behavior of Gaussian- and Slater-type functions near the nuclei and to imperfections of the reciprocal-space fit. An EF map is displayed which allows useful visualization of the lattice EF effects in the crystal structure of formamide. Analysis of experimental 100 K X-ray data of Fe(CO)5 yields the value of the nuclear quadrupole moment Q(57Fem) = 0.12 × 10−28 m2 after taking into account Sternheimer shielding/antishielding effects of the core. This value is in excellent agreement with that reported by Su & Coppens [Acta Cryst. (1996), A52, 748–756] but slightly smaller than the generally accepted value of 0.16 ± 5% × 10−28 m2 obtained from combined theoretical/spectroscopic studies [Dufek, Blaha & Schwarz (1995). Phys. Rev. Lett. 25, 3545–3548].
51 citations
TL;DR: The potentially important dietary antioxidant, quercetin 3-O-β- d -glucoside, has been 13C-labelled at C-2 of the flavonoid unit by synthesis in 15% yield over five steps from [13C] carbon dioxide.
26 citations
TL;DR: It is concluded that the Ni-N and Ni-O bonds have an intermediate character, with a significant shared interaction, but with a substantial ionic component, and a previously unrecognized intramolecular H...H interaction in the macrocyclic ligand.
Abstract: The experimental charge density in the title complex has been re-examined. The original work, reported some 8 years ago [Smith et al. (1997). J. Am. Chem. Soc. 119, 5028–5034], was undertaken using a very early version of the XD software, which contained serious programming errors. A re-refinement, using the original data and a recent version of the XD software, shows that many of the unusual aspects of this earlier study are artefacts due to these programming errors. The topological properties of the newly obtained experimental density compare well with those calculated from a theoretical DFT (density-functional theory) UHF-SCF (unrestricted Hartree Fock–self-consistent field) density. This report corrects several erroneous conclusions regarding the charge density in the title complex – in particular, the highly unusual diffuse Laplacian distribution about the Ni atom, and the trifurcated bond path from the Ni atom to the alcohol oxygen donor atoms are no longer observed. An examination of a range of topological properties of the metal–ligand bonds leads to the conclusion that the Ni—N and Ni—O bonds have an intermediate character, with a significant shared interaction, but with a substantial ionic component. This new study also reveals a previously unrecognized intramolecular H⋯H interaction in the macrocyclic ligand.
16 citations
TL;DR: The stem bark of Turraeanthus africanus (Meliaceae) yielded a pregnane derivative, 17α,20S-dihydroxypregn-4-ene-3,16-dione, named turraeasterodione.
Abstract: Chemical investigation of the stem bark of Turraeanthus africanus (Meliaceae) afforded a new pregnane derivative, 17α,20S-dihydroxypregn-4-ene-3,16-dione, named turraeasterodione, together with thr...
11 citations
TL;DR: The first structural characterization of substitution derivatives of Fe2Os(C5H9N)2(CO)12 is reported in this paper, where the isonitrile ligands adopt axial positions on the osmium centre and the cluster is isostructural with the Fe2Ru analogue.
Abstract: The preparation of the mixed-metal cluster, [Fe2Os(C5H9N)2(CO)10], and its crystal structure at 100 K are reported. This complex, along with the cluster in the preceding paper, are the first structurally characterized substitution derivatives of Fe2Os(CO)12. The isonitrile ligands adopt axial positions on the osmium centre and the cluster is isostructural with the Fe2Ru analogue.