Confirming a predicted selection rule in inelastic neutron scattering spectroscopy: the quantum translator-rotator H2 entrapped inside C60.

We report an inelastic neutron scattering (INS) study of a H2 molecule encapsulated inside the fullerene C60 which confirms the recently predicted selection rule, the first to be established for the INS spectroscopy of aperiodic, discrete molecular compounds. Several transitions from the ground state of para-H2 to certain excited translation-rotation states, forbidden according to the selection rule, are systematically absent from the INS spectra, thus validating the selection rule with a high degree of confidence. Its confirmation sets a precedent, as it runs counter to the widely held view that the INS spectroscopy of molecular compounds is not subject to any selection rules.

Symmetry-breaking in the endofullerene H2O@C660 revealed in the quantum dynamics of ortho and para-water: a neutron scattering investigation.

Inelastic neutron scattering (INS) has been employed to investigate the quantum dynamics of water molecules permanently entrapped inside the cages of C60 fullerene molecules. This study of the supramolecular complex, H2O@C60, provides the unique opportunity to study isolated water molecules in a highly symmetric environment. Free from strong interactions, the water molecule has a high degree of rotational freedom enabling its nuclear spin isomers, ortho-H2O and para-H2O to be separately identified and studied. The INS technique mediates transitions between the ortho and para spin isomers and using three INS spectrometers, the rotational levels of H2O have been investigated, correlating well with the known levels in gaseous water. The slow process of nuclear spin conversion between ortho-H2O and para-H2O is revealed in the time dependence of the INS peak intensities over periods of many hours. Of particular interest to this study is the observed splitting of the ground state of ortho-H2O, raising the three-fold degeneracy into two states with degeneracy 2 and 1 respectively. This is attributed to a symmetry-breaking interaction of the water environment.

Field dependence of the relaxation of 79Br in KBr and its use as a temperature calibrant.

The longitudinal relaxation time of (79)Br nuclei in KBr is field independent, between 4.7 T and 14.1 T. The results suggest that inconsistencies in the literature are due to differences in the experimental set-ups. The limitations of KBr as temperature calibrant are discussed.

High resolution 11B NMR of magnesium diboride using cryogenic magic angle spinning.

Static and magic-angle spinning (11)B nuclear magnetic resonance (NMR) data at 4.7 T and 8.5 T have been obtained under cryogenic conditions on a diluted sample of magnesium diboride powder in the normal and superconducting state. The data provide accurate information on the magnetic shift and longitudinal relaxation time down to a temperature of 8 K, with a resolution improvement over the entire temperature range. The onset of superconductivity is unaffected by the sample rotation, as revealed by a steep variation of the magnetic shift just below the critical temperature.

Experimental and computational study of the structural and electronic properties of Fe(II)(2,2'-bipyridine)(mes)2 and [Fe(II)(2,2'-bipyridine)(mes)2]-, a complex containing a 2,2'-bipyridyl radical anion.

Addition of potassium metal and 2,2,2-crypt (4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane) to a tetrahydrofuran (THF) solution of Fe(2,2'-bipyridine)(mes)(2) (1; mes = 2,4,6-Me(3)C(6)H(2)) yielded the anionic complex [Fe(2,2'-bipyridine)(mes)(2)](-) which was isolated as [K(2,2,2-crypt)][Fe(2,2'-bipyridine)(mes)(2)] (2) alongside the side-product [K(2,2,2-crypt)][Fe(mes)(3)] x C(6)H(12) (3). A compositionally pure sample of 2 was obtained by dissolving a mixture of 2 and 3 in dry pyridine and layering the resulting solution with toluene. Solid state magnetic susceptibility measurements on 1 reveal Curie-Weiss paramagnetic behavior with a molar magnetic moment of 5.12(1) mu(B) between 20 and 300 K, a value which is in line with the expected iron(II) spin-only value of 4.90 mu(B). The magnetic measurements carried out on 2 reveal more complex temperature dependent behavior consistent with intramolecular antiferromagnetic coupling (J = -46 cm(-1)) between the unpaired electrons of the iron(II) ion (S(Fe) = 2) and a pi* orbital of the bipyridyl radical (S(bipy) = 1/2). Structural data, Mossbauer and electron paramagnetic resonance (EPR) spectroscopic measurements, and density functional theory (DFT) calculations are all consistent with this model of the electronic structure. To the best of our knowledge, species 2 represents the first crystallographically characterized transition metal complex of the 2,2'-bipyridyl ligand for which magnetic, spectroscopic, and computational data indicate the presence of an unpaired electron in the pi* antibonding orbital.

Reactivity studies of group 15 Zintl ions towards homoleptic post-transition metal organometallics: a 'bottom-up' approach to bimetallic molecular clusters.

Reactions between ethylenediamine (en) solutions of the intermetallic Zintl phases K(3)E(7) (E = P, As) and a series of homoleptic post-transition metal organometallics such as Cu(5)(Mes)(5), M(C(6)H(5))(2) (M = Zn, Cd) and In(C(6)H(5))(3) have yielded a family of novel bimetallic cluster anions. These new species were isolated as [K(2, 2,2-crypt)](+) salts in [K(2,2,2-crypt)](4)Cu(2)E(14) (E = P (1), As (2)), [K(2,2,2-crypt)](4)ZnE(14) (E = P (3), As (4)), [K(2,2,2-crypt)](4)CdP(14) x 6py (5) and [K(2,2,2-crypt)](2)E(7)InPh(2) (E = P (6), As (7)). Species 2, 3, 5 and 6 were crystallographically characterised by single-crystal X-ray diffraction. The stability of all of the cluster anions in solution was confirmed by electrospray mass-spectrometry and by (1)H, (13)C{(1)H} and (31)P{(1)H} NMR spectroscopy when possible.

[Pb9CdCdPb9]6-: a Zintl cluster anion with an unsupported cadmium-cadmium bond.

Reaction of an ethylenediamine solution of the intermetallic Zintl phase K4Pb9 with dimesitylcadmium yielded the dimeric Zintl ion [Pb9Cd-CdPb9]6- in low crystalline yield. The cluster anion exhibits a Cd-Cd bond and was structurally characterised by single crystal X-ray diffraction in [K(2,2,2-crypt)]6[Cd2Pb18].2en (1). DFT was also used to explore the bonding in the hexa-anionic cluster.

Synthesis and characterization of alkali-metal salts of 2,2'- and 2,4'-bipyridyl radicals and dianions.

The reaction of ethylenediamine (en) solutions of 2,2'- and 2,4'-bipyridine (bipy) with varying stoichiometric amounts of potassium and rubidium metal resulted in the isolation of compositionally pure solids containing the respective bipyridyl radical anions (2,2'- and 2,4'-bipy(*-)) and dianions (2,2'- and 2,4'-bipy(2-)). These species were structurally characterized by single-crystal X-ray diffraction in K(2,2'-bipy)(en) (1a), K(4)(2,2'-bipy)(4)(en)(4) (1b), Rb(2)(2,2'-bipy)(en)(2) (2), K(2,4'-bipy)(en) (3), K(4)(2,4'-bipy)(2)(en)(3.5) (4), and Rb(4)(2,4'-bipy)(2)(en)(3.5) (5). The crystallographic results obtained allow for interesting relationships to be drawn between the electronic structure of the bipyridyl moieties and metric structural data. Further characterization of the solids by means of powder X-ray diffraction, elemental analysis, electron paramagnetic resonance, and IR and Raman spectroscopy is also reported. These studies provide a comprehensive overview of the structural and spectroscopic properties of these often-cited yet elusive air- and moisture-sensitive species, helping to complement the existing data in the chemical literature.

Reductive cleavage of Zn-C bonds by group 14 Zintl anions: synthesis and characterisation of [E9ZnR]3- (E = Ge, Sn, Pb; R = Mes, iPr).

The reaction of ethylenediamine solutions of K(4)E(9) (E = Ge, Sn, Pb) with diaryl and dialkyl organozinc reagents ZnMes(2) and Zn(i)Pr(2) yielded the functionalized Zintl ions, closo-[E(9)ZnR](3-) (R = Mes: E = Ge (1), Sn (2), Pb (3); R = (i)Pr: E = Ge (4), Sn (5), Pb (6)). These reactions proceed via reductive zinc-carbon bond activation of the organometallic reagents by the free solvated electrons present in ethylenediamine solutions of intermetallic Zintl phases. The functionalized cluster anions 1, 2 and 4-6 were characterized in the solid-state as [K(2,2,2-crypt)](+) salts by single-crystal X-ray diffraction and elemental analysis, while the presence of all six cluster anions in solution was confirmed by (1)H and (13)C{(1)H} NMR spectroscopy and electrospray mass spectrometry.

Coupling reactions of functionalized Zintl ions [E9Cd(C6H5)]3- (E = Sn, Pb) with tributyltinhydride: synthesis and isolation of {Sn9CdSn[(CH2)3CH3]3}3-.

Reaction of ethylenediamine solutions of K(4)E(9) (E = Sn, Pb) with diphenylcadmium yielded the Cd(C(6)H(5))-functionalized Zintl ions, closo-[E(9)Cd(C(6)H(5))](3-) (E = Sn (1); Pb (2)). Solution reactivity studies of 1 with tributyltinhydride in pyridine revealed that the cluster is capable of undergoing a coupling reaction to yield the tributyltin-functionalized cluster, closo-{Sn(9)CdSn[(CH(2))(3)CH(3)](3)}(3-) (3). In-situ monitoring of this reaction by (1)H and (13)C{(1)H} NMR spectroscopy reveals the formation of the tributyltin functionalized cluster anion in addition to free benzene. Species 1-3 were characterized in the solid-state as [K(2,2,2-crypt)](+) salts by single crystal X-ray diffraction and elemental analysis, while the presence of all three cluster anions in solution was confirmed by (1)H and (13)C{(1)H} NMR spectroscopy and electrospray mass-spectrometry.

Synthesis and isolation of [Fe@Ge(10)](3-): a pentagonal prismatic Zintl ion cage encapsulating an interstitial iron atom.

Reaction of an ethylenediamine (en) solution of the Zintl phase precursor K(4)Ge(9) with FeAr(2) (Ar = 2,6-Mes(2)C(6)H(3)) in the presence of 2,2,2-crypt (4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane) yielded the endohedral Zintl ion [Fe@Ge(10)](3-) (1) which was crystallographically characterized as a [K(2,2,2-crypt)](+) salt in [K(2,2,2-crypt)](3)[Fe@Ge(10)]*2en. This unprecedented Zintl ion exhibits a pentagonal prismatic 10-atom germanium cage with an interstitial iron atom in the central cavity. Confirmation of the existence of the cluster anion in solution was corroborated by positive and negative ion mode electrospray mass spectrometry.

[Hg(3)(Ge(9))(4)](10-): a nanometric molecular rod precursor to polymeric mercury-linked cluster chains.

Reaction of an ethylenediamine solution of K(4)Ge(9) with Hg(C(6)H(5))(2) yielded [Hg(3)(Ge(9))(4)](10-), an unprecedented mercury-linked molecular rod consisting of four nine-atom germanium clusters.

Synthesis and characterization of the 4,4'-bipyridyl dianion and radical monoanion. A structural study.

The reaction of ethylenediamine solutions of 4,4'-bipyridine with varying stoichiometric amounts of sodium resulted in the isolation of the 4,4'-bipyridyl radical anion (44bipy(*-)) and the unprecedented 4,4'-bipyridyl dianion (44bipy(2-)). The radical was characterized by single-crystal X-ray diffraction in Na(44bipy)(en) (1) and Na2(44bipy)2(en)2 (2) and the dianion in Na 2(44bipy)(en)2 (3), allowing for interesting correlations to be drawn between electronic structure and metric structural data. Further characterization of the solids by means of powder X-ray diffraction, electron paramagnetic resonance, and/or elemental analysis is also reported.

Close-packed C(70)(3-) phases - synthesis, structure, and electronic properties.

The high symmetry and resulting electronic degeneracy of the C(60)(3)(-) anion is viewed as the key molecular feature in the high superconducting transition temperatures of fulleride and oxidized fullerene systems. The experimental evaluation of this hypothesis requires the synthesis of face-centered cubic (fcc) trivalent fulleride anion salts derived from higher fullerenes such as C(70), which have thus far proved elusive with only stable A(1)C(70), A(4)C(70), and A(6)C(70) phases known. In this paper, we report the synthesis of fcc A(3)C(70) phases stabilized by size-matching the tetrahedral site with the sodium cation. The structures are strongly dependent on the cooling protocol due to the existence of metastable partially or completely orientationally disordered phases. EPR data indicate that the phases are metallic but not superconducting. The densities of states at the Fermi level appear too low to give superconductivity at above 5 K, consistent with recent observations that four electrons per C(70) anion are required for superconductivity. Size-matching on both the octahedral and tetrahedral sites is required for A(3)C(70) stability - K(2)CsC(70) is only stable at elevated temperature and Na(2)C(70) is unstable, the composition corresponding to C(70) and a sodium-rich trigonal phase.