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Spin crossover (SCO) complexes can reversibly switch between low spin (LS) and high spin (HS) states, affording possible applications in sensing, displays, and molecular electronics. Dinuclear SCO complexes with access to [LS–LS], [LS–HS], and [HS–HS] states may offer increased levels of functionality. The nature of the SCO interconversion in dinuclear complexes is influenced by the local electronic environment. We report the synthesis and characterization of [{FeIII(tpa)}2spiro](PF6)2(1), [{FeIII(tpa)}2Br4spiro](PF6)2(2), and [{FeIII(tpa)}2thea](PF6)2(3) (tpa = tris(2-pyridylmethyl)amine, spiroH4= 3,3,3′,3′-tetramethyl-1,1′-spirobi(indan)-5,5′,6,6′-tetraol, Br4spiroH4= 3,3,3′,3′-tetramethyl-1,1′-spirobi(indan)-4,4′,7,7′-tetrabromo-5,5′,6,6′-tetraol, theaH4= 2,3,6,7-tetrahydroxy-9,10-dimethyl-9,10-dihydro-9,10-ethanoanthracene), utilizing non-conjugated bis(catecholate) bridging ligands. In the solid state, magnetic and structural analysis shows that 1remains in the [HS–HS] state, while 2and 3undergo a partial SCO interconversion upon cooling from room temperature involving the mixed [LS–HS] state. In solution, all complexes undergo SCO from [HS–HS] at room temperature, via [LS–HS] to mixtures including [LS–LS] at 77 K, with the extent of SCO increasing in the order 1< 2< 3. Gas phase density functional theory calculations suggest a [LS–LS] ground state for all complexes, with the [LS–HS] and [HS–HS] states successively destabilized. The relative energy separations indicate that ligand field strength increases following spiro4–< Br4spiro4–< thea4–, consistent with solid-state magnetic and EPR behavior. All three complexes show stabilization of the [LS–HS] state in relation to the midpoint energy between [LS–LS] and [HS–HS]. The relative stability of the [LS–HS] state increases with increasing ligand field strength of the bis(catecholate) bridging ligand in the order 1< 2< 3. The bromo substituents of Br4spiro4–increase the ligand field strength relative to spiro4–, while the stronger ligand field provided by thea4–arises from extension of the overlapping π-orbital system across the two catecholate units. This study highlights how SCO behavior in dinuclear complexes can be modulated by the bridging ligand, providing useful insights for the design of molecules that can be interconverted between more than two states.

Valence tautomerism (VT) and spin crossover (SCO) are promising avenues for developing a range of molecular materials for sensing, memory, and optoelectronic applications. However, these phenomena arise only when specific metal–ligand combinations are employed. The underexplored combination of cobalt(II/III) paired with bis((aryl)imino)acenapthene (Ar-BIAN) ligands, which can exist as neutral Ar-BIAN0(L0), monoanionic radical Ar-BIAN•–(L•–), and dianionic Ar-BIAN2–(L2–) forms, has potential to afford both VT and SCO. Aiming to develop a new family of switchable molecules, we systematically explored a dual-tuning approach by varying the redox state and aryl substituents in a series of homoleptic [Co(Ar-BIAN)3]n+complexes (Ar = Ph, n= 2 (12+), 1 (1+), 0 (1); Ar = 3,5-CF3-Ph, n= 0 (2); Ar = 4-MeO-Ph, n= 2 (32+), 0 (3)). As a prelude to synthetic and experimental studies, density functional theory (DFT) calculations were used to explore the structure and relative energies of the different electronic forms of each complex, comprising different cobalt oxidation and spin states and different ligand oxidation states. Except for compound 3, DFT identified a HS-CoII-L0containing ground state for all complexes, precluding thermally induced SCO or VT. For 3, calculations suggested a possible thermally accessible LS-CoIII-(L•–)3⇌ HS-CoII-(L•–)2(L0) VT interconversion. Experimentally, structural and magnetic data reveal a HS-CoII-L0containing ground state for all six compounds in the solid state, including 3, discounting thermally induced VT or SCO. In solution, electrochemical and spectroscopic analysis also indicate that all compounds exist as the HS-CoII-L0-containing electromer at 298 K. Intervalence charge transfer (IVCT) bands observed for neutral 1, 2, and 3at room temperature suggest the mixed-valence HS-CoII-(L•–)2(L0) charge distribution. However, cooling 3to 243 K in acetonitrile uniquely affords a substantial reduction in the intensity of this IVCT band, consistent with thermally induced VT interconversion to the LS-CoIII-(L•–)3ground state as predicted by DFT calculations. This study emphasizes the utility of computationally guided molecular design for complicated systems with redox activity at the metal and multiple ligands, thus opening new avenues for tuning electronic structure and developing new families of switchable molecules.

Photophysical and magnetic properties arising from both ground and excited states of lanthanoid ions are relevant for numerous applications. These properties can be substantially affected, both adversely and beneficially, by ligand-to-metal charge-transfer (LMCT) states. However, probing LMCT states remains a significant challenge in f-block chemistry, particularly in the solid state. Intriguingly, the europium compounds [EuIII(18-c-6)(X4Cat)(NO3)]·MeCN (18-c-6 = 18-crown-6; X = Cl (tetrachlorocatecholate, 1-Eu) or Br (tetrabromocatecholate, 2-Eu) are distinctly darkly-colored, in marked contrast to the analogues with other lanthanoid ions in the 1-Lnand 2-Lnseries (Ln = La, Ce, Nd, Gd, Tb, and Dy). Herein, we report a multi-technique investigation of these compounds that has allowed elucidation of the LMCT character of the relevant absorption bands using magnetometry, absorption and emission spectroscopies, and solid-state electrochemistry. To support experimental observations, we present a semi-quantitative multireference ab initiomodel that (i) captures the anomalously low-lying LMCT excited state observed in the visible spectrum of 1-Eu(and its absence in the other 1-Lnanalogues); (ii) elucidates the contribution of the LMCT excitation to the crystal field split 7FJground-state wave functions; and (iii) identifies the crucial role played by radial dynamical correlation of the EuIII4f electrons in the description of the LMCT excited state, modeled by the inclusion of 4f → 5f excitations in the optimized wave function. By providing a set of experimental and theoretical tools, this work establishes a framework for the elucidation of LMCT excited states in lanthanoid compounds in the solid state.

The ability to identify promising candidate switchable molecules computationally, prior to synthesis, represents a considerable advance in the development of switchable molecular materials. Even more useful would be the possibility of predicting the switching temperature. Cobalt-dioxolene complexes can exhibit thermally induced valence tautomeric switching between low-spin CoIII-catecholate and high-spin CoII-semiquinonate forms, where the half-temperature (T1/2) is the temperature at which there are equal amounts of the two tautomers. We report the first simple computational strategy for accurately predicting T1/2values for valence tautomeric complexes. Dispersion-corrected density functional theory (DFT) methods have been applied to the [Co(dbdiox)(dbsq)(N2L)] (dbdiox/dbsq•–= 3,5-di-tert-butyldioxolene/semiquinonate; N2L = diimine) family of valence tautomeric complexes, including the newly reported [Co(dbdiox)(dbsq)(MeO-bpy)] (1) (MeO-bpy = 4,4′-dimethoxy-2,2′-bipyridine). The DFT strategy has been thoroughly benchmarked to experimental data, affording highly accurate spin-distributions and an excellent energy match between experimental and calculated spin-states. Detailed orbital analysis of the [Co(dbdiox)(dbsq)(N2L)] complexes has revealed that the diimine ligand tunes the T1/2value primarily through π-acceptance. We have established an excellent correlation between experimental T1/2(toluene) values for [Co(dbdiox)(dbsq)(N2L)] complexes and the calculated lowest unoccupied molecular orbital energy of the corresponding diimine ligand. The model affords accurate T1/2(toluene) values for [Co(dbdiox)(dbsq)(N2L)] complexes, with an average error of only 3.7%. This quantitative and simple DFT strategy allows experimentalists to not only rapidly identify proposed VT complexes but also predict the transition temperature. This study lays the groundwork for future in silicoscreening of candidate switchable molecules prior to experimental investigation, with associated time, cost, and environmental benefits.

A single-crystal structure analysis of sincosite from the South Rasmussen Ridge mine, Idaho, USA has confirmed it as the first natural occurrence with triclinic symmetry. Previous work on the mineral, based on limited electron diffraction and single crystal studies, together with the indexing of powder X-ray diffraction data, have described it as having tetragonal symmetry; although hydrothermally prepared synthetic sincosite is triclinic. The unit cell parameters are a= 6.3531(12), b= 6.3567(14), c= 6.6050(18) Å, α = 106.995(22), β = 94.115(19), γ = 90.006(16)°,and the space group is P1. The crystal structure was refined to wR obs= 0.11 for 783 reflections with I> σ(I). The structure refinement and electron probe micro analysis both confirm the composition as Ca(VO) 2(PO4)2·4H2O.

Valence tautomerism (VT) involves a reversible stimulated intramolecular electron transfer between a redox-active ligand and redox-active metal. Bis(dioxolene)-bridged dinuclear cobalt compounds provide an avenue toward controlled two-step VT interconversions of the form {CoIII-cat-cat-CoIII} ⇌ {CoIII-cat-SQ-CoII}⇌{CoII-SQ-SQ-CoII} (cat2–= catecholate, SQ•–= semiquinonate). Design flexibility for dinuclear VT complexes confers an advantage over two-step spin crossover complexes for future applications in devices or materials. The four dinuclear cobalt complexes in this study are bridged by deprotonated 3,3,3′,3′-tetramethyl-1,1′-spirobi(indan)-5,5′,6,6′-tetraol (spiroH4) or 3,3,3′,3′-tetramethyl-1,1′-spirobi(indan)-4,4′,7,7′-tetrabromo-5,5′,6,6′-tetraol (Br4spiroH4) with Mentpa ancillary ligands (tpa = tris(2-pyridylmethyl)amine, n= 0–3 corresponds to methylation of the 6-position of the pyridine rings). Complementary structural, magnetic, spectroscopic, and density functional theory (DFT) computational studies reveal different electronic structures and VT behavior for the four cobalt complexes; one-step one-electron partial VT, two-step VT, incomplete VT, and temperature-invariant {CoIII-cat-cat-CoIII} states are observed. Electrochemistry, DFT calculations, and the study of a mixed-valence {ZnII-cat-SQ-ZnII} analog have allowed elucidation of thermodynamic parameters governing the one- and two-step VT behavior. The VT transition profile is rationalized by (1) the degree of electronic communication within the bis(dioxolene) ligand and (2) the matching of cobalt and dioxolene redox potentials. This work establishes a clear path to the next generation of two-step VT complexes through incorporation of mixed-valence class II and class II-III bis(dioxolene) bridging ligands with sufficiently weak intramolecular coupling.

The reaction of yttrium or cerium nitrate and tetrachloro- or tetrabromocatecholate (X4Cat2–with X = Cl or Br) has afforded the compounds (Et3NH)2[{Y(Cl4Cat)(H2O)2}2(μ-Cl4Cat)2]·2MeOH·2H2O (1-Cl), (Et3NH)2[{Y(Br4Cat)(H2O)2}2(μ-Br4Cat)2]·1.5MeCN (1-Br), (Et3NH)4[(Cl4Cat)(H2O)2Y(μ-Cl4Cat)2Y(Cl4Cat)2]·2.5MeOH·3.5H2O (2-Cl), (Et3NH)4[{Y(Cl4Cat)(Cl4CatH)(H2O)}2(μ-Cl4Cat)2]·4H2O (3-Cl), (Et3NH)7[{CeIV(Cl4CatH)(NO3)(μ2-Cl4Cat)3}2CeIII](NO3)2(4-Cl), and (Et3NH)4[CeIV(X4Cat)4] (5-Xwith X = Cl, Br). Small variations of the reaction stoichiometry and crystallization methods allow the isolation of dinuclear yttrium complexes with four, five, and six tetrachlorocatecholate ligands in 1-Cl, 2-Cl, and 3-Cl, respectively. Single crystal X-ray diffraction studies of these compounds reveal a conserved tetrachlorocatecholate-bridged dinuclear yttrium core in each case, but with different peripheral ligation. A key feature of the core unit is Y···ClC(Ar) intramolecular interactions with a catecholate chloro substituent ortho to one of the coordinating oxygen atoms. The tetrabromocatecholate analogue 1-Brhas also been obtained. Applying similar methods to redox-active cerium, rather than yttrium, instead affords an unusual mixed-valence trinuclear {CeIIICeIV2} complex in 4-Cl, as well as two mononuclear cerium(IV) complexes in 5-Cland 5-Br. Density functional theory calculations confirm the [CeIV(Cl4Cat)4]4–charge distribution for 5-Cl.

An occurrence of an unusual, green-coloured mawbyite was found coating arsenopyrite in a specimen from the Lagoa mine, Northern Portugal. Electron microprobe analyses combined with a single-crystal structure refinement gives the formula as PbFe3+Fe2+0.4Zn 0.6(AsO 4)2O H(H2O). The change of color from the usual bright red or orange color of mawbyite is attributed to the high concentration of divalent cations, Fe2+and Zn, in the metal atom site.

The crystal structure of segelerite, Ca2Mg2 Fe 1.4 3 + Al0.6(PO4)4(OH)2(H2O)8, from the Mount Deverell variscite deposit, Western Australia, has been refined using single-crystal X-ray data to wR obs = 0.048 for 2082 unique reflections and all H atoms were located during the refinement. Cell parameters are a = 14.7772(2) Å, b = 18.7079(2) Å, c = 7.2424(1) Å, space group Pbca. The H-bonding scheme is described and compared to that for the combinatorial polymorph, jahnsite. The crystal structures of both minerals comprise heteropolyhedral slabs of composition [XM1 Fe 2 3 + (OH)2(PO4)4], that are linked together via corner-sharing of PO4 tetrahedra with isolated [M2(Op)2(H2O)4] octahedra. The structures differ in the mode of linkage of the M2 octahedra, which is via trans Op ligands in segelerite and via both trans and cis Op ligands in jahnsite. In segelerite, X = M1 = Ca, whereas in jahnsite-group minerals, X = Ca, Na, Mn2+ and M1 = Mn2+, Mg2+, Fe2+, Fe3+. X and M1 alternate along the 7 Å axis and it is proposed that different magnitudes of rotation of the Fe3+ octahedra about the 7 Å axis to accommodate the different coordination requirements of the X and M1 cations drives the symmetry changes in the two minerals so that a strong H-bonding network is maintained.

The family of complexes of general formula [Co(Mentpa)(Xdiox)]+(tpa = tris(2-pyridylmethyl)amine, n= 0–3 corresponds to successive methylation of the 6-position of the pyridine rings; X = Br4, Cl4, H4, 3,5-Me2, 3,5-tBu2; diox = dioxolene) was investigated by density functional theory (DFT) calculations to predict the likelihood of valence tautomerism (VT). The OPBE functional with relativistic and solvent corrections allowed accurate reproduction of trends in spin-state energetics, affording the prediction of VT in complex [Co(Me3tpa)(Br4diox)]+(1+). One-electron oxidation of neutral precursor [CoII(Me3tpa)(Br4cat)] (1) enabled isolation of target compounds 1(PF6)and 1(BPh4). Solution variable-temperature UV–vis absorption and Evans method magnetic susceptibility data confirm DFT predictions that 1+exists in a temperature-dependent valence tautomeric equilibrium between low-spin Co(III)-catecholate and high-spin Co(II)-semiquinonate forms. The solution VT transition temperature of 1+is solvent-tunable with critical temperatures in the range of 291–359 K for the solvents measured. Solid-state magnetic susceptibility measurements of 1(PF6)and 1(BPh4)reveal the onset of VT transitions above room temperature.

Determination of the crystal structure of a new calcium alumoferrite has proved it to be amonoclinicvariant of the previously determined SFCA-type, triclinic SFCA-II. It has formed during firing mixtures of ternary phase compositions in the CaO-Fe2O3-Al2O3system (CF2A) under reducing conditions. Monoclinic SFCA-II has the cell dimensions a = 10.335, b = 17.987, c = 10.488 Å, β = 109.50°, V = 1838 Å3, Z = 8, and space group symmetryP2/n. Its composition, determined from the crystal structure refinement, is Ca1.2Fe 3+4.0Fe 2+1.8Al2O12, (M9O12). Monoclinic SFCA-II is a disordered structure composed of polysomatic sequences of pyroxene (P) and spinel (S) modules and, in this context, may be represented by the polysomatic formulation . Further, a crystal structure for a monoclinicvariant of triclinic SFCA-I is proposed. The unit cell dimensions of this phase are a = 10.34, b = 21.44, c = 10.50 Å, β = 109.96°, P21/nsymmetry. The ideal composition of this phase is Ca 2Fe2+8Fe3+8Al4O28, (M11O14). In this case the structure may be represented by the polysomatic formulation of pyroxene (P) and spinel (S) modules as .

Inelastic neutron scattering (INS) has been used to investigate the crystal field (CF) magnetic excitations of the analogs of the most representative lanthanoid–polyoxometalate single-molecule magnet family: Na9[Ln(W5O18)2] (Ln = Nd, Tb, Ho, Er). Ab initio complete active space self-consistent field/restricted active space state interaction calculations, extended also to the Dy analog, show good agreement with the experimentally determined low-lying CF levels, with accuracy better in most cases than that reported for approaches based only on simultaneous fitting to CF models of magnetic or spectroscopic data for isostructural Ln families. In this work we demonstrate the power of a combined spectroscopic and computational approach. Inelastic neutron scattering has provided direct access to CF levels, which together with the magnetometry data, were employed to benchmark the ab initio results. The ab initio determined wave functions corresponding to the CF levels were in turn employed to assign the INS transitions allowed by selection rules and interpret the observed relative intensities of the INS peaks. Ultimately, we have been able to establish the relationship between the wave function composition of the CF split LnIIIground multiplets and the experimentally measured magnetic and spectroscopic properties for the various analogs of the Na9[Ln(W5O18)2] family.

Eight new members of a family of mixed-metal (Mo,W) polyoxometalates (POMs) with amino acid ligands have been synthesized and investigated in the solid state and solution using multiple physical techniques. While the peripheral POM structural framework is conserved, the different analogues vary in nuclearity of the central metal–oxo core, overall redox state, metal composition, and identity of the zwitterionic α-amino acid ligands. Structural investigations reveal site-selective substitution of Mo for W, with a strong preference for Mo to occupy the central metal–oxo core. This core structural unit is a closed tetrametallic loop in the blue reduced species and an open trimetallic loop in the colorless oxidized analogues. Density functional theory calculations suggest the core as the favored site of reduction and reveal that the corresponding molecular orbital is much lower in energy for a tetra- versus trimetallic core. The reduced species are diamagnetic, each with a pair of strongly antiferromagnetically coupled MoVcenters in the tetrametallic core, while in the oxidized complexes all Mo is hexavalent. Solution small-angle X-ray scattering and circular dichroism (CD) studies indicate that the hybrid POM is stable in aqueous solution on a time scale of days within defined concentration and pH ranges, with the stability enhanced by the presence of excess amino acid. The CD experiments also reveal that the amino acid ligands readily exchange with other α-amino acids, and it is possible to isolate the products of amino acid exchange, confirming retention of the POM framework. Cyclic voltammograms of the reduced species exhibit an irreversible oxidation process at relatively low potential, but an equivalent reductive process is not evident for the oxidized analogues. Despite their overall structural similarity, the oxidized and 2e-reduced hybrid POMs are not interconvertible because of the respective open- versus closed-loop arrangement in the central metal–oxo cores.

Recent advances in single-molecule magnet (SMM) research have placed great value on interpretation of inelastic neutron scattering (INS) data for rare earth (RE)-containing SMMs. Here, we present the synthesis of several rare earth complexes where combined magnetic and INS studies have been performed, supported by ab initiocalculations. The reaction of rare earth nitrate salts with 2,2′-bipyridine (2,2′-bpy) and tetrahalocatecholate (X4Cat2–, X = Br, Cl) ligands in methanol (MeOH) afforded two new families of compounds [RE(2,2′-bpy)2(X4Cat)(X4CatH)(MeOH)] (X = Br and RE = Y, Eu, Gd, Tb, Dy, Ho, Yb for 1-RE; X = Cl and RE = Y, Tb, Dy, Ho, and Yb for 2-RE). Addition of triethylamine (Et3N) to the reaction mixture delivered Et3NH[RE(2,2′-bpy)2(Br4Cat)2] (3-RE, RE = Er and Yb). Interestingly, cerium behaves differently to the rest of the series, generating (2,2’-bpyH)2[Ce(Br4Cat)3(2,2′-bpy)] (4-Ce) with tetravalent Ce(IV) in contrast to the trivalent metal ions in 1–3. The static magnetic properties of 1-RE(RE = Gd, Tb, Dy and Ho) were investigated in conjunction with INS measurements on 1-Y, 1-Tb, and 1-Hoto probe their ground state properties and any crystal field excitations. To facilitate interpretation of the INS spectra and provide insight into the magnetic behavior, ab initiocalculations were performed using the single-crystal X-ray diffraction structural data of 1-RE(RE = Tb, Dy and Ho). The ab initiocalculations indicate ground doublets dominated by the maximal angular momentum projection states of Kramers type for 1-Dyand Ising type for 1-Tband 1-Ho. Dynamic magnetic susceptibility measurements indicate that 1-Dyexhibits slow magnetic relaxation in the presence of a small applied magnetic field mainly through Raman pathways. Inelastic neutron scattering spectra exhibit distinct transitions corresponding to crystal field-induced tunneling gaps between the pseudo-doublet ground state components for 1-Tband 1-Ho, which is one of the first direct experimental measurements with INS of such tunneling transitions in a molecular nanomagnet. The power of high-resolution INS is demonstrated with evidence of two distinct tunneling gaps measurable for the two crystallographically unique Tb coordination environments observed in the single crystal X-ray structure.

Optimization of literature synthetic procedures has afforded, in moderate yield, homogeneous and crystalline samples of the five analogues Na11[{RE(OH2)}3CO3(PW9O34)2] (1-RE; RE = Y, Tb, Dy, Ho, and Er). Phase-transfer methods have allowed isolation of the mixed salts (Et4N)9Na2[{RE(OH2)}3CO3(PW9O34)2] (2-RE; RE = Y and Er). The isostructural polyanions in these compounds are comprised of a triangular arrangement of trivalent rare-earth ions bridged by a μ3-carbonate ligand and sandwiched between two trilacunary Keggin {PW9O34} polyoxometalate ligands. Alternating-current (ac) magnetic susceptibility studies of 1-Dy, 1-Er, and 2-Erreveal the onset of frequency dependence for the out-of-phase susceptibility in the presence of an applied magnetic field at the lowest measured temperatures. Inelastic neutron scattering (INS) spectra of 1-Hoand 1-Erexhibit transitions between the lowest-lying crystal-field (CF) split states of the respective J= 8 and 15/2ground-state spin–orbit multiplets of the HoIIIand ErIIIions. Complementary ab initio calculations performed for these two analogues allow excellent reproduction of the experimental magnetic susceptibility and low-temperature magnetization data and are in reasonable agreement with the experimental INS data. The ab initio calculations reveal that the slight difference in coordination environments of the three LnIIIions in each complex gives rise to differences in the CF splitting that are not insignificant. This theoretical result is consistent with the observation of multiple relaxation processes by ac magnetic susceptibility and the broadness of the measured INS peaks. The ab initio calculations also indicate substantial mixing of the MJcontributions to the CF split energy levels of each LnIIIion. Calculations indicate that the CF ground states of the HoIIIcenters in 1-Hoare predominantly comprised of contributions from small MJ, while those of the ErIIIcenters in 1-Erare predominantly comprised of contributions from large MJ, giving rise to slow magnetic relaxation. Although no direct evidence for intramolecular RE···RE magnetic coupling is observed in either magnetic or INS studies, on the basis of the ab initio calculations, we find noncollinear magnetic axes in 1-Erthat are coplanar with the erbium triangle and radially arranged with respect to the triangle’s centroid; thus, we argue that the absence of magnetic coupling in this system arises from dipolar and antiferromagnetic superexchange interactions that cancel each other out.

The crystal structures of two inter-grown variants of the mineral cupropavonite, ideal composition AgCu2PbBi5S10, were previously reported in a single crystal extracted from type specimen USNM92902 from Hall's Valley, Park County, Colorado. Here we report the chemistry of the separate intergrowths from a similar crystal from the same specimen, determined by electron-probe (EMP) analysis of the two. In addition, the crystal structure of naturally formed pavonite, Ag0.67Cu0.33Bi2.66Pb0.33S5, and preliminary verification of the crystal structure of an orthorhombic modification of berryite, ideally Cu3Ag2Pb3Bi7S16, are presented and discussed.

Two structural variants of minerals with the ideal composition AgCu2PbBi5S10 have been found in the one crystal obtained from a specimen of USNM92902, which is the type specimen of berryite, Hall's Valley, Park County, Colorado, held at the Smithsonian National Museum of Natural History. Both have the unit cell a = 13.3551(6), b = 4.0064(2), c = 32.7835(17) Å, ß = 93.397(4)°, space group C2/m. Crystal structure analysis has shown one to have a structure represented by the notation 5,5P used to designate members of the pavonite, or in this case, cupropavonite homologous series. Regular alternation of pavonite-like layers with N = 5 occur in this structure. The other structure may be represented by the notation 4,6P, because, in this case, pavonite-like layers with N = 4 and N = 6 alternate in the structure. This results in them both having the same ideal composition and unit cell of previously defined for cupropavonite. At this stage for ease of reference, and discussion, 5,5P is called cupropavonite (5,5), and 4,6P is called cupropavonite (4,6). This is to retain (some) consistency with the guidelines presented for mineral names by the Commission on New Minerals and New Mineral Names (CNMMN) in their example of nomenclature for variable-fit homologous series. Density Functional Theory analysis of the structures indicate both to be stable, with 5,5P somewhat more so than 4,6P.

Selenian kobellite is orthorhombic, Pnnm, with unit cell a = 22.6686(6), b = 34.2577(7), c = 4.04091(8)Å. The crystal structure was refined using 3259 unique intensity data with I > 4 s(I) out of a total of 30469 independent reflections measured with a single crystal diffractometer. The determined structural arrangement differs in minor ways from that reported by Miehe (1971). Selenian kobellite contains only about 1.4–1.6 Se atoms out of a total of 17.5 (S+Se) anions per asymmetric formula unit. As such, and for the present, it continues to be best described as selenian kobellite, rather than the proposed (but not accepted), new mineral name, selenokobellite, suggested by Ödman in 1942.

The crystal structure of ramdohrite, Pb5.9Fe0.1Mn0.1In0.1Cd0.2Ag2.8Sb10.8S24, from the Chocaya mine, Potosí, Bolivia, determined by Makovicky and Mumme from film data in 1983, was refined from single-crystal diffractometer data to the R value 0.060, based on 5230 reflections [I > 2s(I)] from a twinned crystal. Lattice parameters are a = 8.7348(3), b = 13.0543(4), c = 19.3117(6) Å, and ß = 90.179(2)°, space group P21/n.

The mechanism of stabilization of positive charge on carbon by sulfur, selenium, or tellurium at the β-position has been investigated kinetically, by measurement of rate enhancements, and structurally, by variation of the bond strength to the leaving group. Stabilization can occur either nonvertically with formation of a bridged intermediate or vertically through hyperconjugation within an open carbocation. We observed large rate enhancements (10⁵ for S, 10⁶ for Se) in 97 % aqueous trifluoroethanol with trifluoroacetate as the leaving group. These enhancements are consistent with either mechanism. Product structures also are consistent with either mechanism. Nine crystal structures revealed that the bond to the leaving group (C&bond;O) is lengthened by the presence of S or Se at the β-position, in proportion to the basicity of the leaving group. This lengthening is not accompanied by angle distortions expected for the bridging mechanism. The crystallographic data support vertical (hyperconjugative) character along the reaction coordinate, more so for selenium than sulfur.

The mechanism of stabilization of positive charge on carbon by sulfur, selenium, or tellurium at the β‐position has been investigated kinetically, by measurement of rate enhancements, and structurally, by variation of the bond strength to the leaving group. Stabilization can occur either nonvertically with formation of a bridged intermediate or vertically through hyperconjugation within an open carbocation. We observed large rate enhancements (105for S, 106for Se) in 97 % aqueous trifluoroethanol with trifluoroacetate as the leaving group. These enhancements are consistent with either mechanism. Product structures also are consistent with either mechanism. Nine crystal structures revealed that the bond to the leaving group (CO) is lengthened by the presence of S or Se at the β‐position, in proportion to the basicity of the leaving group. This lengthening is not accompanied by angle distortions expected for the bridging mechanism. The crystallographic data support vertical (hyperconjugative) character along the reaction coordinate, more so for selenium than sulfur.

The first series of mononuclear thiomolybdenyl complexes, Tp*Mo^VSX2 [Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate, X/X2 = anion/dianion], has been prepared. The complexes, which have been characterized by analytical, mass spectrometric, spectroscopic and X-ray crystallographic studies, provide insights into the electronic nature and chemistry of the catalytically and biologically important thiomolybdenyl unit.

Solution phase ligand substitution reactions of [Pt(dien)Cl]⁺ and [Pt(Me₅dien)Cl]⁺ (Me₅dien = N,N,N',N",N"-pentamethyldiethylenetriamine) have been monitored using electrospray ionization mass spectrometry. The [Pt(Me₅dien)Cl]⁺ ion undergoes much slower ligand substitution than [Pt(dien)Cl]⁺, which is consistent with the crystal structure of [Pt(Me₅dien)Cl]⁺ determined, which suggests steric crowding (relative to the [Pt(dien)Cl]⁺ structure) induced by the buttressing methyl groups. In addition, the gas phase collision induced dissociation reactions of [Pt(dien)X]ⁿ⁺ ions (n = 1, X = bromide, iodide, thiocyanate, cyanate, azide or nitrite; n = 2, X = pyridine) formed via solution phase ligand substitution have been examined. In most cases the ligand is lost as HX, giving rise to the co-ordinatively unsaturated [Pt(dien) − H]⁺ ion. Noteable exceptions include n = 1, where X = N₃⁻ or NO₂⁻, which instead exhibit ligand fragmentation via loss of N₂ and NO respectively to yield the novel platinum species [Pt(dien)N]⁺ and [Pt(dien)O]⁺. The structures of these ions have been examined using density functional calculations at the B3LYP/LAV1S level of theory.

For cycloadduct (6), derived by reaction of the (Z)-oxy diene (7) with the dienophile (8), the newly formed cyclohexene ring is shown by spectroscopic and X-ray crystal structure analysis to be based on the half-chair conformation (9). This contrasts with analogous diastereomeric adducts from (E)-oxy dienes, which are based on the ring-flipped conformation (4). The determinant for this conformational difference is suggested to be the stereoelectronic preference of the allylic oxy substituent, in (4) and (9), for a pseudoaxial orientation to the double bond of the cyclohexene system. Keywords. X-Ray crystallography; cycloaddition; Diels–Alder; conformation.

The complex [Co(en)2(DPPZ)] (ClO4)3(3) has been synthesized, and the crystal structures of this complex and those of [Co(en)2(bpy)] Br(ClO4)2(1) and [Co(en)2(phen)] Br3(2) have been determined. Crystal data for (1): M614 . 13, monoclinic, space group C2/c(No. 15), a16 . 7834(16), b16 . 308(3), c8 . 3167(15) Å, β104 . 932(11)°, V2199 . 4(6) Å, F(000) 1240, Z4, Dc1 . 855 g cm−3, µ2 . 895 cm−1, Mo Kα (graphite monochromatized) radiation, γ 0 . 71073 Å, T293(1) K. Crystal data for (2): M599 . 07, triclinic, space group P1 (No. 2), a7 . 7113(11), b10 . 633(2), c12 . 9884(18) Å, α 85 . 745(15), b78 . 258(11), γ 74 . 967(16)°, V1006 . 7(3) Å, F(000) 588, Z2, Dc1 . 976 g cm−3, µ6 . 819 cm−1, MoKα (graphite monochromatized) radiation, γ 0 . 71073 Å, T293(1) K. Crystal data for (3): M773 . 44, monoclinic, space group P21/c(No. 14), a20 . 296(2), b9 . 6197(11), c15 . 725(2) Å, β92 . 850(10)°, V3066 . 4(6) Å, F(000) 1579, Z4, Dc1 . 675 g cm−3, µ0 . 898 cm−1, MoKα(graphite monochromatized) radiation, γ 0 . 71073 Å, T293(1) K. In all three complexes the cobalt is in the usual octahedral environment, with the cations being linked by hydrogen bonds between the amine hydrogens and the anions into extended structures.

Hydrated crystals of copper(II) colchiceine belong to the tetragonal space group P432I2 with a 13·415(1), c50·169(8) Å and Z8. The structure has been refined to a conventional Rfactor of 0·077 for 4560 observed data. The tropolonic oxygens from two colchiceine molecules are coordinated to the copper atom in this bis-chelated complex to form a square planar arrangement. The sites of three of the waters are clearly defined, but the others are disordered over seven partially occupied sites. An intricate hydrogen-bonding system links the complex and water molecules into a three-dimensional network in the crystal.

The complex LW VS(µ-S) 2W VS(S 2PPh 2) [L = tris(3,5-dimethylpyrazol-1-yl)hydroborate] results from the reaction of LW VIO 2Cl with PPh 3 in refluxing pyridine, followed by the addition of NH 4S 2PPh 2and reflux for a further 4 days. Crystals of LWS(µ-S) 2WS(S 2PPh 2)·0.5CH 2Cl 2are monoclinic and belong to space group Ccwith a12.356(2), b30.067(6), c22.082(4) Å, β96.08(2)° and Z8. Refinement of 10507 data measured with Mo Kα radiation converged at R0.0466 and Rw0.1421. The two independent molecules in the unit cell are dinuclear with a syn-[W 2S 2(µ-S) 2] 2+core. One tungsten centre is further coordinated by a tridentate L ligand, making it six-coordinate with a distorted octahedral geometry while the other bears a bidentate dithiophosphinate ligand and is five-coordinate and square- pyramidal in geometry. The terminal thio–tungsten distances average 2.120 Å, and the parameters of the core [W–W av. 2.832 Å, W–(µ-S) av. 2.311 Å, S–W–S av. 100.2°, W–S–W av. 75.2°] are typical of syn-[W 2S 2(µ-S) 2] 2+complexes.

Two photochemical pathways to paclitaxel-like oxetan rings have been examined. In the first approach, an intramolecular Paternò–BÜchi reaction on a 6,7-enal was attempted without success. The intermolecular variation using a bicyclic alkene in the presence of either benzaldehyde or acetophenone delivered oxetans whose regiochemistry was the same as that found in paclitaxel but opposite in stereochemistry. The crystal structures of a key intermediate diol and a photochemically generated oxetan are reported.

The preparation of dimethyl 2-bromocubane-1,4-dicarboxylate (3) is described starting from the readily available (3aα,4β,7α,7aα)-2,4-dibromo-3a,4,7,7a-tetrahydro-4,7-methano-1H-indene-1,8-dione 8-ethylene ketal (4).

Abstract:  Synthesis of complexes cis,cis-WVOXL (X=Cl, NCS), cis,trans-WVOXL (X=Cl, OPh, SPh) and cis,trans-WVIE2L (E2=O2, OS, S2) of the title ligand LH2 are reported. cis,cis-WVOCIL crystallises in space group P21/c with a=13.6541(9) Å, b=7.1555(11) Å, c=18.198(2) Å, β=95.294(6)°, V=1770.4(3) Å3 and Z=4 while the cis,trans isomer crystallises in space group P21/n with a=10.361(3) Å, b=14.141(4) Å, c=12.213(5) Å, β=102.56(3)°, V=1747(2) Å3 and Z=4. cis,trans-WVIS2L crystallises in space group P21/n with a=10.645(2) Å, b=13.929(2) Å, c=12.189(2) Å, β=103.14(2)°, V=1760(1) Å3 and Z=4. A short CH3···Cl distance of 3.067(7) Å and an acute OWCl angle of 94.1(2)° are seen in cis,cis-WVOClL, which converts to the cis,trans form on heating in MeCN. The latter isomer features a CH3···Cl distance of 3.38(2) Å and an OWCl angle of 105.1(8)°. Electrochemical and EPR data are reported. In particular, cis,trans-WVIE2L may be reduced to [WVE2L]–. EPR properties of these anions and those of complexes WVOXL are discussed in the context of WV centres in tungsten enzymes.

A Sigmosceptrellasp. of sponge collected during trawling operations in the Great Australian Bight, Australia, has yielded a series of new norterpenes. These include a new bisnorditerpene, sigmosceptrin-A (5); two new norditerpenes, sigmosceptrin-B (14) and sigmosceptrin-C (15), isolated as their methyl esters (6) and (7) respectively; and an ethylated artefact, sigmosceptrin-B ethyl ester (8). Complete stereostructures were assigned to the sigmosceptrins by spectroscopic analysis, chemical degradation, derivatization, and by a single-crystal X-ray structural analysis. A biosynthetic pathway is proposed that requires a common biosynthetic precursor to both the sigmosceptrins and norterpene cyclic peroxides.

The crystal structure of 11‐[4‐(1,3‐benzodioxol‐5‐yl­methyl)­piperazino]‐8‐chloro‐5H‐dibenzo­[b,e][1,4]­diazepine, C25H23ClN4O2, confirms the buckled nature of the dibenzodiazepine nucleus, with the central seven‐membered heterocycle in a boat conformation and the dihedral angle between the planes of the aromatic rings being similar to that found for the parent compound, clozapine. The piperazine ring displays an almost perfect chair conformation, with the piperonyl group assuming an equatorial orientation. The relative position of the dibenzodiazepine and piperazine ring systems is controlled by the planarity of the piperazine N atom in the amidine moiety.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.