Vulcano : tre secoli di mineralogia

Va ricordato, con immenso motivo di orgoglio e senza pecca di retorica, che il sito delle isole Eolie è “un eccezionale esempio dell’attività di costruzione e distruzione di isole operata dal vulcanesimo e testimoniano un fenomeno vulcanico tuttora in corso”, rivestendo “una importanza internazionale per la vulcanologia” e che, “studiate già a partire dal XVIII secolo, hanno fornito alle opere di vulcanologia la descrizione di due tipi di eruzione (vulcaniana e stromboliana)”, rappresentando da oltre due secoli, una tappa importante nella formazione di tutti i geologi: questa la motivazione suggellata dell’Unesco per il prestigioso riconoscimento attribuito all’arcipelago di “Patrimonio dell’Umanità”..

Lattice-dynamical calculations on some rigid organic molecules

Several physical-chemical properties in crystals formed by "rigid" organic molecules have been calculated by means of different semiempirical atom-atom potential functions. For nine different substances, vibration frequencies, dispersion curves, and "crystallographic" temperature factors have been evaluated, and as an example the density of states for two of them are also reported. Experimental data are in excellent to fair agreement with results obtained by use of "Williams IVa" functions; some of these results can be advantageously used for libration correction of bond lengths that are determined by x-ray or neutron diffraction. Among the examined substances, some anomalies are found for pyrene crystals, which confirm in this case a rather unusual way of packing

Atomic thermal parameters and thermodynamic functions for chrysoberyl (BeAl2O4) from vibrational spectra and transfer of empirical force fields

Using empirical atomic charges and valence force fields derived from a best fit to the Raman-IR spectra, and applying a rigid-ion Born-von Karman model, atomic thermal parameters have been calculated for chrysoberyl (BeA1204). The agreement with the experimental values (redetermined here for this purpose) is good; and excellent agreement with the experimental data is obtained for the estimates of some thermodynamic functions such as entropy and the molar heat. As for other oxides and silicates, the zero-point contribution is particularly important with respect to both the vibrational energy and to the mean-square amplitude of motion (about 83 and 70% of the value at room temperature, respectively). In order to test transferability of the force fields, the vibrational frequencies have also been calculated using empirical valence force-field parameters derived from a best fit to the Raman-IR spectra of corundum (A1203) and bromellite (BeO), without fitting the chrysoberyl spectra. The agreement with the experimental values is good, especially for the low frequencies. However, there is significant disagreement for the higher frequencies, which apparently require larger stretching-force constants than for both corundum and bromellite: these constants also appear to be more dependent upon bond distance (especially for the Bc O bonds). This behaviour may reflect some inadequacy of the rigidion model used here for these calculations. However, the agreement with the experimental atomic thermal parameters and thermodynamic functions is good, because the lowest energy vibrational levels (corresponding to the softest modes, including the acoustic branches near the origin of the Brillouin zone) are the most important for these applications

Crystal engineering of coordination polymers and architectures using the [Cu(2,2 '-bipy)](2+) molecular corner as building block (bipy=2,2 '-bipyridyl)

The [Cu(2,2'-bipy)](2+) corner unit (1) (2,2'-bipy = 2,2'-bipyridyl), made available by the metathesis of the chlorides in [Cu(2,2'-bipy)Cl-2] with poorly coordinating anions [triflate (1a), BF4- (1b) and NO3- (1c)], has been reacted with a variety of bifunctional ligands, such as 4,4'-bipyridyl (4,4'-bipy), trans-4,4'-azobis(pyridine) (azpy), 1,2-bis(4-pyridyl) ethane (bpetha), trans-1,2-bis(4-pyridyl) ethene (bpethe), 1,3-bis(4-pyridyl) propane (bpp), pyrazine (pyz), i-nicotinate (i-nic) and others. Interesting motifs have been obtained and characterized, including one-dimensional polymeric chains of different kinds, molecular rings and other architectures, depending on the ligand and the counterion. Zig-zag chains exhibiting a variated period have been observed within the species [(1)(4,4'-bipy)(CF3SO3)](CF3SO3) (2a), [(1)(azpy)(H2O)(CF3SO3)](CF3SO3) (3a), [(1)(bpethe)(BF4)](BF4) (2b), [(1)(azpy)(H2O)](NO3)(2)center dot H2O (2c) and [(1)(i-nic)(H2O)](NO3)center dot 2H(2)O (3c). Though the topology of these species is not exceptional, one of them (2c) exhibits a peculiar supramolecular organization of the chains, resulting in warp-and-woof two-dimensional sheets. With the non-rigid ligands bpp and bpetha other motifs can be obtained: the former ligand gives a festoon polymer, [(1)(bpp)(EtOH)](BF4) 2 (3b), while molecular rings are generated with the latter one in the species [(1)(bpetha)(CF3SO3)(2)](2) (4a). Pyrazine with 1a gives dinuclear species that are joined by triflate anions into ladder-like polymers in [{(1)(H2O)(CF3SO3)}(2)(pyz)](CF3SO3)(2) (5a), exhibiting in the crystal structure channels running parallel to the ladders. With the asymmetric ligand 2,4'-bipyridyl (2,4'-bipy) the monomeric species [(1)(2,4'-bipy)(H2O)(BF4)(2)] (4b) is obtained, that forms 1D chains via hydrogen bonds. A different starting species, obtained from [Cu(2,2'-bipy) Cl2] by partial metathesis of the chlorides was also employed: reaction with heptanedinitrile (hdn) gives the derivative [{(1)Cl}(2)(hdn)](BF4)(2) (5b), consisting of chains of dinuclear [(2,2'-bipy) Cu(mu-Cl)(2)Cu(2,2'-bipy)] moieties joined by the bidentate flexible ligand

Reticular synthesis and the design of new materials

The long-standing challenge of designing and constructing new crystalline solid-state materials from molecular building blocks is just beginning to be addressed with success. A conceptual approach that requires the use of secondary building units to direct the assembly of ordered frameworks epitomizes this process: we call this approach reticular synthesis. This chemistry has yielded materials designed to have predetermined structures, compositions and properties. In particular, highly porous frameworks held together by strong metal-oxygen-carbon bonds and with exceptionally large surface area and capacity for gas storage have been prepared and their pore metrics systematically varied and functionalized.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62718/1/nature01650.pd

PANICHIITE, NATURAL AMMONIUM HEXACHLOROSTANNATE(IV), (NH4)2SnCl6, FROM LA FOSSA CRATER, VULCANO, AEOLIAN ISLANDS, ITALY

Panichiite, ammonium hexachlorostannate(IV), (NH4)2SnCl6, is a new mineral species found in a medium-temperature intracrater fumarole (~250\ub0C) at La Fossa crater, Vulcano Island, Aeolian Islands, Sicily, Italy. The mineral occurs as aggregates of minute colorless octahedra up to 0.2 mm in diameter on fragments of altered pyroclastic breccia, in association with alunite, anhydrite, bismuthinite, godovikovite, demicheleite-(Br) (BiSBr), BiSCl (IMA 2008\u2013020) and two other new species, a sodium ammonium aluminum sulfate chloride (IMA 2008\u2013057) and an ammonium bismuth chloride that is presently under study. Panichiite is cubic, space group Fm3m (no. 225), with Z = 4; the unit-cell parameter a is 10.064(1) \uc5, and V is equal to 1019.4(2) \uc53. The X-ray powder-diffraction pattern is in excellent agreement with that of the synthetic compound; the strongest six reflections [dobs in \uc5(I)(hkl)] are: 5.811(100)(111), 5.032(73)(200), 2.516(69)(400), 3.035(48)(311), 1.779(42)(440), and 2.250(39)(420). Chemical analyses obtained with an electron microprobe in energy-dispersion mode gave, on average, Cl 56.57, Sn 31.62, Br 1.53, K 1.05, total 90.77, with NH4+ (by difference) 9.23, for a total of 100.00 wt.%, corresponding to the empirical formula [(NH4)1.90K0.10]S2.00Sn0.99(Cl5.94Br0.07)S6.01. The calculated density for the compound with the above empirical formula is 2.423 g/cm3. The index of refraction n obtained using immersion methods is 1.68(1) (l = 589 nm). The structure, including the positions of the hydrogen atoms of the ammonium ion, was refined from single-crystal diffraction data to a final R of 0.030 for 153 independent observed reflections [I > 2s(I)]. The six equivalent Sn\u2013Cl distances in the octahedral SnCl62\u2013 ion are 2.429(1) \uc5, and the Cl...N distances are 3.559(1) \uc5. The mineral (IMA 2008\u2013005) is named in honor of Prof. Ugo Panichi, a pioneer in the study of minerals from Vulcano

THE OCCURRENCE OF LAFOSSAITE AT VESUVIUS

As a part of a joint project concerning the study of fumarole minerals of the Italian volcanoes, carried out in collaboration with the Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Napoli - Osservatorio Vesuviano, a systematic investigation of old fumarole mineral samples was undertaken. The presence of natural thallium chloride lafossaite, first described at La Fossa crater...Società Italiana di Mineralogia e Petrologia c/o Dipartimento di Scienze della Terra - PisaPublishedTorino3.5. Geologia e storia dei vulcani ed evoluzione dei magmiope

Hephaistosite, TlPb2Cl5, a new thallium mineral species from La Fossa crater, Vulcano, Aeolian islands, Italy

Hephaistosite, TlPb2Cl5, a newly discovered species of thallium lead chloride, was found in a high-temperature fumarole (~400°C) at the rim of La Fossa crater, Vulcano Island, Aeolian archipelago, Sicily, Italy. The mineral occurs as aggregates of pale yellow-green crystals tabular on {010} up to 0.1 mm in length on fragments of altered pyroclastic breccia, in association with bismuthinite (Bi2S3), cotunnite (PbCl2), challacolloite (KPb2Cl5) and pseudocotunnite (K2PbCl4). The mineral is monoclinic, space group P21/c. Cell parameters refined from powder-diffraction data are: a 8.9477(6), b 7.9218(7), c 12.4955(5) Å, b 90.092(4)°, V 885.70(7) Å3, with Z = 4. The strongest six reflections in the X-ray powder-diffraction data [d (in Å)(I)(hkl)] are: 3.696(100)(013), 3.971(83)(020), 2.109(45)(402,215), 2.569(42)(204), 1.848(41)(142,026), and 2.851(38)(213). Crystals of hephaistosite show the forms {010}, {101}, {110}, {100}, {001}, and {011}. Chemical analyses obtained by EDS microprobe gave, on average, in wt.%, Tl 23.78, K 0.01, Pb 51.78, Cl 21.40, Br 1.34, F 0.17, for a total of 98.48, corresponding to an empirical formula (based on 8 apfu) of Tl0.94Pb2.01(Cl4.85Br0.14F0.07)S5.06. Hephaistosite is isostructural with challacolloite; intermediate members of the series between the two species occur in the same fumarole. The calculated density for the synthetic compound (TlPb2Cl5) is 5.932 g/cm3. The mean index of refraction n, obtained from a natural sample using Brewster angle measurement, is 2.0(1). The structure was refined using two different crystals, with Tl:K atom ratios of 86:14 and 64:36; the final R index is 0.028 and 0.038, respectively. The mineral, approved by the IMA Commission on New Minerals, Nomenclature and Classification (No. 2006–043), is named in honor of the ancient Greek god of fire, Hephaistos (Hephaestus, Hfasto), whose workshops were alleged to be located at Vulcano