Crystal Structure Investigations of Amide Sulfate Tetrahydrates with Divalent Cations

Single crystals of three amide sulfate tetrahydrate compounds, Ca(NH2SO3)2 ⋅ 4H2O, Mn(NH2SO3)2 ⋅ 4H2O and Ni(NH2SO3)2 ⋅ 4H2O, were synthesized by controlled evaporation of aqueous Solutions. The crystal structures were investigated using single-crystal X-ray diffraction methods. Ca(NH2SO3)2 ⋅ 4H2O: space group C2/c, Z = 4, a = 11.616(3) Å, b = 7.761(2) Å, c = 11.638(3) Å, β = 98.93(1)°, V = 1036.47 Å3, R1 = 0.026; Mn(NH2SO3)2 ⋅ 4H2O: space group P21/c, Z = 2, a = 6.143(2) Å, b = 5.324(2) Å, c = 15.441(5) Å, β = 91.72(1)°, V= 504.78 Å3, R1 = 0.024; Ni(NH2SO3)2 ⋅ 4H2O: space group P1̅, Z= 1, a = 6.331(8) Å, b = 6.731(9) Å, c = 6.784(8) Å, α = 88.93(9)°, β = 67.87(5)°, γ = 67.76(6)°, V = 245.27 Å3, R1 = 0.030. In Ca(NH2SO3)2 ⋅ 4H2O antiprismatic CaO8 polyhedra share four oxygen atoms with NH2SO3 tetrahedra forming sheets parallel (001). In Mn(NH2SO3)2 ⋅ 4H2O and Ni(NH2SO3)2 ⋅ 4H2O, MnO6 octahedra and NiN2O4 octahedra, respectively, are linked by common corners with two NH2SO3 tetrahedra forming isolated groups. These units are interconnected by hydrogen bonds only to form three-dimensional framework structures. The amide sulfate group has a distorted tetrahedral configuration with mean S−O and S−N bond lengths of 1.449 and 1.654 Å, respectively. The average cat-ion-oxygen distances are 2.456 Å (Ca−O), 2.173 Å (Mn-O), and 2.049 Å (Ni−O), both Ni−N bond lengths are 2.153 Å. Three different types of hydrogen bonds are observed in the title compounds, namely O−H⋅⋅⋅O bonds ranging from 2.680 to 2.968 A, N−H⋅⋅⋅O bonds between 2.966 and 3.339 Å, and one O−H⋅⋅⋅N bond with 2.905 Å. Generally, observed interatomic bond lengths and angles comply well with crystal Chemical expectations

Crystal Structure Investigations of Amide Sulfate Tetrahydrates with Divalent Cations

Single crystals of three amide sulfate tetrahydrate compounds, Ca(NH2SO3)2 ⋅ 4H2O, Mn(NH2SO3)2 ⋅ 4H2O and Ni(NH2SO3)2 ⋅ 4H2O, were synthesized by controlled evaporation of aqueous Solutions. The crystal structures were investigated using single-crystal X-ray diffraction methods. Ca(NH2SO3)2 ⋅ 4H2O: space group C2/c, Z = 4, a = 11.616(3) Å, b = 7.761(2) Å, c = 11.638(3) Å, β = 98.93(1)°, V = 1036.47 Å3, R1 = 0.026; Mn(NH2SO3)2 ⋅ 4H2O: space group P21/c, Z = 2, a = 6.143(2) Å, b = 5.324(2) Å, c = 15.441(5) Å, β = 91.72(1)°, V= 504.78 Å3, R1 = 0.024; Ni(NH2SO3)2 ⋅ 4H2O: space group P1̅, Z= 1, a = 6.331(8) Å, b = 6.731(9) Å, c = 6.784(8) Å, α = 88.93(9)°, β = 67.87(5)°, γ = 67.76(6)°, V = 245.27 Å3, R1 = 0.030. In Ca(NH2SO3)2 ⋅ 4H2O antiprismatic CaO8 polyhedra share four oxygen atoms with NH2SO3 tetrahedra forming sheets parallel (001). In Mn(NH2SO3)2 ⋅ 4H2O and Ni(NH2SO3)2 ⋅ 4H2O, MnO6 octahedra and NiN2O4 octahedra, respectively, are linked by common corners with two NH2SO3 tetrahedra forming isolated groups. These units are interconnected by hydrogen bonds only to form three-dimensional framework structures. The amide sulfate group has a distorted tetrahedral configuration with mean S−O and S−N bond lengths of 1.449 and 1.654 Å, respectively. The average cat-ion-oxygen distances are 2.456 Å (Ca−O), 2.173 Å (Mn-O), and 2.049 Å (Ni−O), both Ni−N bond lengths are 2.153 Å. Three different types of hydrogen bonds are observed in the title compounds, namely O−H⋅⋅⋅O bonds ranging from 2.680 to 2.968 A, N−H⋅⋅⋅O bonds between 2.966 and 3.339 Å, and one O−H⋅⋅⋅N bond with 2.905 Å. Generally, observed interatomic bond lengths and angles comply well with crystal Chemical expectations

Sr-bearing high-pressure tourmaline from the Kreuzeck Mountains, Eastern Alps, Austria

A detailed investigation was conducted on high-pressure (~1.4 GPa) tourmaline from an Eoalpine mafic eclogite, which occurs in the Kreuzeck Mountains, Eastern Alps, Austria. Tourmaline from this locality contains the highest amount of Sr²⁺ (up to 0.68 wt% SrO) known to date. The space group is R3m with unit-cell parameters a = 15.944(1), c = 7.202(1) Å, V = 1585.5(3) ų. Analyses by a combination of electron microprobe, optical absorption spectroscopy and crystal-structure refinement (R1 = 1.31%) result in the structural formula ^X(Na_(0.85)Ca_(0.08)Sr_(0.06)K_(0.01))_(Σ1.00)^Y(Mg_(1.68)Al_(0.70) Fe_(0.37)³⁺Ti_(0.10)⁴⁺Fe_(0.11)²⁺Ca_(0.03)Cr_(0.01)³⁺)_(Σ3.00)^Z (Al_(5.15)Mg_(0.80)Fe_(0.05)³⁺)_(Σ6.00)^T(Si_(5.82)B_(0.10)Al_(0.08)O_(18)) (BO₃)₃^V(OH)₃^W [O_(0.45)(OH)_(0.35)F_(0.20)]. The T site contains mainly Si and additionally small amounts of B and Al. According to optical absorption spectroscopy (using the band near 1120 nm), the Fe³⁺/Fe ratio is 79 ± 2%, suggesting that this high-pressure tourmaline crystallized under oxidizing conditions. It has a significant oxy-dravite component. A near-rim zone contains 0.6 wt% Cr₂O₃, 0.5 wt% PbO₂, 0.2 wt% NiO and 0.1 wt% V₂O₃. Only a small F content was found by structure refinement. There is no evidence for significant X-site vacancy in the investigated tourmaline zones. We assume that the original boron source for tourmaline crystallization in the eclogite, i.e. tourmaline-bearing pegmatites in the country-rock, were influenced by a Sr-bearing marble

Fluor-schorl, a new member of the tourmaline supergroup, and new data on schorl from the cotype localities

Fluor-schorl, NaFe^(2+) _3Al_6Si_6O_(18)(BO_3)_3(OH)_3F, is a new mineral species of the tourmaline supergroup from alluvial tin deposits near Steinberg, Zschorlau, Erzgebirge (Saxonian Ore Mountains), Saxony, Germany, and from pegmatites near Grasstein (area from Mittewald to Sachsenklemme), Trentino, South Tyrol, Italy. Fluor-schorl was formed as a pneumatolytic phase and in high-temperature hydrothermal veins in granitic pegmatites. Crystals are black (pale brownish to pale greyish-bluish, if distance (r^2 = 0.93). This correlation indicates that Fe^(2+)-rich tourmalines from the investigated localities clearly tend to have a F-rich or F-dominant composition. A further strong positive correlation (r^2 = 0.82) exists between the refined F content and the Y–W (F,OH) distance, and the latter may be used to quickly estimate the F content

Limitations of Fe^(2+) and Mn^(2+) site occupancy in tourmaline: Evidence from Fe^(2+)- and Mn^(2+)-rich tourmaline

Fe^(2+)- and Mn^(2+)-rich tourmalines were used to test whether Fe^(2+) and Mn^(2+) substitute on the Z site of tourmaline to a detectable degree. Fe-rich tourmaline from a pegmatite from Lower Austria was characterized by crystal-structure refinement, chemical analyses, and Mössbauer and optical spectroscopy. The sample has large amounts of Fe^(2+) (~2.3 apfu), and substantial amounts of Fe^(3+) (~1.0 apfu). On basis of the collected data, the structural refinement and the spectroscopic data, an initial formula was determined by assigning the entire amount of Fe^(3+) (no delocalized electrons) and Ti^(4+) to the Z site and the amount of Fe^(2+) and Fe^(3+) from delocalized electrons to the Y-Z ED doublet (delocalized electrons between Y-Z and Y-Y): X(Na_(0.9)Ca_(0.1)) ^Y(Fe^(2+)_(2.0)Al_(0.4)Mn^(2+)_(0.3)Fe^(3+)_(0.2)) ^Z(Al_(4.8)Fe^(3+)_(0.8)Fe^(2+)_(0.2)Ti^(4+)_(0.1)) ^T(Si_(5.9)Al_(0.1))O_(18) (BO_3)_3^V(OH)_3 ^W[O_(0.5)F_(0.3)(OH)_(0.2)] with α = 16.039(1) and c = 7.254(1) Å. This formula is consistent with lack of Fe^(2+) at the Z site, apart from that occupancy connected with delocalization of a hopping electron. The formula was further modified by considering two ED doublets to yield: ^X(Na_(0.9)Ca_(0.1)) ^Y(Fe^(2+)_(1.8)Al_(0.5)Mn^(2+)_(0.3)Fe^(3+)_(0.3)) ^Z(Al_(4.8)Fe^(3+)_(0.7)Fe^(2+)_(0.4)Ti^(4+)_(0.1)) ^T(Si_(5.9_Al_(0.1))O_(18) (BO_3)_3 ^V(OH)_3 ^W[O_(0.5)F_(0.3)(OH)_(0.2)]. This formula requires some Fe^(2+) (~0.3 apfu) at the Z site, apart from that connected with delocalization of a hopping electron. Optical spectra were recorded from this sample as well as from two other Fe^(2+)-rich tourmalines to determine if there is any evidence for Fe^(2+) at Y and Z sites. If Fe^(2+) were to occupy two different 6-coordinated sites in significant amounts and if these polyhedra have different geometries or metal-oxygen distances, bands from each site should be observed. However, even in high-quality spectra we see no evidence for such a doubling of the bands. We conclude that there is no ultimate proof for Fe^(2+) at the Z site, apart from that occupancy connected with delocalization of hopping electrons involving Fe cations at the Y and Z sites. A very Mn-rich tourmaline from a pegmatite on Elba Island, Italy, was characterized by crystal-structure determination, chemical analyses, and optical spectroscopy. The optimized structural formula is ^X(Na_(0.6)□_(0.4)) ^Y(Mn^(2+)_(1.3)Al_(1.2)Li_(0.5)) ^ZAl_6 ^TSi_6O_(18) (BO_3)_3 ^V(OH)_3 ^W[F_(0.5)O_(0.5)], with α = 15.951(2) and c = 7.138(1) Å. Within a 3σ error there is no evidence for Mn occupancy at the Z site by refinement of Al ↔ Mn, and, thus, no final proof for Mn^(2+) at the Z site, either. Oxidation of these tourmalines at 700–750 °C and 1 bar for 10–72 h converted Fe^(2+) to Fe^(3+) and Mn^(2+) to Mn^(3+) with concomitant exchange with Al of the Z site. The refined ^ZFe content in the Fe-rich tourmaline increased by ~40% relative to its initial occupancy. The refined YFe content was smaller and the distance was significantly reduced relative to the unoxidized sample. A similar effect was observed for the oxidized Mn^(2+)-rich tourmaline. Simultaneously, H and F were expelled from both samples as indicated by structural refinements, and H expulsion was indicated by infrared spectroscopy. The final species after oxidizing the Fe^(2+)-rich tourmaline is buergerite. Its color had changed from blackish to brown-red. After oxidizing the Mn^(2+)-rich tourmaline, the previously dark yellow sample was very dark brown-red, as expected for the oxidation of Mn^(2+) to Mn^(3+). The unit-cell parameter α decreased during oxidation whereas the c parameter showed a slight increase