Bernward Engelen

Strong hydrogen bonds in acid selenites : correlation of infrared spectroscopic and structural data

Abstract Several hitherto unknown acid selenites of divalent metals have been prepared and characterized by means of infrared spectroscopy and X-ray structure determination. The relations between the OH⋯O stretching and bending vibrations and the OH⋯O distances of the strongly hydrogen—bonded hydroxyl groups of these compounds and of some other acid selenites are presented. They are discussed with respect to the nature of the ABC trio-bands in the ν(OH) stretching mode region of strongly hydrogen-bonded systems.

Very low H -O -H bending frequencies. IV. Fourier transform infrared spectra of synthetic dittmarite

The Fourier transform infrared spectra of MgNH4PO4·H2O (the synthetic analogue of the mineral dittmarite) and of a series of its partially deuterated analogues have been studied as a part of our continuous work on compounds exhibiting very low water bending frequencies. Although, the presence of ammonium bands makes the assignments in this case more difficult than for the potassium analogues, the isomorphism between the compounds of the MNH4PO4·H2O type (M ¼ Mg, Co, Ni, Mn and one of the polymorphs of CdNH4PO4·H2O) and those which contain potassium instead of ammonium as well as the careful analysis of the spectra warrant the conclusion that in the presently studied compound the water bending mode appears at a frequency which is far more than 100 cm 21 lower than in the gaseous water. The spectra clearly show that the ammonium ions in the structure are involved in quite strong hydrogen bonds, a characteristic which is a precondition for a material to behave as a protonic conductor. q 2002 Elsevier Science B.V. All rights reserved.

Infrared and Raman Spectra of Magnesium Ammonium Phosphate Hexahydrate (Struvite) and Its Isomorphous Analogues

The three investigated compounds — KMgPO4·6H2O (KMP), NH4MgPO4·6H2O (NMP) and NH4MgAsO4·6H2O (NMA) — are characterized by the existence, in their structure, of quite strong Ow⋯O hydrogen bonds (of which some are among the shortest of this type ever found in crystalline hydrates, the Ow⋯O distances being slightly above 260 pm). Reflecting the strength of the hydrogen bonds, a broad and structured feature extending from ≈ 4000 down to ≈ 2000 cm−1 is found in the infrared spectra. Although not as rich in detail as the infrared spectra, the Raman ones are similar in appearance. Rather surprisingly, the spectral picture is not very different in the case of the two phosphate compounds (KMgPO4·6H2O and NH4MgPO4·6H2O) although N-H stretching bands are expected in the same region of the spectrum of NMP. Thus, obviously, the intensity of the feature in the O-H/N-H stretching region is due mainly to modes of the water molecules whereas the NH4 stretches contribute to a lesser degree to the shape and intensity. The comparison of the spectra in the O-D/N-D stretching region confirms this.

STRONG HYDROGEN BONDS IN CA(HSEO3)2.H2O CRYSTAL STRUCTURE AND TEMPERATURE INDUCED FORMATION OF ABC BANDS

Abstract Ca(HSeO 3 ) 2 ·H 2 O is a model compound for the formation of AB and ABC multi band systems in the OH stretching mode region of oxo acids, acid oxo salts or other compounds with strong hydrogen bonds. It was obtained from aqueous solutions of Ca(HSeO 3 ) 2 and has been investigated by means of single crystal X-ray diffraction measurements at ambient temperature and temperature dependent powder X-ray diffraction and IR measurements. From the single crystal X-ray measurements, the H-bond scheme of Ca(HSeO 3 ) 2 ·H 2 O including a hexacyclic H-bond system was determined. The temperature dependent IR and X-ray data mainly result in (i) a reversible phase transition between or at T 1 ≈ 200 and T 2 ≈ 305 K, (ii) a strong reversible contraction of the hexacyclic H-bond system, and (iii) a correlated, reversible formation of a γ(OH) and a C band in the out-of-plane bending and OH stretching mode region of the SeOH group, respectively. These findings are discussed with respect to the AB/ABC band transition in the vibrational spectra of Ca(HSeO 3 ) 2 ·H 2 O and the formation of ABC multi band systems of the other compounds mentioned above.

Lattice vibration spectra Part LVIII. OD(OH) frequency versus H-bond distance correlation diagrams: a case study for isomorphic M(SO32·3H2O (MMg, Mn, Fe, Co, Ni, Zn)

Abstract The uncloupled ν OD band frequencies of matrix isolated HDO molecules in isostructural MSO 3 ·3H 2 O (MMg, Mn, Fe, Co, Ni, Zn) have been assigned to the six different H positions in the structure by Raman single crystal techniques. The physical basis of this technique presented first in 1984 is described. The water molecules H 2 O I and II are extremely asymmetric, i.e. the most asymmetric known so far, forming a very strong and a mediate H-bond each. The bifurcated H-bonds of H 2 O III reveal a dynamic behaviour, as possibly common for bifurcated hydrogen bonds. The strength of the H-bonds present as well as the correlation between the OD(OH) band frequencies and the H⋯O hydrogen bond distances obtained from neutron diffraction studies are discussed in terms of the different acceptor strength (basicity) of the H-bond acceptor groups (SO 2− 3 , H 2 O), the synergetic effect, and the repulsive forces at the respective lattice sites. The increase of the H-bond donor strength (acidity) of the water molecules owing to metal—oxygen interactions (MOH 2 ) (synergetic effect) resembles that of the acid strengths of M(H 2 O) 2+ 6 of the metal ions involved.

Polylithiumorganische Verbindungen. XI: 1,4-Disila[6]radialene in zwei stabilen konformationsisomeren Formen, Twist- und Sesselkonformation, die sich bei Raumtemperatur nicht ineinander umwandeln

Abstract The reaction of dichlorosilanes with 3,4-dilithio-2,5-dimethyl-2,4-hexadiene yields 1,4-disila[6]radialenes in two stable conformational isomers, twist and chair, which do not interconvert at room temperature. The formation of the chair conformers is kinetically favoured. Of the two trans conformers, which are of equal thermodynamic stability, X-ray structures are presented.

Kristallstruktur von MnSO3 • H2O , eine fastsymmetrische schichtstruktur / Crystal structure of MnSO3 • H2O, a nearly symmetrical layer structure

The crystal structure of MnSO3H2O , space group P21/n, Z = 4. Dx = 2.842(2) g · cm-3, a = 4.843(3), b = 12.807(6), c = 5.762(4) Å, β = 90.39(4)° has been determined. MnSO3·H2O crystallizes in a hitherto unknown structure type, which is closely related to that of orthorhombic MnSeO3· D2O. Coordination of Mn is octahedral involving O atom s from one water moleculeo and four different sulfite ions. The Mn-O distances range from 2.136(3) to 2.285(3)Å . The S-O distances are 1.552(3), 1.556(3) and 1.482(3)!Å. The MnO6 octahedra form layers parallel (010) by sharing four equatorial vertices. The layers are connected by weak hydrogen bonds and shifted laterally by 0.7 Å from the arrangement with m symmetry, found in MnSeO3·D2O. Due to this shift, the water molecule is asymmetrically bonded, as shown by both the O-H···O distances (2.967(4)-3.834(5)Å) and the OD stretching modes (2554 and 2576 cm-1) of partly deuterated samples

Zur Polymorphie des Cadmiumsulfits, Kristallstrukturen von CdSO3-I, CdSO3-II und CdSO3-III / Polymorphic Cadmium Sulfites, Crystal Structures of CdSO3-I, CdSO3 -II, and CdSO3-III

The crystal structures of the anhydrous cadmium sulfites CdSO3-I (P21/c, Z=4), CdSO3-II (P21/c, Z=8), and CdSO3-III (R3̄̄, Z=18 for the hexagonal cell) have been determined by means of single crystal X-ray diffraction data. The final R for the 1475, 2349, and 2138 observed reflections are 0.040, 0.034, and 0.073. Coordination of Cd is trigonal-prismatic, a hitherto unknown coordination of Cd in salts of oxoacids, in CdSO3-I and CdSO3-II, and octahedral in CdSO3-III. The CdO6-polyhedra are arranged in two-dimensional (CdSO3-I) and three-dimensional (CdSO3-II and CdSO3-III) networks. SO32- groups act as monodentate and in CdSO3-I and CdSO3-II also as bidentate ligands. Cd−O distances range from 224.5(3) to 244.6(3) pm, with an average of 231.5 pm for the trigonal-prismatic and of 231.0 pm for the octahedral coordination. S−O dis-tances range from 152.3(3) to 155.3(3) pm with an average of 153.7 pm, the O−S−O angles from 99.2(2) to 106.7(3)° with an average of 103.2°.

Kristallstruktur von MgSO3·H2O/Crystal Structure of Mg SO3·H2O

Abstract The crystal structure of MgSO3·H2O , space group P21 /ln, Z = 4, Dx = 2.415 g·cm-3 , a = 4.699(1), b = 12.751(3), c = 5.618(1) Å, β = 90.49(3)°, was determined by single crystal X-ray diffraction. MgSO3·H2O crystallizes in the MnSO3·H2O type. The structure consists of buckled trans layers ∞[MgSO3·H2O], which are built up from strongly distorted MgO5(H2O) octahedra sharing four equatorial vertices, and of trigonal pyramidal SO32- ions. It is closely related to the structures of orthorhombic MnSeO3·D2O and monoclinic ZnSeO3·H2O . The Mg-O distances range from 2.051(3) to 2.175(4) Å. The S-O distances (1.543(3), 1.547(3) and 1.493(3) Å) and the O-S-O angles (98.4(2) and 2x 106.0(2)°) correspond to those in MnSO3·H2O . The distortion of the MO5(H2O) octahedra (M = Mg, Mn) and of the SO32- ions is smaller in MgSO3·H2O , but with greater deviations from m symmetry. The distances between the H-connected ∞2[MSO3·H2O] layers are greater in MgSO3·H2O , indicating weaker inter-layer hydrogen bonds. The lateral arrangement of the ∞2[MSO3·H2O] layers is nearly the same in both sulfite monohydrates.

Zur Kenntnis der Hydrate des Mangan- und Zinksulfits. Röntgenographische, thermoanaly tische, Raman- und IR-spektroskopische Untersuchungen / Hydrates of Manganese and Zinc Sulfite. X-ray, Thermoanalytical, Raman, and IR Data

X-ray, IR and Raman data as well as thermoanalytical measurements (DTA, TG, and DTG) of several new hydrates, viz. MnSO3 · 2 ½ H2O, MnSO3 · 2 H2O, ZnSO3 · 3 H2O, β-ZnSO3 · 2 ½ H2O, and γ-ZnSO3 · 2 ½ H2O, and of previously reported hydrates in the systems MnSO3-H2O, ZnSO3-H2O, and MnSO3-ZnSO3-H2O are presented. Furthermore, the formation of mixed crystals is studied in the system MnSO3-ZnSO3-H2O. The following crystal data have been determined by single crystal measurements: MnSO3 · 2 ½ H2O (P41212) : a = b = 968.4(1), c = 1040.9(1) pm, Z = 8, MnSO3 · 2 H2O (P21/n): a = 650.9(1), b = 873.8(1), c = 774.7(1) pm, β = 99.80(1)°, Z = 4, ZnSO3 · 3 H2O (Pnma): a = 953.6(1), b = 553.0(1), c = 941.9(1) pm, Z = 4, β-ZnSO3 · 2 ½ H2O (P41212): a = b = 952.1(1), c = 1025.4(1) pm, Z = 8, γ-ZnSO3 · 2 ½ H2O (with small amount of Mn2+) (o-rh.): a = 1493(1), b = 1812(2), c = 753(1) pm, Z = 16, ZnSO3 · ½ H2O (mon.): a = 1326.7(5), b = 706.3(2), c = 834.4(1) pm, β = 117.41(3)°, Z = 8. The IR spectra show that, with the exception of γ-ZnSO3 · 2 ½ H2O, both weak and strong hydrogen bonds are present in the sulfite hydrates. Under an SO2 atmosphere the sulfite hydrates can be dehydrated without simultaneous dissociation to the oxide and sulfur dioxide. The isotypic hydrates β-MnSO3 · 3 H2O and ZnSO3 · 3 H2O (β-MnSO3 · 3 H2O type), and MnSO3 · 2 H2O and ZnSO3 · 2 H2O (ZnSeO3 · 2 H2O type) form complete mixed crystal series. Solid solutions are also formed from α-MnSO3 · 3 H2O (α-FeSO3 · 3 H2O type), γ-ZnSO3 · 2 ½ H2O, MnSO3 · 1 H2O, and ZnSO3 · ½ H2O. No incorporation of Mn or Zn could be observed for α-ZnSO3 · 2 ½ H2O and the isotype hydrates MnSO3 · 2 ½ H2O and β-ZnSO3 · 2 ½ H2O (CoSO3 ½ 2 ½ H2O type)