Vibrational spectroscopy of the borate mineral henmilite Ca₂Cu[B(OH)₄]₂(OH)₄.
Henmilite is a triclinic mineral with the crystal structure consisting of isolated B(OH)(4) tetrahedra, planar Cu(OH)(4) groups and Ca(OH)(3) polyhedra. The structure can also be viewed as having dimers of Ca polyhedra connected to each other through 2B(OH) tetrahedra to form chains parallel to the C axis. The structure of the mineral has been assessed by the combination of Raman and infrared spectra. Raman bands at 902, 922, 951, and 984 cm(-1) and infrared bands at 912, 955 and 998 cm(-1) are assigned to stretching vibrations of tetragonal boron. The Raman band at 758 cm(-1) is assigned to the symmetric stretching mode of tetrahedral boron. The series of bands in the 400-600 cm(-1) region are due to the out-of-plane bending modes of tetrahedral boron. Two very sharp Raman bands are observed at 3559 and 3609 cm(-1). Two infrared bands are found at 3558 and 3607 cm(-1). These bands are assigned to the OH stretching vibrations of the OH units in henmilite. A series of Raman bands are observed at 3195, 3269, 3328, 3396, 3424 and 3501 cm(-1) are assigned to water stretching modes. Infrared spectroscopy also identified water and OH units in the henmilite structure. It is proposed that water is involved in the structure of henmilite. Hydrogen bond distances based upon the OH stretching vibrations using a Libowitzky equation were calculated. The number and variation of water hydrogen bond distances are important for the stability off the mineral.
Stretching frequency versus bond distance correlation of OD(H)⋯Y (Y N, O, S, Se, Cl, Br, I) hydrogen bonds in solid hydrates
From a compilation of spectroscopic and structural data of solid hydrates 61 different compounds containing more than 250 OD(H)⋯Y groups have been selected, for which uncoupled OD stretching frequencies, hydrogen bond distances and assignments of sufficient reliability and accuracy are available. ν(OD) versus R(O⋯Y) and R(H⋯Y) diagrams and calculated correlation curves are presented for Y  N, O, S, Se, Cl, Br, I. Depending on the scatter of points and the number of data included in the plots the predictive value and the statistical significance varies from very high for O, S and Cl acceptors down to rather poor for Br and I acceptors. At equal bond distances the frequencies may differ by up to about 150 cm−1 depending on the specific chemical nature of the proton acceptors included in a plot, while the influence of different cation—water contacts is less significant and distinct. Anion effects play, therefore, a dominant role in producing large scatters, while action effects and experimental inaccuracies are of minor importance. Furthermore it is shown, that the relation between ν(OD) and ν(OH) frequencies is almost perfect and the frequency—distance correlations involving ν(OD) are also representative without serious restrictions for corresponding correlations involving ν(OH).
Police and Political Violence in the 1960s and 1970s: Germany and Italy in a Comparative Perspective
Notwithstanding the significant differences between the German and Italian police models (federal and civil vs. centralised and militarised), in both countries the confrontation with the protest movements of the 1960s and 1970s had a profound impact on police conceptions and public order strategies. Police forces in some German federal states (West Berlin) followed a hard line until the late 1960s, while in others (Munich, Hamburg) reforms to the Weimar-centred police intervention tactics took place beginning in the early to mid-1960s. In Italy, traditional police conceptions and strategies remained largely unchanged and re-emerged in 1968. Here, a movement from within the police led to the demilitarisation and unionisation of the state police in 1981. In both countries, fighting left-wing terrorism in the 1970s stimulated technical modernisation and enhanced the centralisation of the police. In critical response to police tactics, in the late 1970s Germany police matters were increasingly perceived as a concern not only of the state but of civil society—even if policing remained a highly contested terrain. In Italy, such matters largely remained state concerns in which only politicians and internal security specialists were entitled to intervene.