Es werden die Schwingungsfrequenzen des NH‐Ions in Erdalkaliamiden angegeben und Kraftkonstanten eines modifizierten Valenzkraftfeldes berechnet. Zwischen den Valenzkraftkonstanten für die NH‐Bindung und den Ionenradien der Kationen besteht annähernd ein linearer Zusammenhang. Hierfür wird eine physikalische Deutung gegeben.
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I has an anion dimer with 3Sax... During recent two decades, methods for the synthesis of duster compounds based on the [M3~3-X)(uz-X2)3] q (M3X~7) fragment, where X = O (/z3-position), S, Se; M = Mo, W (q = + 4), V (q = + 3), Re (q = + 5), have been developed. For a few dozens of these compounds, crystal structures were determined. Our previous analysis of intermolecular (interionic) contacts in these structures shows that almost all of them have clear-cut specific nonvalent interactions (SNI), giving rise to short contacts called specific nonvalent contacts (SNC) X...Y (where X is a chalcogen atom within the dichalcide group XZ, and Y is a halogen, chalcogen, N, etc. atom entering the counterion or the ion of the same charge) [1].In the M3X~7 cluster fragment, the X atoms of the X 2 groups are coordinated asymmetrically with respect to the M 3 plane and are inclined to it at angles of ~30~ three X atoms (below called equatorial and denoted as Xeq ) lie virtually in the plane, and the other three atoms (below called axial and denoted as Xax ) deviate from the plane by about 2/~ to the opposite side of the (P3-X) ligand. This difference between the atoms is also manifested by their participation in SNC: in almost all structures, the axial atoms are involved in so-called axial (3Xax...Y) contacts (the Y atom lies at the intersection of three X-X lines at equal distances from the three X atoms), whereas the equatorial atoms form several shortened contacts with donor atoms. In [1] it was shown that these interactions play a critical role in formation of crystal packing.In the salts of cluster ions M3XTHal ~-(M = Mo, W; X = S, Se; Hal = C1, Br), two types of interactions are realized: 1) the single CI-anion interacts with three axial sulfur atoms to form the Mo3S7C173-anion (S...C1 -3.0 .~); 2) two M3XTHal ~-anions form a centrosymmetric dimer in the crystal due to the contacts between the terminal Hal t Deceased.
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