Alkali metal halides tetramers

The alkali metal halides, MX, fonn solids at room temperature. The best known member of the family, NaCl, melts at 801°, the vapor pressure reaches 1 torr at 865°, and the melt boils at 1413°. The dominant species in gaseous alkali metal halides is the monomeric formula unit, MX(g), but smaller amounts of dimers (M2X2), trimers (M3X3) and tetramers (M4X4) have also been detected by mass spectroscopy. Information about the monomeric molecules obtained by spectroscopic studies at high temperatures is collected in Table 5.1 [1]. 

Table 5.2. Coordination numbers, C, Madelung constants, M, and calculated bond distance ratios, R R, for gaseous, monomeric alkali metal halides MX, gaseous square dimers M2X2, for cubic tetramers M4X4 and for MX crystals with rock-salt structures.

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