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Abstract:
K2W6Br14 (I), Rb2W6Br14 (II), and Cs2W6Br14 (III) were formed by
reactions of W6Br12 With the corresponding alkali metal bromides in
evacuated silica tubes with a temperature gradient of 925 K/915 K. (I)
crystallizes in the cubic space group Pn(3) over bar (no. 201), a =
13.808 Angstrom, Z = 4, cP88. (II) crystallizes in the monoclinic space
group C2/c (no. 15), a = 20.301 Angstrom, b = 15.396 Angstrom, c = 9.720
Angstrom, beta = 115.69 degrees, Z = 4, mC88. (III) crystallizes in the
trigonal space group <P(3)over bar>1c (no. 163), a = 10.180 Angstrom, c
= 15.125 Angstrom; Z = 2, hP44. The crystal structures are composed of
the isolated [(W6Br8i)Br-6(a)](2-) cluster anions and the alkali metal
cations ((d) over bar(W-W) = 2.635(2) Angstrom, (d) over bar(W-Br-i) =
2.624(4) Angstrom, (d) over bar(W-Br-a) = 2.595(4) Angstrom).