SYNTHESIS AND CRYSTAL STRUCTURES OF [Na(CH3OH)5]2[M6Br8(OCH3)6] (M = Mo , W)
I. Bašic1, N. Brnicevic1, Z. Zhihong2 and R. E. McCarley2
1Ruder Boškovia Institute, Bijenieka
54, 10001 Zagreb, Croatia
2Ames Laboratory and
Iowa State University, Ames, Iowa, USA
Keywords: hexanuclear cluster alkoxides,
molybdenum bromo cluster, tungsten bromo cluster, crystal structures
So far there is no solved crystal
structure for the hexanuclear tungsten halide cluster alkoxide
family with [W6X8]4+ (X =
halogen) unit. The reactions of [M6Br8]4+
(M = Mo, W) with an excess of NaOCH3 in dry and inert
atmosphere resulted with crystallization of orange colored single
crystals of the composition [Na(CH3OH)5]2[M6Br8(OCH3)6],
M = Mo 1, W 2. Crystal structures of the triclinic
compounds 1 and 2 were solved and refined from
single crystal X-ray diffraction data. Both compounds crystallize
in the triclinic space group P1- (No. 2) with Z = 1 and unit cell
parameters:
1: a = 10.810(3) A, b = 12.270(2) A, c =
10.779(3) A, a = 97.31(2)°, b = 119.36(2)°, g = 95.42(2)°, R = 0.065;
2: a = 10.764(5) A, b = 10.818(5) A, c =
12.219(4) A, a = 95.21(3)°, b = 97.35(3)°, g = 119.41(3)°, R = 0.068.
Clusters 1 and 2
contain [Na(CH3OH)5]+ complex
cation and [M6Br8(OCH3)6]2-
cluster anion. An inversion center is located in the middle of
the M6 octahedra. Each anion is surrounded by six
cations being interconnected with hydrogen bonds (in the range
2.65 A
to 2.80 A) between methanol molecules from the
[Na(CH3OH)5]+ cation and oxygen
from coordinated methoxo groups of the [M6Br8(OCH3)6]2-
anion in a three-dimensional network. The system of hydrogen
bonds influences the M-O interatomic distances in the [M6Br8(OCH3)6]2-
anion. Namely, some oxygen atoms from coordinated methoxo groups
are involved in two hydrogen bonds having as the consequence the
elongation of the M-O interatomic distances [1]. Small
difference in M-M bond distances (2.629 A and 2.616 A, average) and M-Br bond distances
(2.622 A
and
2.618 A,
average) for clusters 1 and 2, respectively,
indicate the lanthanoide contraction similar to the phenomenon
already observed for CsErM6Br18 [2], [M6Br12(H2O)6][HgBr4]·12H2O
[3] and [M6Cl12(EtOH)6][(Mo6Cl8)Cl6]·6EtOH
[4],
M = Nb, Ta. The structures of 1 and 2 are closely
related to that of [Na(CH3OH)5]2[Mo6Cl8(OCH3)6]
[5]. The Na-O bond distances (average 2.32 A) are similar to those found in [Na2(CH3OH)9][Ta6Cl12(OCH3)6]·3CH3OH
(average 2.37 A) [6].