SYNTHESIS AND CRYSTAL STRUCTURE OF [Ta6Cl12(PrCN)6][(Ta6Cl12)Cl6]·2PrCN - Compound with mixed-charge cluster units
S. Širac1, N. Brnicevic1, I. Bašic1, P. Planinia1 and R. McCarley2
1Ruder
Boškovia Institute, 10001 Zagreb, Croatia
2Ames Laboratory and Iowa State University,
Ames, Iowa, USA
Keywords: hexanuclear cluster, tantalum chloro cluster,
mixed-charge cluster, crystal structure, butyronitrile complex
The title compound has been prepared by the reaction of [Ta6Cl12(EtOH)6]Cl2 with butyronitrile molecules in the presence of limited amount of air [1]. The cluster crystallizes in the triclinic space group P1- (No. 2) with Z = 1 and the unit cell parameters: a = 12.618(8) A, b = 13.189(2) A, c = 12.216(2) A, a = 93.31(2)o, b = 94.14(3)o, g = 93.95(3)o, R = 0.0894.
Two homonuclear mixed-charge cluster units: [Ta6Cl12]2+
in the [Ta6Cl12(PrCN)6]2+
cation and [Ta6Cl12]4+ in the
[(Ta6Cl12)Cl6]2-
anion are the main structural features of [Ta6Cl12(PrCN)6][(Ta6Cl12)Cl6]·2PrCN
cluster. Based on this phenomenon this compound represents the
first example of coexistence of differently charged [M6X12]n+
(n = 2, 4) units in the solid state chemistry of the hexanuclear
halide clusters of niobium and tantalum. The average Ta-Ta bond
distance in [Ta6Cl12(PrCN)6]2+
(2.868 A) cluster cation is considerably shorter than in [(Ta6Cl12)Cl6]2-
(2.973 A) cluster anion. The former value is closely related to
those found in [Ta6Cl12(EtOH)6][(Mo6Cl8)Cl6]·6EtOH
(2.872 A) [2], or trans-[(Ta6Cl12)Cl2(PEt3)4]·CHCl3
(2.901 A) [3] with [Ta6Cl12]2+
unit, while the latter is related to the value of 2.962 A found
in the cluster H2[(Ta6Cl12)Cl6]·6H2O
containing [Ta6Cl12]4+ unit
[4]. Consequently, the mean value of the Ta-Cl bond
distance in [Ta6Cl12(PrCN)6]2+
cation of 2.459 A is longer than the corresponding mean value of
bond distance (2.425 A) in [(Ta6Cl12)Cl6]2-
anion. The other interatomic distances, angles and some
properties of the cluster will be discussed in terms of the
simultaneous presence of mixed-charge cluster units.