298 Inorganic Chemistry, Vol. 13, No. 2,1974
F. W. Koknat and R. E. McCarley
Figure 1. The arrangement of tetramethylammonium ions between two close-packed layers of [(Nb,Cl,,)CI, J 3 - cluster anions as seen in the [ O O l ] projection. In this view the trigonal c axis is tilted a few degrees from the direction perpendicular t o the plane o f the figure. Only terminal chlorine atoms of the cluster anion are shown.
” Cl(6).3 Figure 2. The structure o f the [(Nb,Cl,,)Cl,]’-
cluster anion.
to two different Nb( 1)-Nb(2) bond distances, 2.967 and 2.972 8. The most striking deviation from strict octahedral symmetry however is a downward shift of the terminal chlorine atoms Cl(5) and Cl(6). Apparently the tetrahedral holes in this structure are somewhat small for the tetramethylammonium groups, and lateral pressure from carbon atoms C( 1) forces terminal chlorine atoms Cl(6) to leave their “ideal” positions and move downward parallel to the trigonal c axis into the octahedral holes. Terminal chlorine atoms
C1(5), in a likewise crowded situation with carbon atoms C(2), cannot move upward into the octahedral holes since they are in an eclipsed configuration with carbon atoms C(3) from the tetramethylammonium groups that occupy the octahedral holes. Instead, they move downward toward the “equator” of the cluster, thereby pressing together niobium atoms Nb( 1). As a result, niobium-terminal chlorine and niobiumniobium distances differ noticeably. They are 2.494 A for Nb(1)-Cl(5), 2.540 8 for Nb(2)-C1(6), 2.942 A for Nb(1)Nb(l), and 2.989 A for Nb(2)-Nb(2). Of particular interest in this study is the effect of oxidation on the structure of the (Nb6C118)n-anion, which can be evaluated by a comparison of bond distances and angles in the threefold negative anion of [(CH,),N], [(Nb6Cllz)Cl6] with corresponding data for the fourfold and twofold negative anions of &Nb6C11811and [(CH3)4N]2[(Nb6C112)C16]’6 as given in Table 111. Also contained in Table I11 are bond distances and angles for Nb6C11410and for (pyH)2Nb6Clls .24 A comparison of the data for [(CH3)4N]2Nb6C118and (pyH12Nb6Cl18which contain the same (Nb6Cl18)~-anion shows that the cations in these compounds apparently have some influence on bond distances and angles in the Nb6C118 complex anion. The following discussion will therefore be based on data for [(CH3)4N]2Nb6C118and [(CH3)4N]3Nb6C1~8, (24) B. Spreckelmeyer and H. G. Schnering, 2. Anovg. Allg.
Chem., 386, 2 1 ( 1 9 7 1 ) .
Polynuclear Metal Halides Table 11. InteratomicDistances (A) and Angles (deg) in [(CH 3I$) 3 [(Nb,a, X 1 6 I a 3 IntramolecularInteratomic Intramolecular Anglc:s Distances 60.2(1) Nb(l),l-Nb(l),2 2.942 (7) Nb(1),2-Nb(l),l-Nb(2),3 60.4(1) Nb(l),l-Nb(2),2 2.967(4) Nb(1),3-Nb(l),l-Nb(2),2 60.4 (2) Nb(l),l-Nb(2),3 2.972 (5) Nb(2),2-Nb(l),l-Nb(2),3 59.9 (1) Nb(2),1-Nb(2),2 2.989(7) Nb(2),2-Nb(2),1-Nb(1),3 59.7(1) Nb(l),l-Nb(2),1 4.197(3) Nb(2),3-Nb(2),1-Nb( 1),2 59.4(2) Nb(l),l-C1(1),3 2.51 (1) Nb(1),2-Nb(2),1 -Nb( 1),3 90.5(2) Nb(l),l-Cl(2),2 2.38(1) Nb(1),2-Nb(l),l-Nb(2),2 90.4(1) Nb(l),l-Cl(3),2 2.43(2) Nb( 1),3-Nb( 1),1-Nb(2),3 89.5 (1) Nb(l),l-C1(3),3 2.39(2) Nb(2),2-Nb(2),1-Nb(1),2 89.6(1) Nb(2),1-C1(1),2 2.47(1) Nb(2),3-Nb(2),1-Nb(1),3 Nb(2),1-C1(2),3 2.34(1) Cl(5),24:1(5),14(6),3 59.3(2) Nb(2),141(4),2 2.43 (1) Cl(5),3-Cl(5),1-Cl(6),2 60.8(3) Nb(2),141(4),3 2.46 (1) C1(6),2-C1(5),141(6),3 59.4 (2) 61.1(2) Nb(l),l-Cl(5),1 2.49 (1) Cl(6),2-Cl(6) J - W13 59.5 (2) Nb(2),1
