Gibt es AB_n‐Moleküle mit anomaler Struktur? v₃ von TiF₄ und TiF₃ sowie ihre Bedeutung für die Struktur von TiF₂

Abstract

Es gibt keinen Hinweis darauf, daß auch nur ein Dihalogenid eines Elementes der ersten Übergangsreihe nichtlinear wäre. Dieser Schluß wird aus der Tatsache gezogen, daß früher „nichtlinearem”︁ TiF2 zugeordnete IR‐Banden definitiv von trigonal‐planarem TiF3 herrühren. Die früheren Matrixisolationsstudien, aus denen auf ein 120°‐TiF2 geschlossen worden war, galten als Eckpfeiler der Theorie anomaler MF2‐Moleküle.

TiF2: Linear or Bent?

“…Therefore, the bands at about 740 cm À1 originally assigned to TiF 2 were considered to be almost certainly due to TiF 3 . [4] Hence, the reported 1308 bond angle of TiF 2 is actually that of 1208 in TiF 3, and analysis of the Ti isotope pattern confirmed this. [4] Although not explicitly stated in the previous paper, [4] Figure 1 gives an estimate of about 670 cm À1 for the n 3 mode of linear TiF 2 .…”

“…[4] Hence, the reported 1308 bond angle of TiF 2 is actually that of 1208 in TiF 3, and analysis of the Ti isotope pattern confirmed this. [4] Although not explicitly stated in the previous paper, [4] Figure 1 gives an estimate of about 670 cm À1 for the n 3 mode of linear TiF 2 . The only other experimental report on molecular TiF 2 is a matrix ESR report published in 1977 in which the data were reported to be consistent with a bent triplet structure; however, the signals were weak and broad with no observable Ti or F hyperfine couplings.…”

“…The Ti data point marked + is for the original n 3 value of TiF 2 , assuming linearity; it moves further away from the line if the molecule is bent. Given the good fit to the other elements, this was a good indication that the IR data supposedly for TiF 2 was erroneous, probably owing to the complexity of the titanium fluoride vapor-phase system and high volatility of TiF 4 . The IR bands originally assigned to TiF 3 at about 790 cm À1 were reassigned to TiF 4 on the basis of gas-phase [6] and matrix data [4] obtained from the evaporation of TiF 4 .…”

“…[8] The w 3 value was 705 cm À1 for the 3 AE g À state and 695 cm À1 for the 3 D g state. The better agreement between calculated and experimental vibrational data for TiCl 2 than TiF 2 was commented on, [8] but the unreliability [4] of the published TiF 2 experimental data [3] was not noted. Therefore, as highlighted by Beattie, [1] TiF 2 is the key molecule in understanding the geometric and electronic structures of the first-row transition-metal dihalides, and the aim of this investigation was to obtain the first reliable experimental values of the n 3 vibrational mode of molecular In these spectra the titanium isotope pattern (central intense peak with a pair of weaker bands of similar intensity on each side) on bands A, B, and C is masked by site effects, and the presence of these is not surprising as they have been observed previously for TiF 4 , [3,4] TiF 3 , [7] TiCl 2 , [9] and VF 3 [10] in both Ar and Ne matrices.…”

“…An early (1969) matrix isolation IR study of the vaporization of TiF 3 /Ti mixtures indicated a bond angle of about 1308 for TiF 2 . [3] However, in 1989 Beattie et al showed that this value was unreliable [4] by using a plot of the simple valence force field (SVFF) force constants (f r Àf rr ) from the n 3 values of MF 2 versus those of MCl 2 , as indicated in Figure 1 (this is essentially identical to Figure 1 in reference [4] except that the data is limited to linear species, and to those which are considered reliable [1,2,5] ). The straight line is a fit to the solid circles of the Cr, Mn, Fe, Co, Ni, and Zn data.…”