5,6-Dihydro-1,10-phenanthroline-1,10-diium μ-oxido-bis[pentafluoridotantalate(V)]

In the title compound, (C12H12N2)[Ta2F10O], the doubly protonated 5,6-dihydro-1,10-phenantroline-1,10-diium cation is located on a twofold rotation axis, whereas the isolated [Ta2OF10]2− dianion has -1 symmetry. In the so far unknown dianion, the symmetry-related TaV atoms are octahedrally coordinated by five F atoms and a bridging O atom, the latter being located on an inversion centre. The two pyridine rings in the cation make a dihedral angle of 22.8 (4)°. The cations and dianions are arranged in layers parallel to (100) and are connected through N—H⋯F and C—H⋯F hydrogen-bonding interactions into a three-dimensional structure.

In the title compound, (C 12 H 12 N 2 )[Ta 2 F 10 O], the doubly protonated 5,6-dihydro-1,10-phenantroline-1,10-diium cation is located on a twofold rotation axis, whereas the isolated [Ta 2 OF 10 ] 2À dianion has 1 symmetry. In the so far unknown dianion, the symmetry-related Ta V atoms are octahedrally coordinated by five F atoms and a bridging O atom, the latter being located on an inversion centre. The two pyridine rings in the cation make a dihedral angle of 22.8 (4) . The cations and dianions are arranged in layers parallel to (100) and are connected through N-HÁ Á ÁF and C-HÁ Á ÁF hydrogenbonding interactions into a three-dimensional structure.

Zhao-Hui Meng, Yu-Quan Feng and Xin-Feng Chen Comment
Metal oxyfluorides have received considerable attention in recent years due to their structure-related properties such as ferroelectricity, piezoelectricity and second-order nonlinear optical activity (Hagerman & Poeppelmeier, 1995;Halasyamani & Poeppelmeier, 1998;Welk et al., 2002). In this article, we report on a new oxidofluoridotantalate with composition [C 12 H 12 N 2 ][Ta 2 OF 10 ] that was obtained by means of a two-step hydrothermal method.
The title compound ( Fig. 1) contains one diprotonated 5,6-dihydro-1,10-phenantroline-1,10-diium cation (symmetry 2) and one [Ta 2 OF 10 ] 2dianion (symmetry 1). In the latter, the Ta V ion is coordinated by five fluorine atoms and one oxygen atom, forming an octahedral coordination geometry. It is noteworthy that the title compound features the first oxidofluoridotantalate with composition [Ta 2 OF 10 ] 2-. The cation is not flat, as can be expected from the 5,6-dihydro bridging sp 3 carbon atoms, with a dihedral angle of of 22.8 (4)° between the two pyridine rings. The cations and dianions are arranged in layers parallel to (100) and are connected through N-H···F and C-H···F hydrogen bonding interactions into a three-dimensional structure (Fig. 2).
It should be noted that the hydrothermal conditions make it possible that parts of the fluorine atoms are replaced by OHions. To exclude the presence of the latter, additional characterisation methods were employed (see details in the experimental part). Moreover, IR spectroscopy revealed no inclusion of OHin the compound (Fig. 3).

Refinement
The H atoms bonded to C and N were positioned geometrically and refined using a riding model, with C-H = 0.93 Å for H atoms bound to sp 2 C atoms, and 0.97 Å for H atoms bound to sp 3 C atoms, and with N-H = 0.86 Å, and with U iso (H) = 1.2 (1.5) times U eq (C), and U iso (H) = 1.2 times U eq (N), respectively. The highest and lowest remaining electron density was located 0.84 Å and 0.72 Å from atom Ta1.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq