Structural and spectroscopic properties of trans-difluoro(1,4,8,12-tetraazacyclopentadecane)chromium(III) perchlorate hydrate.

The structure of [CrF 2 ([15]aneN 4 )]ClO 4 ·H 2 O ([15]aneN 4  = 1,4,8,12-tetraazacyclopentadecane) has been determined by a single-crystal X-ray diffraction study at 173 K. The complex crystallizes in the space group P 1 − of the triclinic system with two mononuclear formula units in a cell of dimensions a  = 9.6117(7) A, b  = 10.2882(7) A, c  = 11.0001(7) A and α  = 99.7570(10)°, β  = 105.6080(10)° and γ  = 113.7130(10)°. The complex cation unit has its central Cr atom in an octahedral coordination with four nitrogen atoms and two fluorine atoms in a trans position. Three six-membered and one five-membered chelate rings of the [15]aneN 4 ligand are in a chair–twist(skew)–chair– gauche conformation sequence. The gauche five-membered ring is disordered with the twist six-membered ring opposite. The four H atoms in the chiral N atoms have the trans- II (CTCg) type configuration. The mean Cr N and Cr F bonds are 2.095(2) and 1.8752(13) A, respectively. The IR and visible spectral properties are consistent with the result of X-ray crystallography. The resolved band maxima of the electronic d–d spectrum are fitted with secular determinant for quartet state energy of d 3 configuration in tetragonal field including configurational but neglecting spin-orbit coupling. It is confirmed that the fluoride has strong σ- and π-donor properties toward the chromium(III) ion and the nitrogen atoms of the [15]aneN 4 ligand also have a strong σ-donor character.