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

The structure of [CrF2([15]aneN4)]ClO4·H2O ([15]aneN4 = 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 P1− of the triclinic system with two mononuclear formula units in a cell of dimensions a = 9.6117(7) Å, b = 10.2882(7) Å, c = 11.0001(7) Å 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]aneN4 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 CrN and CrF bonds are 2.095(2) and 1.8752(13) Å, 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 d3 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]aneN4 ligand also have a strong σ-donor character.