SYNTHESES, STRUCTURES AND MAGNETIC-PROPERTIES OF FLUORO-BRIDGED DINUCLEAR AND TETRANUCLEAR CHROMIUM(III) COMPLEXES WITH TETRAHYDROSALEN AND SUBSTITUTED TETRAHYDROSALEN DERIVATIVES AS LIGANDS - CRYSTAL-STRUCTURE OF AN ETHOXO-FLUORO-BRIDGED DICHROMIUM(III) COMPLEX AND A TETRAFLUORO-BRIDGED TETRACHROMIUM(III) COMPLEX
Bottcher, A; Elias, H; Glerup, J; Neuburger, M; Olsen, CE; Paulus, H; Springborg, J; Zehnder, M
A series of novel fluoro-bridged di- and tetranuclear chromium(III) complexes have been synthesized by the reaction of trans-[Cr(py)(4)F-2]ClO4 in organic solvents with tetrahydrosalen and substituted tetrahydrosalen derivatives L(1)-L(6) (L(i) denotes divalent anions of H(2)L(i)).
The ligands H(2)L(1) and H(2)L(2) have been described previously and the syntheses of the new tetrahydrogenated substituted derivatives of H-2[H-4]salen: H(2)L(3), H(2)L(4), H(2)L(5) and H(2)L(6) and the parent diimines are given in the present study (H(2)L(1)=N,N'-bis(2-hydroxybenzyl)-1,2-ethanediamine, H(2)L(2)= N,N'-bis(3-tert-butyl-2-hydroxy-5-methylbenzyl)-1,2-ethanediamine H(2)L(3)=N,N'-bis(2-hydroxybenzyl)-trans-(S,S)-1,2-cyclohexanediamne, H(2)L(4)=N,N'-bis(2-hydroxybenzyl)-cis-1,2-cyclohexanediamine, H(2)L(5)=N,N'-bis(3-tert-butyl-2-hydroxy-5-methylbenzyl) -trans-(S,S)-1,2-cyclohexanediamine, H(2)L(6)=N,N'-bis(3-tert-butyl-2-hydroxy-5-methylbenzyl)-cis-1,2-cyclohexanediamine).
Four new fluoro-bridged complexes with the stoichiometric formulae [CrLF](q) (L=L(1), L(2), L(3) and L(6)) were obtained from the reaction of trans-[Cr(py)(4)F-2]ClO4 and L in 2-methoxyethanol. The complex [(CrL(5))(2)(F)(CH3CH2O)].H2O was obtained similarly using ethanol as solvent. The crystal structures of two of these complexes have been solved: [(CrL(5))(2)(F)(CH3CH2O].H2O and [CrL(1)F](4). For [(CrL(5))(2)(F)(CH3CH2O)].H2O the crystal system is monoclinic, the lattice constants are a=25.274(2), b=9.009(1), c=18.182(2) Angstrom, beta=128.024(9)degrees, the volume of the unit cell is 3261.93(65) Angstrom(3). The space group is C2. The refinement of 353 variables includes 2585 of the 3620 independent reflections. The final residual is 5.03%.
The dinuclear molecule consists of two slightly distorted octahedrally cis-coordinated chromium(III) atoms bound together by a fluoride bridge and an ethoxo bridge. The Cr-F-Cr angle is 103.9 degrees and the Cr-O-Cr angle is 101.3 degrees. The corresponding Cr-F and Cr-O distances are 1.975 and 2.009 Angstrom, respectively. The molecule is optically active, and it is shown that the absolute configuration of the dinuclear molecule is Delta(S,S),Delta(S,S), where Delta refers to the two chiral centers of the cyclohexane ring.
For [CrL(1)F](4) the crystal system is monoclinic, the lattice constants are a=18.292(5), b=18.599(5), c=17.974(5) Angstrom, beta=95.34(1)degrees, the volume of the unit cell is 6088.36 Angstrom(3). The space group is C2/c. The refinement of 397 variables includes 3979 of the 4289 independent reflections. The final residual is 6.59%. The tetranuclear molecule consists of a Cr4F4 ring in which the chromium(III) atoms are linked by fluoride bridges, which have Cr-F-Cr angles of 148.0 and 150.5 degrees and Cr-F distances of 1.925-1.945 Angstrom. The coordination geometry around each chromium(III) atom is a slightly distorted octahedron with cis configuration and the chelate is alternating Delta and Lambda, so the molecule may be described (ignoring lattice induced distortions) as a mesod-Delta,Lambda,Delta,Lambda isomer.
From the magnetic susceptibility of these compounds it is concluded that they are weakly coupled antiferromagnetic or ferromagnetic polynuclear species. The susceptibility data for the complex [(CrL(5))(2)(F)(C2H5O)] are indicative of a weak antiferromagnetic coupling. The susceptibility data for the complexes [CrL(2)F](2) and [CrL(6)F](2) are very similar and suggest that they are weakly ferromagnetically coupled, which is rather unusual for polynuclear chromium(III) complexes. The magnetic susceptibilities of [CrL(1)F](4) and [CrL(3)F](4) (measured in the temperature range 3-400 K) are very similar and show the expected behaviour characteristic for weakly antiferromagnetically coupled tetranuclear chromium(III) complexes.