SYNTHESES, STRUCTURES AND MAGNETIC-PROPERTIES OF FLUORO-BRIDGED DINUCLEAR AND TETRANUCLEAR CHROMIUM(III) COMPLEXES WITH TETRAHYDROSALEN ANDSUBSTITUTED TETRAHYDROSALEN DERIVATIVES AS LIGANDS - CRYSTAL-STRUCTURE OF AN ETHOXO-FLUORO-BRIDGED DICHROMIUM(III) COMPLEX AND A TETRAFLUORO-BRIDGED TETRACHROMIUM(III) COMPLEX

A series of novel fluoro-bridged di- and tetranuclear chromium(III) co mplexes have been synthesized by the reaction of trans-[Cr(py)(4)F-2]C lO4 in organic solvents with tetrahydrosalen and substituted tetrahydr osalen 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 an d the syntheses of the new tetrahydrogenated substituted derivatives o f H-2[H-4]salen: H(2)L(3), H(2)L(4), H(2)L(5) and H(2)L(6) and the par ent diimines are given in the present study )L(1)=N,N'-bis(2-hydroxybe nzyl)-1,2-ethanediamine, H(2)L(2)= -butyl-2-hydroxy-5-methylbenzyl)-1, 2-ethanediamine -hydroxybenzyl)-trans-(S,S)-1,2-cyclohexanediamne, '-b is(2-hydroxybenzyl)-cis-1,2-cyclohexanediamine, 5)=N,N'-bis(3-tert-but yl-2-hydroxy-5-methylbenzyl) -trans-(S,S)-1,2-cyclohexanediamine, drox y-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]C lO4 and L in 2-methoxyethanol. The complex [(CrL(5))(2)(F)(CH3CH2O)].H 2O was obtained similarly using ethanol as solvent. The crystal struct ures of two of these complexes have been solved: [(CrL(5))(2)(F)(CH3CH 2O].H2O and [CrL(1)F](4). For [(CrL(5))(2)(F)(CH3CH2O)].H2O the crysta l 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 u nit cell is 3261.93(65) Angstrom(3). The space group is C2. The refine ment of 353 variables includes 2585 of the 3620 independent reflection s. The final residual is 5.03%. The dinuclear molecule consists of two slightly distorted octahedrally cis-coordinated chromium(III) atoms b ound together by a fluoride bridge and an ethoxo bridge. The Cr-F-Cr a ngle is 103.9 degrees and the Cr-O-Cr angle is 101.3 degrees. The corr esponding Cr-F and Cr-O distances are 1.975 and 2.009 Angstrom, respec tively. The molecule is optically active, and it is shown that the abs olute 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 const ants 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 4 289 independent reflections. The final residual is 6.59%. The tetranuc lear molecule consists of a Cr4F4 ring in which the chromium(III) atom s are linked by fluoride bridges, which have Cr-F-Cr angles of 148.0 a nd 150.5 degrees and Cr-F distances of 1.925-1.945 Angstrom. The coord ination geometry around each chromium(III) atom is a slightly distorte d octahedron with cis configuration and the chelate is alternating Del ta and Lambda, so the molecule may be described (ignoring lattice indu ced 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 spec ies. The susceptibility data for the complex [(CrL(5))(2)(F)(C2H5O)] a re 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 s usceptibilities of [CrL(1)F](4) and [CrL(3)F](4) (measured in the temp erature range 3-400 K) are very similar and show the expected behaviou r characteristic for weakly antiferromagnetically coupled tetranuclear chromium(III) complexes.