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New pyrazole-3,5-dicarboxylato (pzdc) chromate(III) complexes containing linear tetradentate edda (ethylenediamine-N,N′-diacetate), trdda (trimethylenediamine-N,N′-diacetate), or eddp (ethylenediamine-N,N′-dipropionate) were synthesized and characterized by elemental analyses, column chromatography, 2 H NMR, FAB mass spectra, and X-ray analyses. Crystallographic data for Na[Cr 2 (edda) 2 (µ-pzdc)]·5H 2 O (1) are monoclinic with space group P2 1 /n, a ) 11.73(1) Å, b ) 19.475(6) Å, c ) 13.229(6) Å, ) 111.99(5)°, Z ) 4, and a final R factor of 0.056 based on 4673 reflections. Na[Cr 2 (trdda) 2 (µ-pzdc)]·3H 2 O (2) crystallizes in the orthorhombic space group Fdd2, with a ) 16.576(4) Å, b ) 29.235(6) Å, c ) 12.544(5) Å, Z ) 8, and a final R factor of 0.078 based on 2456 reflections. In both complexes two Cr(III) units were bridged by a pzdc. The complex 1 and 2 has a (symcis)-(unsym-cis) edda and (unsym-cis)-(unsym-cis) trdda geometrical configuration, respectively. Unlike the edda and trdda ligands, the eddp ligand formed mononuclear pzdc complexes, which may correspond to two geometrical isomers of unsym-cis-mer-and fac-[Cr(eddp)(pzdc)] 2- (3 and 4). The differences in the formations of the pzdc Cr(III) complexes with the edda-type ligands were demonstrated to arise from the chelate ring sizes and/or the intramolecular interaction such as hydrogen bond and van der Waals contact between two Cr(III)-edda type units. The hydrogen bond between the edda moieties following stereognostic coordination brings about the novel inert unsym-cis configuration in complex 1.

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S-Bridged trinuclear complexes, [CrIII{M(aet)3}2]3+, (M = RhIII (1), IrIII (2); aet = NH2CH2CH2S−) were newly prepared by the reaction of fac(S)-[M(aet)3] with chromium(III) nitrate. They were separated and optically resolved into the ΔΔ, ΛΛ, and ΔΛ isomers. Of these isomers for 1 and 2, the crystal structures of the ΔΛ isomers (1a and 2a) were determined by an X-ray diffraction method. Each of 1a and 2a consists of two fac(S)-[M(aet)3] subunits, a central Cr atom, three nitrates, and three water molecules, [Cr{M(aet)3}2](NO3)3·3H2O, in which three metals are aligned so as to be exactly linear. The central Cr atom is situated in an octahedral environment with the CrIIIS6 chromophore, which is formed by the coordination of two terminal fac(S)-[M(aet)3] units. The other isomers for 1 and 2 were characterized by the absorption and CD spectra, the molar conductivity, and the magnetic susceptibility. Each cyclic voltammogram of ΔΛ-[Cr{M(aet)3}2]3+ in water showed a reversible redox couple (M(IV)/M(III)) and an irreversible reduction wave (Cr(III)/Cr(II)). The stabilities of the S-bridged MCrIIIM complexes are also discussed in relation to the Cr–S bond strengths.

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