The crystal structure of the Cu2Br2(PPh3)3·1.5C6H6 complex has been determined by three dimensional X-ray analysis. The crystals are monoclinic, and the space group is P21/c, with unit-cell parameters of a=14.122 (3), b=19.573 (4), c=25.985 (7) Å, β=128.99 (1)°, and Z=4. In the Cu2Br2(PPh3)3 molecule, one copper atom is three-coordinate, and the other, four-coordinate.
The crystal structures of two diastereoisomeric salts, (+)589-trans(O)-[Co(gly)2en]H-d-tart·3H2O (1) and (−)589-trans(O)-[Co(gly)2en]H-d-tart·H2O (2), have been determined by three-dimensional X-ray analysis. The less-soluble salt (1) is monoclinic; space group, P21; Z=2, a=12.351(5), b=7.671(3), c=10.189(5) Å, and β=110.71(4)° (R=0.043, 2241 reflections). The more-soluble salt (2) is monoclinic; space group, P21; Z=2, a=11.135(4), b=10.037(3), c=7.716(3) Å, and β=98.61(3)° (R=0.064, 2076 reflections). A comparison of the (unit cell volume)/Z values of the two crystals shows that the crystal 1 is more tightly packed than the crystal 2. In both salts, adjacent complex cations form quite similar chain structures linked by (N–H…O) hydrogen bonds. The H-d-tart anions in 1 take a characteristic “head-to-tail” arrangement of an infinite chain of {H-d-tart}∞ along the b-axis. In contrast, this arrangement is not found in the more-soluble salt (2). From these findings, it can be considered that the discrimination of optical isomers in the H-d-tart system originates from the spiral chain structure of {H-d-tart}∞. The absolute configurations of (+)589- and (−)589-trans(O)-[Co(gly)2en]+ are determined to be Λ-δ and Λ-λ respectively. TG and DSC measurements were carried out for both salts, and the ΔH values of the dehydration step were estimated to be 64.4 kJ mol−1 for 1 and 73.0 kJ mol−1 for 2.
It has been found that, in the crystal of Li(+)589-[Cr(en)3] (d-tart)2·3H2O, the complex cation Λ-δδδ-[Cr(en)3]3+ is sandwiched between two crystallographically different d-tartrate anions. The centers of the both anions are located on the threefold axis of the octahedral complex cation and the characteristic local “[Cr(en)3] (d-tart)2” block is formed. The structural feature of this local block bears a close resemblance to that found in (+)589-[Co(en)3] Br·d-tart·5H2O.
The single crystals of the more-soluble diastereoisomeric salt including the hydrogen-d-tartrate anion as a resolving agent, (−)589-[Co(ox)en2]H-d-tart·2H2O, have been newly obtained, and the crystal structure has been determined by three-dimensional X-ray analysis. The crystals are orthorhombic, space group P21212, Z=4, a=16.583(5), b=14.186(5), and c=7.403(2) Å. The structure was solved by the heavy-atom method and refined by the block-diagonal least-squares method to a conventional R-value of 0.044 for the 1907 independent reflections. One of the two ethylenediamine rings is of the ob form. The other ring has a conformational disorder, the proportion of the ob to the lel form being 50:50. The absolute configuration of the complex cation is denoted as Δ[(50%-δ, 50%-λ)δ]. The framework of the crystal structure is built up of a stack of complex cations and H-d-tart anions along the c-axis in a “head-to-tail” arrangement. The shortest interatomic distance between the H-d-tart anions is 2.473 Å(O–H···O), while that between the complex cations is 2.995 Å (N–H···O). A comparison of the crystal structure of the more-soluble diastereoisomer with that of the lesssoluble one revealed that the {H-d-tart}∞ chain is structurally different from that in the latter; the chain is spiral in the latter, but not in the former. The structural feature in the {H-d-tart}∞ chain is considered to play an important role in the discrimination of the chirality of the [Co(ox)en2]+ cation. The conformational disorder is discussed in connection with the dehydration of crystals.
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