Effect of outer sphere anions on the structure and color of nitrosylpentaamminechromium complex |
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Authors: | Haruo AkashiMasayasu Mori Takashi Shibahara |
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Institution: | a Research Institute of Natural Sciences, Okayama University of Science, Ridai-cho, Okayama 700-0005, Japan b Department of Chemistry, Okayama University of Science, 1-1 Ridai-cho, Okayama 700-0005, Japan c Department of Chemistry, Osaka City University, Sugimoto 558-8585, Japan |
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Abstract: | Three kinds of crystalline compounds containing the nitrosylpentaamminechromium complexes Cr(NO)(NH3)5]2+(A) were obtained: chloride ACl2 (red-orange), chloride perchlorate ACl(ClO4) (brown), and perchlorate A(ClO4)2 (green). The cause of the color change of the complex A with the change of outer sphere anions was sought using X-ray structural data of ACl2, ACl(ClO4), and A(ClO4)2. Crystal data: ACl2, orthorhombic, space group Cmcm, a=10.0236 (9) Å, b=9.098 (3) Å, c=10.357(1) Å, V=944.5 (5) Å3, Z=4; ACl(ClO4), tetragonal, space group P4/nmm, a=7.6986 (8) Å, c=9.9566(8) Å, V=590.1 (1) Å3,Z=2; A(ClO4)2, orthorhombic, space group Pnma, a=15.760 (2) Å, b=11.480(2) Å, c=7.920 (2) Å, V=1432.9 (4) Å3, Z=4. The complex cation in ACl2 has a distorted octahedral structure with a linear CrNO moiety. The short CrN (nitrosyl) distance of 1.692 (7) Å indicates the presence of multiple bonding between the chromium atom and the nitrogen atom in the nitrosyl group. The interatomic distances and angles within the complex cations hardly change with the change of the counter anions, while the distances between the complex cations in each crystal increase in the order ACl2<ACl(ClO4)<A(ClO4)2. The bulky perchlorate anions seems to separate the complex cations, while smaller chloride anions are not large enough to separate them. The distance (3.213(5) Å) between O(NO) and N(NH3 in the adjacent complex cation) is rather short in the crystal of ACl2, and there are six hydrogen bonds, where the NO group is surrounded by four NH3 ligands. The distance (4.002(5) Å) between O(NO) and N(NH3) is much longer in the crystal of A(ClO4)2, indicating the presence of no hydrogen bonding. In the crystal of ACl(ClO4) the distance (3.452(4) Å) between O(NO) and N(NH3) is in between those of ACl2 and A(ClO4)2. The presence of hydrogen bonding between O(NO) and N(NH3 in the adjacent complex cation) seems to cause the color change with the change of outer sphere anions. |
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Keywords: | Nitrosyl complexes Chromium Ammine X-ray structures Hydrogen bonding Outer sphere anion |
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