ICYS, National Institute for Materials Science^* Institute of Chemistry, Faculty of Science, Sts. Cyril and Methodius University, Skopje, Macedonia^** X-ray Physics Laboratory, Quantum Beam Center, National Institute for Materials Science, Tsukuba, Ibaraki, Japan^***
○Pance Naumov^* Gligor Jovanovski^** Kenji Sakurai^***

The N-saccharinate ligand of tetrakis(imidazole)tetrakis(saccharinato)dicopper(II) (1) features an acutely short carbonyl bond [1.103(6) Å] [1], which is incompatible with the bridging carbonyl group, other saccharinates [2], the analogous cadmium compound [3], infrared [5] and Raman data [6], bond-order and theoretical calculations [2], and is beyond values expected for electronically-induced effects. Structure re-determination [7] at 298 K showed that the anomaly is due to a minor (1/8) superimposed pseudo-mirror component.

The diffraction and thermal data [8] show that a small portion of the axial N-saccharinate ligands in single crystals of 1 flip around the coordination bond, changing the ratio of the two overlapped mirror-plane isomers.

References:
(1) Liu, S.-X.; Huang, J.-L.; Li, J.-M. Acta Cryst. 1991, C47, 41.
(2) Naumov, P.; Jovanovski, G. Struct. Chem. 2000, 11, 19.
(3) Li, Y.; Ke, Y.; Wang, Q.; Wu., X. Cryst. Res. Technol. 1997, 32, 481.
(4) Naumov, P.; Jovanovski, G. Acta Chim. Slov. 1999, 46, 389.
(5) Naumov, P.; Jovanovski, G. Spectrosc. Lett. 1999, 32, 237.
(6) Naumov, P.; Jovanovski, J. Raman Spectrosc. 2000, 31, 475.
(7) Naumov, P.; Jovanovski, G.; Hu, S.-Z.; Suh, I.-H.; Abdul Razak, I.; Chantrapromma, S.; Fun, H.-K.; Ng, S.-W. Acta Cryst. 2001, C57, 1016.
(8) P. Naumov, G. Jovanovski, K. Sakurai, Cryst. Growth Des. 2006, 6, 815.