Bis[N,N-dimethyl-1-(10H-pyrido[3,2-b][1,4]benzothiazin-10-yl)propan-2-aminium] tetrakis(thiocyanato-κN)cobaltate(II)

The asymmetric unit of the title salt, (C16H20N3S)2[Co(NCS)4], comprises one monovalent isothiopendylium cation and one-half of a divalent thiocyanatocobaltate(II) anion (2 symmetry). The central thiazine ring of the cation is slightly twisted in a boat-like fashion, with r.m.s. deviations from the mean plane of 0.272 (1) and 0.2852 (8) Å for the N and S atoms. The molecular structure of the cation is stabilized by an intramolecular N—H⋯N hydrogen bond. Within the complex anion, the CoII atom is tetrahedrally surrounded by four N atoms of the thiocyanate ligands. π–π stacking, with a distance of 3.7615 (10) Å between the centroids of benzene and pyridine rings, helps to consolidate the packing.


Comment
The molecular structure of isothipendyl, C 16 H 19 N 3 S, is close to that of phenothiazines. Isothipendyl is an antihistamine used in the treatment of allergies. It was also found to be active against parasites causing filariasis (Kinnamon et al., 1994).
Photobiological properties of isothipendyl were also investigated and found to have ultraviolet B (UVB) protective activity (Moreau et al., 1995). Studies also suggest that cobalt and thiocyanates play some role in phototoxicity and in the development of conjugates for photoimmunotherapy (Scott et al., 1990;Hudson et al., 2005). These outcomes arouse our interest and we prepared the title salt [(C 16 H 20 N 3 S) 2 {Co(NCS) 4 }], (I), for structural characterisation.
In the structure of (I), the Co atom of the anion is situated on a twofold rotation axis and is coordinated by four N atoms from four thiocyanate groups in a slightly distorted tetrahedral geometry ( Fig. 1, Table 1). The bond lengths and bond angles of the cobaltate(II) anion are in good agreement with related structures (Shi et al., 2005).
Within the cation the dihedral angles between the benzene and the thiazine rings and between the pyridine and the thiazine rings are 15.73 (8)° and 14.77 (8)°, respectively. The central thiazine ring is slightly twisted as boat like. The deviation of the N and S atoms from the mean plane of the thiazine ring was found to be 0.272 (1) and 0.2852 (8) Å, respectively. The structure displays an intramolecular hydrogen bonding interaction between N3-H3A···N1 ( Fig. 2 & Table 2).

Experimental
The cobalt(II) salt was prepared by a single step method. Isothipendyl in ethanol (5 mmol) was slowly mixed with an ethanolic solution (5 mmol) of Co(SCN) 2 . 2H 2 O. The mixture was kept at room temperature for 30 min and warmed on a water bath (343-353 K) for 1 h. Green crystals suitable for X-ray diffraction were obtained by slow evaporation of the solvent (M.P. 453 K; Yield 79%).
supplementary materials sup-2 Refinement All H atoms were positioned at calculated positions with N-H = 0.91Å, C-H = 0.93 Å for aromatic H atoms, 0.97 Å for methylene H atoms and 0.96Å for methyl H atoms. H atoms were refined using a riding model with U iso (H) = 1.5U eq (C) for methyl H and U iso (H) = 1.2U eq (X) for other atoms (X = N, C). Fig. 1. The molecular structure of the title compound. Displacement ellipsoids are drawn at the 50% probability level. Symmetry code a) -x, y, -z+1/2.