Crystal structure of the co-crystal 4-[(4-carboxyphenyl)disulfanyl]benzoic acid–(1E,4E)-1-N,4-N-bis(pyridin-4-ylmethylidene)cyclohexane-1,4-diamine (1/1), C14H10O4S2⋅C18H20N4

Abstract C32H30N4O4S2, monoclinic, I2/a (no. 15), a = 21.2034(7) Å, b = 5.0614(2) Å, c = 27.5987(12) Å, β = 105.991(4)°, V = 2847.3(2) Å3, Z = 4, Rgt(F) = 0.0431, wRref(F2) = 0.1246, T = 100(2) K.


Experimental details
The C-bound H atoms were geometrically placed (C-H = 0.95-0.99Å) and refined as riding with U iso (H) = 1.2Ueq(C).
The O-bound H atoms were located in difference Fourier maps but were refined with a distance restraint of O-H = 0.84 ± 0.01 Å, and with U iso (H) set to 1.5Ueq(O).

Comment
The isolation and crystallographic characterization of the title co-crystal is a rare example formed by one of the isomeric Schiff bases, N,N′-bis((pyridinen-yl)methylene)cyclohexane-1,4-diamine, for n = 2, 3 and 4 [5].The co-crystal co-former is disulfide 4-[(4carboxyphenyl)disulfanyl]benzoic acid (4-DTBA), whose crystal structure has been reported in the literature [6].The observation of n-DTBA, or its derived di-anion, arises from the oxidation of the n-mercaptobenzene, for n = 2, 3 and 4, starting material, as has been commented upon previously [7][8][9]; the species with a single sulfur bridge has also been found [10].Up to the present time, a characteristic of the aforementioned Schiff bases is their breakdown during co-crystallization [11][12][13][14].Often, this results in isolation   2) Å] confirm the presence of the acid.The carboxyl group is co-planar with the phenyl ring to which it is attached, as seen in the dihedral angle between the two planes of 1.38(8)°.The characteristic orthogonal relationship between the phenyl rings is evidenced by the dihedral angle of 88.41(41)°between them, giving rise to a twisted, U-shaped molecule.The Schiff base is disposed about a center of inversion, as found in the free Schiff base [5].However, a difference between the molecules is apparent in that in the free form [5], the C=C(H)C5H4N residue is almost orthogonal to the best plane through the cyclohexyl ring (which adopts a chair conformation in both structures) as seen in the dihedral angle of 86.01( 5)°.This compares with the comparable angle in the title co-crystal of 38.93(3)°which arises from a twist about the C10-C13 bond, with the C9-C10-C13-N2 torsion angle being −24.0(3)°.
The key hydrogen bonding interactions in the crystal are of the type hydroxy Given the nature of weak interactions sustaining the supramolecular chains into a three-dimensional architecture, the Hirshfeld surfaces as well as the full and delineated twodimensional fingerprint plots were calculated for the individual (symmetry expanded) co-crystal co-formers, using literature procedures [15] and Crystal Explorer 17 [16], in order to determine the most important contacts in the molecular packing.

Table 1 :
Data collection and handling.