Crystal structure of 1-ethyl-2-(1-ethyl-H-quinoline-2-ylidenmethylene)- quinolinium nitrate monohydrate, (C23H25N2)NO3 · H2O

Abstract

Source of materialThe title compound was prepared by adding an equimolar quantity of ethylammonium nitrate to a hot aqueous solution of pseudoisocyanine chloride (approx. 1 wt.-%). After several months at room temperature, crystals of the title compound precipitated. DiscussionThe molecular geometry of the pseudoisocyanine (PIC) cation in the discussed pseudoisocyanine nitrate monohydrate is similar to the geometries of the PIC cations in the known salts PIC chloride monohydrate [1], PIC bromide [2], and PIC iodide [3], As in PIC halides, the PIC cations in the nitrate crystal are arranged in a threadlike formation. A one-dimensional brick stone work arrangement is observed in PIC iodide in such a manner that the ring systems are stacked face-to-face [3]. The structure is nearly the same assumed to be present in aqueous solutions of PIC salts and is referred to as a J-aggregate [4-6], In contrast, in the described PIC nitrate the cations are joined in an alternating fashion. Every other ring system is stacked face-to-face to its neighbour as mentioned above and for the remaining connections the quinoline rings are shifted, so that they overlap only edge-to-edge. A similar structure with alternating connections but partially overlapping ring systems is observed in PIC chloride [7] and PIC bromide [2]. Additionally, specular reflectance spectroscopic measurements on the PIC nitrate crystal and ab-initio calculations for the PIC cation were performed. The results will be published elsewhere together with a detailed discussion focusing on the structure of the J-aggregates. Programs: