Complex formation of N-oxides of pyridine, 2-and 3-picolines, 4-nitropyridine, and 2,6-lutidine with iodine in benzene solutions and binary solid mixtures gives rise to equimolar complexes. In the solid phase, 1 : 2 and 2 : 1 complexes are also formed. Most solid complexes are polymorphous, and the enthalpies of intermolecular bonds in different crystal modifications are different. In solutions, [external] complexes pass into more stable [internal] complexes. The formation enthalpies of external and internal complexes with 2,6-lutidine N-oxides differ two times. Exposure of solid complexes to sun or UV light endows them with several types of coloration centers.N-Oxides of pyridine bases (B) and their complexes are active plant growth stimulators [1]. Enhanced biologic activity is characteristic of complexes containing microelements required for plant nutrition. In has been repeatedly argued in the literature for the expediency and priority of extensive research into the properties of such complexes, as providing insight into the mechanism of their effect on plants and aiding in design of more active biostimulators [2,3].In the present work we made use of IR and electronic spectroscopy, dielcometry, and calorimetry to study the complex formation of iodine and N-oxides of a series of pyridine bases, such as (PyO), 2-and 3-picolines (2-PicO, 3-PicO), 4-nitropyridine (4-NO 2 PyO), and 2,6-lutidine (LutO), and the structure of the resulting complexes. Most emphasis we traditionally put on the complex of iodine with LutO, which is known to possess unique properties [1].Iodine of [Sublimed] grade was repeatedly sublimed in a vacuum, 4-nitropyridine N-oxide was recrystallized from benzene, and the other N-oxides were distilled in a vacuum. The complexes were synthesized by fusing the components in stoichiometric amounts or by mixing benzene or acetone solutions containing stroichiometric amounts of the components. The composition of complexes that precipitated from solutions on evaporation were controlled by elemental analysis. Equimolar complexes were not hygroscopic, their compositions with NaCl and KBr were pressed under pressure at 4000 atm, and no signs of halogen exchange between complexes and matrix were observed. The spectra and electrical characteristics were measures as described above [4], and calorimetric experiments, as described in [5]. Visual analysis of phase equilibria was performed in polarized and nonpolarized light using an SK-14 microscope (Poland).The table lists certain characteristics of complexes I3V, and Fig. 1 depicts dielcometric data (e) for the 2,6-LutO3I 2 3C 6 H 6 ternary system. The extreme points on the composition axis relate to the initial concentrations of base and acid in benzene. The corresponding solutions were mixed in volume ratios, and the volume fraction (g) of one of the solutions varied from 0 to 100%. As seen from the table, in the working concentration range, weakly dissociated equimolar complexes V are formed. Unlike the Py3ICl3PhNO 2 system [1], little B . 2I 2 , as we...
