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The comprehensive description of the crystal structure of a novel 1:1 cocrystal of 3,4,5-trifluorophenylboronic acid with urea, CHBFO·CHNO, is presented. Both components are good candidates for crystal engineering as they can create a variety of supramolecular synthons. The preference for the formation of different hetrosynthons is verified based on theoretical calculations. The syn-anti conformation of boronic acid has been found to be the most favourable in the formation of intermolecular interactions with urea. Moreover, the distortions present in the boron coordination sphere have been described quantitatively based on experimental data according to bond-valence vector model calculations. The results revealed that the deformation of the sphere is typical for a syn-anti conformation of boronic acids. The supramolecular structure of the cocrystal is composed of large synthons in the form of layers made up of O-H...O and N-H...O hydrogen bonds. The layers are joined via N-H...F hydrogen bonds which are unusual for urea cocrystal structures.

The description of a coordination sphere of a central atom/ion and an understanding of factors influencing its geometry in a given family of compounds is undoubtedly an important issue in many areas of chemistry or biochemistry. Methods grounded on structure correlations are often used to examine this problem provided sufficiently large number of crystal data are available. In these methods a bond-valence vector (BVV) model [1] appears to be a simple tool for identification and quantitative estimation of both steric and electronic factors causing the deformation of the coordination sphere. In this contribution the systematic analysis of the geometry of three-coordinated boronic acids derivatives with common [CBO2] skeleton will be presented. These compounds are regarded as a significant group taking into account their wide applications in chemistry, biochemistry and material science. They also give a set comprising over 890 [CBO2] fragments thus the analysis with BVV model should be reliable. In the model, the BVV length is given as s(ij)*(1-s(ij)/Q(ij)), where Q(ij) denote the core charge of the central atom and s(ij) is a scalar bond-valence (BV) relating bond-length with bond-valence by two parameters, r(ij) and b. These empirical BV parameters in exponential equation [2] for B-O and B-C bonds have been determined recently [3] and they amount to r(BO) = 1.364 A, b(BO) = 0.37 for B-O and r(BC) = 1.569, b(BC) = 0.28 A for B-C, respectively. With the calculated BVV lengths the analysis of the distribution of the resultant BVV components allows for a description of both the magnitude and the direction of deformations (see Figure). In-and out-of plane subtle deviations of the "ideal" (sp2) geometry of threecoordinated boron sphere will be discussed and referred to specific modifications of boronic acid. In this context the effect caused by esterification and condensation reactions as well as distortions introduced by intra-and intermolecular hydrogen bonds will be shown. It is worth mentioning that the location of hydrogen atoms on oxygen atoms in syn or anti positions is a key issue in crystal engineering concerning boronic acids. Our contribution will show what kind of strains are introduced while changing from one to another conformation and if the cocrystallization is an effective tool for steering the boronic acid conformation. There will be also a section discussing the out-of-plane distortions, described by vz component of the resultant BVV, where we show that it can be useful for the identification and rough quantification of weak secondary interactions on fourth coordination site of the boron center with the external Lewis base.

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