**7. Some future aims and proposals**

592 Advances in Crystallization Processes

columns, C(O)NHP(O)(NH)2 and C(O)NHP(O)(N)2 as blue and P(O)(NH)x(N)3-x (x = 1, 2, 3)

In phosphoramidates having a P(O)(NH)n(N)m(O)3-(n+m) skeleton (balck), the strongest and weakest N—H…O hydrogen bonds are found for hydrogen bonds in the range of 2.65 to

In compounds containing a P(O)(NH)x(N)3-x skeleton, the strongest N—H…O hydrogen bonds are seen for the HBs in the range of 2.70 to 2.80 Å. The phosphoryl group' involvement in a multi-centered P(O)···[H—N]n (n = 2 & 3) grouping may lead to some weak H-bonds; for example in P(O)[NHC(CH3)3]3 (KABVEP [93]), N…O distances & N—H…O angles are 3.255(4) Å & 111.1(2)°, 3.294(4) Å & 93.4(2)° and 3.159(4) Å & 123.0(2)°, and in P(O)[NH(C6H5)]3 (KEQLUO [95]) these parameters are 3.06 Å & 110° and 3.06 Å & 108°; this weakening of H-bond strength is attributed to the *anti*-cooperativity

Fig. 7. Histogram of the N…O distances in the N—H…O hydrogen bonds in compounds having P(O)(NH)n(N)m(O)3-(n+m) (n = 1, 2; n+m < 3) (black), C(O)NHP(O)(NH)2 and

C(O)NHP(O)(N)2 (blue), and P(O)(NH)x(N)3-x (x = 1, 2, 3) (red) skeletons (the co-crystals and solvated compounds and the compounds having a disorder in the sites involving HB

as red columns.

effect [89].

2.75 Å and 3.20 to 3.30 Å.

interaction were not enumerated).

Phosphorus has a very deep and widespread chemistry and understanding its nature in the compounds is noticeable interest. This may be achieved through the study on collective behaviors of phosphorus compounds in point of view of their different aspects.

The structural investigations and the study on the hydrogen-bond patterns may help to predict the molecular packing from the molecular structure. Moreover, as the biological activity of phosphorus compounds is very important, finding a relationship between the structure and a biological property is beneficial. For example, as well-known, a biological property may be related to the three important factors: lipophilicity, electronic and steric parameters. Probably, part of these factors could be well-understand by considering the crystal structure' study of such compounds; the electronic parameters may be related to the nature of chemical bonds or to the electron density or valence bond in different parts of the molecule. It is believed that, in the first step of interaction with acetylcholinesterase, the phosphoryl group is involving with the enzyme active site through a non-covalent bond; so, considering the non-covalent interaction of phosphoryl group with different atoms such as hydrogen helps to understand that the molecule how much could close to the enzyme active site. The steric parameters may be elucidated from the volume of molecule or considering the V(volume of unit cell)/Z(number of molecules in the unit cell). This may be in fact the practical volume which the molecule has, as the molecule usually cannot be closer to the neighboring molecules from this frontier boundary.

The solubility of molecules in different solvents must be checked in the crystal growth process; so, elucidation of lipophilicity is easy; however, the best method for measuring of this parameter is using of the spectrophotometer. And finally, the steric parameters can simply accessible through a structural study.

Preparation of phosphorus acids of the formula RP(O)(OH)2 may develop the synthesis of the functionalized nano-phosphate materials and also polyoxometalate-based organic/inorganic hybrid compounds in which the phosphorus atom is trapping between

Phosphoramidates: Molecular Packing and Hydrogen

Negari (MSc student) for some computer works.

[1] Allen, F. H. (2002). *Acta Cryst.* B58, 380.

*Phys. Chem. C*114, 2305.

*Chem.* 39, 684.

*Cryst.* C67, o265.

*Acta Cryst.* E67, o1360.

*Acta Cryst.* E67, o1031.

o2524.

calculations.

**10. References** 

**9. Acknowledgements** 

hydrogen-bond is weak due to the anticooperativity effect.

[2] Müller, P. & Siegfried, B. (1972). *Helvetica Chimica Acta*, 55, 2965.

*Aliphatic Nylons, Fire and Polymers,* Chapter 17, pp 214.

& Della Védova, C. O. (2010). *Acta Cryst.* B66, 441.

[15] Pourayoubi, M. & Saneei, A. (2011). *Acta Cryst.* E67, o665.

Bond Strength in Compounds Having a P(O)(N)n(O)3-n (n = 1, 2, 3) Skeleton 595

7. In the multi-centered hydrogen-bond of the type P=O[…H-N]n (n = 2 & 3) the

We wish to collect more structural data about this class of compounds and study the collective behavior of this family in the other domains such as spectroscopy and chemical

M. P. wishes to thank Ferdowsi University of Mashhad for the Research University Grant (No. 15144/2). The authors also thank Dr. Karla Fejfarová for the CSD searches and Monireh

[3] (a) Le Carpentier, J.-M., Schlupp, R. & Weiss, R. (1972). *Acta Cryst.* B28, 1278. (b) Crawford, M.-J., Mayer, P., Nöth, H. & Suter M. (2004). *Inorg. Chem.* 43, 6860. [4] (a) Aas, P. (2004). *Prehospital and Disaster Medicine*, 18, 208. (b) Bhattacharjee, A. K., Kuča,

[5] (a) Rodriguez, J. A. & Fernandez-Garcia, M. (2007). *Synthesis, properties and applications of* 

[6] (a) Nguyen, C. & Kim, J. (2008). *Polym. Degrad. Stabil.* 93, 1037. (b) Levchik, S. V.,

[9] Gholivand, K., Mostaanzadeh, H., Koval, T., Dusek, M., Erben, M. F., Stoeckli-Evans, H.

[10] Pourayoubi, M., Tarahhomi, A., Saneei, A., Rheingold, A. L. & Golen, J. A. (2011). *Acta* 

[13] Pourayoubi, M., Rostami Chaijan, M., Torre-Fernández, L. & García-Granda, S. (2011).

[14] Pourayoubi, M., Rostami Chaijan, M., Torre-Fernández, L. & García-Granda, S. (2011).

[16] Pourayoubi, M., Tarahhomi, A., Rheingold, A. L. & Golen, J. A. (2010). *Acta Cryst.* E66,

[11] Ghadimi, S., Mousavi, S. L. & Javani, Z. (2008). *J. Enz. Inhibit. Med. Chem.* 23, 213. [12] Ekstrom, F., Akfur, C., Tunemalm, A. & Lundberg, S. (2006). *Biochemistry*, 45, 74.

[7] Roush, R. F., Nolan, E. M., Löhr, F. & Walsh, C. T. (2008). *J. Am. Chem. Soc.* 130, 3603. [8] Gholivand, K., Ghadimi, S., Naderimanesh, H. & Forouzanfar, A. (2001). *Magn. Reson.* 

*oxide nanomaterials*, Wiley-interscience, A John Wiley & Sons, INC., Publication. (b) Hirakawa, T., Sato, K., Komano, A., Kishi, Sh., Nishimoto, Ch. K., Mera, N., Kugishima, M., Sano, T., Ichinose, H., Negishi, N., Seto, Y. & Takeuchi, K. (2010). *J.* 

Levchik, G. F. & Murashko, E. A. (2001). *Phosphorus-Containing Fire Retardants in* 

K., Musilek, K. & Gordon, R. K. (2010). *Chem. Res. Toxicol.* 23*,* 26.

the R group from one side and a cluster containing metal-oxygen framework in the other side. These acids may develop the extraction process of cations, too.

Application of phosphoryl donor ligands in preparation of oxo-centered clusters, in which their terminal ligands are replaced by phosphorus compounds, may be interesting for consideration. Preparation of single- enantiomer phosphoramidates by using a chiral primary or secondary amine is easy; it may extend the strategies for the synthesis of chiral phosphoramidates, phosphoric acids, nano-phosphates and so on.

Synthesis of phosphoramidate-based hybrid compounds by using polyoxoanions may be valuable for spending the time on its consideration and experiment. Some of the wellknown hybrids contain the molecule-cation components of the type [B—H…B]+, where the B may be a base such as amide. Designing of such molecule-cation pairs with phosphoramidates, [PO—H…OP]+, may extend the experimental data about the 31P-31P coupling constant through the hydrogen-bond.

The NMR experiments on phosphoramidate-based compounds may develop the study on coupling constants of phosphorus and the other atoms, such as 2J(31P-127Tl) or 2J(31P-39K). These values may apply to evaluate the strengths of P=O—Tl or P=O—K bonds in their complexes.

We wish to develop the spectroscopic features and chemical calculations on phosphorus compounds, preparation of N-deuterated compounds in order to a good assignment of IR and Raman absorption bands, collecting the NMR data such as chemical shifts and short and long-range coupling constants, and finally chemical calculations on hydrogen-bonded molecules in the crystals.
