Synthesis, Spectroscopy, X‐ray Crystallography, and DFT Computations of Nanosized Phosphazenes

Nanoparticles of nine phosphazenes with general formula 4‐CH 3 C 6 H 4 S(O) 2 N=P X 3 [ X = Cl ( A ), NC 4 H 8 ( 1 ), NC 6 H 12 ( 2 ), NC 4 H 8 N–C(O)OC 2 H 5 ( 3 ), NC 4 H 8 N–C(O)OC 6 H 5 ( 4 ), NC 4 H 8 O ( 5 ), NHCH 2 –C 4 H 7 O ( 6 ), N(CH 3 )(C 6 H 11 ) ( 7 ), NHCH 2 –C 6 H 5 ( 8 ), and 2‐NH‐NC 5 H 4 ( 9 )] were synthesized using ultrasonic method and characterized by 1 H, 13 C, 31 P NMR, FT‐IR, fluorescence, as well as UV/Vis spectroscopy and additionally with XRD, FE‐SEM, N 2 sorption, and elemental analysis. The 31 P NMR spectra of compounds 1 – 9 reveal the most up field shift δ( 31 P) for 9 at –11.45 ppm reflecting the most electron donation of 2‐aminopyridinyl rings through resonance to the phosphorus atom. The 1 H, 13 C NMR spectra of 7 exhibit two sets of signals for the hydrogen and carbon atoms of its two isomers present in the solution state in 1:4 ratio. The FE‐SEM micrographs illustrate that the nanoparticles of compounds 1 – 9 have spherical morphology and a size of 27–42 nm. From the XRD patterns, the crystal sizes were estimated to about 24–86 nm. The highest bandgap was measured for 3 (3.81 eV) whereas the smallest was measured for 8 (3.50 eV). The structures of two polymorphs of compound 5 ( 5 , 5′ ) were determined by X‐ray crystallography at 120 K. Both of these polymorphs are triclinic with P 1 space group but 5 has a doubled unit cell volume and two symmetrically independent molecules ( 5a and 5b ). In structures 5a and 5′ , the phosphorus and all endocyclic atoms of two morpholinyl rings display disorder, whereas the molecule 5b does not show disorder. The strong intermolecular O–H ··· O hydrogen bonds plus weak intermolecular C–H ··· O and C–H ··· N interactions create three‐dimensional polymers in the crystalline networks of 5 and 5′ . The DFT computations illustrate that molecule 5b is more stable than 5a by –1.1062 and –0.9779 kcal · mol –1 at B3LYP and B3PW91 levels, respectively. The NBO calculations presented sp 3 d hybridization for phosphorus and sulfur atoms and sp 2 , sp 3 hybrids for the nitrogen and oxygen atoms.