Molecular and crystal structure of the nonlinear optical material: 2-(N-prolinol)-5-nitropyridine (PNP)

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Abstract
The structure [C10H13N3O3,Mr=223.23, monoclinic, P21, a=5.182(1) Å, b=14.964(4) Å, c=7.045(1) Å, β=106.76(1)°, V=523.1 Å3, Z=2, Dx=1.42 Mg mm−3, μ=9.0 cm−1, F(000)=236, 23±1 °C, R=(Σ‖‖F0‖−‖Fc‖‖/Σ‖F0‖) =0.047 based on 930 reflections with F20>3.0σ(F20)] of this compound reveals it to optimally satisfy many of the structural and symmetry restrictions required for optical second harmonic generation (SHG). The molecules are extraordinarily well aligned to optimize noncritically phase matched SHG with the amino nitrogen to nitro nitrogen charge transfer axis making an angle of 59.6° with the unique axis (b). The mean aromatic plane sits nearly perfectly in the (101) crystallographic plane which may be a natural cleavage surface through which normal propagation may produce noncritically phase matched SHG. Powder optical second harmonic generation measurements (λ=1.06μ; Nd‐YAG laser) yield a value of 140.0x relative to powdered urea. Molecules related by a screw operation and the translation [0,0,1] are intermolecularily hydrogen bonded [amino–H/nitro–O; 2.20(10) Å]. The structure is essentially isostructural to the earlier reported structure of N‐(4‐nitrophenyl)‐(L)‐prolinol (NPP) which appears to possess slightly enhanced second harmonic efficiency.