Structural, optical, dielectric, conductivity and solid-state behaviour of 2-methylpropan-2-ammonium 2,4,6-trinitrophenolate (TBAP) single crystal

Abstract

t-butyl ammonium picrate (TBAP) crystallized in a P-1 space group with two molecules per unit cell. The solid has hydrogen bonding (1.86 and 1.88 Å) in the b-axis between the phenolate oxygen and one of the –NH₃⁺ hydrogen. In the unit cell, if one picrate ion is on the left and the cation is on the right along the b-axis. The other molecule is just below along the b-axis with cation on the left and picrate ion on the right disposition. Each phenolate ion forms H-bonding with two different t-butyl ammonium ions. Thus the two cations and two anions are held together by H-bonding. The IR spectrum had characteristic bands due to ν(C−O) phenolic, ν(NO₂), ν(NH₃⁺) and ν(C–H) peaks. The ¹H NMR spectrum showed a broad peak at 7.7 ppm due to NH₃⁺ protons along with the characteristic aromatic and –CH₃ protons. The ¹³C NMR showed peaks due to tertiary (51.15 ppm), aromatic (124–160 ppm) and methyl carbons (27.15 ppm). The peaks at 235 and 380 nm are due to π → π* and n → π* observed from the UV–Visible spectrum and having a band gap of 2.82 eV. The crystal melts at 476.5 K followed by decomposition. The dielectric constant and dielectric loss at 323 K were found to be maximum at lower frequencies. The values are lesser at 373 K and 423 K due to phase changes as shown by DTA. AC conductivity studies indicated that the conductance is maximum at 323 K and lesser at both 373 K and 423 K due to phase changes. The I–V studies showed a negative effect, that is the photocurrent is lower than the dark current due to Fermi energy gaps nearer to VB and CB. The polarizability was found to be 8.342 × 10^–23 cm³ which indicated that the molecule can be used as an optoelectronic material.