  We present an extension and revision of the spectroscopic and structural data
of the mixed stack charge transfer (CT) crystal
3,3$^\prime$,5,5$^\prime$-tetramethylbenzidine--tetrafluoro-tetracyanoquinodimethane
(TMB-TCNQF$_4$), associated with new electric and dielectric measurements.
Refinement of syncrotron structural data at low temperature have led to revise
the previously reported [Phys. Rev. Mat. \textbf{2}, 024602 (2018)] $C2/m$
structure. The revised structure is $P2_1/m$, with two dimerized stacks per
unit cell, and is consistent with the vibrational data. However, polarized
Raman data in the low-frequency region also indicate that by increasing
temperature above 200 K the structure presents an increasing degree of disorder
mainly along the stack axis. This finds confirmation in the analysis of the
anisotropic displacement parameters of the structure. TMB-TCNQF$_4$ is
confirmed to be a narrow gap semiconductor ($E_a \sim 0.3$ eV) with room $T$
conductivity of $\sim 10^{-4}~ \Omega^{-1}$ cm$^{-1}$, while dielectric
measurement have evidenced a typical relaxor ferroelectric behavior already at
room $T$, with a peak in real part of dielectric constant $\epsilon'(T,\nu)$
around 200 K and 0.1 Hz. The relaxor behavior is explained in terms of the
presence of spin solitons separating domains of opposite polarity that yield to
ferrolectric nanodomains.
