  Silver benzeneselenolate [AgSePh] is a coordination polymer that hosts a
hybrid quantum well structure. The recent advancements in the study of its
tightly bound excitons (~300 meV) and photoconductive properties (recently
employed in UV photodetection) makes it an interesting representative of a
material platform that is an environmentally stable alternative to 2D metal
halide perovskites in terms of optoelectronic properties. To this aim, several
challenges are to be addressed, among which the lack of control over the
metal-organic reaction process in the reported synthesis of the [AgSePh]
nanocrystal film (NC). This issue contributed to cast doubts over the origin of
its intra-bandgap electronic states. In this article we study all the steps to
obtain phase pure [AgSePh] NC films, from thin silver films through its
oxidation and reaction via a chemical vapor-solid with benzeneselenol, by means
of UV-vis, XRD, SEM, and AFM. Raman and FTIR spectroscopy are also employed to
provide vibrational peaks assignment, for the first time on this polymer. Our
analysis supports an acid-base reaction scheme based on an acid attacking the
metal oxide precursor, generating water as byproduct of the polymeric
synthesis, speeding up the reaction by solvating the PhSeH. The reaction
readily goes to completion within 30 min in a supersaturated PhSeH / N2
atmosphere at 90 {\deg}C. Our analysis suggests the absence of precursor's
leftovers or oxidized species that could contribute to the intra-gap states. By
tuning the reaction parameters, we gained control on film morphology to obtain
substrate-parallel oriented micro-crystals showing different excitonic
absorption intensities. Finally, centimeters size high quality [AgSePh] NC
films could be obtained, enabling exploitation of their optoelectronic
properties, such as UV photodetection, in large-area applications.
