[Tex/LaTex] Achemso table of content frame

Question

When I include my table of contents image in the tocentry section, the tocentry frame does not cover my image (with dimension 8.5×4.75cm) properly. The frame is wider and shorter in height. In the manual, the height and width of the frame does not agree with what is required by ACS (for example it is 8.5×4.75cm in JPCC). I think the frame is having a dimension incompatible with 8.5×4.75cm due to the following lines in the (manual)

1274 \newlength{\acs@tocentry@width}
1275 \setlength{\acs@tocentry@height}{9 cm}
1276 \setlength{\acs@tocentry@width}{3.5 cm}

If it is correct, I tried changing these values as follows, which is of course wrong as I don't know how to change these values.

\documentclass[journal=jpccck,manuscript=article,layout=twocolumn]{achemso}
\author{One}
\affiliation{someone}
\title{Blank}
\begin{document}

\newlength{\acs@tocentry@height}
\setlength{\acs@tocentry@height}{4.75 cm}
\newlength{\acs@tocentry@width}
\setlength{\acs@tocentry@width}{8.5 cm}

\begin{tocentry} 
\includegraphics{toc.png}
\end{tocentry}

\end{document}  

The error shown is:

Missing number, treated as zero. 
<to be read again>
               @
l.21 \setlength{\acs@tocentry@height}{4.75 cm}

?

The following image shows my TOC image in the black region and the default box in black lines that needs to be modified.

Answer 1

There are a couple of things here. First, you need \makeatletter to access internal commands: see What do \makeatletter and \makeatother do?. Second, you don't want to make new variables, just to set them

\makeatletter
\setlength\acs@tocentry@height{4.75cm}
\setlength\acs@tocentry@width{8.5cm}
\makeatother