Centering text in a diagonally split table cell

Question

I need help centering a hyphen located in a table cell that has a diagonal slash to split the table cell in two. As can be seen in my photo, the hyphen is positioned at the edge of the cell, I would like for it to be centered. I tried searching the forum and could not find an answer. Thanks in advance.

\documentclass[10pt,a4paper]{article}
\usepackage[utf8]{inputenc}
\usepackage{textcomp}
\usepackage{array}
\usepackage{fixltx2e}
\usepackage{tikz}
\usepackage{diagbox}

\begin{document}

\begin{table}[h!]
\centering
{
\renewcommand\arraystretch{2}

\caption{Microscopic binding constants, $K_1$ (bottom) and $K_2$ (top) for various hosts and guests interaction}

\begin{tabular}{|c*{4}{|c}|}
\multicolumn{3}{c}{} \\
\hline
& 5 \si{\milli}M Buffer & 100 \si{\milli}M Buffer & 20\% EtOH & 80\% EtOH \\
\hline

L\textsubscript{M} + P\textsubscript{C} & \diagbox[]{$7.29\times 10^{4}$}{$6.52\times 10^{5}$}& \diagbox[]{$1.16\times 10^{5}$}{$3.95\times 10^{5}$} &\diagbox[]{$4.85\times 10^{4}$}{$1.88\times 10^{6}$}&\diagbox[]{$4.95\times 10^{5}$}{$1.13\times 10^{5}$}\\ 
\hline

L\textsubscript{PY} + P\textsubscript{C} & ? &\diagbox[]{$1.86\times 10^{5}$}{$4.92\times 10^{4}$} & \diagbox[]{$1.28\times 10^{5}$}{$1.31\times 10^{5}$} &\diagbox[]{$2.95\times 10^{5}$}{$1.09\times 10^{4}$}\\

\hline
L\textsubscript{P} + P\textsubscript{C} & \diagbox[]{$5.05\times 10^{3}$}{-}& \diagbox[]{$2.78\times 10^{3}$}{$5.49\times 10^{2}$} &?&\diagbox[]{$7.05\times 10^{3}$}{$5.09\times 10^{4}$}\\
\hline

L\textsubscript{I} + P\textsubscript{C} &?&?& \diagbox[]{$4.74\times 10^{4}$}{$1.25\times 10^{5}$}& \diagbox[]{$1.05\times 10^{6}$}{$9.90\times 10^{4}$}\\
\hline

\end{tabular}
}
\end{table}

\end{document}

Also, is there a way to remove the two corner lines of the empty table cell (North West)?

Answer 1

You could put the hyphen in a parbox and play around with its sizes and alignments.

% arara: pdflatex

\documentclass[a4paper]{article}
\usepackage[utf8]{inputenc}
\usepackage{array}
\usepackage{diagbox}
\usepackage{caption}
\usepackage{siunitx}
\usepackage{mathtools}
\newcommand*{\ethanol}{EtOH}
\newcommand*{\MBC}[2]{\text{#1}_{\mathrm{#2}}}

\begin{document}    
    \begin{table}[h!]
        \centering
            \renewcommand\arraystretch{1.2}         
            \caption[Microscopic binding constants]{Microscopic binding constants, $K_1$ (bottom) and $K_2$ (top) for various hosts and guests interaction}
            \begin{tabular}{|*{5}{c|}}\cline{2-5}
                \multicolumn{1}{c|}{}& \SI{5}{\milli M} Buffer & \SI{100}{\milli M} Buffer & \SI{20}{\percent} \ethanol & \SI{20}{\percent} \ethanol \\
                \hline              
                $\MBC{L}{M} + \MBC{P}{C}$ & \diagbox[]{$7.29\times 10^{4}$}{$6.52\times 10^{5}$}& \diagbox[]{$1.16\times 10^{5}$}{$3.95\times 10^{5}$} &\diagbox[]{$4.85\times 10^{4}$}{$1.88\times 10^{6}$}&\diagbox[]{$4.95\times 10^{5}$}{$1.13\times 10^{5}$}\\ 
                \hline              
                $\MBC{L}{PY} + \MBC{P}{C}$ & ? &\diagbox[]{$1.86\times 10^{5}$}{$4.92\times 10^{4}$} & \diagbox[]{$1.28\times 10^{5}$}{$1.31\times 10^{5}$} &\diagbox[]{$2.95\times 10^{5}$}{$1.09\times 10^{4}$}\\             
                \hline
                $\MBC{L}{P} + \MBC{P}{C}$ & \diagbox[]{$5.05\times 10^{3}$}{\parbox[c][.4cm][b]{.6cm}{--}}& \diagbox[]{$2.78\times 10^{3}$}{$5.49\times 10^{2}$} &?&\diagbox[]{$7.05\times 10^{3}$}{$5.09\times 10^{4}$}\\
                \hline              
                $\MBC{L}{I} + \MBC{P}{C}$ &?&?& \diagbox[]{$4.74\times 10^{4}$}{$1.25\times 10^{5}$}& \diagbox[]{$1.05\times 10^{6}$}{$9.90\times 10^{4}$}\\
                \hline              
            \end{tabular}
    \end{table} 
\end{document}

This table does not fit on one page, so I won't upload an image.