\documentclass{article}
\usepackage{threeparttable}
\usepackage{multirow}
\usepackage{booktabs}
\usepackage{xcolor}
\usepackage{tikz}
\begin{document}
\begin{table}[!ht]
\setlength\tabcolsep{0pt}
\centering
\begin{threeparttable}
\begin{tabular}{@{\extracolsep{2ex}}*{2}{cc}}
\toprule
1.4142135623730951 & 1.2352131000001e7 \\
1.0607182119320439e8 & 0.0011096125449903673 \\
1.23456 \& 0.0012345 & \begin{tabular}{@{}c@{}}1.23456 \\ 0.0012345\end{tabular} \\
\bottomrule
\end{tabular}
\end{threeparttable}
\end{table}
\end{document}