Controlling vertical space in displayed math mode

Question

Apparently \hspace works inside displayed math mode to move formulas horizontally, but it seems that \vspace is ignored when I want to moved them vertically. I would like to control the vertical separation between two formulas inside \begin{equation} \end{equation}, is this possible?

Here it is an example of what I want (using an ugly trick):

\documentclass[12pt]{article}
\usepackage{amsmath}
\usepackage{ytableau}
\begin{document}
\vbox{
\ytableausetup{boxsize=1em}
\begin{equation}
\ydiagram{2,1} 
\qquad
\ydiagram{1} 
\end{equation}
\vspace{-7.0mm}
\begin{equation*}
\hspace{3mm}\ydiagram{1+1,2}
\qquad
\ydiagram{1,1} 
\end{equation*}
}
\end{document}

Answer 1

Avoid putting display math environments one after the other (use a multiline environment such as align if that's needed. \vbox shouldn't be used within a latex document.

\documentclass[12pt]{article}
\usepackage{amsmath}
\usepackage{ytableau}
\begin{document}

\ytableausetup{boxsize=1em}
\begin{equation}
\ydiagram{2,1} 
\raisebox{-1.25em}{\hspace{-1.75em}\ydiagram{1+1,2}}
\quad
\ydiagram{1} 
\raisebox{-1.25em}{\hspace{-.75em}\ydiagram{1,1}}
\end{equation}

\end{document}

Answer 2

I suggest using \makebox and \raisebox. The top diagram can be set in a box as wide as the requested displacement, the bottom one moved down by 1em (the size of a square) plus the displacement.

\documentclass[12pt]{article}
\usepackage{amsmath}
\usepackage{ytableau}
\usepackag-e{calc}
\begin{document}

\begin{equation}
\ytableausetup{boxsize=1em}
\begin{gathered}% for vertical centering
\makebox[1mm][l]{\ydiagram{2,1}}
\raisebox{-1em-1mm-\fboxrule}{\ydiagram{1+1,2}}
\qquad
\makebox[1mm][l]{\ydiagram{1}}
\raisebox{-1em-1mm-\fboxrule}{\ydiagram{1,1}}
\end{gathered}
\end{equation}

\end{document}

The -\fboxrule is a refinement to get the same displacement horizontally and vertically.