\multirow - Long name breaking/ruining layout

Question

When I use this tabular enviroinment, for some reason the second-lowest row gets messed up badly. Can anybody please tell me how to fix this?

\documentclass[11pt, a4paper, fleqn, parskip]{scrartcl}

\usepackage[utf8x]{inputenc}
\usepackage[ngerman]{babel}
\usepackage{mathtools, amssymb}
\usepackage{a4wide}
\usepackage{multirow}

\begin{document}
\begin{tabular}{|c|c|} \hline
    $[a, b] := \{x \in \mathbb{R}: a \leq x \leq b\}$ & kompaktes Intervall \\ \hline
    $(a, b) := \{x \in \mathbb{R}: a < x < b\}$ & offenes, beschr"anktes Intervall \\ \hline
    $[a, b) := \{x \in \mathbb{R}: a \leq x < b\}$ & \multirow{2}{*}{halboffenes, beschr"anktes Intervall} \\
    $(a, b] := \{x \in \mathbb{R}: a < x \leq b\}$ \\ \hline
    $[a, \infty) := \{x \in \mathbb{R}: a \leq x\}$ \\ \multirow{2}{*}{abgeschlossenes, unbeschr"anktes Intervall} \\
    $(-\infty, b] := \{x \in \mathbb{R}: x \leq b\}$ \\ \hline
    $(a, \infty) := \{x \in \mathbb{R}: a < x\}$ & \multirow{2}{*}{offenes, unbeschr"anktes Intervall} \\
    $(-\infty, b) := \{x \in \mathbb{R}: x < b\}$ \\ \hline
\end{tabular}
\end{document}

Answer 1

You missed some ampersands (&) below the row that contains multirow command:

\documentclass[11pt, a4paper, fleqn, parskip]{scrartcl}

\usepackage[utf8x]{inputenc}
\usepackage[ngerman]{babel}
\usepackage{mathtools, amssymb}
\usepackage{a4wide}
\usepackage{multirow}

\begin{document}
\begin{tabular}{|c|c|} \hline
    $[a, b] := \{x \in \mathbb{R}: a \leq x \leq b\}$ & kompaktes Intervall \\ \hline
    $(a, b) := \{x \in \mathbb{R}: a < x < b\}$ & offenes, beschr"anktes Intervall \\ \hline
    $[a, b) := \{x \in \mathbb{R}: a \leq x < b\}$ & \multirow{2}{*}{halboffenes, beschr"anktes Intervall} \\
    $(a, b] := \{x \in \mathbb{R}: a < x \leq b\}$ & \\ \hline  %%<<<here
    $[a, \infty) := \{x \in \mathbb{R}: a \leq x\}$ & \multirow{2}{*}{abgeschlossenes, unbeschr"anktes Intervall}  \\
    $(-\infty, b] := \{x \in \mathbb{R}: x \leq b\}$ & \\ \hline %%<<< here
    $(a, \infty) := \{x \in \mathbb{R}: a < x\}$ & \multirow{2}{*}{offenes, unbeschr"anktes Intervall} \\
    $(-\infty, b) := \{x \in \mathbb{R}: x < b\}$ & \\ \hline %%%<<<<<here
\end{tabular}
\end{document}

Answer 2

In your table you have some errors resulting in the bad looking of your table. I suggest you write always the ampersands in the same column as I did. So you find easier missing ampersands in your table. Don't forget to write all necceccary & for your table, even if an empty cell is following.

Package a4wide is outdated, please do not use it longer. See l2tabu.pdf (texdoc l2tabu) for more information.

You will get better looking tables without lines, have a look into package booktabs and its manual (texdoc booktabs).

Corrected and pretty printed MWE:

%http://tex.stackexchange.com/questions/83415/multirow-long-name-breaking-ruining-layout
\documentclass[11pt, a4paper, fleqn, parskip]{scrartcl}

\usepackage[utf8]{inputenc}  % original: utf8x
\usepackage[ngerman]{babel}
\usepackage{mathtools, amssymb}
%\usepackage{a4wide}         % outdated, see l2tabu.pdf
\usepackage{multirow}

\begin{document}
\begin{tabular}{|c|c|} \hline
  $[a, b] := \{x \in \mathbb{R}: a \leq x \leq b\}$ & kompaktes Intervall              \\ \hline
  $(a, b) := \{x \in \mathbb{R}: a < x < b\}$       & offenes, beschränktes Intervall  \\ \hline
  $[a, b) := \{x \in \mathbb{R}: a \leq x < b\}$    & \multirow{2}{*}{halboffenes, beschränktes Intervall} \\
  $(a, b] := \{x \in \mathbb{R}: a < x \leq b\}$    &                                  \\ \hline
  $[a, \infty) := \{x \in \mathbb{R}: a \leq x\}$   & \multirow{2}{*}{abgeschlossenes, unbeschränktes Intervall} \\
  $(-\infty, b] := \{x \in \mathbb{R}: x \leq b\}$  &                                  \\ \hline
  $(a, \infty) := \{x \in \mathbb{R}: a < x\}$      & \multirow{2}{*}{offenes, unbeschränktes Intervall} \\
  $(-\infty, b) := \{x \in \mathbb{R}: x < b\}$     &                                  \\ \hline
\end{tabular}
\end{document}