documentclass{article}

usepackage{amsmath,mleftright}

begin{document}

% Uses amsmath
[
  a begin{pmatrix}
    begin{array}{@{} c | @{hspace{arraycolsep}}}
      b \
      c
    end{array}
    d
  end{pmatrix}
]

% Uses mleftright, but can also just use left/right instead of mleft/mright
[
  a mleft(
    begin{array}{@{} c @{}}
      b \
      c
    end{array}
    middlevert
    d
  mright)
]

end{document}