% used options: used options: -w -t 2 (no cross bond) 
\chemfig{
             % 1
    -[,1.414]% 2
    -[:225,2]% 4
    -[,1.414]% 3
                (
        -[:135,2]% -> 1
                )
}

% added option: --cross-bond 2-4
\chemfig{
                         % 1
                -[,1.414]% 2
    -[:225,2,,,draw=none]% 4          bond 2 -> 4 is not rendered at first
                -[,1.414]% 3
                            (
                    -[:135,2]% -> 1
                            )
                            (%        append cross bond to end of molecule
     -[:90,1.414,,,draw=none]% -> 2 - invisible bond moves the pen to atom 2
     -[:225,2,,,mcfcrossbond]% -> 4 - the cross bond is rendered, applying 
                            )%        the mcfcrossbond tikz key
}