How to have a chord and notes of a different length together on the same stave

Hi,
I am trying to write a piece which has piano as one of the instruments. There is one bar where there is a semibreve chord. I would like to have a dotted minim followed by a crotchet over the semibreve chord on the same stave. When I try and do this using the voices, it doesn't seem to work. Does anyone have any suggestions? I really appreciate your help. Thanks.