Planting raspberries

I expect you already know that at the recommended spacing you only have room for 3 plants - however, they are often sold in 5's and if that's the case I'd be tempted to squeeze all 5 in - they shouldn't get too congested in 3 years, and you could always cut down a few of the canes if they do.

Bear in mind that they will try to spread, and after the first year you may have to keep digging up suckers appearing as if by magic in neighbouring beds.

My raspberry bed was planted originally as 18inch apart for each plant, six of them. The bed is 2ft by 7ft.
That worked for me.
You will find after a few years many more ground runners appearing along the bed that pruned will be ready for the following year or taken as cuttings to move elsewhere.
As mentioned above, you can easily get 5 plants into that space.

All my books say plant 18inch to 2 foot apart and 6 foot between rows.