Using an IOU

It has been suggested (by one of the larger firms actually) that there is a valuable inheritance tax saving to be achieved by one spouse say for example a husband selling property to his wife in return for an IOU. He then gives the IOU to his children as a potentially exempt transfer and so of course on the death of the survivor of donor and spouse (whether it's first or second as far as I can see) there's a deduction for inheritance tax purposes if the seven-year period is achieved.

What do readers think about the efficacy of this (or otherwise); first if it is put into practice relating to a non-main residence property i.e. an investment property; secondly for a second home; and thirdly for the actual main residence. Naturally in the latter two cases the vending spouse would remain...