Phosphorus-silicon double bonds, strength

For many years the occurrence of double and triple bonds such as discussed above for silicon and phosphorus was equally rare among other nonmetals, leading to the conclusion that only C=C, C =N, C 0. NsN. etc. were stable multiple bonds. This, of course, was taken as challenge and much svnthetic work was directed at the problem. None of the multiple bonds between heavier nonmetals is as strong as those between the 2p elements. Some typical estimates of the strength of the n bond (cf. to H,C CH3 as a "standard" from organic chemistry) arc (values in kJ mol-1). ... 

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