THE GEOMETRY OF SIOCN AND SINCO LINKAGES - THE CRYSTAL-STRUCTURES OF (ME(3)SI)(2)(PH(2)MESI)CSIME(2)OCN AND (PHME(2)SI)(3)CSIME(2)NCO

Single crystal X-ray diffraction studies have been carried out on the title compounds (in the case of the cyanate as its methylcyclohexane s olvate). The geometry of the SiNCO fragment in the isocyanate (PhMe(2) Si)(2)CSiMe(2)NCO (angle SiNC = 155.7(5), angle NCO = 175.9(7)degrees, d(Si-N)= 1.739(5), d(N-C)= 1.135(8), d(C-O) 1.174(8) Angstrom) is ver y similar to that in the much less crowded compounds H3SiNCO and ClCH( 2)Me(2)SiNCO, but in all three compounds the Si-N-C angle is a little smaller than in Me(3)SiNCO. In the light of the results the validity o f recent calculations indicating an Si-N-C angle of 180 degrees in H3S iNCO is questioned. In the case of the cyanate (Me(3)Si)(2)(Ph(2)MeSi) CSiMe(2)OCN, disorder results in considerable uncertainty in the geome try of the SiOCN linkage, but the values for the O-C-N and Si-O-C angl es, 175(1)degrees and ca. 124 +/- 6 degrees, respectively, are consist ent with those predicted by the corresponding calculations on H3SiOCN.