{TAIL ~ The synthesis} of {HEAD ~ high quality pure phase crystals} has been complicated by the simultaneous formation of both clathrate type I and clathrate type II structures 
{ TAIL ~ The synthesis } of { HEAD ~ high quality pure phase crystals } has been complicated by the simultaneous formation of both clathrate type I and clathrate type II structures
TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH