Topochemical reactions are a promising method to obtain crystalline polymeric materials with distance-determined regio-or stereoselectivity.It has been concluded on an empirical basis that the closest intermolecular C...Topochemical reactions are a promising method to obtain crystalline polymeric materials with distance-determined regio-or stereoselectivity.It has been concluded on an empirical basis that the closest intermolecular C⋅⋅⋅C distance in crystals of alkynes,d(C⋅⋅⋅C)min,should reach a threshold of∼3Åfor bonding to occur at room temperature.To understand this empirical threshold,we study here the polymerization of acetylene in the crystalline state under high pressure by calculating the structural geometry,vibrational modes,and reaction profile.We find d(C⋅⋅⋅C)min to be the sum of an intrinsic threshold of 2.3Åand a thermal displacement of 0.8Å(at room temperature).Molecules at the empirical threshold move via several phonon modes to reach the intrinsic threshold,at which the intermolecular electronic interaction is sharply enhanced and bonding commences.A distance–vibration-based reaction picture is thus demonstrated,which provides a basis for the prediction and design of topochemical reactions,as well as an enhanced understanding of the bonding process in solids.展开更多
Two new species of Tenthredo pulchra group are described from Hebei,China:Tenthredo lianpo Wei sp.nov.and Tenthredo limu Wei sp.nov.The Tenthredo pulchra group of the genus Tenthredo is proposed herein.The diagnosis o...Two new species of Tenthredo pulchra group are described from Hebei,China:Tenthredo lianpo Wei sp.nov.and Tenthredo limu Wei sp.nov.The Tenthredo pulchra group of the genus Tenthredo is proposed herein.The diagnosis of this species group is briefly discussed.A key to the known species of Tenthredo pulchra group from China is provided.展开更多
Four new species:Siobla elevatina Niu&Wei sp.nov.,S.emeiensis Niu&Wei sp.nov.,S.kangba Niu&Wei sp.nov.,and S.taegeri Niu&Wei sp.nov.are described and illustrated.A key to species of Siobla sturmii grou...Four new species:Siobla elevatina Niu&Wei sp.nov.,S.emeiensis Niu&Wei sp.nov.,S.kangba Niu&Wei sp.nov.,and S.taegeri Niu&Wei sp.nov.are described and illustrated.A key to species of Siobla sturmii group is given.展开更多
基金support of the National Natural Science Foundation of China(NSFC)(Grant Nos.22022101,21875006,11704024,and 12174200)The authors also acknowledge support from the National Key Research and Development Program of China(Grant No.2019YFA0708502)from the Nature Science Foundation of Tianjin(Grant No.20JCYBJC01530).
文摘Topochemical reactions are a promising method to obtain crystalline polymeric materials with distance-determined regio-or stereoselectivity.It has been concluded on an empirical basis that the closest intermolecular C⋅⋅⋅C distance in crystals of alkynes,d(C⋅⋅⋅C)min,should reach a threshold of∼3Åfor bonding to occur at room temperature.To understand this empirical threshold,we study here the polymerization of acetylene in the crystalline state under high pressure by calculating the structural geometry,vibrational modes,and reaction profile.We find d(C⋅⋅⋅C)min to be the sum of an intrinsic threshold of 2.3Åand a thermal displacement of 0.8Å(at room temperature).Molecules at the empirical threshold move via several phonon modes to reach the intrinsic threshold,at which the intermolecular electronic interaction is sharply enhanced and bonding commences.A distance–vibration-based reaction picture is thus demonstrated,which provides a basis for the prediction and design of topochemical reactions,as well as an enhanced understanding of the bonding process in solids.
基金supported by the National Natural Science Foundation of China(31970447,31672344).
文摘Two new species of Tenthredo pulchra group are described from Hebei,China:Tenthredo lianpo Wei sp.nov.and Tenthredo limu Wei sp.nov.The Tenthredo pulchra group of the genus Tenthredo is proposed herein.The diagnosis of this species group is briefly discussed.A key to the known species of Tenthredo pulchra group from China is provided.
基金supported by the National Natural Science Foundation of China (31501885,31970447)the Foundation of Hunan Educational Committee (2016-2330)。
文摘Four new species:Siobla elevatina Niu&Wei sp.nov.,S.emeiensis Niu&Wei sp.nov.,S.kangba Niu&Wei sp.nov.,and S.taegeri Niu&Wei sp.nov.are described and illustrated.A key to species of Siobla sturmii group is given.
