Designing a sensor based on a <i>π</i>-conjugated 6-membered boron ring and its properties

Planar -conjugated borides not only attract fundamental interests in bonding chemistry, but also offers wide-ranging applications in catalysis, bioimaging, and biosensing. To stabilize -conjugated <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:msub><a:mi mathvariant="normal">B</a:mi><a:mn>6</a:mn></a:msub></a:math> rings without out-of-plane bonding, we propose a design strategy that involves inserting low-compressible <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:mi mathvariant="normal">C</c:mi><c:msub><c:mi mathvariant="normal">N</c:mi><c:mn>3</c:mn></c:msub></c:mrow></c:math> triangles into tessellation of <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"><f:msub><f:mi mathvariant="normal">B</f:mi><f:mn>6</f:mn></f:msub></f:math> rings to create planar borides. Based on this concept, we designed the planar hypercoordinate boride <h:math xmlns:h="http://www.w3.org/1998/Math/MathML"><h:mrow><h:mi>ScC</h:mi><h:msub><h:mi mathvariant="normal">N</h:mi><h:mn>3</h:mn></h:msub><h:msub><h:mi mathvariant="normal">B</h:mi><h:mn>6</h:mn></h:msub></h:mrow></h:math>, which features the planar structure and represents a theoretically predicted -conjugated <k:math xmlns:k="http://www.w3.org/1998/Math/MathML"><k:msub><k:mi mathvariant="normal">B</k:mi><k:mn>6</k:mn></k:msub></k:math> ring. The molecular dynamics simulations suggested that <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"><m:msub><m:mi mathvariant="normal">B</m:mi><m:mn>6</m:mn></m:msub></m:math> rings in <o:math xmlns:o="http://www.w3.org/1998/Math/MathML"><o:mrow><o:mi>ScC</o:mi><o:msub><o:mi mathvariant="normal">N</o:mi><o:mn>3</o:mn></o:msub><o:msub><o:mi mathvariant="normal">B</o:mi><o:mn>6</o:mn></o:msub></o:mrow></o:math> remain intact at a high temperature of 1500 K. The metal adsorption energy of <r:math xmlns:r="http://www.w3.org/1998/Math/MathML"><r:msub><r:mi mathvariant="normal">B</r:mi><r:mn>6</r:mn></r:msub></r:math> rings in <t:math xmlns:t="http://www.w3.org/1998/Math/MathML"><t:mrow><t:mi>ScC</t:mi><t:msub><t:mi mathvariant="normal">N</t:mi><t:mn>3</t:mn></t:msub><t:msub><t:mi mathvariant="normal">B</t:mi><t:mn>6</t:mn></t:msub></t:mrow></t:math> is comparable to borophene, and superior to that of graphene and two-dimensional hexagonal boron nitride. As a result, the designed <w:math xmlns:w="http://www.w3.org/1998/Math/MathML"><w:mrow><w:mi>ScC</w:mi><w:msub><w:mi mathvariant="normal">N</w:mi><w:mn>3</w:mn></w:msub><w:msub><w:mi mathvariant="normal">B</w:mi><w:mn>6</w:mn></w:msub></w:mrow></w:math> demonstrates both high stability and chemical activity attributed to <z:math xmlns:z="http://www.w3.org/1998/Math/MathML"><z:mrow><z:mi mathvariant="normal">C</z:mi><z:msub><z:mi mathvariant="normal">N</z:mi><z:mn>3</z:mn></z:msub></z:mrow></z:math> triangles and <cb:math xmlns:cb="http://www.w3.org/1998/Math/MathML"><cb:msub><cb:mi mathvariant="normal">B</cb:mi><cb:mn>6</cb:mn></cb:msub></cb:math> rings, respectively. Consequently, the designed <eb:math xmlns:eb="http://www.w3.org/1998/Math/MathML"><eb:mrow><eb:mi>ScC</eb:mi><eb:msub><eb:mi mathvariant="normal">N</eb:mi><eb:mn>3</eb:mn></eb:msub><eb:msub><eb:mi mathvariant="normal">B</eb:mi><eb:mn>6</eb:mn></eb:msub></eb:mrow></eb:math> could serve as a potential sensor for biomolecules. Moreover, the planar ninefold hypercoordinate Sc weakly bonds to the <hb:math xmlns:hb="http://www.w3.org/1998/Math/MathML"><hb:mrow><hb:msub><hb:mi mathvariant="normal">N</hb:mi><hb:mn>3</hb:mn></hb:msub><hb:msub><hb:mi mathvariant="normal">B</hb:mi><hb:mn>6</hb:mn></hb:msub></hb:mrow></hb:math> wheel, drives a flat band of the orbital, suggesting that flat band can be generated by splitting of <kb:math xmlns:kb="http://www.w3.org/1998/Math/MathML"><kb:mrow><kb:mi mathvariant="normal">d</kb:mi><kb:msup><kb:mrow><kb:mi>z</kb:mi></kb:mrow><kb:mn>2</kb:mn></kb:msup></kb:mrow></kb:math> orbital in planar hypercoordinate crystal field.