nitridoborate

{{Short description|Chemical compounds of boron and nitrogen with metals}}

The nitridoborates are chemical compounds of boron and nitrogen with metals. These compounds are typically produced at high temperature by reacting hexagonal boron nitride (α -BN) with metal nitrides or by metathesis reactions involving nitridoborates. A wide range of these compounds have been made involving lithium, alkaline earth metals and lanthanides, and their structures determined using crystallographic techniques such as X-ray crystallography. Structurally one of their interesting features is the presence of polyatomic anions of boron and nitrogen where the geometry and the B–N bond length have been interpreted in terms of π-bonding.

Many of the compounds produced can be described as ternary compounds of metal boron and nitrogen and examples of these are Li₃BN₂, Mg₃BN₃, La₃B₃N₆, La₅B₄N₉. However, there are examples of compounds with more than one metal, for example La₃Ni₂B₂N₃{{cite journal|last1=Blaschkowski|first1=Björn|last2=Meyer|first2=H.-Jürgen|title=X-Ray Single Crystal Refinement and Superconductivity of La₃Ni₂B₂N₃|journal=Zeitschrift für anorganische und allgemeine Chemie|volume=629|issue=1|year=2003|pages=129–132|issn=0044-2313|doi=10.1002/zaac.200390004}} and compounds containing anions such as Cl⁻, for example Mg₂BN₂Cl.{{cite journal|last1=Somer|first1=Mehmet|last2=Kütükcü|first2=Mehmet Nuri|last3=Gil|first3=Raul Cardoso|last4=Borrmann|first4=Horst|last5=Carrillo-Cabrera|first5=Wilder|title=Mg₂[BN₂]Cl and Mg₈[BN₂]₅I: Novel Magnesium Nitridoborate Halides — Syntheses, Crystal Structures, and Vibrational Spectra|journal=Zeitschrift für anorganische und allgemeine Chemie|volume=630|issue=7|year=2004|pages=1015–1021|issn=0044-2313|doi=10.1002/zaac.200400055}}

Structures and bonding

Examination of the crystallographic data shows the presence of polyatomic units consisting of boron and nitrogen. These units have structures similar to those of isoelectronic anions, which have π-bonded structures. The bonding in some of these compounds is ionic in character, such as Ca₃[BN₂]₂, other compounds have metallic characteristics, where the bonding has been described in terms of π-bonded anions with extra electrons in anti-bonding orbitals that not only cause a lengthening of the B–N bonds but also form part of the conduction band of the solid.{{cite book |last=Meyer |first=H. Jurgen |editor1-last= Meyer|editor1-first= Gerd|editor2-last=Naumann |editor2-first= Dieter|editor3-last=Wesemann |editor3-first= Lars|title=Inorganic Chemistry in Focus III |publisher=Wiley-VCH |year=2006 |pages=121–138 |chapter=Chapter 8: Current State on (B,C,N) compounds of Calcium and Lanthanum|isbn=978-3-527-31510-9}} The simplest ion BNⁿ⁻ is comparable to the {{chem|C|2|2−}} ion, but attempts to prepare the compound CaBN analogous to CaC₂ calcium carbide failed. The bonding of compounds containing the diatomic BN anion have been explained in terms of electrons entering anti-bonding orbitals and reducing the B–N bond order from 3 (triple bond) in BN²⁻ to 2 (double bond) in BN⁴⁻.{{cite journal|last1=Blaschkowski|first1=Björn|last2=Meyer|first2=H.-Jürgen|title=Electronic Conditions of Diatomic (BN) Anions in the Structure of CaNiBN|journal=Zeitschrift für anorganische und allgemeine Chemie|volume=628|issue=6|year=2002|pages=1249|issn=0044-2313|doi=10.1002/1521-3749(200206)628:6<1249::AID-ZAAC1249>3.0.CO;2-S}}

Some nitridoborates are salt-like such as Li₃BN₂, LiCa₄[BN₂]₃ others have a metallic lustre, such as LiEu₄[BN₂]₃. Bonding calculations show that the energy of the valence orbitals of metal atoms of group 2 and lanthanide elements are higher than those of the bonding orbitals in BN_x ions which indicates an ionic like interaction between a metal atom and a BN_x ion. With lanthanide compounds where extra electrons enter the anti-bonding orbitals of an ion there can be a smaller band gap giving the compounds metal like properties such as lustre. With transition metals the d orbitals can be similar in energy to bonding orbitals in the BN anions suggesting covalent interactions.

anion	geometry	Typical B–N bond length (pm)	B-B bond length (pm)	isoelectronic with	Examples of compounds
class="wikitable"
BNⁿ⁻	linear	138–202{{cite journal\|last1=Cava\|first1=R. J.\|last2=Zandbergen\|first2=H. W.\|last3=Batlogg\|first3=B.\|last4=Eisaki\|first4=H.\|last5=Takagi\|first5=H.\|last6=Krajewski\|first6=J. J.\|last7=Peck\|first7=W. F.\|last8=Gyorgy\|first8=E. M.\|last9=Uchida\|first9=S.\|title=Superconductivity in lanthanum nickel boro-nitride\|journal=Nature\|volume=372\|issue=6503\|year=1994\|pages=245–247\|issn=0028-0836\|doi=10.1038/372245a0\|bibcode=1994Natur.372..245C\|s2cid=4345404}}{{cite journal\|last1=Blaschkowski\|first1=Björn\|last2=Jing\|first2=Haipeng\|last3=Meyer\|first3=H.-Jürgen\|title=Nitridoborates of the Lanthanides: Synthesis, Structure Principles, and Properties of a New Class of Compounds\|journal=Angewandte Chemie International Edition\|volume=41\|issue=18\|year=2002\|pages=3322–3336\|issn=1433-7851\|doi=10.1002/1521-3773(20020916)41:18<3322::AID-ANIE3322>3.0.CO;2-8\|pmid=12298029}}			CaNiBN,(Ca²⁺Ni²⁺BN⁴⁻); LaNiBN, (La³⁺Ni²⁺BN⁴⁻(e⁻))
{{chem\|BN\|2\|3−}}	linear	132–137{{cite journal\|last1=Somer\|first1=Mehmet\|last2=Herterich\|first2=Uwe\|last3=Čurda\|first3=Jan\|last4=Carrillo-Cabrera\|first4=Wilder\|last5=Zürn\|first5=Anke\|last6=Peters\|first6=Karl\|last7=Schnering\|first7=Hans Georg von\|title=Darstellung, Kristallstrukturen und Schwingungsspektren neuer ternärer Verbindungen mit dem Anion [N–B–N]³⁻\|journal=Zeitschrift für anorganische und allgemeine Chemie\|volume=626\|issue=3\|year=2000\|pages=625–633\|issn=0044-2313\|doi=10.1002/(SICI)1521-3749(200003)626:3<625::AID-ZAAC625>3.0.CO;2-4}}		[CN₂]²⁻, CO₂	Ca₃(BN₂)₂
{{chem\|BN\|3\|6−}}	trigonal planar	145–149		borate, carbonate ion	La₆(BN₃)O₆
{{chem\|B\|2\|N\|4\|8−}}	planar	147–150	177–182	oxalate ion	La₃B₂N₄, ((La³⁺)₃({{chem\|B\|2\|N\|4\|8−}})(e⁻))
{{chem\|B\|3\|N\|6\|9−}}	planar or chair form	144–151			La₃B₃N₆{{cite journal\|last1=Reckeweg\|first1=Olaf\|last2=Meyer\|first2=H.-Jürgen\|title=Lanthanoidnitridoborate mit sechsgliedrigen B₃N₆-Ringen: Ln₃B₃N₆\|journal=Angewandte Chemie\|volume=111\|issue=11\|year=1999\|pages=1714–1716\|issn=0044-8249\|doi=10.1002/(SICI)1521-3757(19990601)111:11<1714::AID-ANGE1714>3.0.CO;2-X}}

For comparison purposes the following are considered to be typical BN bond lengths{{cite book |last1=Housecroft |first1=Catherine E |last2=Sharpe|first2=Alan G| year=2005 |title=Inorganic Chemistry|edition=2nd |publisher=Pearson education|pages=318|isbn=978-0-13-039913-7 }}

Compound	B–N (pm)	Bond type
class="wikitable"
Me₃N·BBr₃	160.2	single
Me₃N·BCl₃	157.5	single
Cubic BN	157	Single
Hexagonal BN	144.6	intra-layer distance some π-bonding
B(NMe₂)₃	143.9	some π-bonding
Mes₂BNBMes₂	134.5	double bond
(t-Bu)BN(t-Bu)	125.8	triple bond

References

Category:Boron–nitrogen compounds

Category:Anions