DOI:10.1002/chem.201800517 Minireview & Transmutation ElectronicTransmutation (ET): Chemically Turning One Element into Another XinxingZhang,*[a] Katie A. Lundell,[b] JaredK.Olson,[b] Kit H. Bowen,*[c] and Alexander I. Boldyrev*[b] Chem. Eur.J.2018, 24,9200 –9210 9200 2018 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim Minireview Abstract: The concept of electronic transmutation (ET) de- the theoretical andexperimental fronts. Examples on the ET picts the processesthat by acquiring an extra electron, anel- of Group 13 elements into Group 14 elements, Group 14 ele- ement with the atomicnumber Zbegins to have properties ments into Group 15 elements, and Group 15 elements into that were known to only belongtoits neighboringelement Group 16 elements are discussed. Compoundsand chemical with the atomic number Z+1. Based on ET,signature com- bondingcomposed of carbon,silicon, germanium, phospho- pounds and chemical bonds that are composed of certain rous, oxygen and sulfur now have analoguesusing transmu- elements can now be designed and formed by other elec- tated boron, aluminum, gallium, silicon, nitrogen, and phos- tronically transmutated elements. This Minireview summariz- phorous. es the recentdevelopments and applicationsofETonboth Introduction ples on both the theoretical and experimental fronts, and out- look for wider applicationsand future research directions of Despite the successofthe valence-isoelectronic concept in this new concept. many examples of predicting reactivity,structures and exis- tence of compounds, such asimple electroncounting rule can 1. Electronic Transmutation of Group 13 nevertheless easily fail. For instance, being valence-isoelectron- Elements into Group 14 Elements ic to benzene (C6H6), the planar D6h silabenzene molecule Si6H6 is not even aminimum on its potentialenergy surface.[1] The Group 13 elements, such as boron,[19] aluminum,[20] and galli- deformation from this planar structure to its real globalmini- um,[21] are well known to form clustered compounds through mum is attributable to the pseudo-Jahn–Teller effect. In view multicenter bonding, which is largely due to their electron-de- of this, astricter and narrower electronic transmutation (ET) ficient(s2p1 electron configuration) nature. The simplestexam- [2] [22] [23] concept was proposed in 2012, stating that by acquiring an ples are the diborane(B2H6), dialane (Al2H6), and digallane [24] electron, acertain element with the atomic number Zbegins (Ga2H6) molecules, where each of the two bridge hydrogen to behavesimilarly as its neighboringelement Z+ 1. For exam- atomsparticipates in forminga3-center 2-electron (3c–2e) M- ple, the transmutated boron,BÀ ,may well be functioning simi- Hbridge-M (M=B, Al, Ga) bond. Rather distinct from the larly to carbon.The similarities between the transmutated ele- Group 13 elements, Group 14 elements such as carbon, silicon, ment Zand the targeted elementZ+1could range from the and germanium usually form chain or ring compounds as a chemicalbonding they possess to the geometries of the com- result of spn (n= 1, 2, 3) hybridizations. With the difference of poundsthey form, so that many key features that were only one electron, Group 13 and 14 elements behavevery dif- thought only belong to element Z+ 1can now belong to ele- ferently in chemicalbondingand the compounds they can ment Z. Alchemists once spent great efforts in transmutating form. In this section, we discuss the theoretical and experimen- commonelements into precious others, which now we know tal advances of the electronic transmutation of Group 13 ele- is not possible merely with chemistry,but based on ET,the ele- ments into Group 14 elements, where the former yield similar ment Zcan now be chemically “turned into” elementZ+ 1. chemicalbondingand compounds as the latter after transmu- After the proposal of the ET concept, aplethora of successful tation. examples, including the transmutation of Groups 13, 14, and 15 elements into Group 14, 15, and 16 elements, have been re- 1.1. ET of boron into carbon ported.[2–18] In this Minireview,wewill summarize these exam- It is well-known that carbon forms alarge varietyofhydrocar- bons, including aromatic arene, alkane, alkene, and alkyne- [a] Prof. Dr.X.Zhang based compoundsthat feature chain (homocatenation)orring Collaborative Innovation CenterofChemical Science and Engineering College of Chemistry, Nankai University structures. Boron hydrides, or boranes, on the other hand, Tianjin 300071 (P.R.China) prefer clustered structures.Inorder to satisfy the octet rule, E-mail:[email protected] the insufficient electrons in boronlead to the formation of 3c– [b] K. A. Lundell, Dr.J.K.Olson, Prof. Dr.A.I.Boldyrev 2e bonds,based on whichanextensiontomolecular orbital Department of Chemistry and Biochemistry (MO) theory was developed, known as the polyhedralskeletal Utah State University [19] 0300 Old Main Hill, Logan, UT,84322-0300 (USA) electronpairtheory (PSEPT) or simply Wade–Mingos rules. In E-mail:[email protected] this section, we present the successful examples of homo- [c] Prof. Dr.K.H.Bowen catenated and aromatic boron compounds when boron is elec- Departments of Chemistryand Material Science tronically transmutated into carbon. Johns Hopkins University We first discuss the theoretical predictions of homocatenat- Baltimore, MD, 21218 (USA) E-mail:[email protected] ed boron hydrides where the ET concept was firstly pro- [2] The ORCID identification number(s) for the author(s) of this articlecan be posed. Alkanes follow the molecular formula CnH2n+2,sug- found under https://doi.org/10.1002/chem.201800517. gesting that their boron analogues should have the formula of Chem. Eur.J.2018, 24,9200 –9210 www.chemeurj.org 9201 2018 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim Minireview n (BnH2n+2) À,inwhich each boron atom obtains one negative case of Li2B2H6 unless noted. The searchfor the global mini- charge to resemble carbon. These negative charges can be mum structure of the Li2B2H6 molecule was performed using provided by certain electron donors, preferably by alkali metals the Coalescence Kickprogram written by Averkiev.[26] Initially such as Li, so the first obvious example is the BH4À kernel in these calculations wereperformed at arelative low/cheap level [27] the LiBH4 salt, which is isoelectronic and isostructural to CH4, of theory (B3LYP/3–21G )tosearch for alarge quantity of iso- 1 and already commerciallyavailable. Here we focus on the ho- mers, and those lowest energy isomers(DE<60 kcalmolÀ ) mocatenation of boron, and Li2B2H6 seems to be asimple can- were then reoptimized and frequencies were calculated at didate to start with. However,the B Li, H Li, and B Hbond B3LYP/6–311++G**[28] and CCSD(T)/6–311++G**[29] and À À À dissociation energies are not too far away from each other,[25] single point calculations were performed using the RCCSD(T)/ one would expect arelatively flat potential energy surface and aug-cc-pVXZlevels of theory (X=Dand T).[30] The final relative many possible isomers that are close in energy for this mole- energies were obtained through extrapolationoftotal energies cule, which makes athorough, unbiased geometrical searchin- at the CCSD(T) level of theory to the complete basis set limit dispensable but very expensiveinorder to find the real global (CBS) using the Truhlar formula[31] (CCSD(T)/CBS//CCSD(T)/6– minimum. Here we present the detailedcalculation methods 311++G**) and corrected for zero-pointenergies calculated used in reference [2] in order to set an example for the search at CCSD(T)/6–311++G**. Chemical bonding analysis (B3LYP/ of the globalminimum of electronicallytransmutated mole- 6–311++G**) wasperformed using the AdNDPmethod.[32] All cules. The computational methods for other ET molecules in calculations were done using GAUSSIAN 03 and GAUSSI- the rest of this minireview are more or less the same as the AN 09[33] software packages. Molekel 5.4.0.8 was used for MO visualization,[34] and MOLDENt3.4[35] was used for molecular structure visualization. Figure 1A presents the globalminimum of Li2B2H6,which containsone 2c–2eB B s-bond and six 2c–2c B H s-bonds. Xinxing Zhang obtained his B.S. in chemistry À À at Fudan University in Shanghai, China These s-bonds are furtherconfirmed by AdNDP analysis (Fig- (2009), and his PhD at the Johns Hopkins ure 1D). From the structure, the B2H6 kernel is indeed very sim- University in the Kit Bowen research group ilar to the hydrocarbon analog, ethane. However,the interac- (2015).Since 2016, he has been workingasa tion between theLiatoms and the B H kernel appearstobe postdoctoral scholaratCaltech in the J. L. 2 6 Beauchamp research group. His research in- critical to determine the existence of electronic transmutation. terests cover gas phase cluster reactivity and Calculated effective charges are + 0.94 e on each Li atom and j j spectroscopy, as well as the physical chemis- 1.88 e on the B H kernel. Thus, the interaction between À j j 2 6 try and biochemistry at the air–water interfa- the Li and the B H kernel is ionic, and the B H moiety is ces. He startedhis independent research 2 6 2 6 career as aprofessor at Nankai University, Tianjin, China, in 2018. Katie Lundell received her B.S. in chemistry Kit H. Bowen, Jr.received his B.S. in chemistry and biochemistry at Idaho State University in at the University of Mississippi (1970), and his Pocatello, Idaho (2015). Since 2016 she has M.S. (1973) and Ph.D.(1977) in chemistry at been agraduate student in the Alex Boldyrev HarvardUniversity.Hewas also an NSF post- research group. Her research interests are the doc at HarvardUniversity.Dr. Bowen is now study of electronic transmutations and devel- the E. Emmet Reid Professor of Chemistry at opment of newchemical bonding models in the Johns Hopkins University.His research uti- clusters. lizes negativeion photoelectronspectroscopy and surface deposition techniques both of whichare applied to size-selected cluster anions. Jared K. Olson received hisB.S.