Nicholas C. Norman’s research while affiliated with University of Bristol and other places

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Publications (332)


The dn Number in Transition Metal Chemistry: Its Utility and Limitations
  • Article
  • Full-text available

November 2023

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147 Reads

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1 Citation

Chemistry

Nicholas C. Norman

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Paul G. Pringle

The dn number or configuration is a very useful parameter in transition metal chemistry because it conveys information about the expected properties of a d-block metal complex, including its shape, magnetism, thermodynamic stability, kinetic lability, and spectroscopic properties. The dn number can be determined from either the oxidation state (OS) or valence number (VN) of the metal centre, and since, in most cases, these are numerically equal, the derived dn value is the same. However, examples are discussed where the OS and VN are not equal, which results in unavoidable ambiguities in dn values. Following a discussion of these examples, a revised definition of dn is proposed based on the occupation of the frontier molecular orbitals of the complex.

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Hypervalence: A Useful Concept or One That Should Be Gracefully Retired?

October 2022

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129 Reads

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12 Citations

Chemistry

In this essay the origins of the term hypervalence and its application in p-block element chemistry are considered and it is argued that the term should now be consigned to the graveyard of concepts that no longer afford any discernible value or insight, certainly from an educational perspective. In contrast, the educational merits of the octet rule are also examined where it is concluded that this rule does have significant pedagogical value, albeit mostly within the ambit of introductory level explanations. For a few of the chosen exemplar compounds, a selection of orbital-based analyses, at different levels of sophistication, are also considered, and their values appraised together with a brief survey of some of the more general computational studies which have been employed in relation to this topic.



Alan Herbert Cowley. 29 January 1934—2 August 2020

December 2021

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21 Reads

Biographical Memoirs of Fellows of the Royal Society

Richard A. Jones

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Richard A. Kemp

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Jonathan G. Lasch

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[...]

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Nicholas C. Norman

Alan Cowley was one of the most creative main group chemists of his generation, and had a central role in what was often described as the renaissance of main group chemistry. Throughout his career Alan always had an eye for what was new. In his early years as an independent researcher, Alan made many fundamental contributions to the chemistry of phosphorus, not only in terms of the synthesis of new compounds but also in their study by employing novel analytical and computational methods. Starting in the 1980s he was at the forefront of emerging research into low-coordinate phosphorus chemistry and made seminal contributions in the areas of multiply bonded species, such as phosphenium ions and diphosphenes, as well as in the transition metal coordination chemistry of phosphinidenes. In the second half of his career, Alan also turned his attention to the study of single source precursors for important solid-state electronic materials, many of which were far superior to known examples. In all of the many areas in which Alan worked, he was a great collaborator with colleagues and researchers across the world, both in chemistry and in other disciplines. This was made all the easier by Alan's charm and easy-going nature, which was also manifest in the interactions he had with his many group members over a period of almost half a century. Alan was a gentleman in every sense and is much missed by friends, colleagues, collaborators and family.


In defence of oxidation states

November 2021

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90 Reads

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14 Citations

Dalton Transactions

In this Perspective, some of the criticisms which have been made concerning the use of oxidation states are addressed, particularly in the context of the teaching of inorganic chemistry. The Oxidation State method and the Covalent Bond Classification method are compared and contrasted, and it is concluded that while each method has its strengths and weaknesses, both are important in teaching and it should be recognized that no single model or method is appropriate in all circumstances.




Synthesis and X-Ray Crystal Structure of a Polymeric Iodobismuthate Anion

June 2014

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15 Reads

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11 Citations

Zeitschrift fur Naturforschung B

The reaction between [CH2=C(C6H4-4-NO2)CH2NMe3]I and eight equivalents of BiI3 in thf (tetrahydrofuran) afforded, after work-up, dark red crystals of the compound [CH2=C(C6H4-4-NO2)CH2NMe3]n[{Bi2I7}n], the structure of which was established by X -ray crystallography and shown to contain a polymeric iodobismuthate anion. An analogous reaction between [CH3(CH2)2COS(CH2)2N(CH3)3]I and eight equivalents of BiI3 afforded orange crystals of the compound [CH3(CH2)2COS(CH2)2N(CH3)3]4[Bi4I16] which was shown by X -ray crystallography to contain the tetranuclear [Bi4I16]⁴⁻ anion.


Ultra‐Flexible Boron‐Oxygen 3D Solid‐State Networks

December 2013

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42 Reads

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7 Citations

The existence of ultra‐flexible low‐energy forms of boron oxides (B2O3 and BO) is demonstrated, in particular structures in which B3O3 or B4O2 six‐membered rings are linked by single B‐O‐B bridges. The minima in the energy landscapes are remarkably broad; the variation in the internal energies is very small over a very large range of volumes. Such volume changes may even exceed 200%. This remarkable behavior is attributed predominantly to the pronounced angular flexibility of the B‐O‐B bridges linking the rings, which is unusual for a covalent bond. At larger volumes, the structures are nanoporous; the pores collapse upon compression with negligible change in energy, making these suitable as guest‐host materials. In marked contrast, in other materials where low density frameworks have been reported or predicted, such low‐density phases are considerably higher in energy. The flexibility of the structures also offers a resolution of the long‐standing controversy reconciling the structure and density of vitreous B2O3.


A polycyclic borazine radical cation: [1,2-B2{1,2-(MeN)2C6H4}2]˙(+)

September 2013

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27 Reads

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22 Citations

Chemical Communications

The radical cation [1,2-B2{1,2-(MeN)2C6H4}2]˙(+) has been synthesised and its structure and bonding have been probed using a combination of X-ray crystallography, EPR spectroscopy and DFT calculations which show that it represents a new type of radical centred primarily on two N-heterocyclic units joined by a B2 linker but with only a minor contribution from boron-based orbitals.


Citations (49)


... Hybrid halobismuthates are of considerable interest to chemists and materials scientists due to the variety of their physical properties [1][2][3][4][5][6][7][8], which are primarily determined by the different structures of the halobismuthate anions contained in them [9][10][11][12][13][14]. Active study of hybrid bismuth halides began in the 1990s [15,16]. Currently, the attention of researchers is focused on the search for new compounds with low band gaps (E g ) [17] and good optical absorption [18], which are considered as promising light-absorbing materials in photovoltaics [19][20][21], photodetectors [22,23], and photodiodes [24]. ...

Reference:

Crystal Structure and Optical Properties of New Hybrid Halobismuthates of 2,2'-Bipyridinium Derivatives
Synthesis and X-Ray Crystal Structure of a Polymeric Iodobismuthate Anion

Zeitschrift fur Naturforschung B

... Therefore, they consider that the term hypervalent loses its validity and suggest that this term should be replaced by the term hypercoordinated concerning ERMBs and EDMBs. This suggestion is in line with previous proposals to eliminate the term hypervalent [69][70][71][72][73][74][75][76][77][78][79]. ...

Hypervalence: A Useful Concept or One That Should Be Gracefully Retired?

Chemistry

... In compound 2, significant electron density localization at copper can be derived computationally via NBO and QTAIM calculations. Coupled with the relative insensitivity of the charge at magnesium to onward reactivity with hydrogen, this favors the assignment of formal oxidation states of Cu(-I)/Mg(II), albeit with the degree of covalency reflecting the formalisms of the oxidation state model 49 . Conjointly, these data reflect a copper-magnesium bond conforming to a Cu δ--Mg δ+ charge distribution, i.e., compound 2 is expected to act unambiguously as an copper nucleophile. ...

In defence of oxidation states

Dalton Transactions

... Hence, ST scholars advocate for science education to move from linear causal explanations towards considering behavior that emerges from cumulative interactions within a system (Easterbrook, 2014;Forrester, 1994;Gilissen et al., 2020;Hmelo-Silver et al., 2017). Moreover, there is a growing consensus to equip students with the skills of a systems thinking mindset, preparing them as citizens who can apply those thinking skills to understand and solve systems level problems (Michalopoulou et al., 2019;Reynolds et al., 2018). ...

The End of Simple Problems: Repositioning Chemistry in Higher Education and Society Using a Systems Thinking Approach and the United Nations’ Sustainable Development Goals as a Framework
  • Citing Article
  • September 2019

Journal of Chemical Education

... Compound 1 was obtained( 61 %y ield) as ab right orange solid in ao ne-pot procedure,i nvolving sequential treatment of E with nBuLi, PCl 3 , [16] and Mg, [17] bypassing isolationo fi ntermediate LPCl 2 (L = pincer). The 31 PNMR spectrum of 1 displayed as inglet at 150.6 ppm with no PÀHc oupling (Scheme1). ...

Phosphorus Compounds Containing Sterically Demanding Groups
  • Citing Chapter
  • January 2007

... In the specific self-assembled processes, the products are independent of the ligand-to-metal ratios (the results were confirmed by X-ray diffraction). In the three compounds, the protons of hydroxyl groups transfer to pyridyl nitrogen atoms to form pyridinium-4-olate, and similar cases have been reported before [30,31], which leads to rich hydrogen bonds. In compounds 1 and 2, the metal centers coordinate to oxygen atoms, while in 3, the L molecules behave as free molecules. ...

A bis­[penta­iodo­bismuthate(III)] salt of 4-hydroxy­pyridinium

... The reaction between acetonitrile and diphenylborinic anhydride (Fig. 6) illustrates this phenomenon. A variety of nitrogen adducts of BF 3 have been previously characterized crystallographically, and these include amines, imidazole (Barber et al., 2005; Fig. 6D), pyridine, and acetonitrile (Swanson et al., 1969; Fig. 6C) adducts (Barber et al., 2005). It is therefore conceivable that the boron analogs synthesized in the present study can also form coordinate bonds with amino acids (either N3B or O3B). ...

N-Imidazole–boron trichloride adduct

... 94 When treated with pyridine, they are readily cleaved with the formation of the corresponding monomeric complexes [(Py)PdX(1-Ph 2 PCH 2 -1,2-C 2 B 10 H 10 -k 2 -P,B(3/4))] 2 . 94,95 Reactions of carboranylphosphines 1-R 2 P-2-R 0 -1,2-C 2 B 10 H 10 (R ¼ t-Bu, pH; R 0 ¼ H, Me, i-Pr) with Na 2 [PdCl 4 ] in methanol or with [(PhCN) 2 PdCl 2 ] in benzene or tetrahydrofuran lead to four-membered cyclopalladated monomeric [PdCl(1-Ph 2 P-1,2-C 2 B 10 H 10 -k 2 -P,B)(1-Ph 2 P-1,2-C 2 B 10 H 11 -k 1 -P)] and dimeric [PdCl(1-R 2 P-2-R 0 -1,2-C 2 B 10 H 9 -k 2 -P,B)] 2 94,96 Dimeric complexes [PdX(1-Ph 2 P-2-R-1,2-C 2 B 10 H 9 -k 2 -P,B)] 2 (R ¼ H, Me, i-Pr) were also obtained by exchange reactions of cyclopalladated N,N-dibenzylamino complex [PdCl(2-Me 2 NCH 2 C 6 H-k 2 -N,C)] 2 with the corresponding carboranylphosphine ligands in boiling chloroform. 94,95 According to the NMR spectroscopy data, the reactions with 1-Ph 2 P-1,2-C 2 B 10 H 11 and 1-Ph 2 P-2-Me-1,2-C 2 B 10 H 10 lead to a mixture of B(3)Hand B(4)H-activation products, while the reaction with 1-Ph 2 P-2-i-Pr-1,2-C 2 B 10 H 10 , containing a bulky substituent at the neighboring carbon atom, produces exclusively the B(4)H-activation product. ...

Regioselective B-Cyclometalation of a Bulky o-Carboranyl Phosphine and the Unexpected Formation of a Dirhodium(II) Complex
  • Citing Article
  • February 2012

Organometallics

... Possible nanoporous low-density forms of B 2 O 3 containing B 3 O 3 rings have been linked to the ease of vitrification of this system [50] and found to be extremely flexible [51,52]. Starting with some known B 2 O 3 structures, and others constructed from two-dimensional sheets, we explored the effect of replacing each three-coordinated B atom in these polymorphs by a B 3 O 3 ring, itself three-coordinate. ...

Ultra‐Flexible Boron‐Oxygen 3D Solid‐State Networks
  • Citing Article
  • December 2013

... substantive science outreach programmes (e.g. Harrison et al. 2011aHarrison et al. , 2011bSewry et al. 2014) and science discovery centres, botanical gardens and museums (e.g. Tunnicliffe 2001Tunnicliffe , 2010 have all sought to raise the profile of science, provide hands-on experience for children and connect active scientists with school students and their teachers. ...

Publicising chemistry in a multicultural society through chemistry outreach

South African Journal of Science