Spin States in Biochemistry and Inorganic Chemistry

It has long been recognized that metal spin states play a central role in the reactivity of important biomolecules, in industrial catalysis and in spin crossover compounds. As the fields of inorganic chemistry and catalysis move towards the use of cheap, non-toxic first row transition metals, it is essential to understand the important role of spin states in influencing molecular structure, bonding and reactivity.

Spin States in Biochemistry and Inorganic Chemistry provides a complete picture on the importance of spin states for reactivity in biochemistry and inorganic chemistry, presenting both theoretical and experimental perspectives. The successes and pitfalls of theoretical methods such as DFT, ligand-field theory and coupled cluster theory are discussed, and these methods are applied in studies throughout the book. Important spectroscopic techniques to determine spin states in transition metal complexes and proteins are explained, and the use of NMR for the analysis of spin densities is described.

Topics covered include:

DFT and ab initio wavefunction approaches to spin states
Experimental techniques for determining spin states
Molecular discovery in spin crossover
Multiple spin state scenarios in organometallic reactivity and gas phase reactions
Transition-metal complexes involving redox non-innocent ligands
Polynuclear iron sulfur clusters
Molecular magnetism
NMR analysis of spin densities
This book is a valuable reference for researchers working in bioinorganic and inorganic chemistry, computational chemistry, organometallic chemistry, catalysis, spin-crossover materials, materials science, biophysics and pharmaceutical chemistry.

Auteur

Prof. Dr. Marcel Swart, Universitat de Girona, Spain
Marcel Swart is ICREA Research Professor in the Institute of Computational Chemistry Catalysis at the Universitat de Girona, Spain. He is a computational/theoretical chemist working in the field of (bio)chemistry and biomedicine. He has published >100 papers in peer-reviewed scientific journals and has an h-index of 26. He was awarded the Young Scientist 2005 award by ICCMSE (International Conference of Computational Methods in Sciences and Engineering), and was selected as one of the promising young inorganic chemists of "The next generation" that were invited to contribute to a special issue of Inorganica Chimica Acta in 2007, and to a special issue of Polyhedron in 2010.
In 2012, he was awarded the MGMS Silver Jubilee Prize "for his development of new computational chemistry programs, design of new research tools and application to (bio)chemical systems that are highly relevant for society and science." In September 2012 he organized a CECAM/ESF Workshop on "Spin states in biochemistry and inorganic chemistry", highlighted in Nature Chem. 2013, 5, 7-9.

Prof. Dr. Miquel Costas, Universitat de Girona, Spain
Miquel Costas became Professor Titular at the University of Girona in 2003. He has published over 70 papers in international journals that have received over 3470 citations. His research interests involve the study of transition metal complexes involved in challenging oxidative transformations, including functionalization of C-H bonds and water oxidation. These systems commonly operate in multistate reactivity scenarios, implicating multiple spin states.

Échantillon de lecture
1
General Introduction to Spin States

Marcel Swart1,2 and Miquel Costas1

1Institut de Química Computacional i Catàlisi and Departament de Química, Universitat de Girona, Spain

2Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain
1.1 Introduction

Spin is a fundamental property of all elements and molecules, which originates from their unpaired electrons. Spin states have a major role in defining the structure, reactivity, magnetic and spectroscopic properties of a molecule. Furthermore it is possible that more than one spin state is energetically accessible for a given molecule. In such cases, the molecule can accumulate multiple spectroscopic, magnetic and reactivity patterns arising from the different accessible spin states. The ground spin state of most organic molecules is a singlet, that is, they have a closed-shell electronic structure, and other states are energetically not accessible under standard conditions. Important exceptions are carbenes, which can exist as singlet and triplet spin states, and the molecule of dioxygen, whose triplet nature poses kinetic barriers to its thermodynamically favorable reaction with organic matter. The situation is completely reversed when transition metals are present, which makes that different spin states are accessible for the majority of transition metal complexes. This primarily results from the particular nature of d-orbitals of the metals (see Figure 1.1 ) that are close in energy and which can be occupied in different ways depending on the metal oxidation state, its ligands and its coordination geometry (see Figure 1.1 ). This picture can be further complicated when ligands are not redox innocent and can have a spin that can also engage in ferro or anti-ferromagnetic interactions with the spin of the metal center.

Figure 1.1 Transition metal d-orbitals shape (left) and orbital-level diagram (right).

Spin states play an important role [1, 2] in metalloenzymatic reactions (e.g. cytochrome P450cam), in metal-oxo complexes, in spin-crossover compounds and even in catalysis processes mediated by organometallic compounds where different reactions take place via different spin states [3, 4]. However, computational studies have shown that a correct description of the spin state is not trivial [1, 5, 6], and a combination of different density functionals (DFT) and/or ab initio methods may be needed. Experimental studies on biomimetic model complexes, enzymes or spin-crossover compounds have added to the complexity, making the spin state a challenging property that is poorly understood [1]. This was the origin for a CECAM/ESF Workshop organized in Zaragoza in September 2012 [7], leading subsequently to a COST Action (CM1305, ECOSTBio).
1.2 Experimental Chemistry: Reactivity, Synthesis and Spectroscopy

Spin states constitute a fundamental aspect of the electronic structure of molecules, and as such spin determines their electronic properties, magnetism and reactivity. Therefore, rationalization of the latter properties in paramagnetic molecules most often requires determination of their spin state. The most important spectroscopic techniques employed to determine spin states in transition metal complexes and proteins have been discussed in Chapter 4, and the use of nuclear magnetic resonance spectroscopy as a tool to shed information on the electronic structure of paramagnetic metal centers, especially those of metalloenzymes, is described in Chapter 16.

Compounds that can exist in multiple spin states open exciting possibilities in a number of fields. An interesting, widely explored case is transition metal centers in octahedral coordination environments with d-electron configurations d4 to d7, which can exist as high spin (HS) and low spin (LS) (see Chapters 5 and 12). Low

Contenu

About the Editors xv

List of Contributors xvii

Foreword xxi

Acknowledgments xxiii

1 General Introduction to Spin States 1
Marcel Swart and Miquel Costas

1.1 Introduction 1

1.2 Experimental Chemistry: Reactivity, Synthesis and Spectroscopy 2

1.3 Computational Chemistry: Quantum Chemistry and Basis Sets 4

2 Application of Density Functional and Density Functional Based Ligand Field Theory to Spin States 7
Claude Daul, Matija Zlatar, Maja Gruden-Pavlovic and Marcel Swart

2.1 Introduction 7

2.2 What Is the Problem with Theory? 9

2.2.1 Density Functional Theory 9

2.2.2 LF Theory: Bridging the Gap Between Experimental and Computational Coordinat…