Preface ......................................................... v
1 Supramolecular Polymetallic 2D [n × n] Transition Metal
Grids — Approaches to Ordered Molecular Assemblies and
Functional Molecular Devices ................................. 1
Laurence К. Thompson, Louise N. Dawe and Konstantin
V. Shuvaev
1 Convergent Self-assembly .................................. 1
1.1 Introduction and overview ............................ 1
1.2 Polytopic ligands for [n × n] square grids-design
and self-assembly .................................... 3
1.3 Thermodynamic aspects of the formation of
convergent self-assembled grid architectures ......... 5
2 Ligands and Complexes ..................................... 6
2.1 Ditopic ligands and their complexes .................. 6
2.1.1 Homometallic complexes ........................ 8
2.1.1.1 [2 × 2] grids with heterocyclic
diazine (N2) bridging ligands ........ 8
2.1.1.2 Ditopic ligands with more remote
coordination pockets ................ 12
2.1.1.3 Other polynuclear oligomers with
remote ditopic ligands .............. 13
2.1.1.4 [2 × 2] grids with single atom μ-0
and μ-S bridging ditopic ligands .... 14
2.1.1.5 Ditopic hydrazone ligands with
both μ-О or μ-NN bridging modes ..... 16
2.1.1.6 Higher order oligomeric clusters
based on ditopic ligands ............ 19
2.1.2 Heterometallic [2 × 2] and mixed spin state
grids ........................................ 21
2.2 Symmetric tritopic ligands and their complexes ...... 25
2.2.1 Homometallic [3 × 3] grids ................... 25
2.2.2 Heterometallic and mixed spin state
|3 × 3| grids ................................ 29
2.3 Tetratopic ligands and complexes .................... 39
2.3.1 Homometallic [4 × 4] grids ................... 39
2.4 Pentatopic ligands and their complexes .............. 46
2.4.1 Homometallic [5 × 5] grids ................... 46
3 Other Oligomers in the Assembly Process .................. 48
3.1 Incomplete grids, clusters and chains ............... 48
4 Nano-scale Molecular-Based Devices? ...................... 52
5 Conclusions and Future Perspectives ...................... 55
References ............................................... 56
2 Recent Synthetic Results Involving Single Molecule
Magnets ..................................................... 59
Guillem Aramí, Eric J.L. McInnes and Richard
E.P. Winpenny
1 Introduction ............................................. 59
2 A Brief Introduction to the Physics of SMMs .............. 60
3 Further SMMs Based on Mn(III) ............................ 64
3.1 The largest SMM; a [Mn84] torus ..................... 64
3.2 Record spin number, ST = 83/2, but no slow
relaxation .......................................... 65
3.3 Record magnetic anisotropy barrier; a Mn6 cluster ... 66
3.4 Quantum entanglement between SMMs; first
discovered in a pair of Мщ clusters ................. 67
3.5 [Mn3IIIMnIV] clusters with an S = 9/2 ground state ... 68
3.6 The [Mn2IIIMn2II] family of "rhombic" SMMs ............ 71
3.7 Oxime bridged SMMs with the core [Mn3III and
ST = 6 .............................................. 75
3.8 Magnetostructural correlations within a family
of [Mn6III] SMMs ..................................... 78
4 MMs Based on Fe(lll) Ions ................................ 82
5 New SMMs Based on Divalent 3d-Ions ....................... 82
6 Slow Relaxation in Complexes Involving 4f-Elements ....... 90
6.1 Single atom magnets ................................. 90
6.2 Polymetallic 4f-complexes ........................... 91
6.3 Heterometallic 3d-4f SMMs ........................... 94
7 Metallocyanate Based SMMs ................................ 99
8 Conclusions .............................................. 99
References .............................................. 100
3 The Nanoscopic Vis Cluster: A Unique Magnetic
Polyoxometalate ............................................ 109
Boris Tsukerblat and Alex Tarantul
1 The Unique Magnetic Polyoxometalate V15 ................. 109
2 Structure and Superexchange Pathways .................... 111
3 Exchange Interactions within the Triangle Model ......... 115
3.1 Isotropic exchange within the triangle model ....... 115
3.2 'Accidental' degeneracy and spin-frustration ....... 116
3.3 Pseudo-angular momentum representation ............. 118
3.4 Antisymmetric exchange, zero-field splitting ....... 119
3.5 Ab initio calculations ............................. 121
4 Zeeman Levels, Magnetic Anisotropy ...................... 122
5 Electron Paramagnetic Resonance ......................... 124
5.1 EPR spectrum of V15: Role of antisymmetric
exchange and selection rules ....................... 124
5.2 Discussion of the experimental EPR data ............ 129
6 Static Magnetization .................................... 134
6.1 The theoretical model .............................. 134
6.2 Discussion of the experimental magnetization
data ............................................... 137
7 Dynamic Properties, Relaxation, Spin Dynamics ........... 139
7.1 Relaxation mechanisms and magnetic hysteresis ...... 139
7.2 Spin dynamics in the muon scattering experiment .... 143
7.3 Rabi oscillations and implementation of molecular
magnets in quantum computing ....................... 145
8 Spin-vibronic Interaction ............................... 147
8.1 Hamiltonian of spin-vibronic coupling .............. 147
8.2 Adiabatic surfaces ................................. 150
8.3 Influence of the Jahn-Teller effect on the
magnetization ...................................... 155
8.4 Estimation of the vibronic parameters for V15 ...... 159
9 Role of Structural Deformations ......................... 160
9.1 Zero-field splitting in a scalene triangular
system ............................................. 160
9.2 Discussion of inelastic neutron scattering
experiments ........................................ 161
9.3 Energy pattern of a scalene triangular system ...... 164
9.4 Magnetic properties of the scalene systems ......... 166
9.5 Field induced Jahn-Teller instability .............. 167
10 NMR Experiments ......................................... 169
11 Conclusions and Outlook ................................. 172
References .............................................. 174
4 Neutron Spectroscopy of Molecular Nanomagnets .............. 181
Tatiana Guidi
1 Introduction ............................................ 181
2 Neutron Scattering: Basics Principles ................... 182
2.1 Neutron scattering cross section ................... 182
2.1.1 Nuclear scattering .......................... 184
2.1.2 Magnetic scattering ......................... 185
2.2 The time-of-flight technique ....................... 188
3 Exchange Interaction: A Spectroscopic Measurement ....... 189
3.1 Spin dynamics in antiferromagnetic molecular
rings .............................................. 192
3.1.1 Elementary excitations in
antiferromagnetic rings ..................... 193
4 Probing Quantum Coherence ............................... 197
4.1 Tunneling of the Neel vector ....................... 198
4.2 Quantum oscillations of the total spin ............. 201
5 Zero-Field Splitting Anisotropy in High Spin Clusters ... 203
5.1 The giant spin approximation and beyond ........... 203
5.1.1 Beyond the giant spin approximation ......... 208
References .............................................. 210
5 Recent Developments in EPR Spectroscopy of Molecular
Nanomagnets ................................................ 215
Eric J.L. McInnes
1 Beyond the Giant Spin Approximation (GSA) ............... 216
2 Discrete Clusters-of-Clusters ........................... 226
3 Pulsed EPR .............................................. 230
References .............................................. 237
6 Simulating Computationally Complex Magnetic Molecules ...... 241
Larry Engelhardt and Christian Schröder
1 Introduction ............................................ 241
1.1 Scope and purpose .................................. 241
1.2 Introduction to the Heisenberg Hamiltonian ......... 243
1.3 Usefulness and limitations of matrices ............. 246
2 Quantum Monte Carlo Simulations ......................... 247
2.1 Avoiding the 'roadblock' of large matrices ......... 247
2.2 Energy spectrum for symmetric rings ................ 250
2.3 Applications to heterometallic rings ............... 252
2.4 Applications to frustrated magnetic molecules ...... 257
3 Classical Spin Dynamics Simulations ..................... 262
3.1 The classical heisenberg hamiltonian ............... 264
3.2 Classical Monte Carlo simulations .................. 268
3.2.1 The spin equations of motion ................ 271
3.3 Heat bath simulational methods ..................... 274
3.4 Revealing novel physics in magnetic molecules
with classical methods ............................. 277
3.4.1 Competing spin phases and exchange
disorder in the Keplerate type molecules
{Mo72Fe30} and {Mo72O30} ..................... 278
3.4.2 Metamagnetic phase transitions in magnetic
polytopes ................................... 285
3.4.3 Critical slowing-down in Heisenberg
magnetic molecules .......................... 290
4 Summary ................................................. 292
References .............................................. 293
Index ......................................................... 297
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