Valence bond description of antiferromagnetic coupling in transition metal dimers

1981 ◽  
Vol 74 (10) ◽  
pp. 5737-5743 ◽  
Author(s):  
Louis Noodleman
Keyword(s):  
Transition Metal ◽  
Valence Bond ◽  
Antiferromagnetic Coupling

Symmetry Violations in Partially Oxidized One-Dimensional (1D)Transition Metal Polymers. Metal-Ligand-Metal(M-L-M) Bridged Systems

1984 ◽  
Vol 39 (9) ◽  
pp. 807-829
Author(s):  
Michael C. Böhm
Keyword(s):  
Transition Metal ◽  
Density Wave ◽  
Tight Binding ◽  
Mean Field ◽  
Valence Bond ◽  
Hole State ◽  
One Dimensional ◽  
Metal Derivatives ◽  
A Charge ◽  
Metal Ligand

The band structure of the metal-ligand-metal (M-L-M) bridged quasi one-dimensional (1D) cyclopentadienylmanganese polymer, MnCp 1, has been studied in the unoxidized state and in a partly oxidized modification with one electron removed from each second MnCp fragment. The tight-binding approach is based on a semiempirical self-consistent-field (SCF) Hartree-Fock (HF) crystal orbital (CO) model of the INDO-type (intermediate neglect of differential overlap) combined with a statistical averaging procedure which has its origin in the grand canonical ensemble. The latter approximation allows for an efficient investigation of violations of the translation symmetries in the oxidized 1D material. The oxidation process in 1 is both ligand- and metal-centered (Mn 3d-2 states). The mean-field minimum corresponds to a charge density wave (CDW) solution with inequivalent Mn sites within the employed repeat-units. The symmetry adapted solution with electronically identical 3d centers is a maximum in the variational space. The coupling of this electronic instability to geometrical deformations is also analyzed. The ligand amplitudes encountered in the hole-state wave function prevent extremely large charge separations between the 3d centers which are found in ID systems without bridging moieties (e.g. Ni(CN)2-5 chain). The symmetry reduction in oxidized 1 is compared with violations of spatial symmetries in finite transition metal derivatives and simple solids. The stabilization of the valence bond-type (VB) solution is physically rationalized (i.e. left-right correlations between the 3d centers). The computational results derived for 1 are generalized to oxidized transition metal chains with band occupancies that are simple fractions of the number of stacking units and to 1D systems that deviate from this relation. The entropy-influence for temperatures T ≠ 0 is shortly discussed (stabilization of domain or cluster structures).

scholarly journals LARGE N EXPANSION FOR FRUSTRATED AND DOPED QUANTUM ANTIFERROMAGNETS

1991 ◽  
Vol 05 (01n02) ◽  
pp. 219-249 ◽  
Author(s):  
Subir Sachdev ◽  
N. Read
Keyword(s):  
Valence Bond ◽  
Square Lattice ◽  
Antiferromagnetic Coupling ◽  
Spin Correlations ◽  
Range Magnetic Order ◽  
Quantum Antiferromagnets ◽  
Large N ◽  
Expansion Technique ◽  
Quantum Antiferromagnet ◽  
Large N Expansion

A large N expansion technique, based on symplectic (Sp(N)) symmetry, for frustrated magnetic systems is studied. The phase diagram of a square lattice, spin S, quantum antiferromagnet with first, second and third neighbor antiferromagnetic coupling (the J1-J2-J3 model) is determined in the large-N limit and consequences of fluctuations at finite N for the quantum disordered phases are discussed. In addition to phases with long range magnetic order, two classes of disordered phases are found: (i) states similar to those in unfrustrated systems with commensurate, collinear spin correlations, confinement of spinons, and spin-Peierls or valence-bond-solid order controlled by the value of 2S (mod 4) or 2S (mod 2) ; (ii) states with incommensurate, coplanar spin correlations, and unconfined bosonic spin-1/2 spinon excitations. The occurrence of “order from disorder” at large S is discussed. Neither chirally ordered nor spin nematic states are found. Initial results on superconductivity in the t—J model at N=∞ and zero temperature are also presented.

Valence bond analysis of the bonding in transition metal compounds: the RuNO group in nitrosyl complexes

2003 ◽  
Vol 101 (6) ◽  
pp. 715-720 ◽  
Author(s):  
OL'GA V. SIZOVA ◽  
VICTOR I. BARANOVSKI ◽  
NINA V. IVANOVA ◽  
VLADIMIR V. SIZOV
Keyword(s):  
Transition Metal ◽  
Valence Bond ◽  
Transition Metal Compounds ◽  
Metal Compounds ◽  
Nitrosyl Complexes

Transition Metal Thiocyanate Complexes of Picolylcyanoacetamides

2017 ◽  
Vol 70 (5) ◽  
pp. 516 ◽  
Author(s):  
Yuniar P. Prananto ◽  
Aron Urbatsch ◽  
Boujemaa Moubaraki ◽  
Keith S. Murray ◽  
David R. Turner ◽  
...  
Keyword(s):  
Transition Metal ◽  
Transition Metal Complexes ◽  
Short Range ◽  
Sodium Thiocyanate ◽  
Antiferromagnetic Coupling ◽  
Carbonyl Groups ◽  
Ambient Conditions ◽  
One Dimensional ◽  
Thiocyanate Complexes ◽  
Solid State Structures

A variety of transition metal complexes involving picolylcyanoacetamides (pica = NCCH2CONH-R; R = 2-picolyl- (2pica), 3-picolyl- (3pica), 4-picolyl- (4pica)) and thiocyanate have been synthesised and their solid-state structures have been determined. The complexes were all obtained from reactions between the corresponding metals salts and pica ligands with sodium thiocyanate under ambient conditions. Both 3pica and 4pica coordinate to the metal solely through the nitrogen atom of the picolyl group and form discrete tetrahedral [M(NCS)2(pica)2] (3pica; M = Mn, Zn; 4pica; M = Co) and octahedral [M(NCS)2(3pica)4] (M = Co, Fe, Ni) complexes. In addition, one-dimensional N,S-thiocyanate-bridged coordination polymers poly-[M(µ-NCS)2(pica)2] (3pica; M = Cd; 4pica; M = Co, Cd) were obtained. The ligand 2pica gave the discrete octahedral complexes [Co(NCS)2(2pica)2] and [Cd(NO3)2(2pica)2] in which 2pica chelates in a bidentate fashion through its picolyl and carbonyl groups. Magnetic susceptibility measurements on the cobalt(ii) complexes were performed and showed short-range antiferromagnetic coupling for the [Co(NCS)2(4pica)2]n 1D polymer.

scholarly journals Chiral, Heterometallic Lanthanide–Transition Metal Complexes by Design

Inorganics ◽  
2018 ◽  
Vol 6 (3) ◽  
pp. 72 ◽  
Author(s):  
Anders Øwre ◽  
Morten Vinum ◽  
Michal Kern ◽  
Joris van Slageren ◽  
Jesper Bendix ◽  
...  
Keyword(s):  
Transition Metal ◽  
Transition Metal Complexes ◽  
Lewis Acids ◽  
Antiferromagnetic Coupling ◽  
Relaxation Processes ◽  
Coordination Geometry ◽  
Ferromagnetic Coupling ◽  
Metal Acetylacetonates ◽  
Metal Centers ◽  
Tunneling Pathways

Achieving control over coordination geometries in lanthanide complexes remains a challenge to the coordination chemist. This is particularly the case in the field of molecule-based magnetism, where barriers for magnetic relaxation processes as well as tunneling pathways are strongly influenced by the lanthanide coordination geometry. Addressing the challenge of design of 4f-element coordination environments, the ubiquitous Ln(hfac)3 moieties have been shown to be applicable as Lewis acids coordinating transition metal acetylacetonates facially leading to simple, chiral lanthanide–transition metal heterodinuclear complexes. The broad scope of this approach is illustrated by the synthesis of a range of such complexes LnM: LnM(hfac)3(μ2-acac-O,O,O′)3 (Ln = La, Pr, Gd; M = Cr, Fe, Ga), with approximate three-fold symmetry. The complexes have been crystallographically characterized and exhibit polymorphism for some combinations of 4f and 3d metal centers. However, an isostructural set of systems spanning several lanthanides which exhibit spontaneous resolution in the orthorhombic Sohncke space group P212121 is presented here. The electronic structure and ensuing magnetic properties have been studied by EPR spectroscopy and magnetometry. The GdFe, PrFe, and PrCr complexes exhibit ferromagnetic coupling, while GdCr exhibits antiferromagnetic coupling. GdGa exhibits slow relaxation of the magnetization in applied static fields.

Sign in / Sign up

Export Citation Format

Share Document