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Coordination Number and Geometry

Coordination Number and Geometry

For transition metal complexes, the coordination number determines the geometry around the central metal ion. Table 1 compares coordination numbers to molecular geometry. The most common structures of the complexes in coordination compounds are octahedral, tetrahedral, and square planar.

Properties of Transition Metals

Properties of Transition Metals

Transition metals are defined as those elements that have partially filled d orbitals. As shown in Figure 1, the d-block elements in groups 3–12 are transition elements. The f-block elements, also called inner transition metals (the lanthanides and actinides), also meet this criterion because the d orbital is partially occupied before the f orbitals.

Coordination Compounds and Nomenclature

Coordination Compounds and Nomenclature

In most main group element compounds, the valence electrons of the isolated atoms combine to form chemical bonds that satisfy the octet rule. For instance, the four valence electrons of carbon overlap with electrons from four hydrogen atoms to form CH4. The one valence electron leaves sodium and adds to the seven valence electrons of chlorine to form the ionic formula unit NaCl (Figure 1a). Transition metals do not normally bond in this fashion. They primarily form coordinate covalent bonds, a...

Colors and Magnetism

Colors and Magnetism

Color in Coordination Complexes
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human...

Valence Bond Theory

Valence Bond Theory

Coordination compounds and complexes exhibit different colors, geometries, and magnetic behavior, depending on the metal atom/ion and ligands from which they are composed. In an attempt to explain the bonding and structure of coordination complexes, Linus Pauling proposed the valence bond theory, or VBT, using the concepts of hybridization and the overlapping of the atomic orbitals. According to VBT, the central metal atom or ion (Lewis acid) hybridizes to provide empty orbitals of suitable...

Crystal Field Theory - Tetrahedral and Square Planar Complexes

Crystal Field Theory - Tetrahedral and Square Planar Complexes

Tetrahedral Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...

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The Synthesis, Characterization and Reactivity of a Series of Ruthenium N-triphosPh Complexes

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Three-Coordinate Rhodium Complexes in Low Oxidation States.

Víctor Varela-Izquierdo¹, José A López¹, Bas de Bruin²

¹Departamento de Química Inorgánica, Instituto de Síntesis Química y Catálisis Homogénea (ISQCH), CSIC, Universidad de Zaragoza, Pedro Cerbuna 12, 50009, Zaragoza, Spain.

Chemistry (Weinheim an Der Bergstrasse, Germany)

|January 28, 2020

Summary

Chemists have synthesized novel low-coordinate rhodium complexes in low oxidation states. This research details the preparation of rhodium(-I), rhodium(0), and rhodium(I) compounds, advancing coordination chemistry.

Keywords:

NHC ligands low-valent metal-metal bond rhodium tri-coordinate

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Published on: December 29, 2016

Area of Science:

Inorganic Chemistry
Organometallic Chemistry
Coordination Chemistry

Background:

Synthesizing low-coordinate and low-valent metal compounds presents a significant challenge in preparative chemistry.
Rhodium complexes are crucial in catalysis and materials science, necessitating exploration of diverse coordination environments and oxidation states.

Purpose of the Study:

To prepare and fully characterize novel low-coordinate rhodium complexes in unusual oxidation states (-I, 0, and I).
To investigate the electronic structure and reactivity of these unique rhodium species.

Main Methods:

Reduction of a dimeric rhodium precursor, [{Rh(μ-Cl)(IPr)(dvtms)}₂], using KC₈ to yield rhodium(-I) and rhodium(0) complexes.
Oxidation or silver salt abstraction to generate the rhodium(I) cation.
Characterization techniques including spectroscopy and X-ray crystallography to confirm structures and electronic properties.

Main Results:

Successful synthesis and characterization of trigonal rhodium(-I) and rhodium(0) complexes, K[Rh(IPr)(dvtms)] and [Rh(IPr)(dvtms)].
Isolation of a rare trigonal pyramidal rhodium(I) cation, [Rh(IPr)(dvtms)]⁺.
Identification of the rhodium(0) complex as a fully metal-centered radical with an unpaired electron in the d_z2 orbital.
The rhodium(-I) complex acts as a nucleophile, forming a metal-metal bond with a gold(I) complex.

Conclusions:

This study successfully demonstrates the preparation of unprecedented low-coordinate rhodium complexes in low oxidation states.
The findings provide new insights into the electronic structure and reactivity of low-valent transition metal compounds.
The reported metal-metal bond formation opens avenues for designing novel multi-metallic systems.