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Crystal Field Theory - Octahedral Complexes

Crystal Field Theory - Octahedral Complexes

Crystal Field Theory
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...

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,...

Network Covalent Solids

Network Covalent Solids

Network covalent solids contain a three-dimensional network of covalently bonded atoms as found in the crystal structures of nonmetals like diamond, graphite, silicon, and some covalent compounds, such as silicon dioxide (sand) and silicon carbide (carborundum, the abrasive on sandpaper). Many minerals have networks of covalent bonds.
To break or to melt a covalent network solid, covalent bonds must be broken. Because covalent bonds are relatively strong, covalent network solids are typically...

Metallic Solids

Metallic Solids

Metallic solids such as crystals of copper, aluminum, and iron are formed by metal atoms. The structure of metallic crystals is often described as a uniform distribution of atomic nuclei within a “sea” of delocalized electrons. The atoms within such a metallic solid are held together by a unique force known as metallic bonding that gives rise to many useful and varied bulk properties.
All metallic solids exhibit high thermal and electrical conductivity, metallic luster, and malleability....

Ionic Crystal Structures

Ionic Crystal Structures

Ionic crystals consist of two or more different kinds of ions that usually have different sizes. The packing of these ions into a crystal structure is more complex than the packing of metal atoms that are the same size.
Most monatomic ions behave as charged spheres, and their attraction for ions of opposite charge is the same in every direction. Consequently, stable structures for ionic compounds result (1) when ions of one charge are surrounded by as many ions as possible of the opposite...

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...

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Related Experiment Video

Updated: Sep 13, 2025

Microfluidic-based Synthesis of Covalent Organic Frameworks COFs: A Tool for Continuous Production of COF Fibers and Direct Printing on a Surface

Microfluidic-based Synthesis of Covalent Organic Frameworks COFs: A Tool for Continuous Production of COF Fibers and Direct Printing on a Surface

Published on: July 10, 2017

Polyhedral Crystal Films of Covalent Organic Frameworks.

Xiansong Shi¹, Qixing Liu¹, Haipei Shao²

¹Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, Singapore 117585, Singapore.

Journal of the American Chemical Society

|July 29, 2025

Summary

Researchers developed a scalable method for creating highly crystalline covalent organic framework (COF) films with polyhedral textures. These advanced COF films demonstrate tunable properties and enhanced performance for energy and environmental applications.

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Microfluidic-based Synthesis of Covalent Organic Frameworks COFs: A Tool for Continuous Production of COF Fibers and Direct Printing on a Surface

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Area of Science:

Materials Science
Nanotechnology
Chemical Engineering

Background:

Porous crystal films, particularly covalent organic frameworks (COFs), hold significant promise for energy and environmental solutions.
Achieving polyhedral textures in COF films, indicative of their crystalline nature, has been a persistent challenge in materials science.

Purpose of the Study:

To develop a scalable and adaptable synthesis strategy for producing COF films with exceptional crystalline order and polyhedral textures.
To investigate the properties and potential applications of these novel COF films, focusing on their thermal and sensing capabilities.

Main Methods:

A biphasic synthesis strategy was employed under ambient conditions to control polycrystal formation and substrate-based crystal growth.
Characterization techniques including electron microscopy and Brunauer-Emmett-Teller (BET) analysis were used to assess film structure and surface area.
Anisotropic thermal properties and sensor performance were evaluated to correlate film crystallinity with device functionality.

Main Results:

Scalable synthesis of pyrene (Py)-COF polyhedral crystal films with tunable nanometer-scale thicknesses on a wafer scale was achieved.
A Py-1P film exhibited a record-high BET surface area for COF films of comparable pore size, along with notable chemical stability.
Anisotropic thermal responses and dynamically adaptive thermal expansion coefficients were observed, linked to the [001] lattice direction.

Conclusions:

The developed biphasic strategy offers precise control over COF film formation, overcoming previous limitations in achieving crystalline polyhedral textures.
These highly crystalline COF films demonstrate significant potential for advanced applications in sensing and other areas due to their unique properties and stability.
This research advances the field of COF films, opening new avenues for film science and the development of next-generation energy and environmental technologies.