The X-ray single crystal diffractometer reveals the three-dimensional structure of molecules through the interaction between X-rays and regularly arranged atoms in the crystal, combined with precision instruments and mathematical calculations. The principle and process are as follows:

Core principles: X-ray diffraction and Bragg equation

When monochromatic X-rays (such as CuK α radiation from a copper target) are irradiated onto a single crystal, the regularly arranged atomic spacing in the crystal is on the order of magnitude of the X-ray wavelength, and the scattered X-rays from the atoms interfere, producing strong diffraction in a specific direction (the direction satisfying the Bragg equation n λ=2dsin θ). Among them, λ is the wavelength of X-rays, d is the interplanar spacing, θ is the incident angle, and n is the diffraction order. The diffraction direction is directly related to the crystal structure, and each crystal produces a unique diffraction pattern.

Key steps: From diffraction data to three-dimensional structure

Data collection:

The instrument controls the rotation of the crystal through a high-precision angle measuring instrument (such as a four circle diffractometer), so that different crystal planes satisfy the diffraction conditions in sequence. A detector (such as a photon counting CCD) captures diffraction signals, records the position and intensity of diffraction points, and forms a two-dimensional diffraction pattern containing crystal structure information.

Mathematical inversion:

The intensity of diffraction points is related to the distribution of atoms in the unit cell. Convert diffraction data into a three-dimensional distribution map of electron density within the unit cell through Fourier transform. The atomic position corresponds to the peak electron density, thereby determining parameters such as atomic coordinates, bond length, and bond angle.

Structural validation and optimization:

By combining chemical bond information (such as bond length range) and symmetry analysis, the initial structural model is modified to ultimately determine the precise three-dimensional configuration of the molecule.

Technical advantages and application scenarios

Atomic level resolution: can accurately determine atomic positions, reveal molecular stereoisomers, chirality, and crystal stacking patterns.

Wide applicability: From simple inorganic substances to complex biomolecules (such as protein ligand complexes), this technology can be used to analyze their structures.

Key applications: In drug development, this technology can determine drug crystal forms and optimize molecular design; In materials science, assisting in the design of metal organic frameworks (MOFs) or covalent organic frameworks (COFs) materials with specific properties.