Titanium Hydride Complex BaCa₂Ti₂H₁₄ with 9-Fold Coordination

Area of Science:

• Solid-state chemistry
• Materials science
• Inorganic chemistry

Background:

• Titanium hydrides are of interest for their unique electronic and structural properties.
• Understanding coordination environments in metal hydrides is crucial for designing new materials.
• High-pressure synthesis enables the discovery of novel compounds not accessible under ambient conditions.

Purpose of the Study:

• To synthesize and characterize a novel titanium hydride complex under high pressure.
• To elucidate the crystal structure and coordination environment of the new titanium hydride.
• To investigate the electronic and optical properties of the synthesized compound.

Main Methods:

• High-pressure synthesis techniques.
• X-ray diffraction for crystal structure determination.
• Optical spectroscopy (UV-Vis) for band gap measurement.
• Density functional theory (DFT) calculations for electronic structure analysis.

Main Results:

• Successful synthesis of a novel titanium hydride, BaCa2Ti2H14, under high pressure.
• Discovery of a unique dinuclear [Ti2H14]6- complex with 9-fold hydride coordination in a monocapped square antiprism geometry.
• Observation of a wide band gap of 2.25 eV, classifying BaCa2Ti2H14 as a band insulator.
• DFT calculations indicate the valence band top is dominated by H-1s states.

Conclusions:

• The novel dinuclear titanium hydride complex BaCa2Ti2H14 exhibits unusual 9-fold coordination stabilized by multi-center bonding.
• The material's electronic structure suggests potential for high-temperature superconductivity upon doping or application of pressure.
• This discovery expands the known structural diversity of metal hydrides and highlights pathways for designing novel functional materials.