Borates are emerging as a versatile class of optical materials for modulating the light supplied by common laser sources. Consequently, sustained and consistent efforts have been made by chemists and material scientists towards exploring and investigating new borates with unique crystal structures or properties. Over the past decades, more than 1000 borates, including borate minerals and synthetic inorganic borates, have been discovered and characterized as a significant component of multiple functional materials. From the point of view of the structure-propertyrelationships, the multifunction of borates arises from the vacant p orbitalsof boron that can reversibly interact with oxygen nucleophiles to construct the [BO3]3- triangles or the [BO4]5-tetrahedra.With respect to the polymerized B-O units, edge-sharing connection can occur only between two [BO4]5- units in very few borates. To date, there are only less than 20 borates containing the edge-sharing [BO4]5-tetrahedra, which were obtained under the preferred high-pressure conditions.To date, KZnB3O6with edge-sharing [BO4]5- configuration is the sole borate that discoveredunder ambient pressure. During the last decades, hundreds of borates were discovered under atmospheric pressure, but no more disorder-free borates contain edge-sharing [BO4]5-tetrahedra.

Recently, a research group led by Prof. ShiliePan at Xinjiang Technical Institute of Physics & Chemistry, Chinese Academy of Science,hassuccessfully synthesized a new edge-sharing [BO4]5-tetrahedra containingborateunderthe atmospheric pressure condition. The study was published inChemical Communications with title of “Li4Na2CsB7O14: anew edge-sharing [BO4]5-tetrahedracontainingborate with high anisotropic thermal expansion”.

Single crystals of Li4Na2CsB7O14 were obtained by high-temperature solution method in an open system.The crystal structure was solved and refined based on the collected singlecrystal X-ray diffraction data, which confirms the existence of edge-sharing [BO4]5-tetrahedra.The unprecedented [B14O28]14-fundamental building block in Li4Na2CsB7O14has never been reported in any other borates.The infraredspectra and calculatedvibrational modes also confirm the existence of unique edge-sharing [BO4]5-tetrahedra. Phonon dispersion spectrum as well as the function between the total energy and volume per atom confirms itsdynamic stability. With the cooperation of Prof. Gang Wang from Institute of Physics, Chinese Academy of Sciences, the thermal expansion coefficients have been measured, results show that Li4Na2CsB7O14exhibits an unusual anisotropic thermal expansion and can be used as a new thermal expansion material.