Details of crystal structure and solid-state coordination Chemistry of MBO 3 (M = Ti, V, Cr, Fe)

Transition-metal orthoborates (MBO 3 ; M = Ti, V, Cr, Fe) provide well-defined model systems for investigating the interplay among precursor chemistry, phase formation, crystal structure, electronic structure, and functional properties in borate materials. Their structures contain isolated trigonal-planar BO 3 units interconnected with transition-metal–oxygen polyhedra, providing a common basis for systematic comparison. However, studies of TiBO 3 (Titanium orthoborate), VBO 3 (Vanadium orthoborate), CrBO 3 (Chromium orthoborate), and FeBO 3 (Iron orthoborate) have largely addressed individual aspects of their crystal chemistry, synthesis, or physical properties, while the relationships among precursor chemistry, reaction pathways, phase evolution, and material properties remain insufficiently integrated. This review therefore critically examines the crystal chemistry, precursor chemistry, synthesis routes, phase-evolution pathways, and structure–property relationships of these four orthoborates. Particular emphasis is placed on experimentally established phase formation and crystallization behavior, including the roles of precursor composition, thermal treatment, diffusion, competing phases, and reaction conditions. Experimental results obtained for CrBO 3 and FeBO 3 in our studies are considered together with published data, whereas TiBO 3 and VBO 3 are evaluated primarily from the available literature. The four orthoborates are comparatively assessed in terms of crystal structure, transition-metal electronic configuration, magnetic and optical behavior, and reported functional properties, while differences in experimental conditions and limitations of cross-study comparisons are considered. Rather than treating synthesis and properties independently, this review establishes how precursor chemistry and phase evolution influence structural characteristics and, consequently, material properties. Finally, unresolved issues, including incomplete understanding of phase boundaries and crystallization pathways, limited comparable quantitative datasets, and insufficient characterization under relevant operating conditions, are identified as priorities for future research.