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Elongated, hexagonal-prismatic seed crystals are the starting point for the hierarchical growth of anisotropic spherical aggregates of fluorapatite in gelatin matrices. Discrete dumbbell-shaped aggregates (scanning electron microscope image shown on the right) are formed by self-similar, branched, needlelike upgrowths at both ends of the seeds. With successive generations, these aggregates close to give pheres with diameters of up to 400 μm. The system makes it possible to monitor the development of antibiotic information pattern into the macroscopic range

Borophosphates (intermediate compounds of the system MxOy-B2O3-P2O5-(H2O)) contain complex anionic structures built of BO4, BO3, and PO4 groups and their partially protonated species, respectively. A first approach to the development of a structural chemistry of borophosphates is based on linking principles of the primary building units following the general Line of silicate crystal chemistry. The crystal structures of borophosphates are first divided into anhydrous and hydrated phases. Further gradings are based on the (molar) B:P ratios. The structural chemistry of borophosphate anions already extends from isolated species, oligomers, rings, and chains to layers and frameworks. Additional characteristics are integration of planar BO3 groups, preferred formation of 3-membered rings, and unusual branching of tetrahedral chains. P-O-P linking in borophosphates is not observed up to now

A concept for the classification of crystalline (metallo)borophosphates in terms of structural chemistry is proposed and the compounds known to date are classified in an overview. Similarities and differences with (alumo)silicates and Liebau's classification are discussed with respect to the observation that the different borate and phosphate complexes are not interconnected arbitrarily in borophosphates. By combination and extension of existing concepts for silicates and borates a hierarchical system based on oligomeric building units has been developed. The observed connection rules are rationalized and the strong influence of the composition on dimensionality and structural motifs of the formed anions is pointed out. Likewise the effect of OH groups is taken into account by grading anions according to the degree of protonation (ratio O:OH). A general distinction is made between tetrahedral and mixed coordinated borophosphates. Metalloborophosphates are treated separately as special cases of borophosphates. Finally, anion‐substituted compounds, border cases, and borate‐phosphates complete the overview.

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Vertex‐sharing BO4 and PO4 tetrahedra form the framework of the title compounds. Ca[BPO5] and Sr[BPO5] crystallize in the stillwellite structural type and contain tetrahedral chain anions [BPO], which can be described as loop‐branched “dreier” single chains. In Ba3[BP3O12] the tetrahedral anions form “zweifach” open “vierer” single chains. Given these results and the known linking modes of tetrahedral units, it is expected that borophosphates with layered and framework structures, as well as microporous structures, can be found.

The crystal chemistry of ternary and quaternary phases of the systems A/AE - TE - N (A = alkali metal; AE = alkaline earth metal; TE = transition element) is predominantly characterized by the presence and formation of complex nitridometalate onions. A suitable classification of the nitrido-compounds is based on the correlation between coordination-numbers (TE), oxidation states (TE) and the specific structural characteristics of the anionic partial structures