A new approach to synthesis of functional derivatives of 7,8-dicarba-nido-undecaborate anion based on ring-opening of its cyclic oxonium derivatives [10-(CH 2 ) 4 O-7,8-C 2 B 9 H 11 ] and [10-O(CH 2 CH 2 ) 2 O-7,8-C 2 B 9 H 11 ] with various nucleophiles was developed. Both cyclic oxonium derivatives can be obtained as single isomers by reaction of the parent anion [7,8-C 2 B 9 H 12 ] -with mercury(II) chloride in the corresponding solvents. Mechanism of formation of the cyclic oxonium derivatives of 7,8-dicarba-nido-undecaborate anion was proposed. A series of 7,8-dicarba-nido-undecaborate derivatives with terminal carboxylic and azide functions were prepared by the ring-opening reactions of the cyclic oxonium derivatives with substituted phenolate and azide ions, respectively.

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1. Broad-scale assessment of biodiversity is needed for detection of future changes across substantial regions of the Arctic. Presently, there are large data and information gaps in species composition and richness of the freshwater planktonic and meiobenthos communities of the Russian Arctic. Analysis of these data is very important for identifying the spatial distribution and temporal changes in species richness and diversity of rotifers, cladocerans, and copepods in the continental Russian Arctic.2. We investigated biogeographic patterns of freshwater plankton and meiobenthos from c. 67° to 73°N by analysing data over the period 1960-2017. These data include information on the composition of rotifers, cladocerans, and copepods obtained from planktonic and meiobenthic samples, as well as from subfossil remains in bottom sediments of seven regions from the Kola Peninsula in the west, to the Indigirka River Basin (east Siberia) in the east. 3. Total richness included 175 species comprised of 49 rotifer genera, 81 species from 40 cladoceran genera, and 101 species from 42 genera of calanoid, cyclopoid, and harpacticoid copepods. Longitudinal trends in rotifer and micro-crustacean diversity were revealed by change in species composition from Europe to eastern Siberia. The most common and widespread species were 19 ubiquitous taxa that included Kellicottia longispina (Rotifera), Chydorus sphaericus s. lat. (Cladocera), Heterocope borealis, Acanthocyclops vernalis, and Moraria duthiei (Copepoda). The highest number of rare species was recorded in the well-studied region of the Bolshezemelskaya tundra and in the Putorana Plateau.4. The total number of copepod and rotifer species in both Arctic lakes and ponds tended to increase with latitude. Relative species richness of copepods was positively associated with waterbody area, elevation, and precipitation, while relative species richness of cladocerans was positively related to temperature. This result is consistent with known thermophilic characteristics of cladocerans and the cold tolerance properties of copepods, with the former being dominant in shallow, warmer waterbodies of some western regions, and the latter being dominant in This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.