The title compound, s-fac-[Co(dien)2][B7O9(OH)6].9H2O(1) (dien = HN(CH2CH2NH2)2), has been prepared as a crystalline solid in moderate yield (35%) from the reaction of B(OH)3 with [Co(dien)2][OH]3 in aqueous solution (10:1 ratio). The structure contains a novel polyborate anion [B7O9(OH)6] 3-which is structurally based on the known 'ribbon' isomer of [B7O9(OH)5] 2-, with an additional [OH] -group coordinated to a B atom in one of the outer boroxole rings. Compound 1 is formed by a self-assembly process in which the cation and anion mutually template themselves from equilibrium mixtures under reaction conditions. The [B7O9(OH)6] 3-, anions are H-bonded to each other in layers with 'cavities' suitable for the [Co(dien]2] 3+ complex. Three [B7O9(OH)6] 3-anions are in the secondary coordination sphere (via H-bonds) of each cation, with each anion H-bonded to three cations.
___________________________________________________________________________Polyborate anions are conveniently classified as either 'condensed' (polymeric chains, sheets or networks) or 'isolated' with discrete anionic moieties. Salts containing polyborate anions have attracted recent attention due to their possible applications as luminescent, second harmonic generation, ferroelectric, flame retardant and non-linear optical materials [1]. Isolated polyborate anions are readily synthesised by solvothermic methods [2] or by the addition of B(OH)3 to a basic aqueous solution containing a potential templating cation [3]. Self-assembled products arise since B(OH)3 in basic aqueous solution exists as a dynamic combinatorial library of a number of polyborate anions [4]. In general, pentaborate(1-) salts (containing the [B5O6(OH)4] -anion) are formed because these salts have a strong H-bonded anionic lattice and this lattice is sufficiently flexible to accommodate many small to medium sized cations [5]. Salts containing polyborate anions other than pentaborate(1-) are relatively rare [6]. We are interested in the synthesis of structurally novel polyborate anions and have adopted a strategy of templating such species by the use of sterically demanding and/or highly charged cations [7]. Herein, we report the self-assembly of a salt containing a novel isolated heptaborate(3-) anion, partnered with cationic transition-metal coordination complex. This salt's thermal properties, and its structure as determined by single-crystal XRD are also reported. [8]. Compound 1 was initially characterized by elemental analysis, IR and NMR ( 1 H, 13 C, and 11 B) spectroscopy, and by thermal (TGA/DSC) analysis (air). The thermal and spectroscopic data indicated that 1 was not a pentaborate(1-) salt. In particular, the compound displayed several BO bands in the IR spectra but the diagnostic pentaborate(1-) peak (926 cm -1 ) [9] was absent. At 'infinite' dilution its 11 B NMR spectrum gave a single peak at +12.3 ppm, rather than at +16.1 [5] which would be indicative of pentaborate(1-). This higher field 11 B signal would be more consistent with a lower B/charge ra...