N→Sn-Coordinated Stannaoxidoborates Containing a SnB4O6 Unit

We report here the synthesis of new N→Sn-coordinated stannaoxidoborates H­[LSnB4O6R4] {L = [2,6-(Me2NCH2)­C6H3]− and R = Ph (6), 4-Br-Ph (7), 3,5-(CF3)2-Ph (8), and 4-CHO-Ph (9)} containing a nonsymmetric SnB4O6 unit. Compounds 6–9 represent new derivatives of the pentaborates [B5O6R4]− in which the central boron is substituted by a tin atom. Compounds 6–9 were characterized by means of elemental analysis, electrospray ionization mass spectrometry, and NMR spectroscopy and in the case of 6–8 also by single-crystal X-ray diffraction analysis. The structures of N→Sn-coordinated stannaoxidoborates 6–8 consist of a spirobicyclic arrangement, with two six-membered SnB2O3 rings at the tin atom providing the new stannaoxidoborate [LSnB4O6R4]− motif, which is compensated for by the proton atom coordinated to the Me2N group of the ligand L. The linear and thermal properties of 6–9 were studied with the help of electronic absorption spectra and differential scanning calorimetry. In addition, the presence of the nonsymmetric stannaoxidoborate SnB4O6 unit in 6, 7, and 9 prompted us to investigate their second-order nonlinear-optical properties.