A nonmetal pentaborate [C6H13N2][B5O6(OH)4] (1) has been synthesized by 1,4-diazabicyclo[2.2.2] octane (DABCO) and boric acid, and characterized by single-crystal X-ray diffraction, FTIR, elemental analysis, and thermogravimetric analysis. Compound 1 crystallizes in the monoclinic system with space group Cc (no. 9), a=10.205(2) Å, b=14.143(3) Å, c=11.003(2) Å, β=113.97(3)°, V=1451.1(5) Å3, Z=4. The anionic units, [B5O6(OH)4]−, are interlinked via hydrogen bonding to form a three-dimensional (3D) supramolecular network containing large channels, in which the protonated [C6H13N2]+ cations are located. Second-harmonic generation (SHG) measurements on the powder samples reveal that 1 exhibits SHG efficiency approximately 0.9 times that of potassium dihydrogen phosphate (KDP).The protonated [C6H13N2]+ cations and the polyanions [B5O6(OH)4]− form a 3D supramolecular network by extensive hydrogen bonds and electrostatic attraction. This compound shows NLO properties and the SHG efficiency is approximately 0.9 times that of KDP.

The regioselectivity of Diels-Alder cycloaddition of 1,3-butadiene to C59XH (X=N, B) has been studied theoretically by means of the semiempirical AM1 and DFT (B3LYP/6-31G*) methods. The mechanisms of the cycloaddition on some selected 6.6 bonds of C59XH (X=N, B) have been analyzed. For C59NH, the activation energies become lower with the addition site increasingly farther from the N atom; however, they are all higher than that of the reaction of 1,3-butadiene with C60. In contrast to C59NH, for the cycloaddition to C59BH, the activation energies corresponding to 2,12/r- and 2,12/f-transition states, in which the addition sites are the nearest ones to the B atom, are the lowest ones, and are lower than that of the reaction of 1,3-butadiene with C60 by over 18 kJ·mol−1, and the products corresponding to these two transition states are the most stable ones. The different electronic natures of N and B atoms results in different effects on the Diels-Alder reactions of 1,3-butadiene with C59NH and C59BH; the former makes the reactivity of C59NH reduced and the latter makes the reactivity of C59BH enhanced, relative to that of C60.

The structures and stabilities of C60−n(NH)n (n=2–3) isomers have been investigated by AM1 and B3LYP/6-31G* methods. The lowest energy structure of C58(NH)2 is 1,9/16,17-isomer, in which the second pair of N and H substitute and add, respectively, on a 6–6 bond located on the equator. The most stable isomer of C57(NH)3 contains a pyrrole moiety, the driving force governing the stabilities of C57(NH)3 isomers may be the formation of the local aromatic substructure. The calculations indicate that N and H atoms contiguously substitute and add, respectively, on the adjacent 6–6 double bond that is energetically unfavorable.