The alkali metal borides tend to be boron-rich, involving appreciable boron–boron bonding involving deltahedral structures, and are thermally unstable due to the alkali metals having a very high vapour pressure at elevated temperatures.
ðɪ ˈælkəlˌaɪ mˈɛɾəl bˈoːɹaɪdz tˈɛnd təbi bˈoːɹɑːnɹˈɪtʃ, ɪnvˈɑːlvɪŋ ɐpɹˈiːʃiəbəl bˈoːɹɑːn bˈoːɹɑːn bˈɑːndɪŋ ɪnvˈɑːlvɪŋ dˌɛltɐhˈiːdɹəl stɹˈʌktʃɚz, ænd ɑːɹ θˈɜːməli ʌnstˈeɪbəl dˈuː tə ðɪ ˈælkəlˌaɪ mˈɛɾəlz hˌævɪŋ ɐ vˈɛɹi hˈaɪ vˈeɪpɚ pɹˈɛʃɚɹ æɾ ˈɛlɪvˌeɪɾᵻd tˈɛmpɹɪtʃɚz.