Alkali metals also readily form complexes with crown ethers (e.g. 12-crown-4 for Li+, 15-crown-5 for Na+, 18-crown-6 for K+, and 21-crown-7 for Rb+) and cryptands due to electrostatic attraction.
ˈælkəlˌaɪ mˈɛɾəlz ˈɔːlsoʊ ɹˈɛdili fˈɔːɹm kˈɑːmplɛksᵻz wɪð kɹˈaʊn ˈiːθɚz ˈiː.dʒˈiː. twˈɛlvkɹˈaʊn fˈoːɹ fɔːɹ lˈaɪ plˈʌs, fˈɪftiːŋkɹˈaʊn fˈaɪv fɔːɹ nˈɑː plˈʌs, ˈeɪtiːŋkɹˈaʊn sˈɪks fɔːɹ kˈeɪ plˈʌs, ænd twˈɛnti wˈʌŋkɹˈaʊn sˈɛvən fɔːɹ ˌɑːɹbˈiː plˈʌs ænd kɹˈɪptændz dˈuː tʊ ɪlˌɛktɹoʊstˈæɾɪk ɐtɹˈækʃən.