Alkali metal cations do not usually form coordination complexes with simple Lewis bases due to their low charge of just +1 and their relatively large size; thus the Li+ ion forms most complexes and the heavier alkali metal ions form less and less (though exceptions occur for weak complexes).
ˈælkəlˌaɪ mˈɛɾəl kˈæɾaɪənz duːnˌɑːt jˈuːʒuːəli fˈɔːɹm koʊˈɔːɹdᵻnˈeɪʃən kˈɑːmplɛksᵻz wɪð sˈɪmpəl lˈuːɪs bˈeɪsᵻz dˈuː tə ðɛɹ lˈoʊ tʃˈɑːɹdʒ ʌv dʒˈʌst plˈʌs wˈʌn ænd ðɛɹ ɹˈɛlətˌɪvli lˈɑːɹdʒ sˈaɪz; ðˈʌs ðə lˈaɪ plˈʌs ˈaɪɑːn fˈɔːɹmz mˈoʊst kˈɑːmplɛksᵻz ænd ðə hˈɛviɚɹ ˈælkəlˌaɪ mˈɛɾəl ˈaɪɑːnz fˈɔːɹm lˈɛs ænd lˈɛs ðˌoʊ ɛksˈɛpʃənz əkˈɜː fɔːɹ wˈiːk kˈɑːmplɛksᵻz.