Rubidium and caesium can form a great variety of suboxides with the metals in formal oxidation states below +1.
ɹuːbˈɪdiəm ænd sˈiːsiəm kæn fˈɔːɹm ɐ ɡɹˈeɪt vɚɹˈaɪəɾi ʌv sʌbˈɑːksaɪdz wɪððə mˈɛɾəlz ɪn fˈɔːɹməl ˌɑːksɪdˈeɪʃən stˈeɪts bᵻlˌoʊ plˈʌs wˈʌn.