I can see two possibilities.
(a) Two coordinate bonds
#color(white)(mmmm)"H"color(white)(mmmmmmmmmml)"H"#
#color(white)(mmmml)|color(white)(mmmmmmmmmmm)|#
#"M"^"n+" + ":O:" + "M"^"n+" → "M"^"(n-1)+""—"stackrelcolor(blue)("+2")("O")"—""M"^"(n-1)+"#
#color(white)(mmmml)|color(white)(mmmmmmmmmmm)|#
#color(white)(mmmm)"H"color(white)(mmmmmmmmmmll)"H"#
(b) One coordinate and one π bond
#color(white)(mmmm)"H"color(white)(mmmmmml)"H"#
#color(white)(mmmml)|color(white)(mmmmmmm)|#
#"M"^"n+" + ":O:" → "M"^"(n-2)+""="stackrelcolor(blue)("+2")("O")"#
#color(white)(mmmml)|color(white)(mmmmmmm)|#
#color(white)(mmmm)"H"color(white)(mmmmmmll)"H"#
In each case, the +2 formal charge on oxygen would make it highly acidic.
The #"O"# atom would lose a proton, and there would again be one shared lone pair.
