What is the best way to concatenate dataframe with 2 different pattern in R

I've several dataframes :

toto1_1 <- as.data.frame(x=1:3)
toto1_2 <- as.data.frame(x=1:3)
titi1_1 <- as.data.frame(x=1:3)
titi1_2 <- as.data.frame(x=1:3)

What is the best way to concatenate this tables using 2 différents patterns?

Thank u