Would a dataframe of NAs work?
something like:
data.frame(matrix(NA, nrow = 2, ncol = 3))
if you need to be more specific about the data type then may prefer: NA_integer_, NA_real_, NA_complex_, or NA_character_ instead of just NA which is logical
Something else that may be more specific that the NAs is:
data.frame(matrix(vector(mode="numeric",length = 6), nrow = 2, ncol = 3))
where the mode can be of any type. See ?vector