I want to concatenate two dataframes by using the following expression 

```
new_data = pd.concat([first_data, second_data], axis=1)

```

first\_data:

```
id      Col1      Col2     Col3
1       aaaa      bbbb     cccc      
2       dddd      eeee     ffff
3       gggg      hhhh     iiii

```

Second Data:

```
Col4    Col5
mmmm    nnnn
oooo    pppp
qqqq    rrrr

```

I get this problem: 

```
id      Col1      Col2     Col3      Col4    Col5
1       nan       nan      nan       mmmm    nnnn
2       nan       nan      nan       oooo    pppp
3       nan       nan      nan       qqqq    rrrr
4       aaaa      bbbb     cccc      nan     nan
5       dddd      eeee     ffff      nan     nan
6       gggg      hhhh     iiii      nan     nan

```