Andrew Marvell "To His Coy Mistress" and Christopher Marlowe's "The Passionate Shepherd to His Love" have similar theme: carpe diem. Compare and contrast the structures and the tones of thes two poems.

Both poems are indeed about carpe diem in the realm of love. The speakers of both are impetuous, impassioned lovers trying to persuade the object of their affections in wasting no time to belong to one another. Both are also written in iambic tetrameter, with four iambs per line, so their structures are similar too. However, while Marlowe's poem is joyous (some have argued too naive and earnest), Marvell's is more concerned with the passage of time and the need to appreciate youth while it lasts.
"The Passionate Shepherd to His Love" is all about the physical pleasures the shepherd promises his love. He invokes images such as beds of roses and nature to entice the lover. The nature images are meant to suggest a pastoral setting which is separate from the bustle and stress of a city. He is promising simple pleasures and true love, and as a result, its tone is passionate and joyful.
"To His Coy Mistress" is the far more urgent poem, its tone one of haste and near-desperation. The poet stresses to his reluctant beloved that they will not be young forever. One of the poem's most haunting images is that of the tomb:

Thy beauty shall no more be found;
Nor, in thy marble vault, shall sound
My echoing song; then worms shall try
That long-preserved virginity,
And your quaint honour turn to dust,
And into ashes all my lust;
The grave’s a fine and private place,
But none, I think, do there embrace.

The poet wants his beloved to realize that time does not stop and that they must consummate their love while youth is still theirs. He invokes the threat of death as a way of persuading the beloved to make up her mind at once.