Я взял не тот ключ и не смог открыть дверь.

Because the past tense in Russian agrees with the speaker’s gender and number.

• взял = masculine singular
• взяла = feminine singular
• взяли = plural

So Я взял... means the speaker is male.
If a woman says it, she would say Я взяла не тот ключ и не смогла открыть дверь.

взял is the perfective past form of взять, while брал is the imperfective past form of брать.

Here, взял is used because the sentence describes one completed action: the speaker took a key.

• Я взял не тот ключ = I took the wrong key.
• Я брал не тот ключ would sound more like I was taking / used to take the wrong key, or it would shift attention away from the completed result.

In this context, the completed action matters, because it led to the next result: the speaker couldn’t open the door.

Literally, не тот ключ means not that key or not the one needed.

In Russian, the pattern не тот / не та / не то / не те is very commonly used to mean:

• the wrong one
• not the right one
• not the one intended

So:

• не тот ключ = the wrong key
• не та книга = the wrong book
• не те люди = the wrong people

This is a very natural Russian way to express the idea.

Because ключ is the direct object of взял, so it is in the accusative case.

However, for masculine inanimate nouns, the accusative singular is usually the same as the nominative singular.

So:

• nominative: ключ
• accusative: ключ

That is why the form does not change.

Because they are negating different things.

• не тот ключ = not the right key / the wrong key
• не смог открыть дверь = was not able to open the door

So the sentence contains two separate negatives, each with its own job.

This is not strange in Russian. It is just:

1. the key was the wrong one
2. as a result, the speaker could not open the door

This is an important aspect difference.

• не смог = did not manage to, failed to
• не мог = could not, often focusing more on inability or impossibility

In this sentence, не смог открыть дверь suggests a specific unsuccessful attempt. The speaker tried to open the door, but it didn’t work.

So:

• Я не смог открыть дверь = I couldn’t open the door / I failed to open the door
• Я не мог открыть дверь can also mean I couldn’t open the door, but it often sounds more like I was unable to, rather than highlighting the failed result of that particular attempt

Here, не смог fits very naturally because the story is about a concrete event.

Because открыть is the perfective infinitive, and here the meaning is about a single completed result: opening the door successfully.

After смочь / не смочь, Russian often uses a perfective infinitive when talking about whether someone managed to complete a one-time action.

• не смог открыть дверь = did not manage to open the door

If you used открывать, it would point more to the process or repeated action, which does not fit as well here.

дверь is also a direct object, so it is indeed in the accusative case.
But for many inanimate feminine nouns, the accusative is the same as the nominative.

So:

• nominative: дверь
• accusative: дверь

That is why the form looks unchanged.

Correct: Russian does not have articles like a and the.

So Russian simply says:

• не тот ключ
• дверь

and the exact English article depends on context:

• the wrong key
• the door

Russian relies on context, word choice, and sometimes word order instead of articles.

The given word order is the most neutral and natural:

Я взял не тот ключ и не смог открыть дверь.

Russian word order is more flexible than English, but changing it usually changes the emphasis, not the basic meaning.

For example:

• Я взял не тот ключ... = neutral
• Не тот ключ я взял... = emphasizes the wrong key
• Дверь я не смог открыть = emphasizes the door

So the original sentence is the standard, unmarked way to say it.

и means and. It joins the two parts of the sentence:

1. Я взял не тот ключ
2. не смог открыть дверь

Together, they form a natural sequence:

• I took the wrong key
• and as a result, I couldn’t open the door

Russian often uses и exactly the way English uses and.

Yes, very naturally.

Because of не смог открыть дверь, the sentence strongly suggests a real situation: the speaker took the wrong key and then tried to open the door but failed.

That is one reason смог works so well here: it often implies an attempt plus the result of that attempt.