Is it acceptable to give used clothes as expiation for breaking a vow (kafaarat yameen)?

Firstly: 

The expiation for breaking
a vow is explained in the verse in which Allaah says (interpretation of the
meaning): 

“Allaah will not punish
you for what is unintentional in your oaths, but He will punish you for your
deliberate oaths; for its expiation (a deliberate oath) feed ten Masaakeen
(poor persons), on a scale of the average of that with which you feed your
own families, or clothe them or manumit a slave. But whosoever cannot afford
(that), then he should fast for three days. That is the expiation for the
oaths when you have sworn. And protect your oaths (i.e. do not swear much).
Thus Allaah makes clear to you His Ayaat (proofs, evidences, verses,
lessons, signs, revelations, etc.) that you may be grateful”

[al-Maa’idah 5:89]

It has been discussed in
detail in the answer to question no.
45676. 

It is permissible to
delegate someone to feed or clothe poor people, whether that is a charity or
an individual whom you know, but you have to make sure that the one whom you
delegate will not give it in the form of cash, but will give food to ten
poor persons. 

It should be noted that
what is required with regard to the expiation for breaking an oath, if it is
to be given in the form of food, is to give the average type of food. It
does not have to be the best type of food, and it is not permissible to give
the least type, rather it should be of average quality, because Allaah says
(interpretation of the meaning): “for its expiation (a deliberate oath)
feed ten Masaakeen (poor persons), on a scale of the average of that with
which you feed your own families” [al-Maa’idah 5:89]. 

In that case, setting it at
100 riyals is not accurate, because he may be rich, in which case the
average food that he eats will be worth much more than that. Or he may be
poor, in which case the average food that he eats will be worth less than
that. Each person must give expiation in the form of his own average food,
whether he is rich or poor. 

Secondly: 

The kind of clothing that
is acceptable for the expiation for breaking an oath is that which is
suitable for praying in, such as a thobe or an izaar (lower garment) and
rida’ (upper garment). It is not stipulated that it should be new, so it is
permissible to give old clothes so long as they have not become worn out and
useless. 

Ibn Qudaamah (may Allaah
have mercy on him) said: It is permissible to give them old or new clothes,
unless they are worn out and useless; that is not acceptable because it is
faulty. End quote from al-Mughni (10/9).  

Al-‘Adawi said in his
commentary on Sharh al-Risaalah (2/26): Is it essential that the
clothes be new or not?  

It seems that this is not
essential; rather if they are still in good condition then they are like new
clothes. End quote. 

If you gave ten sets of
clothing to a charity that would distribute them to the poor, then that is
acceptable. 

And Allaah knows best.