The formal procedure would be something along these lines:
- Write up a list of the items.
- Take photos.
- Write to him by mail, and by registered post (paper print-outs of photos), setting a date (say, 30 days hence) by which he should collect the items, failing which they will be destroyed or disposed of.
- Once week before the date, second him another letter, enclosing a copy of the first, and naming it "second and final reminder".
- Make sure that you're available (or someone else you send in your stead) at a time that he can fetch the items. In other words, ensure that you are not the one preventing him from finding a convenient time.
- If you receive no response and no collection within the time you have specified, get rid of the items.
However, there might be more peaceful ways to go about it, depending on what you'd best like to achieve, and on the likely ramifications that you could anticipate, given the nature of the relationship and of the divorce. Only you know your and his circumstances. You could choose from any other option such as:
- send the same letter to his sister/friend/father/new partner and ask him/her to come over and fetch the stuff on his behalf
- ask those same people if you could bring/send his stuff to them to keep for him or give to him
- pack it up in bags or boxes and take it to his/their place yourself
- pack it up in proper postal boxes and post it to him/them
- ask him if there is some other address to which he would like you to deliver or post the items
- inform his lawyer that the items are there, that you have tried some or all of the above steps and had no response, and that you are therefore going to have to dispose of the items by 30 days from now, unless you receive a firm commitment of a mutually suitable time and date when the goods will be collected, or an address to where you should send/deliver them (within Switzerland), by 14 days from now.
There's also the question of the costs. Before you write to anyone, work out what the transport would actually cost.
If it's a few boxes of a few kg each, and if he doesn't live on the other side of the world, and if you are wanting peace and closure, it might be worth your while accepting that you'll probably end up paying for the postage or delivery costs, just to get the stuff out of your space, rather than insisting that he should cover that cost.