If you're trying to create a clan but the game tells you its name is invalid, you must try something else. The one you attempted either began with a special character (or hashtag), or contained a string of characters black-listed in one of the many languages Clash of Clans supports.
We want to give you plenty of freedom to choose a clan name that you can relate to. With our global player-base, we also need to take various languages and cultures into account when processing choices. Keep trying different combinations, and I'm sure you'll find something that fits your clan.