Is a divorce effective upon a man's wife if he swore by divorce that he would "not speak" to a female colleague, and then he spoke to her, or is expiation required?

Swearing an oath by divorce has the ruling of a conditional divorce. Divorce occurs by it upon the fulfillment of the condition sworn upon. However, writing "divorce" is considered a 'kinayah' (allusion) and does not result in divorce unless the husband intends it. The decisive factor is his intention. If he intended divorce, then divorce occurs. If he only intended to swear an oath, then there is a difference of opinion on it, and the majority view is that divorce occurs. It should be noted that it is forbidden to converse with a non-mahram woman except out of necessity and to the extent of that necessity. The permissible oath is to swear by Allah the Almighty, whereas swearing by divorce is among the oaths of the dissolute.