ernennen zu
to appoint as
To officially and formally place someone in an office, function, or position.
Der Vorstand hat sie zur neuen Leiterin der Marketingabteilung ernannt.
The board appointed her as the new head of the marketing department.

to appoint
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to appoint as
To officially and formally place someone in an office, function, or position.
Der Vorstand hat sie zur neuen Leiterin der Marketingabteilung ernannt.
The board appointed her as the new head of the marketing department.

'Ernennen' (to appoint) is an inseparable verb because it begins with the prefix 'er-'. The prefix remains firmly attached to the verb in all sentence forms and tenses.
Man hat ihn zum neuen Direktor ernannt.
He was appointed the new director.
The verb 'ernennen' (to appoint) follows a fixed pattern: you appoint someone (accusative) to/as something (dative). The preposition 'zu' is essential here.
Der König ernannte den General zum Feldmarschall.
The king appointed the general as field marshal.
This verb is mainly used in formal and official contexts, for example in politics, professional life, or honors. It is rather rare in everyday speech.
Die Universität wird sie zur Ehrenprofessorin ernennen.
The university will appoint her as an honorary professor.
to explain / declare
'erklären' and 'ernennen' can both occur in official situations. With 'für ... erklären', someone or something is officially given a status or quality, for example 'für gültig' (valid) or 'für beendet' (over / finished). 'ernennen' is used only for people who are officially given a position, office, or function. Learners may confuse the words because both sound formal. The simple difference is: you appoint a person to a role, but you declare something or someone valid, free, ill, or finished.

Die Schulleitung ernennt Frau Becker zur neuen Leiterin der Bibliothek.
The school administration appoints Ms. Becker as the new head of the library.
Nach der Prüfung erklärte die Kommission den Antrag für gültig.
After the review, the committee declared the application valid.