Compounds of Formula (I), wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6, X, and n are as defined for Formula (I) in the description, processes for the preparation of the compounds and new intermediates employed in the preparation, pharmaceutical compositions containing the compounds, and the use of the compounds in the treatment or prevention of neurological and psychiatric disorders associated with glutamate dysfunction.