Provided herein are multicyclic compounds of formula (IVa), shown below, wherein R1, R2, R3, R4, R5, R6, R7, m, and n are defined herein elsewhere, methods of their synthesis, pharmaceutical compositions comprising the compounds, and methods of their use. The compounds provided herein are useful for the treatment, prevention, and/or management of various neurological disorders, including but not limited to, psychosis and schizophrenia.