1,​3,​8-​Triazaspiro[4.5]​decan-​4-​one, 3-​[(3-​fluorophenyl)​methyl]​-​8-​[4-​(4-​fluorophenyl)​-​4-​oxobutyl]​-​1-​phenyl-​, (2Z)​-​2-​butenedioate (1:1)