The formal syntax of R4RS through R7RS disallow unsigned imaginary numbers. Here is how the test Schemes handle the input 35i:
Undefined variable: Racket, Gauche, MIT, Chicken (with or without the numbers egg), Bigloo, Guile, SISC, SCM, Chez, JScheme, STklos, Shoe, TinyScheme, Scheme 9, S7, BDC, XLisp, Rep, Schemik, Elk, Sizzle, FemtoLisp, Inlab
Unsupported lexical syntax: Scheme48/scsh, Larceny, Ypsilon, IronScheme, NexJ, KSI, SigScheme, SXM, Dfsch, Owl Lisp
Equivalent to +35i: Kawa, Vicare, Chibi, RScheme (does not support complex numbers), UMB
Returns a so-called generic object: Llava