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, Sagittarius
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