<===> input.scss
@function test () {
  $m: ();
  $abc: (a b c d e f g h i j k);

  @for $index from 1 through length($abc) {;
    $m: map-merge($m, (nth($abc, $index):$index) );
  }

  @return $m;
}

test {
  content: inspect(test());
}
<===> output.css
test {
  content: (a: 1, b: 2, c: 3, d: 4, e: 5, f: 6, g: 7, h: 8, i: 9, j: 10, k: 11);
}