how to manipulate w,x,y,z in order to mirror pose

Here is my object
http://www.fotosik.pl/pokaz_obrazek/pelny/bee882bcfadd4e82.html
which spine is turned from right to left.
I want to have mirrored pose so turned it from left to right.
I have coordinates:
location.x = 0, y =0, z = 0
rotation.w = 0.997, x = 0.006092, y = -0.07665, z = 0
In the attached figure You see coordinate system of my bone: green arrow is X, blue is Y, red is Z

What I may say is that if I change rotation.w to -0.997 I have desired effect, however move from initial position to final one is with bug - please see how intermediate pose looks like:
http://www.fotosik.pl/pokaz_obrazek/pelny/0f61d71999dd714f.html
So that there must be some other solution.

I found somewhere the information that I should negate either X,Y or W,Z in my case, where XY is the plane over which I do mirror. Could anybody confirm that it is a good approach?