How to print OptmInfo (output) after fitting with lsqcurvefit

Hello! I have the following code and I need to know Rsdnrm (resnorm) and the number of iterations:

[k,Rsdnrm,Rsd,ExFlg,OptmInfo,Lmda,Jmat]=lsqcurvefit(@kinetics,k0,tdata,cdata);

fprintf('\tRsdnrm:\t %1.4g \n',Rsdnrm)

fprintf('\tOptmInfo:\t %1.4g \n',OptmInfo)

For the last line it returns the error:

Error using fprintf

Function is not defined for 'struct' inputs.

I understand the error but I am very new using matlab so I don't know how to fix it.

Thanks in advance!