IEC 62271-100 is applicable to a.c. circuit-breakers designed for indoor or outdoor installation and for operation at frequencies of 50 Hz and 60 Hz on systems having voltages above 1 000 V.
IEC standard does not required specific tests for using at 60 Hz but there are mainly two important points in concern.
1) Rated short-circuit making current:
"For a rated frequency of 60 Hz and the standard value of the time constant of 45 ms it is equal to 2,6 times the r.m.s. value of the a.c. component of its rated short-circuit breaking current".
"Tests performed at 50 Hz on switching devices of the open type should be deemed to prove the performance of the switching device when rated at 60 Hz, provided that the temperature-rise values recorded during the tests at 50 Hz do not exceed 95 % of the maximum permissible values".
In conclusion, for both concerns above mentioned, LF circuit breakers are capable to operate at 50 or 60 Hz.
For cmpany declration purpose, please contact the respective MV product manager to issue such a declaration in accordance with above argument.
Additional remark: regarding your question on the motor mechanism, it shall not be affected by operation on 60Hz.
However, care shall be taken in case you will use AC type releases (closing and/or opening releses), you have then to select the right reference according to the supply voltage (see attached order form from LF catalog).