How to use CRON expression in Batch Class in Salesforce?

In Scheduler class, we can execute at a specified time. What we are trying to do is Schedule a Batch. E.g.:
SendEmailToAccountAndContactBatch schedulable = new SendEmailToAccountAndContactBatch();
String sch = ‘0 0 13 ? MON,TUE,WED,THU,FRI ‘;
system.schedule(‘SendEmailToAccountAndContactBatch’, sch, schedulable);
database.executebatch(schedulable);