In C# there's a
var smallDateTimeMin = DateTime(1900, 1, 1);
var smallDateTimeMax = DateTime(2079, 6, 6);
There is no
smalldatetime equivalent in
System.Data.SqlTypes. Nor is there an equivalent for the new
datetime2 type. So I wouldn't expect min-max constants for those types in the .NET framework.
But the types are well documented on MSDN:
Date and time data from January 1, 1753 through December 31, 9999, to an accuracy of one three-hundredth of a second (equivalent to 3.33 milliseconds or 0.00333 seconds). Values are rounded to increments of .000, .003, or .007 seconds, as shown in the table.
So you can easily define your own min-max constants.