Complexation of Cu(NO3)(2) with 4-aminopyrimidine (4APM) in methanol gave [Cu(4APM)(NO3)(OCH3)](n) which crystallizes in a trigonal space group R (3) over bar The three-dimensional network affords a tube-like cavity. Magnetic measurements revealed the presence of considerably large antiferromagnetic interaction due to the four-mernbered Cu2O2 structure.