SAN ANTONIO — Hartman vREIT XXI Inc. has purchased the Spectrum Building, a 10-story office asset located at 613 N.W. Loop 410 in San Antonio’s North Central submarket, for $16.5 million. The sales price, which included a buyer’s auction premium, equates to about $94 per square foot. The 175,314-square-foot office building was 87.7 percent leased at the time of sale. The seller was not disclosed.