use strict;
use warnings;
use XML::Simple;
use Data::Dumper;

my $xml;
{
    local $/='';
    $xml = <DATA>;
}

my $xs = XML::Simple->new();
my $ref = $xs->XMLin($xml);

print Dumper($ref);

__DATA__
<xml><ComplexComponent1 molecule_idref="1"/>
<ComplexComponent2 molecule_idref="2"/><ComplexComponent3 molecule_idref="3"/>
<ComplexComponent4
molecule_idref="4"/><ComplexComponent5
molecule_idref="5"/>
</xml>